Journal of Experimental Botany, Vol. 53, No. 377, pp. 2039-2055,
October 1, 2002
© 2002 Oxford University Press
Ethylene biosynthesis and action in tomato: a model for climacteric fruit ripening
Received 11 April 2002; Accepted 2 July 2002
Plant Science Division, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, UK
Abbreviations: ABA, abscisic acid; ACC, 1-aminocyclopropane-1-carboxylic acid; ACS, ACC synthase; ACO, ACC oxidase; PLP, pyridoxal-5'-phosphate; MAP3K, mitogen activated kinase kinase kinase; ERE, ethylene responsive element; PG, polygalacturonase, GUS, ß-glucuronidase; HPOs, unsaturated fatty acid hydroperoxides; LOX, lipoxygenase; ADH, alcohol dehyrogenase.
 |
Abstract |
|---|
 Top Abstract IntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
Elucidating the mechanisms involved in ripening of climacteric fruit and the role that ethylene plays in the process are key to understanding fruit production and quality. In this review, which is based largely on research in tomato, particular attention is paid to the role of specific isoforms of ACC synthase and ACC oxidase in controlling ethylene synthesis during the initiation and subsequent autocatalytic phase of ethylene production during ripening. Recent information on the structure and role of six different putative ethylene receptors in tomato is discussed, including evidence supporting the receptor inhibition model for ripening, possible differences in histidine kinase activity between receptors, and the importance of receptor LeETR4 in ripening. A number of ethylene-regulated ripening-related genes are discussed, including those involved in ethylene synthesis, fruit texture, and aroma volatile production, as well as experiments designed to elucidate the ethylene signalling pathway from receptor through intermediate components similar to those found in Arabidopsis, leading to transcription factors predicted to control the expression of ethylene-regulated genes.
Key words: Key words: Carotenoid, climacteric, ethylene receptor, ethylene signal transduction, lipoxygenase, MAPKinase, tomato.
|
Introduction |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
Fruit ripening is a complex, genetically programmed process that culminates in dramatic changes in colour, texture, flavour, and aroma of the fruit flesh. Due to the economic importance of fruit crop species these processes have been, and continue to be, studied extensively at both the biochemical and genetic levels. Fruits with different ripening mechanisms can be divided into two groups; climacteric, in which ripening is accompanied by a peak in respiration and a concomitant burst of ethylene, and non-climacteric, in which respiration shows no dramatic change and ethylene production remains at a very low level. In tomato and other climacteric fruits such as apple, melon and banana the ethylene burst is required for normal fruit ripening, as illustrated by the slowing or inhibition of ripening in ethylene-suppressed transgenic plants (Oeller et al., 1991; Theologis et al., 1993; Picton et al., 1993; Ayub et al., 1996). Furthermore, it has been shown that ethylene affects the transcription and translation of many ripening-related genes (Gray et al., 1994; Deikman 1997; Giovannoni, 2001). However, although ethylene is the dominant trigger for ripening in climacteric fruit, it has been suggested that both ethylene-dependent and ethylene-independent gene regulation pathways coexist to co-ordinate the process in climacteric and non-climacteric fruit (Lelievre et al., 1997).
Two systems of ethylene regulation have been proposed to operate in climacteric plants. System 1 is functional during normal vegetative growth, is ethylene auto-inhibitory and is responsible for producing basal ethylene levels that are detected in all tissues including those of non-climacteric fruit. System 2 operates during the ripening of climacteric fruit and senescence of some petals when ethylene production is autocatalytic. Ripening usually commences in one region of a fruit, spreading to neighbouring regions as ethylene diffuses freely from cell to cell and integrates the ripening process throughout the fruit.
The aim of this review is to bring together recent advances made in understanding ethylene biosynthesis and the regulatory role of the phytohormone ethylene in tomato fruit ripening (Fig. 1A). Tomato is a good model system for studying the role that ethylene plays in ripening due to its relatively small genome, well-characterized developmental mutants, ease of genetic manipulation, relatively short life cycle, and its economic importance as a crop species. As ripening progresses, fruit colour changes from green to red as chloroplasts are transformed into chromoplasts, chlorophyll is degraded and carotenoids accumulate. Fruit softening and textural changes occur as the fruit cell wall is modified and partially disassembled by enzymes and the ripe flavour develops as specific volatiles increase and the sugar–acid balance alters. Many components of biochemical pathways involved in pigmentation, cell wall metabolism, carbohydrate metabolism, ethylene biosynthesis, and signal transduction have been identified through alteration of their expression in transgenic plants (Gray et al., 1994; Deikman, 1997; Giovannoni, 2001; Ciardi and Klee, 2001). Differential screening of cDNA libraries has also proved a useful tool in identifying genes that are differentially regulated during ripening in tomato and other fruit (Slater et al., 1985; Dopico et al., 1993; Deikman, 1997; Aggelis et al., 1997; Zegzouti et al., 1999). In addition to ripening, ethylene is also known to be involved in other processes such as pathogen and wounding responses, leaf senescence and abiotic and biotic stress responses; so too are other hormones such as abscisic acid (ABA) and sugar signalling (reviewed in Gazzarrini and McCourt, 2001). This cross talk between signalling pathways makes the process of unravelling the role that ethylene plays in fruit ripening complex, as alteration of ethylene levels may result in the unexpected or unrecognized modification of another signalling pathway.
|
|
Ethylene biosynthesis |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
The pathway of ethylene synthesis is well established in higher plants (reviewed in Bleecker and Kende, 2000). Ethylene is formed from methionine via S-adenosyl-L-methionine (AdoMet) and the cyclic non-protein amino acid 1-aminocyclopropane-1-carboxylic acid (ACC). ACC is formed from AdoMet by the action of ACC synthase (ACS) and the conversion of ACC to ethylene is carried out by ACC oxidase (ACO) (Kende, 1993). In addition to ACC, ACS produces 5'-methylthioadenosine, which is utilized for the synthesis of new methionine via a modified methionine cycle. This salvage pathway preserves the methylthio group through every revolution of the cycle at the cost of one molecule of ATP. Thus high rates of ethylene biosynthesis can be maintained even when the pool of free methionine is small. Two other ethylene-regulated genes have been identified that may play a possible role in the methionine cycle, E4, a putative methionine sulphoxide reductase protein and ER69 a putative cobalamine-independent methionine synthase (Montgomery et al., 1993a; Zegzouti et al., 1999). In this pathway it is well known that biosynthesis is subject to both positive and negative feedback regulation (Kende, 1993). Positive feedback regulation of ethylene biosynthesis is a characteristic feature of ripening fruits and senescing flowers in which exposure to exogenous ethylene or propylene results in a large increase in ethylene production due to the induction of ACS and ACO. Both of these enzymes are encoded by small multigene families and their expression is differentially regulated by various developmental, environmental and hormonal signals (Kende, 1993; Zarembinski and Theologis 1994; Barry et al., 2000; Llop-Tous et al., 2000).
At least eight ACS genes have been identified in tomato (LEACS1A, LEACS1B and LEACS2–7), (Zarembinski and Theologis, 1994; Oetiker et al., 1997; Shiu et al., 1998) and many others have been identified in both climacteric and non-climacteric fruits such as melon, cucumber and citrus (Nakajima et al., 1990; Yamamoto et al., 1995; Wong et al., 1999). However, the role that ACS plays in ripening has been most widely studied in tomato. ACS shows homology to pyridoxal-5'-phosphate (PLP)-dependent aminotransferases and mutant complementation studies have shown that the enzyme can act as a dimer (Tarun and Theologis, 1998). Recent studies of the ACS crystal structure (Capitani et al., 1999) and PLP co-factor binding (Huai et al., 2001) have confirmed similarity between the ACS catalytic binding site and those of other PLP-dependent aminotransferases. The presence of LEACS2 and LEACS4 transcripts during ripening has been well documented (Rottmann et al., 1991; Olson et al., 1991; Yip et al., 1992; Lincoln et al., 1993; Barry et al., 2000). Recent work has also confirmed the presence of LEACS1A and LEACS6 in tomato fruit before the onset of ripening and shown that each ACS in fruit has a different expression pattern (Fig. 1B) (Barry et al., 2000).
Analysis of ACS gene induction in mutant fruit with disrupted ethylene signalling has been used to identify which ACS gene is ethylene-regulated. The Never ripe (Nr) mutant cannot perceive ethylene due to a mutation in the ethylene-binding domain of the NR ethylene receptor (Lanahan et al., 1994; Wilkinson et al., 1995). Fruit from the ripening inhibitor (rin) mutant do not show autocatalytic ethylene production (Herner and Sink, 1973) and cannot transmit the ethylene signal downstream to ripening genes due to a mutation in the RIN transcription factor (Vrebalov et al., 2002). Nr and rin mutant fruit have shown that LEACS2 expression requires ethylene whereas LEACS1A and LEACS4 exhibited only slightly delayed expression in Nr indicating that ethylene is not responsible for regulation of these genes (Barry et al., 2000). All four fruit ACS genes showed the same expression patterns in rin fruit as in mature green wild-type fruit, but did not show any ripening-related changes of expression (Barry et al., 2000). Therefore, it has been proposed that LEACS1A and LEACS6 are involved in the production of system 1 ethylene in green fruit (Barry et al., 2000). System 1 continues throughout fruit development until a competence to ripen is attained, whereupon a transition period is reached, during which LEACS1A expression increases and LEACS4 is induced. During this transition period, system 2 ethylene synthesis (autocatalysis) is initiated and maintained by ethylene-dependent induction of LEACS2 (Barry et al., 2000). Antisense inhibition of LEACS2, which also down-regulated LEACS4, reduced ripening-related synthesis of ethylene to 0.1% of control fruit. The antisense fruit displayed an abnormal pattern of ripening such as reduced lycopene accumulation, delayed softening and a much reduced climacteric peak (Oeller et al., 1991).
Some debate exists as to whether ACS enzymes are regulated transcriptionally, post-transcriptionally or post-translationally and whether ethylene plays a role in this regulation (Kende, 1993; Olson et al., 1995; Oetiker et al., 1997). In vitro analysis of LEACS2 enzyme activity has shown that the deletion of 52 amino acids from the C-terminus increases enzyme activity (Li and Mattoo, 1994; Li et al., 1996). However, it has recently been shown that LEACS2 is phosphorylated in wounded tomato fruit and is not truncated (Tatsuki and Mori, 2001). Sequence analyses have identified a conserved domain that is considered to be the phosphorylation site (F/L)RLS(F/L). Recombinant LEACS3 and LEACS2 containing this domain were phosphorylated in vitro whereas LEACS4 was not phosphorylated and does not contain this site (Tatsuki and Mori, 2001). It seems that the role of phosphorylation is not to regulate the specific activity of the enzyme but to control the rate of enzyme turnover (Spanu et al., 1994). The possibility that ACS phosphorylation regulates ethylene production is supported by the finding that mutation of the C-terminal domain of Arabidopsis ACS5 induces the eto2-1 mutant to overproduce ethylene (Vogel et al., 1998). Furthermore, observations by Ecker that the ETO1 protein bound to ACS5 in vitro and inhibited its activity has led to speculation that the ETO1 protein may be involved in a protein degradation pathway (Cosgrove et al., 2000; Tatsuki and Mori, 2001). Therefore; it is possible that phosphorylation of ACS protects the protein from degradation, which in turn could cause ACS to accumulate and ACS activity to increase, accounting for the burst of ethylene produced by ripening fruit (Tatsuki and Mori, 2001).
Initially it was thought that ACS activity was the key step in controlling the production of ethylene and that ACO activity was constitutive (Yang and Hoffman, 1984; Theologis et al., 1993). However, the role that ACO activity plays in the regulation of ethylene biosynthesis has become apparent in recent years. The rise in ACO activity precedes ACS activity in preclimacteric fruit in response to ethylene, indicating that ACO activity is important for controlling ethylene production (Lui et al., 1985). Examination of ACO mRNA expression patterns in various tissues and different developmental stages provided further evidence for the regulatory role that ACO plays in ethylene production during fruit ripening (Holdsworth et al., 1987; Hamilton et al., 1990; Balague et al., 1993; Barry et al., 1996). Historically, studying ACO has proved to be problematic due to the lack of an in vitro assay and difficulties encountered during purification (Kende, 1993). The first ACO gene was identified through antisense expression of a clone, pTOM13, then of unknown function (Holdsworth et al., 1987). mRNA expression patterns showed the pTOM13 gene was expressed in both ripening tomatoes and wounded leaves and down-regulation of this gene produced transgenic tomato plants with reduced levels of ethylene synthesis and ACO activity (Hamilton et al., 1990). The role of this enzyme in ethylene biosynthesis from ACC was confirmed by expression of pTOM13 in yeast and Xenopus oocytes, where the pTOM13-encoded protein was shown to convert ACC to ethylene, with the correct stereospecificity (Hamilton et al., 1991; Spanu et al., 1991). A further three ACO genes have been identified in tomato in response to wounding and during flower development, leaf and flower senescence and fruit ripening (Holdsworth et al., 1988; Barry et al., 1996; Blume and Grierson, 1997; Nakatsuka et al., 1998; Llop-Tous et al., 2000). ACO genes have also been identified in petunia, mung bean and other climacteric fruit such as melon, avocado, apples, and bananas (reviewed in Jiang and Fu, 2000).
ACO enzymes are members of the Fe(II-dependent family of oxidases/oxygenases (Hamilton et al., 1990; Prescott, 1993). In vitro ACO activity requires ascorbate as a substrate and the CO2 produced during the climacteric peak is thought to activate the enzyme in vivo (Dong et al., 1992; Smith and John, 1993). Two models have been proposed for the production of ethylene from ACC. In the first model the ascorbate association with the Fe(II) ion activates a bound O2 to yield high-valent iron-oxo species that oxidizes ACC to release ethylene (Zhang et al., 1997). More recently, it has been suggested that the role of the Fe(II) ion is to bind ACC and O2 simultaneously and promote electron transfer, which initiates catalysis of ACC to ethylene (Rocklin et al., 1999).
Analysis of ACO gene expression patterns in ripening fruit shows that each gene is highly regulated with transcripts of individual members accumulating to varying degrees at distinct developmental stages (Barry et al., 1996). LEACO1 and, at a lower level LEACO3, are expressed at the onset of fruit ripening. LEACO1 transcripts peak at breaker +3 and then fall back to levels observed at breaker, whereas LEACO3 transcripts are only transiently expressed at breaker before disappearing. Therefore it is likely that the first step in catalytic ethylene biosynthesis is the de novo synthesis of ACO1, the ethylene produced induces ACS gene expression, which in turn produces more ACC.
|
Ethylene perception and signal transduction in ripening fruit |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
During climacteric fruit ripening, the burst of autocatalytic ethylene co-ordinates and accelerates the ripening process. Although ethylene cannot induce immature tomato fruit to ripen rapidly, exposure will hasten its onset by shortening the ‘green life’, as in banana. The exact mechanisms of ethylene signal transduction are not yet fully understood, however, seedlings that show disruption of the normal triple response phenotype have given valuable insights into ethylene perception and signalling. Analysis of Arabidopsis mutants that display either etiolated growth in the presence of ethylene in the dark or show a constitutive triple response in the absence of the hormone, have led to the identification of five ethylene receptors and a number of components of the signal transduction pathway.
Ethylene receptors have homology to bacterial two-component receptors, which consist of a sensor protein, and a separate response regulator protein that function together, allowing bacteria to respond to different environmental conditions (Chang and Stewart, 1998). All ethylene receptors have a sensor domain that can be subdivided into a transmembrane domain and a GAF domain (found in cGMP phosphodiesterases, adenylate cyclases and Fh1a transcription factors), a histidine kinase domain and a response domain. The GAF domain binds cyclic nucleotides in a number of bacterial proteins, and the chromophore in the plant photoreceptor phytochrome (Aravind and Ponting, 1997), however, the function of this domain in the ethylene receptors is unknown. The binding of ethylene to the receptor is mediated by a copper co-factor (Rodriguez et al., 1999) and comparison with bacterial two component systems suggests a phosphorelay may pass the signal downstream. The presence of ethylene has been shown transiently to increase polypeptide phosphorylation in vivo (Raz and Fluhr, 1993). CTR1, a protein kinase with homology to the Raf family of mitogen-activated protein kinase kinase kinase (MAP3K) has been identified as the next component of the signal transduction pathway (Kieber et al., 1993). CTR1 is a negative regulator of the signal transduction pathway as CTR1 mutants constitutively respond to ethylene even in its absence. The N-terminus of CTR1 interacts with two ethylene receptors, ETR1 and ERS1 (Clark et al., 1998) and the current model of ethylene action suggests that, in the absence of the hormone, receptors signal to the negative regulator CTR1 and the response pathway is blocked. Binding of ethylene by the receptors releases the negative regulator allowing ethylene responses to occur (Bleecker et al., 1998). However, ethylene promotes MAPK activity, suggesting that both negative and positive ethylene signal transduction may be mediated through MAP kinase cascades (Novikova et al., 2000). Several excellent reviews concerning ethylene-mediated responses at the level of the ethylene receptor and down-stream signalling components have recently been published (Stepanova and Ecker, 2000; Bleecker and Kende, 2000; Ciardi and Klee, 2001; Chang and Stadler, 2001), therefore, this review will concentrate only on ripening-related ethylene perception and signal transduction.
A family of at least six putative ethylene receptors, LeETR1, LeETR2 (Zhou et al., 1996; Lashbrook et al., 1998), NR (Wilkinson et al., 1995; Payton et al., 1996), LeERT4, LeETR5 (Tieman and Klee, 1999), and LeETR6 (Ciardi and Klee, 2001) and two CTR1 homologues, TCTR2 (Lin et al., 1998) and ER50 (Zegzouti et al., 1999), have been identified in tomato. Each ethylene receptor is expressed in different temporal and spatial patterns dependent on developmental stage and external stimuli. LeETR1 and LeETR2 are expressed constitutively in all tissues throughout development, NR is up-regulated at anthesis and both NR and LeETR4 are up-regulated during ripening, senecence, abscission (Payton et al., 1996; Tieman et al., 2000) and pathogen infection (Ciardi et al., 2000). LeETR5 is also expressed in fruit, flowers and during pathogen infection (Tieman and Klee, 1999). Five consensus motifs named, H, N, G1 F, and G2, which are key features of bacterial histidine kinases are present in LeETR1, LeETR2 and NR, although NR lacks the response domain as in Arabidopsis ERS1 type receptors (Hua et al., 1995, 1998). In LeETR4 and LeETR5 the third and fourth motifs are highly divergent and the putative autophosphorylated HIS residue in the histidine kinase domain of LeETR5 is absent (Tieman and Klee, 1999), indicating that one or several ethylene receptors do not have histidine kinase activity although they all bind ethylene in vitro (Ciardi and Klee, 2001). Homodimerization of ETR1 is known to occur (Schaller et al., 1995; Rodriguez et al., 1999) although heterodimerization has not yet been proven. It has been proposed that the response regulator of ETR1 forms a homodimer when unphosphorylated (Muller-Dieckmann et al., 1999) and that phosphorylation of the receptor in the presence of ethylene causes monomerization of the response regulator that may, in turn, inactivate CTR1 (Chang and Stadler, 2001).
Ethylene receptors are, at least in some cases, ethylene-inducible and it has been demonstrated that increased levels of receptor reduces ethylene sensitivity, supporting the negative regulation of ethylene receptors model (Ciardi et al., 2000). As NR and LeETR4 genes are up-regulated during ripening, they have both been targeted for antisense experiments. However, down-regulation of NR had no obvious effects on ethylene signalling and ripening apart from elevated expression of LeETR4, indicating that LeETR4 could be compensating for NR (Tieman et al., 2000). By contrast, antisense repression of the mutant NR gene in the Nr background produced fruit that ripened normally indicating that the NR ethylene receptor is not required for ripening and confirming the receptor inhibition model of ethylene signalling (Fig. 2A, B) (Hackett et al., 2000). It is now becoming apparent that LeETR4 plays an important role in ripening. Uniquely, down-regulation of LeETR4 produces an ethylene hypersensitive phenotype that includes accelerated ripening (Tieman et al., 2000), whereas in Arabidopsis increased ethylene sensitivity is not observed until three receptors have been knocked out (Hua and Meyerowitz, 1998). This difference suggests that another level of ethylene signal transduction may be required in climacteric plants in contrast to Arabidopsis. Over-expression of NR in tomato plants with reduced levels of LeETR4 eliminates ethylene sensitivity, further indicating that despite differences in protein structure, ethylene receptors are functionally redundant (Tieman et al., 2000). These observations have led to the hypothesis that LeETR4 may monitor the levels of receptor and initiate the synthesis of new receptors as an ethylene response occurs, thus maintaining homeostasis in the ethylene response (Tieman et al., 2000).
|
While receptor genes have been isolated from tomato, few putative ethylene signal transduction components from this species have been described. A gene, TCTR2, for which the encoded protein is 41% identical to CTR1, was recently reported (Lin et al., 1998). Identification of another CTR1-like protein, ER50 (Zegzouti et al., 1999) suggests that there may be multiple MAP3Ks regulating different pathways in which ethylene is involved. TCTR2 mRNA is constitutively expressed and expression is not up-regulated by exposure to exogenous ethylene (Z Lin, Santalla, RM Hackett, D Grierson, unpublished results). However, in fruit, the CTR1-like ER50 mRNA is up-regulated by exogenous ethylene and during ripening, which is intriguing as CTR1 is thought to act as a negative regulator of the ethylene response (Zegzouti et al., 1999).
Analysis of Arabidopsis ethylene triple response signalling mutants has identified other proteins, EIN2, EIN3, EIN5, and EIN6, which act as positive regulators downstream in the ethylene-signalling pathway. EIN2, an unknown membrane protein with N-terminal sequence similarity to mammalian metal-ion transport NRAMP proteins, is required for ethylene signalling (Alonso et al., 1999). Overexpression of the C-terminal domain in the ein2 mutant will partially restore downstream responses to jasmonic acid and paraquat, but not ethylene, indicating that this protein functions in at least two different signalling pathways (Alonso et al., 1999). EIN3 and EIN3-like (EIL) proteins belong to a family of transcription factors that work downstream from EIN2 (Chao et al., 1997; Alonso et al., 1999). EIN3, EIL1 and EIL2 bind in a sequence-specific manner to the primary ethylene-response element (PERE) of ERF1, an ethylene inducible gene that belongs to the Ethylene Response Element Binding Protein (EREBP) family of DNA binding proteins (Solano et al., 1998). ERF1 directly activates transcription of a wide variety of ethylene-responsive pathogenesis-related genes by binding to the GCC-box, indicating that a transcriptional cascade is involved in ethylene signalling. ERN1, a nuclear localized negative regulator of ethylene responses that acts downstream of EIN3 has also been identified recently (Trentmann, 2000).
Three genes with homology to the Arabidopsis EIN3 have been cloned from tomato, LeEIL1–3, all of which were shown to be functional by mutant complementation in Arabidopsis, and have been shown to play a role in regulating ethylene responses (Tieman et al., 2001). Transgenic tomato plants with reduced levels of either one or more LeEIL genes showed that LeEILs are functionaly redundant positive regulators of many ethylene responses (Tieman et al., 2001). The LeEIL transcription factors are believed to regulate the ERF1 transcription factors, and a possible signal transduction pathway from the receptor to ERF1 is illustrated in Fig. 3. However, although an ethylene-related signal-transduction pathway from EIN3 to ERF1 to pathogenesis related (PR) proteins has been established in Arabidopsis (reviewed in Deikman, 1997; Solano et al., 1998) and from EREBPs to PR proteins in tomato (Gu et al., 2000), a similar route from EIN3 to fruit ripening has yet to be elucidated in tomato.
|
|
Gene regulation during ripening |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
As ripening progresses, the expression of many genes has been shown to be initiated or up-regulated (Table 1). Analysis of ripening-related gene expression in mutant or transgenic plants has indicated the presence of two types of gene regulation, ethylene-dependent gene regulation and ethylene-independent gene regulation. (DellaPenna et al., 1989; Oeller et al., 1991; Theologis et al., 1993; Picton et al., 1993). These phenomena are both illustrated by examination of expression patterns of ripening-related cDNA clones in antisense ACO tomato fruit (Picton et al., 1993). However it has been found that certain ripening-related genes are more sensitive to low levels of ethylene than others (Lincoln and Fischer, 1988b; Sitrit and Bennett, 1998), and that the residual ethylene levels in low ethylene transgenic fruit may affect the pattern of ripening gene expression (Theologis et al., 1993; Klee, 1993; Picton et al., 1993; Sitrit and Bennett, 1998). Molecular characterization of the promoter regions of ripening-related genes has begun to unravel the mechanisms by which genes are regulated and the role that ethylene plays. One of the motifs identified has been the ethylene-responsive element (ERE), an 8 bp motif, A(A/T)TTCAAA (Montgomery et al., 1993b; Itzhaki et al., 1994) The transcription of E4 and E8 in fruit is stimulated by ethylene (Lincoln et al., 1987). However, E4 expression in leaves is also induced by ethylene but E8 expression is not, suggesting that ethylene regulation of these genes is tissue specific or developmentally regulated (Lincoln and Fischer, 1988a). Analysis of the E8 gene promoter has shown that the DNA sequences required for ethylene-regulated transcription, organ specificity and ethylene-independent ripening-related transcription are distinct (Deikman et al., 1992, 1998). Although the functions of E4 and E8 during ripening are unknown, the predicted peptides encoded by these genes show significant similarity to methionine sulphoxide reductase protein and a dioxygenase with similarity to ACC oxidase, respectively (Montgomery et al., 1993a; Deikman et al., 1998).
|
Antisense suppression of E8 in transgenic tomato fruit results in increased ethylene production indicating that E8 participates in feedback regulation of ethylene during ripening (Kneissl and Deikman, 1996). Analysis of the E4 promoter has shown that ethylene responsiveness requires a minimum of two co-operative cis elements, an upstream regulatory element and a downstream regulatory element (Xu et al., 1996). An EREBP that interacts with one of the elements is present in unripe fruit, indicating that this may act as a repressor of E4 transcription and may be inactivated by ethylene (Montgomery et al., 1993a). Another DNA binding protein, E4/E8BP, has been identified that interacts with both E4 and E8 promoter sequences (Cordes et al., 1989). Mutational analysis of the E4/E8BP DNA binding sequence of E4 has shown that it is involved in modulating E4 transcription and it was proposed that this sequence may function as part of an ethylene response complex (Xu et al., 1996). Subsequently, a cDNA with similar DNA-binding specificity was cloned and expression rates were found to be higher in fruit and increased during ripening, suggesting that E4/E8BP-1 may play a role in ripening (Coupe and Deikman, 1997). Polygalacturonase (PG) promoter analysis has also revealed the presence of ethylene-inducible elements with similarity to the promoters of E4 and E8 (Nicholass et al., 1995). LEACO1 promoter GUS fusions have identified that the region between –396 and –1825 upstream of the LEACO1 sequence is sufficient to confer strong and specific induction of GUS expression in situations known to be accompanied by strong ethylene production (Blume and Grierson, 1997). Sequence analysis of the LEACO1 promoter (Blume et al., 1997) has identified several regions of homology to the promoters of the ripening specific genes 2A11 and E4 between –1722 and –590 (Cordes et al., 1989; Pear et al., 1989), as well as a TCA motif present in stress and pathogen genes (Goldsbrough et al., 1993) and ethylene responsive elements (ERE) found in carnation and tomato E4 (Fig. 4) (Itzhaki et al., 1994; Blume and Grierson, 1997). The –396 region of the LEACO1 promoter–GUS fusion induces the same GUS expression pattern, but with 330-fold lower GUS activities than observed with the –1825 promoter. However, expression of this GUS fusion is not ethylene inducible, indicating that LEACO1 is also regulated by ethylene-independent factors (Itzhaki et al., 1994; Blume and Grierson, 1997). Inconsistencies in transcript accumulation observed during LEACO1 promoter–GUS fusion analyses suggest that during autocatalytic ethylene production, LEACO1 transcription rate and mRNA stability may be enhanced, indicating a level of post-transcriptional control (Blume and Grierson, 1997).
|
Differential display of mRNA has recently been used to isolate novel early ethylene-regulated genes from ethylene-treated late immature green tomato (Zegzouti et al., 1999). On the basis of sequence homology, many of the isolated clones appear to be regulatory proteins involved in signal transduction pathways. Three clones show homology to proteins involved in transcriptional and post-transcriptional regulation of gene expression. ER24, shows 47% identity with a transcriptional co-activator, multi-protein bridging factor 1 (MFB1), that forms part of the TAF (TATA box–binding protein association factors) complex required for transcription activation and, therefore, may form a complex with EREBPs to activate genes such as E4 and E8. ER49 shows similarity to a mitochondrial translational elongation factor. ER68 shows homology to the DEAD (containing the Asp, Ala, Glu, Asp type motif) box ATPase/RNA helicases that facilitates gene expression by unwinding RNA molecules (Zegzouti et al., 1999).
Novel ethylene-regulated ripening-related cDNA clones have recently been isolated from melon using differential display (Hadfield et al., 2000). Furthermore, analysis of ACO antisense melon has revealed that some ripening-related events such as degreening of the rind and cell separation in the peduncular zone are totally dependent on ethylene, whereas other ripening-related events, such as softening and membrane deterioration, are dependent only partially on ethylene (Flores et al., 2001). Thus it appears that some aspects of ethylene-dependent gene expression are conserved between climacteric fruits such as melon and tomato. However, there are examples of ethylene-dependant gene regulation in non-climateric fruits. Degreening of the rind in citrus fruit is prevented by ethylene antagonists (Goldschmit et al., 1993) whereas expression of chlorophyllase (Chlase 1), the enzyme catalysing the first step in the chlorophyll degradation pathway in oranges is enhanced by exogenous application of ethylene (Jacob-Wilk et al., 1999).
|
Colour development |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
The characteristic pigmentation of red ripe tomato fruit is due to the deposition of lycopene, the predominant carotenoid found in tomato fruit, and ß-carotene, which are associated with the change from green to red as chloroplasts are transformed to chromoplasts. At the breaker stage of tomato ripening, i.e. when a red/orange coloration becomes apparent to the human eye, lycopene begins to accumulate and its concentration increases 500-fold in ripe fruits (Fraser et al., 1994). Although genes encoding the majority of the carotenoid biosynthesis enzymes have been cloned, the regulation of this pathway is poorly understood. Therefore, the analysis of ripening mutants is a useful tool for exploring the regulation of this process. Carotenoids are formed by the condensation of two molecules of geranylgeranyl pyrophosphate (GGPP), the ubiquitous isoprenoid precursor, to produce phytoene, which is catalysed by the enzyme phytoene synthase (PSY). A series of dehydrogenation reactions, catalysed by phytoene and
-carotene desaturases, converts phytoene into lycopene. The function of the Psy gene was confirmed by the production of transgenic plants with altered levels of Psy expression. Antisense suppression of a ripening-related clone pTOM5 (Psy1) resulted in yellow tomatoes with disrupted lycopene accumulation (Bird et al., 1991) whereas over-expression of pTOM5 in the mutant yellow flesh tomato restored lycopene synthesis (Fray and Grierson, 1993). Due to the beneficial anti-oxidant properties of lycopene, researchers have tried transgenic approaches to increase tomato fruit lycopene content. However, this has resulted in unwanted pleiotropic effects, such as co-suppression of endogenous Psy genes and dwarfism due to adverse changes in metabolism (Fray et al., 1995). Recently a bacterial Psy has been over-expressed successfully in tomato resulting in 1.8-fold and 2.2-fold increases in tomato lycopene and ß-carotene, respectively (Fraser et al., 2002). Biochemical data obtained from analysis of the colourless non-ripening mutant Cnr suggests that carotenoid formation is dependent on an accessible pool of GGPP (Fraser et al., 2001). The Cnr mutation is the result of a lesion in a single gene that has pleiotropic effects on ripening, including a lack of pigmentation and minimal softening, indicating that the Cnr gene is required for normal ripening (Thompson et al., 1999). The Cnr mutant exhibits reduced levels of GGDP, low levels of total carotenoids and undectectable levels of phytoene and lycopene. As levels of other related isoprenoids were similar to that of wild type it is possible that an as yet unidentified GGPP synthase (two have been identified from Arabidopsis: Scolnik and Bartley, 1996), is responsible for the production of GGPP that is committed to the carotenoid pathway. Cloning of Cnr may thus provide valuable insight into ripening-related carotenoid formation. However, the characterization of other colour mutant phenotypes has contributed to the understanding of carotenoid biosynthesis. Map-based cloning of two mutant genes Beta (B), a single dominant mutation that increases ß-carotene in the fruit, and old-gold (og), a recessive mutation that abolishes ß-carotene and increases lycopene, has revealed that B encodes a novel type of lycopene ß-cyclase, an enzyme that converts lycopene to ß-carotene. Null mutations in the B gene are responsible for the phenotype in og mutants (Ronen et al., 2000).
The high-pigment mutant (hp) exhibits twice the normal level of carotenoids (Bramley, 1997), increased plastid number (Yen et al., 1997) and an exaggerated photomorphogenic de-etiolation response, indicating that hp-1 may influence phytochrome signalling (Peters et al., 1992). Analysis of phytochrome levels in mutant and wild-type seedlings has indicated that the wild-type HP-1 acts as a negative regulator of phytochrome signal transduction (Peters et al., 1992). The hp-2 mutant, which is non-allelic to hp-1 but exhibits a similar phenotype, is homologous to Arabidopsis DE-ETIOLATED 1 (Pepper et al., 1994; Mustilli et al., 1999) indicating that light signalling plays an important role in fruit pigment accumulation. Recent work (Alba et al., 2000) has further confirmed the role that light plays in phytochrome mediated carotenoid biosynthesis (Khudairi and Arboleda, 1971). Alba et al. (2000) have shown that red light treatment of mature green fruit resulted in increased lycopene accumulation that could be reversed by exposure to far red light. Continued research in this area is necessary to establish if crosstalk occurs between ethylene and phytochrome signal transduction pathways during fruit ripening. However, crosstalk between phytochrome signalling and PR gene expression has been observed in Arabidopsis (Genoud and Metraux, 1999)
|
Cell wall softening |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
Due to the economic importance of post-harvest deterioration of fruit crops, enzymes that are implicated in cell wall softening have been examined by transgenic manipulation and in vitro assays. A comprehensive review of this topic has recently been published (Brummell and Harpster, 2001) therefore this review will not cover all the data concerning cell wall softening enzymes but rather draw attention to enzymes that exhibit ethylene regulation. During ripening partial disassembly of the fruit cell wall is largely responsible for softening and textural changes. As ripening progresses, the cell wall becomes increasingly hydrated as the pectin rich middle lamella is modified and partially hydrolysed. The changes in cohesion of the pectin gel governs the ease with which one cell can be separated from another, which in turn affects the final texture of the ripe fruit. In soft fruit such as tomato this process occurs early in ripening (Crookes and Grierson, 1983) whereas in crisp fruits such as apple it is a late-ripening process.
The tomato fruit PG is a major cell wall polyuronide degrading enzyme. It is transcriptionally activated during ripening (DellaPenna et al., 1989; Montgomery et al., 1993b) and the PG promoter sequence contains ethylene-dependent ripening-specific control elements (Nicholass et al., 1995). Analysis of low ethylene transgenic tomato plants has shown that induction of PG mRNA occurs at very low ethylene levels (Sitrit and Bennett, 1998). The observations that PG is synthesized de novo during the onset of ripening (Tucker and Grierson, 1982) and purified extracts were able to break down fruit cell walls in vitro (Crookes and Grierson, 1983) made this enzyme a good target for antisense suppression (Sheehy et al., 1988; Smith et al., 1988). Although PG activity in homozygous transgenic plant lines was reduced to 1% of the normal value, the ripe fruit were only slightly firmer leading to the conclusion that PG is not the major determinant of tomato fruit softening (Grierson and Schuch, 1993). However, low PG fruit are more resistant to splitting, mechanical damage and pathogen infection (Gray et al., 1994; Cooper et al., 1998). Analysis of low PG fruit cell walls showed reduced amounts of water-soluble polyuronides, matched by an increase in calcium carbonate-soluble polyuronides suggesting that PG depolymerizes covalently bound pectin allowing it to solublize into an aqueous fraction (Smith et al., 1990; Carrington et al., 1993). Identification of tomato lines in which the PG gene has been functionally inactivated by the insertion of a transposable element show a similar phenotype to the transgenic low PG tomatoes, although polyuronide depolymerization was not examined (Cooley and Yoder, 1998). PG extracted from cell walls may be associated with a 38 kDa glycoprotein, known as the PG ß-subunit or converter, that has not been shown to possess any intrinsic enzyme activity (reviewed in Brummell and Harpster, 2001). However, transgenic plants suppressed for this protein exhibit increased fruit softening during ripening, higher extractable PG activity and more polyuronide solublization, indicating that this protein may be distributed throughout the cell wall to control PG diffusion or action during ripening (Chun and Huber, 2000).
During ripening, pectin methylesterase (PME) is responsible for de-esterification of the highly methyl-esterified polygalacturonans in the cell wall. Esterification drops from 90% in mature green fruit to 35% in red ripe fruit and this makes the polyuronides susceptible to degradation by PG (Koch and Nevins, 1989; Carpita and Gibeaut, 1993). PME is present as a small gene family in tomato, some members of which are highly homologous. PME protein is found in most plant tissues with three isoforms being specific to fruit, one of which, PME1, peaks at breaker (Hall et al., 1993, 1994; Gaffe et al., 1994, 1997). PME-suppressed transgenic plants did not exhibit altered fruit softening during ripening, although pectin fragments extracted from cell walls showed an increase in fragment size and methyl esterification (Tieman et al., 1992; Hall et al., 1993). However, suppression of PME in over-ripe fruit caused an almost complete loss of tissue integrity, therefore PME plays little role in ripening but does affect fruit senescence (Tieman and Handa, 1994). Recent cloning of two ripening-related Rab GTPases has provided evidence that ethylene may regulate vesicular transport between different cellular compartments (Zegzouti et al., 1999; Lu et al., 2001). Interestingly, tomato plants expressing an antisense Rab11 GTPase gene show reduced levels of PG and PME and reduced fruit softening, indicating that Rab11 GTPase plays a role in trafficking of cell-wall modifying enzymes (Lu et al., 2001).
Early in ripening polymeric galactose within the wall begins to be broken down into free galactose and the rise in free galactose continues throughout ripening. The enzyme responsible for this is ß-galactosidase, which is encoded by a gene family of at least seven members, all of which display different patterns of expression during fruit ripening (Smith and Gross, 2000). Analysis of ß-galactosidase-suppressed transgenics and ripening mutants (Carey et al., 1995; Smith and Gross, 2000) has shown that one gene family member, TBG4, may be regulated by ethylene and that strong suppression of ß-galactosidase activity early in ripening can reduce fruit softening by up to 40% (DL Smith, KC Gross, unpublished results, cited in Brummell and Harpster, 2001).
Expansins are cell wall localized enzymes that are thought to cause cell wall loosening by reversibly disrupting the hydrogen bonds between cellulose microfibrils and matrix polysaccharides (Cosgrove, 2000). At least six different expansin genes are expressed during tomato fruit development (Brummell et al., 1999), one of which, EXP1, is ethylene-regulated and is specific for fruit with mRNA transcripts accumulating either just before or at breaker stage (Rose et al., 1997). These results indicate that several enzymes are regulated by ethylene during ripening, but their precise role in fruit softening remains to be elucidated.
|
Volatile production |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
The concentration of organic acids and sugars has an important influence on the taste of ripening fruits. The characteristic flavour of edible fruits results from the aroma volatiles produced within the fruit during ripening and on maceration. The volatile profile of fruits determined by gas chromatography and mass spectroscopy is complex, including many alcohols, aldehydes and esters. Previous studies indicate that the differences in flavour between tomato varieties is due, at least in part, to variation in aroma volatile production (Brauss et al., 1998). Over 400 volatile compounds are detected in tomato fruit (Hobson and Grierson, 1993), although a group of seven including hexanal, hexenal, hexenol, 3-methylbutanal, 3-methylbutanol, methylnitrobutane, and isobutylthiazole are amongst the most important contributors to fruit aroma. These flavour volatiles are formed by several different pathways: 3-methylbutanal and 3-methylbutanol are formed by the deamination and decarboxylation of amino acids whereas hexanal, hexenal and hexenol are formed by lipid oxidation of unsaturated fatty acids on the maceration of fruit. Hexanal and hexenal arise through the activity of lipoxygenases (LOX), which catalyse the hydroperoxidation of polyunsaturated fatty acids containing a cis,cis-pentadiene structure. In plants, reaction intermediates are unsaturated fatty acid hydroperoxides (HPOs), which give rise to the C6 aldehydes through the action of hydroperoxide lyases (HPO-lyase). Two groups of HPO-lyases cleave either 9-(S)-HPOs or 13-(S)-HPOs, generating two C9 fragments, or a C6 and a C12 fragment, respectively (Hatanaka, 1993).
In tomato fruit, linoleic and linolenic acid are the main LOX substrates, and the majority of HPOs found in tomato fruit, however, are 9-isomers. It appears that the 13-isomers, which are produced in a much smaller proportion, are metabolized further to produce flavour volatiles and compounds involved in defence, such as jasmonic acid (JA) (Galliard and Matthew, 1977; Regdel et al., 1994; Smith et al., 1997). The main aldehydes produced are hexanal and hexenal (Galliard and Matthew, 1977), and these aldehydes can then be further transformed into hexenol and hexanol by the action of alcohol dehydrogenase (ADH).
Tomato LOX consists of a family of at least five genes, TomloxA and TomloxB (Ferrie et al., 1994), TomloxC and Tomlox D (Heitz et al., 1997), and TomloxE (NCBI Accession AY008278). Analysis of the role that ethylene plays in the regulation of TomloxA, TomloxB and TomloxC during tomato ripening has shown that the individual isoforms are differentially regulated and may have different functions (Griffiths et al., 1999a). Levels of TomloxA mRNA decrease as ripening progresses and this is delayed in the mutants, Nr and rin as well as sense suppressed ACO1 (low ethylene) fruit, indicating that this gene is regulated by both ethylene and developmental factors (Griffiths et al., 1999a). TomloxB expression increases during ripening and is regulated by ethylene, since the mutant and low ethylene transgenic fruit show reduced expression. TomloxC transcripts increase in response to ethylene, however, ethylene treatment of mature green fruit does not induce expression. This would indicate the presence of a developmental pathway that initiates expression and an ethylene component that enhances mRNA levels once expression has been initiated by the developmental pathway (Griffiths et al., 1999a).
Silencing of TomloxA and TomloxB, by antisense gene knockout, failed to reduce flavour volatiles in ripening fruit and did not alter the levels of TomloxC mRNA (Griffiths et al., 1999b), suggesting that TomloxC may encode the major fruit lipoxygenase involved in flavour volatile production. TomloxC and the mainly leaf expressed TomloxD differ from the other LOX enzymes in that they are chloroplast targeted (Heitz et al., 1997). It therefore seems likely that during ripening TomloxC utilizes the polyunsaturated fatty acids from the redundant thylakoid structures as a substrate to produce the aroma volatiles hexanal and hexanol. TomloxD is thought to function in the octadecanoid defence signalling pathway which is activated in response to herbivore and pathogen attack (Heitz et al., 1997). Suppression of the Arabidopsis chloroplast atLOX2 gene, which is most similar to TomloxD, resulted in the absence of wound-inducible jasmonic acid (JA) accumulation and reduced expression of the wound- and JA-inducible vsp gene (Bell et al., 1995). Therefore, it appears that LOX has a dual role in both volatile production and defence signalling. Recent work with Arabidopsis has provided evidence that atLOX2 is a translation initiation factor-4e-binding protein and that this interaction may play a regulatory role given the numerous examples of products of LOX activity, such as JA, found to be involved in translational activation (Freire et al., 2000). Therefore the ethylene-dependent and independent regulation of LOX genes may orchestrate many aspects of fruit ripening and defence against pathogens.
Alcohol dehydrogenase (ADH) has also been shown to play a role in hexanol and hexenol accumulation in ripening tomato fruit (Speirs et al., 1998). Two ADHs have been indentified in tomato, ADH1 which is found only in pollen, seeds and young seedlings (Tanksley, 1979) and ADH2 which accumulates during the later stages in ripening commitant with the accumulation of flavour volatiles (Chen and Chase, 1993; Longhurst et al., 1994). Genetic manipulation of ADH2 levels in ripening tomato fruit has been shown to affect the balance of some flavour aldehydes and alcohols and fruits with increased ADH2 levels had a more intense ‘ripe fruit’ flavour (Speirs et al., 1998). Tomato ADH2 has not been identified as ethylene inducible. However, it is induced by low oxygen stress and it is likely that increasing ADH2 activity during ripening is a function of decreasing oxygen concentration within ripening fruit (Speirs et al., 2002).
Ethylene has also been shown to be important in the production of aroma volatiles in Charentais melon fruit, as antisense suppression of ethylene production results in strong inhibition of aroma (Ayub et al., 1996; Bauchot et al., 1998). The melon aroma volatile profile mainly consists of volatile esters and, although little information exists regarding the biosynthetic pathways involved, the last step in their formation is catalysed by acyl-transferases (AAT) (Fellman et al., 2000). AATs are a super family of multifunctional AATs and are implicated in diverse biochemical pathways such as fruit ripening, the production of epicuticular waxes and benzoyltransfer reactions (St-Pierre et al., 1998). A ripening-related gene, MEL2, isolated from melon fruit (Aggelis et al., 1997), has been identified as an ATT by expression in yeast (Yahyaoui et al., 2002). Recent analysis of antisense ACO melon has shown that fruit treated with the ethylene antagonist 1-methylcyclopropane have a 50% reduction in AAT activity. This indicates that the last step of alcohol acetylation comprises ethylene-independent and ethylene-dependent AATs (Flores et al., 2002). MEL2 also shows similarity to pTOM36 isolated from a tomato fruit-ripening library (Davies and Grierson, 1989). Although the function of this gene has not been fully investigated, ripening tomato does produces aromatic esters. An AAT gene that plays a crucial role in flavour biogenesis has also been recently cloned from strawberry, a non-climacteric fruit, indicating that AATs are not exclusively regulated by ethylene (Aharoni et al., 2000).
|
Concluding remarks |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
It can be seen that fruit ripening and the role that ethylene plays in its regulation is complex. Identification of additional components involved in ethylene signal transduction, the further characterization of ripening mutants, and additional studies on the biochemistry of ripening are essential for complete understanding of the ripening process. There are similarities between non-climacteric and climacteric fruit ripening and certain ethylene-dependent events in climacteric fruit are observed, apparently in the absence of or with extremely low levels of ethylene, in non-climacteric fruits. Therefore, understanding what controls these processes in non-climacteric ripening may prove pertinent to gaining full understanding of climacteric fruit ripening and vice versa.
|
References |
|---|
|
TopAbstractIntroductionEthylene biosynthesisEthylene perception and signal...Gene regulation during ripeningColour developmentCell wall softeningVolatile productionConcluding remarksReferences |
|---|
Aggelis A, John I, Karvouni Z, Grierson D. 1997. Characterization of two cDNA clones for mRNAs expressed during ripening of melon (Cucumis melo L.) fruits. Plant Molecular Biology 33, 313–322.[Web of Science][Medline]
Aharoni A, Keizer LCP, Bouwmeester HJ et al. 2000. Identification of the SAAT gene involved in strawberry flavor biogenesis by use of DNA microarrays. The Plant Cell 12, 647–661.
Alba R, Cordonnier-Pratt MM, Pratt LH. 2000. Fruit-localized phytochromes regulate lycopene accumulation independently of ethylene production in tomato. Plant Physiology 123, 363–370.
Alonso JM, Hirayama T, Roman G, Nourizadeh S, Ecker JR. 1999. EIN2, a bifunctional transducer of ethylene and stress responses in Arabidopsis. Science 284, 2148–2152.
Aravind L, Ponting CP. 1997. The GAF domain: an evolutionary link between diverse phototransducing proteins. Trends in Biochemical Science 22, 458–459.
Ayub R, Guis M, BenAmor M, Gillot L, Roustan JP, Latche A, Bouzayen M, Pech JC. 1996. Expression of ACC oxidase antisense gene inhibits ripening of cantaloupe melon fruits. Nature Biotechnology 14, 862–866.
Balague C, Watson CF, Turner AJ, Rouge P, Picton S, Pech JC, Grierson D. 1993. Isolation of a ripening and wound-induced cDNA from Cucumis melo L. encoding a protein with homology to the ethylene-forming enzyme. European Journal of Biochemistry 212, 27–34.[Web of Science][Medline]
Barry CS, Blume B, Bouzayen M, Cooper W, Hamilton AJ, Grierson D. 1996. Differential expression of the 1-aminocyclopropane-1-carboxylate oxidase gene family of tomato. The Plant Journal 9, 525–535.[Web of Science][Medline]
Barry CS, Llop-Tous MI, Grierson D. 2000. The regulation of 1-aminocyclopropane-1-carboxylic acid synthase gene expression during the transition from system-1 to system-2 ethylene synthesis in tomato. Plant Physiology 123, 979–986.
Bauchot AD, Mottram DS, Dodson AT, John P. 1998. Effect of aminocyclopropane-1-carboxylic acid oxidase antisense gene on the formation of volatile esters in cantaloupe charentais melon (cv. Vedrandais). Journal of Agricultural and Food Chemistry 46, 4787–4792.[Web of Science]
Bell E, Creelman RA, Mullet JE. 1995. A chloroplast lipoxygenase is required for wound-induced jasmonic acid accumulation in Arabidopsis. Proceedings of the National Academy of Sciences, USA 92, 8675–8679.
Bird CR, Ray JA, Fletcher JD, Boniwell JM, Bird AS, Teulieres C, Blain I, Bramley PM, Schuch W. 1991. Using antisense RNA to study gene-function: inhibition of carotenoid biosynthesis in transgenic tomatoes. Bio-Technology 9, 635–639.
Bleecker AB, Esch JJ, Hall AE, Rodriguez FI, Binder BM. 1998. The ethylene-receptor family from Arabidopsis: structure and function. Philosophical Transactions of the Royal Society of London, Series B 353, 1405–1412.
Bleecker AB, Kende H. 2000. Ethylene: a gaseous signal molecule in plants. Annual Review of Cell and Developmental Biology 16, 1–40.[Web of Science][Medline]
Blume B, Barry CS, Hamilton AJ, Bouzayen M, Grierson D. 1997. Identification of transposon-like elements in non-coding regions of tomato ACC oxidase genes. Molecular and General Genetics 254, 297–303.
Blume B, Grierson D. 1997. Expression of ACC oxidase promoter–GUS fusions in tomato and Nicotiana plumbaginifolia regulated by developmental and environmental stimuli. The Plant Journal 12, 731–746.[Web of Science][Medline]
Bramley P. 1997. The regulation and genetic manipulation of carotenoid biosynthesis in tomato fruit. Pure and Applied Chemistry 69, 2159–2162.[Web of Science]
Brauss MS, Linforth RST, Taylor AJ. 1998. Effect of variety, time of eating, and fruit-to-fruit variation on volatile release during eating of tomato fruit (Lycopersicon esculentum). Journal of Agricultural and Food Chemistry 46, 2287–2292.
Brummell DA, Harpster MH. 2001. Cell wall metabolism in fruit softening and quality and its manipulation in transgenic plants. Plant Molecular Biology 47, 311–340.[Web of Science][Medline]
Brummell DA, Harpster MH, Civello PM, Palys JM, Bennett AB, Dunsmuir P. 1999. Modification of expansin protein abundance in tomato fruit alters softening and cell wall polymer metabolism during ripening. The Plant Cell 11, 2203–2216.
Capitani G, Hohenester E, Feng L, Storici P, Kirsch JF, Jansonius JN. 1999. Structure of 1-aminocyclopropane-1-carboxylate synthase, a key enzyme in the biosynthesis of the plant hormone ethylene. Journal of Molecular Biology 294, 745–756.[Web of Science][Medline]
Carey AT, Holt K, Picard S, Wilde R, Tucker GA, Bird CR, Schuch W, Seymour GB. 1995. Tomato exo-(1-4)-ß-D-galactanase: isolation, changes during ripening in normal and mutant tomato fruit, and characterization of a related cDNA clone. Plant Physiology 108, 1099–1107.[Abstract]
Carpita NC, Gibeaut DM. 1993. Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth. The Plant Journal 3, 1–30.[Medline]
Carrington CMS, Greve LC, Labavitch JM. 1993. Effect of the antisense polygalaturonase gene on cell wall changes accompanying ripening in transgenic tomatoes. Plant Physiology 103, 429–434.[Abstract]
Chang C, Stadler R. 2001. Ethylene hormone receptor action in Arabidopsis. Bioessays 23, 619–627.[Web of Science][Medline]
Chang C, Stewart RC. 1998. The two-component system: regulation of diverse signaling pathways in prokaryotes and eukaryotes. Plant Physiology 117, 723–731.
Chao QM, Rothenberg M, Solano R, Roman G, Terzaghi W, Ecker JR. 1997. Activation of the ethylene gas response pathway in Arabidopsis by the nuclear protein ETHYLENE-INSENSITIVE3 and related proteins. Cell 89, 1133–1144.[Web of Science][Medline]
Chen ARS, Chase T. 1993. Alcohol-dehydrogenase-2 and pyruvate decarboxylase induction in ripening and hypoxic tomato fruit. Plant Physiology and Biochemistry 31, 875–885.[Web of Science]
Chun J-P, Huber DJ. 2000. Reduced levels of ß-subunit protein influence tomato fruit firmness, cell-wall ultrastructure, and PG2-mediated pectin hydrolysis in excised pericarp tissue. Journal of Plant Physiology 157, 153–160.[Web of Science]
Ciardi J, Klee H. 2001. Regulation of ethylene-mediated responses at the level of the receptor. Annals of Botany 88, 813–822.
Ciardi JA, Tieman DM, Lund ST, Jones JB, Stall RE, Klee HJ. 2000. Response to Xanthomonas campestris pv. vesicatoria in tomato involves regulation of ethylene receptor gene expression. Plant Physiology 123, 81–92.
Clark KL, Larsen PB, Wang XX, Chang C. 1998. Association of the Arabidopsis CTR1 Raf-like kinase with the ETR1 and ERS ethylene receptors. Proceedings of the National Academy of Sciences, USA 95, 5401–5406.
Cooley MB, Yoder JL. 1998. Insertional inactivation of the tomato polygalacturonase gene. Plant Molecular Biology 38, 521–530.[Web of Science][Medline]
Cooper W, Bouzayen M, Hamilton A, Barry C, Rossall S, Grierson D. 1998. Use of transgenic plants to study the role of ethylene and polygalacturonase during infection of tomato fruit by Colletotrichum gloeosporioides. Plant Pathology 47, 308–316.[Web of Science]
Cordes S, Deikman J, Margossian LJ, Fischer RL. 1989. Interaction of a developmentally regulated DNA-binding factor with sites flanking two different fruit ripening genes from tomato. The Plant Cell 1, 1025–1034.
Cosgrove DJ. 2000. Loosening of plant cell walls by expansins. Nature 407, 321–326.[Medline]
Cosgrove DJ, Gilroy S, Kao T-H, Ma H, Schultz JC. 2000. Plant signalling 2000. Cross talk among geneticists, physiologists, and ecologists. Plant Physiology 124, 499–505.
Coupe SA, Deikman J. 1997. Characterization of a DNA-binding protein that interacts with 5' flanking regions of two fruit-ripening genes. The Plant Journal 11, 1207–1218.[Web of Science][Medline]
Crookes PR, Grierson D. 1983. Ultrastructure of tomato fruit ripening and the role of polygalacturonase isozymes in cell wall degradation. Plant Physiology 72, 1088–1093.
Davies KM, Grierson D. 1989. Identification of cDNA clones for tomato Lycopersicon esculentum (Mill.) mRNAs that accumulate during fruit ripening and leaf senescence in response to ethylene. Planta 179, 73–80.[Web of Science]
Deikman J. 1997. Molecular mechanisms of ethylene regulation of gene transcription. Physiologia Plantarum 100, 561–566.
Deikman J, Kline R, Fischer RL. 1992. Organization of ripening and ethylene regulatory regions in a fruit-specific promoter from tomato (Lycopersicon-esculentum). Plant Physiology 100, 2013–2017.
Deikman J, Xu RL, Kneissl ML, Ciardi JA, Kim KN, Pelah D. 1998. Separation of cis elements responsive to ethylene, fruit development, and ripening in the 5'-flanking region of the ripening-related E8 gene. Plant Molecular Biology 37, 1001–1011.[Web of Science][Medline]
DellaPenna D, Lincoln JE, Fischer RL, Bennett AB. 1989. Transcriptional analysis of polygalacturonase and other ripening associated genes in Rutgers, rin, nor, and Nr tomato fruit. Plant Physiology 90, 1372–1377.
Dong JG, Fernandezmaculet JC, Yang SF. 1992. Purification and characterization of 1-aminocyclopropane-1-carboxylate oxidase from apple fruit. Proceedings of the National Academy of Sciences, USA 89, 9789–9793.
Dopico B, Lowe AL, Wilson ID, Merodio C, Grierson D. 1993. Cloning and characterization of avocado fruit messenger-RNAs and their expression during ripening and low-temperature storage. Plant Molecular Biology 21, 437–449.[Web of Science][Medline]
Fellman JK, Miller TW, Mattison DS, Mattheis JP. 2000. Factors that influence biosynthesis of flavor compounds in apple fruits. Hortscience 35, 1026–1033.[Web of Science]
Ferrie BJ, Beaudoin N, Burkhart W, Bowsher CG, Rothstein SJ. 1994. The cloning of two tomato lipoxygenase genes and their differential expression during fruit ripening. Plant Physiology 106, 109–118.[Abstract]
Flores F, El Yahaoui F, de Billerbeck G, Romojaro F, Latche A, Bouzayen M, Pech JC, Ambid C. 2002. Role of ethylene in the biosynthetic pathway of aliphatic ester aroma volatiles in Charentais Cantaloupe melons. Journal of Experimental Botany 53, 201–206.
Flores FB, Martinez-Madrid MC, Sanchez-Hidalgo FJ, Romojaro F. 2001. Differential rind and pulp ripening of transgenic antisense ACC oxidase melon. Plant Physiology and Biochemistry 39, 37–43.[Web of Science]
Fraser PD, Bramley P, Seymour GB. 2001. Effect of the Cnr mutation on carotenoid formation during tomato fruit ripening. Phytochemistry 58, 75–79.[Web of Science][Medline]
Fraser PD, Romer S, Shipton CA, Mills PB, Kiano JW, Misawa N, Drake RG, Schuch W, Bramley PM. 2002. Evaluation of transgenic tomato plants expressing an additional phytoene synthase in a fruit-specific manner. Proceedings of the National Academy of Sciences, USA 99, 1092–1097.
Fraser PD, Truesdale MR, Bird CR, Schuch W, Bramley PM. 1994. Carotenoid biosynthesis during tomato fruit-development. Plant Physiology 105, 405–413.[Abstract]
Fray RG, Grierson D. 1993. Molecular-genetics of tomato fruit ripening. Trends in Genetics 9, 438–443.[Web of Science][Medline]
Fray RG, Wallace A, Fraser PD, Valero D, Hedden P, Bramley PM, Grierson D. 1995. Constitutive expression of a fruit phytoene synthase gene in transgenic tomatoes causes dwarfism by redirecting metabolites from the gibberellin pathway. The Plant Journal 8, 693–701.[Web of Science]
Freire MA, Tourneur C, Granier F, Camonis J, El Amrani A, Browning KS, Robaglia C. 2000. Plant lipoxygenase 2 is a translation initiation factor-4E-binding protein. Plant Molecular Biology 44, 129–140.[Web of Science][Medline]
Gaffe J, Mishra KK, Tiznado ME, Handa AK. 1997. Functional expression of a ubiquitously expressed tomato pectin methylesterase gene in transgenic tobacco plants. Plant Physiology 114, 1311–1311.[Web of Science]
Gaffe J, Tieman DM, Handa AK. 1994. Pectin methylesterase isoforms in tomato (Lycopersicon esculentum) tissues: effects of expression of a pectin methylesterase antisense gene. Plant Physiology 105, 199–203.[Abstract]
Galliard T, Matthew JA. 1977. Lipoxygenase-mediated cleavage of fatty acids to carbonyl fragments in tomato fruit. Phytochemistry 16, 339–343.[Web of Science]
Gazzarrini S, McCourt P. 2001. Genetic interactions between ABA, ethylene and sugar signaling pathways. Current Opinion in Plant Biology 4, 387–391.[Web of Science][Medline]
Genoud T, Metraux JP. 1999. Crosstalk in plant cell signaling: structure and function of the genetic network. Trends in Plant Science 4, 503–507.[Web of Science][Medline]
Giovannoni J. 2001. Molecular biology of fruit maturation and ripening. Annual Review of Plant Physiology and Plant Molecular Biology 52, 725–749.[Web of Science][Medline]
Goldsbrough AP, Albrecht H, Stratford R. 1993. Salicylic acid-inducible binding of a tobacco nuclear protein to a 10 bp sequence which is strongly conserved amongst stress-inducible genes. The Plant Journal 3, 563–571.[Web of Science][Medline]
Goldschmit EE, Huberman M, Goren R. 1993. Probing the roles of endogenous ethylene in the degreening of citrus fruit with ethylene antagonists. Plant Growth Regulation 12, 325–329.[Web of Science]
Gray JE, Picton S, Giovannoni JJ, Grierson D. 1994. The use of transgenic and naturally-occurring mutants to understand and manipulate tomato fruit ripening. Plant, Cell and Environment 17, 557–571.
Grierson D, Schuch W. 1993. Control of ripening. Philosophical Transactions of the Royal Society of London, Series B 342, 241–250.
Griffiths A, Barry C, Alpuche-Solis AG, Grierson D. 1999a. Ethylene and developmental signals regulate expression of lipoxygenase genes during tomato fruit ripening. Journal of Experimental Botany 50, 793–798.
Griffiths A, Prestage S, Linforth R, Zhang JL, Taylor A, Grierson D. 1999b. Fruit-specific lipoxygenase suppression in antisense-transgenic tomatoes. Postharvest Biology and Technology 17, 163–173.[Web of Science]
Gu YQ, Yang C, Thara VK, Zhou J, Martin GB. 2000. Pti4 is induced by ethylene and salicylic acid, and its product is phosphorylated by the Pto kinase. The Plant Cell 12, 771–785.
Hackett RM, Ho CW, Lin ZF, Foote HCC, Fray RG, Grierson D. 2000. Antisense inhibition of the Nr gene restores normal ripening to the tomato Never-ripe mutant, consistent with the ethylene receptor-inhibition model. Plant Physiology 124, 1079–1085.
Hadfield KA, Dang T, Guis M, Pech JC, Bouzayen M, Bennett AB. 2000. Characterization of ripening-regulated cDNAs and their expression in ethylene-suppressed Charentais melon fruit. Plant Physiology 122, 977–983.
Hall LN, Bird CR, Picton S, Tucker G, Seymour GB, Grierson D. 1994. Molecular characterisation of cDNA clones representing pectin esterase isozymes from tomato. Plant Molecular Biology 25, 313–318.[Web of Science][Medline]
Hall LN, Tucker GA, Smith CJS et al. 1993. Antisense inhibition of pectin esterase gene-expression in transgenic tomatoes. The Plant Journal 3, 121–129.[Web of Science]
Hamilton A, Lycett GW, Grierson D. 1990. Antisense gene that inhibits synthesis of the hormone ethylene in transgenic plants. Nature 346, 284–287.[Web of Science]
Hamilton AJ, Bouzayen M, Grierson D. 1991. Identification of a tomato gene for the ethylene-forming enzyme by expression in yeast. Proceedings of the National Academy of Sciences, USA 88, 7434–7437.
Hatanaka A. 1993. The biogeneration of green odor by green leaves. Phytochemistry 34, 1201–1218.[Web of Science]
Heitz T, Bergey DR, Ryan CA. 1997. A gene encoding a chloroplast-targeted lipoxygenase in tomato leaves is transiently induced by wounding, systemin, and methyl jasmonate. Plant Physiology 114, 1085–1093.[Abstract]
Herner RC, Sink K. 1973. Ethylene production and respiratory behavior of the rin tomato mutant. Plant Physiology 52, 38–42.
Hobson G, Grierson D. 1993. Tomato. In: G Seymour, J Taylor, G Tucker. eds. Biochemistry of fruit ripening. London UK, Chapman and Hall: 405–442.
Holdsworth MJ, Bird CR, Ray J, Schuch W, Grierson D. 1987. Structure and expression of an ethylene-related mRNA from tomato. Nucleic Acids Research 15, 731–739.
Holdsworth MJ, Schuch W, Grierson D. 1988. Organization and expression for a wound/ripening-related small multigene family from tomato. Plant Molecular Biology 11, 81–88.[Web of Science]
Hua J, Chang C, Sun Q, Meyerowitz EM. 1995. Ethylene insensitivity conferred by Arabidopsis ERS gene. Science 269, 1712–1714.
Hua J, Meyerowitz EM. 1998. Ethylene responses are negatively regulated by a receptor gene family in Arabidopsis thaliana. Cell 94, 261–271.[Web of Science][Medline]
Hua J, Sakai H, Nourizadeh S, Chen QHG, Bleecker AB, Ecker JR, Meyerowitz EM. 1998. EIN4 and ERS2 are members of the putative ethylene receptor gene family in Arabidopsis. The Plant Cell 10, 1321–1332.
Huai Q, Xia YH, Chen YQ, Callahan B, Li N, Ke HM. 2001. Crystal structures of 1-aminocyclopropane-1-carboxylate (ACC) synthase in complex with aminoethoxyvinylglycine and pyridoxal- 5'-phosphate provide new insight into catalytic mechanisms. Journal of Biological Chemistry 276, 38210–38216.
Itzhaki H, Maxson JM, Woodson WR. 1994. An ethylene-responsive enhancer element is involved in the senescence-related expression of the carnation glutathione-S-transferase (GST1) gene. Proceedings of the National Academy of Sciences, USA 91, 8925–8929.
Jacob-Wilk D, Holland D, Goldschmidt EE, Riov J, Eyal Y. 1999. Chlorophyll breakdown by chlorophyllase: isolation and functional expression of the Chlase1 gene from ethylene-treated citrus fruit and its regulation during development. The Plant Journal 20, 653–661.[Web of Science][Medline]
Jiang YM, Fu JR. 2000. Ethylene regulation of fruit ripening: molecular aspects. Plant Growth Regulation 30, 193–200.[Web of Science]
Kende H. 1993. Ethylene biosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology 44, 283–307.[Web of Science]
Khudairi AK, Arboleda OP. 1971. Phytochrome-mediated carotenoid biosynthesis and its influence by plant hormones. Physiologia Plantarum 24, 18–22.
Kieber JJ, Rothenberg M, Roman G, Feldman KA, Ecker JR. 1993. CTR1, a negative regulator of the ethylene response way in Arabidopsis, encodes a member of the Raf family of protein kinases. Cell 72, 427–441.[Web of Science][Medline]
Klee HJ. 1993. Ripening physiology of fruit from transgenic tomato (Lycopersicon esculentum) plants with reduced ethylene synthesis. Plant Physiology 102, 911–916.[Abstract]
Kneissl ML, Deikman J. 1996. The tomato E8 gene influences ethylene biosynthesis in fruit but not in flowers. Plant Physiology 112, 537–547.[Abstract]
Koch JL, Nevins DJ. 1989. Use of purified tomato polygalacturonase and pectinmethylesterase to identify developmental changes in pectins. Plant Physiology 91, 241–255.
Lanahan MB, Yen HC, Giovannoni JJ, Klee HJ. 1994. The Never ripe mutation blocks ethylene perception in tomato. The Plant Cell 6, 521–530.[Abstract]
Lashbrook CC, Tieman DM, Klee HJ. 1998. Differential regulation of the tomato ETR gene family throughout plant development. The Plant Journal 15, 243–252.[Web of Science][Medline]
Lelievre JM, Latche A, Jones B, Bouzayen M, Pech JC. 1997. Ethylene and fruit ripening. Physiologia Plantarum 101, 727–739.
Li N, Huxtable S, Yang SF, Kung SD. 1996. Effects of N-terminal deletions on 1-aminocyclopropane-1-carboxylate synthase activity. FEBS Letters 378, 286–290.[Web of Science][Medline]
Li N, Mattoo AK. 1994. Deletion of the carboxyl-terminal region of 1- aminocyclopropane-1-carboxylic acid synthase, a key protein in the biosynthesis of ethylene, results in catalytically hyperactive, monomeric enzyme. Journal of Biological Chemistry 269, 6908–6917.
Lin Z, Hackett RM, Payton S, Grierson D. 1998. A tomato sequence (AJ005077) encoding an Arabidopsis CTR1 homologue. Plant Physiology 117, 1125.
Lincoln JE, Campbell AD, Oetiker J, Rottmann WH, Oeller PW, Shen NF, Theologis A. 1993. Le-Acs4, a fruit ripening and wound-induced 1-aminocyclopropane-1-carboxylate synthase gene of tomato (Lycopersicon esculentum): expression in Escherichia coli, structural characterization, expression characteristics, and phylogenetic analysis. Journal of Biological Chemistry 268, 19422–19430.
Lincoln JE, Cordes S, Read E, Fischer RL. 1987. Regulation of gene expression ethylene during Lycopersicon esculentum (tomato) fruit development. Proceedings of the National Academy of Sciences, USA 84, 2793–2797.
Lincoln JE, Fischer RL. 1988a. Diverse mechanisms for the regulation of ethylene-inducible gene expression. Molecular and General Genetics 212, 71–75.
Lincoln JE, Fischer RL. 1988b. Regulation of gene expression by ethylene in wild-type and rin tomato fruit (Lycopersicon esculentum) fruit. Plant Physiology 88, 370–374.
Llop-Tous I, Barry CS, Grierson D. 2000. Regulation of ethylene biosynthesis in response to pollination in tomato flowers. Plant Physiology 123, 971–978.
Longhurst T, Lee L, Hinde R, Brady C, Speirs J. 1994. Structure of the tomato Adh 2 gene and Adh 2 pseudogenes, and a study of Adh 2 gene expression in fruit. Plant Molecular Biology 26, 1073–1084.[Web of Science][Medline]
Lu CG, Zainal Z, Tucker GA, Lycett GW. 2001. Developmental abnormalities and reduced fruit softening in tomato plants expressing an antisense Rabl1 GTPase gene. The Plant Cell 13, 1819–1833.
Lui Y, Hoffman NE, Yang SF. 1985. Promotion by ethylene of the capacity to convert 1-aminocyclopropane-1-carboxylic acid to ethylene in preclimacteric tomato and cantaloupe fruit. Plant Physiology 77, 407–411.
Montgomery J, Goldman S, Deikman J, Margossian L, Fischer RL. 1993a. Identification of an ethylene-responsive region in the promoter of a fruit ripening gene. Proceedings of the National Academy of Sciences, USA 90, 5939–5943.
Montgomery J, Pollard V, Deikman J, Fischer RL. 1993b. Positive and negative regulatory regions control the spatial- distribution of polygalacturonase transcription in tomato fruit pericarp. The Plant Cell 5, 1049–1062.
Muller-Dieckmann HJ, Grantz AA, Kim SH. 1999. The structure of the signal receiver domain of the Arabidopsis thaliana ethylene receptor ETR1. Structure with Folding and Design 7, 1547–1556.
Mustilli AC, Fenzi F, Ciliento R, Alfano F, Bowler C. 1999. Phenotype of the tomato high pigment-2 mutant is caused by a mutation in the tomato homolog of DEETIOLATED1. The Plant Cell 11, 145–157.
Nakajima N, Mori H, Yamazaki K, Imaseki H. 1990. Molecular cloning and sequence of a complementary-DNA encoding 1-aminocyclopropane-1-carboxylate synthase induced by tissue wounding. Plant and Cell Physiology 31, 1021–1029.
Nakatsuka A, Murachi S, Okunishi H, Shiomi S, Nakano R, Kubo Y, Inaba A. 1998. Differential expression and internal feedback regulation of 1-aminocyclopropane-1-carboxylate synthase, 1-aminocyclopropane-1-carboxylate oxidase, and ethylene receptor genes in tomato fruit during development and ripening. Plant Physiology 118, 1295–1305.
Nicholass FJ, Smith CJS, Schuch W, Bird CR, Grierson D. 1995. High-levels of ripening-specific reporter gene-expression directed by tomato fruit polygalacturonase gene-flanking regions. Plant Molecular Biology 28, 423–435.[Web of Science][Medline]
Novikova GV, Moshkov IE, Smith AR, Hall MA. 2000. The effect of ethylene on MAPKinase-like activity in Arabidopsis thaliana. FEBS Letters 474, 29–32.[Web of Science][Medline]
Oeller PW, Wong LM, Taylor LP, Pike DA, Theologis A. 1991. Reversible inhibition of tomato fruit senescence by antisense RNA. Science 254, 437–439.
Oetiker JH, Olson DC, Shiu OY, Yang SF. 1997. Differential induction of seven 1-aminocyclopropane-1-carboxylate synthase genes by elicitor in suspension cultures of tomato (Lycopersicon esculentum). Plant Molecular Biology 34, 275–286.[Web of Science][Medline]
Olson DC, Oetiker JH, Yang SF. 1995. Analysis of Le-ACS3, a 1-aminocyclopropane-1-carboxylic acid synthase gene expressed during flooding in the roots of tomato plants. Journal of Biological Chemistry 270, 14056–14061.
Olson DC, White JA, Edelman L, Harkins RN, Kende H. 1991. Differential expression of two genes for 1-aminocyclopropane-1-carboxylate synthase in tomato fruits. Proceedings of the National Academy of Sciences, USA 88, 5340–5344.
Payton S, Fray RG, Brown S, Grierson D. 1996. Ethylene receptor expression is regulated during fruit ripening, flower senescence and abscission. Plant Molecular Biology 31, 1227–1231.[Web of Science][Medline]
Pear JR, Ridge N, Rasmussen R, Rose RE, Houck CM. 1989. Isolation and characterization of a fruit-specific cDNA and the corresponding clone from tomato. Plant Molecular Biology 13, 639–651.[Web of Science][Medline]
Pepper A, Delaney T, Washburn T, Poole D, Chory J. 1994. DET1, a negative regulator of light-mediated development and gene expression in Arabidopsis, encodes a novel nuclear-localized protein. Cell 78, 109–116.[Web of Science][Medline]
Peters JL, Schreuder MEL, Verduin SJW, Kendrick RE. 1992. Physiological characterization of a high-pigment mutant of tomato. Photochemistry and Photobiology 56, 75–82.[Web of Science]
Picton S, Barton SL, Bouzayen M, Hamilton AJ, Grierson D. 1993. Altered fruit ripening and leaf senescence in tomatoes expressing an antisense ethylene-forming enzyme transgene. The Plant Journal 3, 469–481.[Web of Science]
Prescott AG. 1993. A dilemma of dioxygenases (or where biochemistry and molecular biology fail to meet). Journal of Experimental Botany 44, 849–861.
Raz V, Fluhr R. 1993. Ethylene signal is transduced via protein phosphorylation events in plants. The Plant Cell 5, 523–530.[Abstract]
Regdel D, Kuhn H, Schewe T. 1994. On the reaction specificity of the lipoxygenase from tomato fruits. Biochimica et Biophysica Acta 1210, 297–302.[Medline]
Rocklin AM, Tierney DL, Kofman V, Brunhuber NMW, Hoffman BM, Christoffersen RE, Reich NO, Lipscomb JD, Que L. 1999. Role of the nonheme Fe(II) center in the biosynthesis of the plant hormone ethylene. Proceedings of the National Academy of Sciences, USA 96, 7905–7909.
Rodriguez FI, Esch JJ, Hall AE, Binder BM, Schaller GE, Bleecker AB. 1999. A copper cofactor for the ethylene receptor ETR1 from Arabidopsis. Science 283, 996–998.
Ronen G, Carmel-Goren L, Zamir D, Hirschberg J. 2000. An alternative pathway to beta-carotene formation in plant chromoplasts discovered by map-based cloning of Beta and old- gold color mutations in tomato. Proceedings of the National Academy of Sciences, USA 97, 11102–11107.
Rose JKC, Lee HH, Bennett AB. 1997. Expression of a divergent expansin gene is fruit-specific and ripening-regulated. Proceedings of the National Academy of Sciences, USA 94, 5955–5960.
Rottmann WH, Peter GF, Oeller PW, Keller JA, Shen NF, Nagy BP, Taylor LP, Campbell AD, Theologis A. 1991. 1-Aminocyclopropane-1-carboxylate synthase in tomato is encoded by a multigene family whose transcription is induced during fruit and floral senescence. Journal of Molecular Biology 222, 937–961.[Web of Science][Medline]
Schaller GE, Ladd AN, Lanahan MB, Spanbauer JM, Bleecker AB. 1995. The ethylene response mediator ETR1 from Arabidopsis forms a disulfide-linked dimer. Journal of Biological Chemistry 270, 12526–12530.
Scolnik PA, Bartley GE. 1996. A table of some cloned plant genes involved in isoprenoid biosynthesis. Plant Molecular Biology Reporter 14, 305–319.
Sheehy RE, Kramer M, Hiatt WR. 1988. Reduction of polygalacturonase activity in tomato fruit by antisense RNA. Proceedings of the National Academy of Sciences, USA 85, 8805–8809.
Shiu OY, Oetiker JH, Yip WK, Yang SF. 1998. The promoter of LE-ACS7, an early flooding-induced 1- aminocyclopropane-1-carboxylate synthase gene of the tomato, is tagged by a Sol3 transposon. Proceedings of the National Academy of Sciences, USA 95, 10334–10339.
Sitrit Y, Bennett AB. 1998. Regulation of tomato fruit polygalacturonase mRNA accumulation by ethylene: a re-examination. Plant Physiology 116, 1145–1150.
Slater A, Maunders MJ, Edwards K, Schuch W, Grierson D. 1985. Isolation and characterisation of cDNA clones for tomato polygalacturonase and other ripening related proteins. Plant Molecular Biology 5, 137–147.[Web of Science]
Smith CJS, Watson CF, Morris PC, Bird CR, Seymour GB, Gray AJ, Arnold C, Tucker GA, Schuch W, Harding S, Grierson D. 1990. Inheritance and effect on ripeing of antisense polygalacturonase genes in transgenic tomatoes. Plant Molecular Biology 14, 369–379.[Web of Science][Medline]
Smith CJS, Watson CF, Ray J, Bird CR, Morris PC, Schuch W, Grierson D. 1988. Antisense RNA inhibition of polygalacturonase gene expression in transgenic tomatoes. Nature 334, 724–726.[Web of Science]
Smith DL, Gross KC. 2000. A family of at least seven beta-galactosidase genes is expressed during tomato fruit development. Plant Physiology 123, 1173–1183.
Smith JJ, John P. 1993. Activation of 1-aminocyclopropane-1-carboxylate oxidase by bicarbonate carbon-dioxide. Phytochemistry 32, 1381–1386.[Web of Science]
Smith JJ, Linforth R, Tucker GA. 1997. Soluble lipoxygenase isoforms from tomato fruit. Phytochemistry 45, 453–458.[Web of Science]
Solano R, Stepanova A, Chao QM, Ecker JR. 1998. Nuclear events in ethylene signaling: a transcriptional cascade mediated by ETHYLENE-INSENSITIVE3 and ETHYLENE-RESPONSE-FACTOR1. Genes and Development 12, 3703–3714.
Spanu P, Grosskopf DG, Felix G, Boller T. 1994. The apparent turnover of 1-aminocyclopropane-1-carboxylate synthase in tomato cells is regulated by protein- phosphorylation and dephosphorylation. Plant Physiology 106, 529–535.[Abstract]
Spanu P, Reinhardt D, Boller T. 1991. Analysis and cloning of the ethylene-forming enzyme from tomato by functional expression of its messenger-RNA in Xenopus laevis oocytes. EMBO Journal 10, 2007–2013.[Web of Science][Medline]
Speirs J, Corel R, Cain P. 2002. Relationship between ADH activity, ripeness and softness in six tomato cultivars. Scientia Horticulturae 93, 137–142.
Speirs J, Lee E, Holt K, Yong-Duk K, Steele N, Loveys B, Schuch W. 1998. Genetic manipulation of alcohol dehydrogenase levels in ripening tomato fruit affects the balance of some flavor aldehydes and alcohols. Plant Physiology 117, 1047–1058.
Stepanova AN, Ecker JR. 2000. Ethylene signaling: from mutants to molecules. Current Opinion in Plant Biology 3, 353–360.[Web of Science][Medline]
St-Pierre B, Laflamme P, Alarco AM, De Luca V. 1998. The terminal O-acetyltransferase involved in vindoline biosynthesis defines a new class of proteins responsible for coenzyme A-dependent acyl transfer. The Plant Journal 14, 703–713.[Web of Science][Medline]
Tanksley SD. 1979. Linkage, chromosomal association and expression of Adh-1 and Pgm-2 in tomato. Biochemical Genetics 17, 1159–1167.[Web of Science][Medline]
Tarun AS, Theologis A. 1998. Complementation analysis of mutants of 1-aminocyclopropane-1-carboxylate synthase reveals the enzyme is a dimer with shared active sites. Journal of Biological Chemistry 273, 12509–12514.
Tatsuki M, Mori H. 2001. Phosphorylation of tomato 1-aminocyclopropane-1-carboxylic acid synthase, LE-ACS2, at the C-terminal region. Journal of Biological Chemistry 276, 28051–28057.
Theologis A, Oeller PW, Wong LM, Rottmann WH, Gantz DM. 1993. Use of a tomato mutant constructed with reverse genetics to study fruit ripening, a complex developmental process. Developmental Genetics 14, 282–295.[Web of Science][Medline]
Thompson AJ, Tor M, Barry CS, Vrebalov J, Orfila C, Jarvis MC, Giovannoni JJ, Grierson D, Seymour GB. 1999. Molecular and genetic characterization of a novel pleiotropic tomato-ripening mutant. Plant Physiology 120, 383–389.
Tieman DM, Ciardi JA, Taylor MG, Klee HJ. 2001. Members of the tomato LeEIL (EIN3-like) gene family are functionally redundant and regulate ethylene responses throughout plant development. The Plant Journal 26, 47–58.[Web of Science][Medline]
Tieman DM, Handa AK. 1994. Reduction in pectin methylesterase activity modifies tissue integrity and cation levels in ripening tomato (Lycopersicon esculentum Mill) fruits. Plant Physiology 106, 429–436.[Abstract]
Tieman DM, Harriman RW, Ramamohan G, Handa AK. 1992. An antisense pectin methylesterase gene alters pectin chemistry and soluble solids in tomato fruit. The Plant Cell 4, 667–679.
Tieman DM, Klee HJ. 1999. Differential expression of two novel members of the tomato ethylene-receptor family. Plant Physiology 120, 165–172.
Tieman DV, Taylor MG, Ciardi JA, Klee HJ. 2000. The tomato ethylene receptors NR and LeETR4 are negative regulators of ethylene response and exhibit functional compensation within a multigene family. Proceedings of the National Academy of Sciences, USA 97, 5663–5668.
Trentmann SM. 2000. ERN1, a novel ethylene-regulated nuclear protein of Arabidopsis. Plant Molecular Biology 44, 11–25.[Web of Science][Medline]
Tucker GA, Grierson D. 1982. Synthesis of polygalacturonase during tomato fruit ripening. Planta 155, 64–67.[Web of Science]
Vogel JP, Woeste KE, Theologis A, Kieber JJ. 1998. Recessive and dominant mutations in the ethylene biosynthetic gene ACS5 of Arabidopsis confer cytokinin insensitivity and ethylene overproduction, respectively. Proceedings of the National Academy of Sciences, USA 95, 4766–4771.
Vrebalov J, Ruezinsky D, Padmanabhan V, White R, Medrano D, Drake R, Schuch W, Giovannoni J. 2002. A MADS-box gene necessary for fruit ripening at tomato Ripening-inhibitor (Rin) locus. Science 296, 343–346.
Wilkinson J, Lanahan M, Yen H, Giovannoni J, Klee H. 1995. An ethylene-inducible component of signal transduction encoded by Never-ripe. Science 270, 1807–1809.
Wong WS, Ning W, Xu PL, Kung SD, Yang SF, Li N. 1999. Identification of two chilling-regulated 1-aminocyclopropane-1-carboxylate synthase genes from citrus (Citrus sinensis Osbeck) fruit. Plant Molecular Biology 41, 587–600.[Web of Science][Medline]
Xu RL, Goldman S, Coupe S, Deikman J. 1996. Ethylene control of E4 transcription during tomato fruit ripening involves two cooperative cis elements. Plant Molecular Biology 31, 1117–1127.[Web of Science][Medline]
Yahyaoui FEL, Wongs-Aree C, Latché A, Hackett R, Grierson D, Pech JC. 2002. Molecular and biochemical characteristics of a gene encoding an alcohol acyltransferase involved in the generation of aroma volatile esters during melon ripening. European Journal of Biological Chemistry 269, 2359–2366.
Yamamoto M, Miki T, Ishiki Y, Fujinami K, Yanagisawa Y, Nakagawa H, Ogura N, Hirabayashi T, Sato T. 1995. The synthesis of ethylene in melon fruit during the early-stage of ripening. Plant and Cell Physiology 36, 591–596.
Yang SF, Hoffman NE. 1984. Ethylene biosysnthesis and its regulation in higher plants. Annual Review of Plant Physiology 35, 155–189.[Web of Science]
Yen HC, Shelton BA, Howard RL, Lee S, Vrebalov J, Giovannoni JJ. 1997. The tomato high-pigment (hp) locus maps to chromosome 2 and influences plastome copy number and fruit quality. Theoretical and Applied Genetics 95, 1069–1079.[Web of Science]
Yip WK, Moore T, Yang SF. 1992. Differential accumulation of transcripts for 4 tomato 1-aminocyclopropane-1-carboxylate synthase homologs under various conditions. Proceedings of the National Academy of Sciences, USA 89, 2475–2479.
Zarembinski TI, Theologis A. 1994. Ethylene biosynthesis and action: a case of conservation. Plant Molecular Biology 26, 1579–1597.[Web of Science][Medline]
Zegzouti H, Jones B, Frasse P, Marty C, Maitre B, Latche A, Pech JC, Bouzayen M. 1999. Ethylene-regulated gene expression in tomato fruit: characterization of novel ethylene-responsive and ripening-related genes isolated by differential display. The Plant Journal 18, 589–600.[Web of Science][Medline]
Zhang ZH, Barlow JN, Baldwin JE, Schofield CJ. 1997. Metal-catalyzed oxidation and mutagenesis studies on the iron(II) binding site of 1-aminocyclopropane-1-carboxylate oxidase. Biochemistry 36, 15999–16007.[Medline]
Zhou DB, Kalaitzis P, Mattoo AK, Tucker ML. 1996. The mRNA for an ETR1 homologue in tomato is constitutively expressed in vegetative and reproductive tissues. Plant Molecular Biology 30, 1331–1338.[Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  D. Cantu, B. Blanco-Ulate, L. Yang, J. M. Labavitch, A. B. Bennett, and A. L.T. Powell Ripening-Regulated Susceptibility of Tomato Fruit to Botrytis cinerea Requires NOR But Not RIN or Ethylene Plant Physiology, July 1, 2009; 150(3): 1434 - 1449. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Z. Lin, S. Zhong, and D. Grierson Recent advances in ethylene research J. Exp. Bot., June 30, 2009; (2009) erp204v1. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Zhang, B. Yuan, and P. Leng The role of ABA in triggering ethylene biosynthesis and ripening of tomato fruit J. Exp. Bot., April 1, 2009; 60(6): 1579 - 1588. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. A. Mueller, R. K. Lankhorst, S. D. Tanksley, J. J. Giovannoni, R. White, J. Vrebalov, Z. Fei, J. van Eck, R. Buels, A. A. Mills, et al. A Snapshot of the Emerging Tomato Genome Sequence The Plant Genome, March 1, 2009; 2(1): 78 - 92. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Ioannidi, M. S. Kalamaki, C. Engineer, I. Pateraki, D. Alexandrou, I. Mellidou, J. Giovannonni, and A. K. Kanellis Expression profiling of ascorbic acid-related genes during tomato fruit development and ripening and in response to stress conditions J. Exp. Bot., February 1, 2009; 60(2): 663 - 678. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Zhu, E. P. Beers, and R. Yuan Aminoethoxyvinylglycine Inhibits Fruit Abscission Induced by Naphthaleneacetic Acid and Associated Relationships with Expression of Genes for Ethylene Biosynthesis, Perception, and Cell Wall Degradation in 'Delicious' Apples J. Amer. Soc. Hort. Sci., November 1, 2008; 133(6): 727 - 734. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. El-Sharkawy, W. S. Kim, S. Jayasankar, A. M. Svircev, and D. C. W. Brown Differential regulation of four members of the ACC synthase gene family in plum J. Exp. Bot., May 1, 2008; 59(8): 2009 - 2027. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X.-r. Yin, K.-s. Chen, A. C. Allan, R.-m. Wu, B. Zhang, N. Lallu, and I. B. Ferguson Ethylene-induced modulation of genes associated with the ethylene signalling pathway in ripening kiwifruit J. Exp. Bot., May 1, 2008; 59(8): 2097 - 2108. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. S. Khan and Z. Singh 1-Methylcyclopropene Application and Modified Atmosphere Packaging Affect Ethylene Biosynthesis, Fruit Softening, and Quality of 'Tegan Blue' Japanese Plum During Cold Storage J. Amer. Soc. Hort. Sci., March 1, 2008; 133(2): 290 - 299. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. D. Fraser, E. M.A. Enfissi, J. M. Halket, M. R. Truesdale, D. Yu, C. Gerrish, and P. M. Bramley Manipulation of Phytoene Levels in Tomato Fruit: Effects on Isoprenoids, Plastids, and Intermediary Metabolism PLANT CELL, October 1, 2007; 19(10): 3194 - 3211. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Chaib, M.-F. Devaux, M.-G. Grotte, K. Robini, M. Causse, M. Lahaye, and I. Marty Physiological relationships among physical, sensory, and morphological attributes of texture in tomato fruits J. Exp. Bot., June 1, 2007; 58(8): 1915 - 1925. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Pasentsis, V. Falara, I. Pateraki, D. Gerasopoulos, and A. K. Kanellis Identification and expression profiling of low oxygen regulated genes from Citrus flavedo tissues using RT-PCR differential display J. Exp. Bot., June 1, 2007; 58(8): 2203 - 2216. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Hayama, T. Shimada, H. Fujii, A. Ito, and Y. Kashimura Ethylene-regulation of fruit softening and softening-related genes in peach J. Exp. Bot., December 1, 2006; 57(15): 4071 - 4077. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. K. Shukla, A. K. Shasany, M. M. Gupta, and S. P. S. Khanuja Transcriptome analysis in Catharanthus roseus leaves and roots for comparative terpenoid indole alkaloid profiles J. Exp. Bot., November 1, 2006; 57(14): 3921 - 3932. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Ma, H. Tan, X. Liu, J. Xue, Y. Li, and J. Gao Transcriptional regulation of ethylene receptor and CTR genes involved in ethylene-induced flower opening in cut rose (Rosa hybrida) cv. Samantha J. Exp. Bot., August 1, 2006; 57(11): 2763 - 2773. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Moore, P. Payton, M. Wright, S. Tanksley, and J. Giovannoni Utilization of tomato microarrays for comparative gene expression analysis in the Solanaceae J. Exp. Bot., November 1, 2005; 56(421): 2885 - 2895. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Alba, P. Payton, Z. Fei, R. McQuinn, P. Debbie, G. B. Martin, S. D. Tanksley, and J. J. Giovannoni Transcriptome and Selected Metabolite Analyses Reveal Multiple Points of Ethylene Control during Tomato Fruit Development PLANT CELL, November 1, 2005; 17(11): 2954 - 2965. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Genard and B. Gouble ETHY. A Theory of Fruit Climacteric Ethylene Emission Plant Physiology, September 1, 2005; 139(1): 531 - 545. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Fonseca, L. Monteiro, M. G. Barreiro, and M. S. Pais Expression of genes encoding cell wall modifying enzymes is induced by cold storage and reflects changes in pear fruit texture J. Exp. Bot., August 1, 2005; 56(418): 2029 - 2036. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Yuan, Z. Wu, I. A. Kostenyuk, and J. K. Burns G-protein-coupled {alpha}2A-adrenoreceptor agonists differentially alter citrus leaf and fruit abscission by affecting expression of ACC synthase and ACC oxidase J. Exp. Bot., July 1, 2005; 56(417): 1867 - 1875. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. A. Mueller, T. H. Solow, N. Taylor, B. Skwarecki, R. Buels, J. Binns, C. Lin, M. H. Wright, R. Ahrens, Y. Wang, et al. The SOL Genomics Network. A Comparative Resource for Solanaceae Biology and Beyond Plant Physiology, July 1, 2005; 138(3): 1310 - 1317. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Katz, J. Riov, D. Weiss, and E. E. Goldschmidt The climacteric-like behaviour of young, mature and wounded citrus leaves J. Exp. Bot., May 1, 2005; 56(415): 1359 - 1367. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Matarasso, S. Schuster, and A. Avni A Novel Plant Cysteine Protease Has a Dual Function as a Regulator of 1-Aminocyclopropane-1-Carboxylic Acid Synthase Gene Expression PLANT CELL, April 1, 2005; 17(4): 1205 - 1216. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. K. Bruno and C. M. Wetzel The early light-inducible protein (ELIP) gene is expressed during the chloroplast-to-chromoplast transition in ripening tomato fruit J. Exp. Bot., December 1, 2004; 55(408): 2541 - 2548. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Yokotani, S. Tamura, R. Nakano, A. Inaba, and Y. Kubo Characterization of a novel tomato EIN3-like gene (LeEIL4) J. Exp. Bot., December 1, 2003; 54(393): 2775 - 2776. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. J. White Recent advances in fruit development and ripening: an overview J. Exp. Bot., October 1, 2002; 53(377): 1995 - 2000. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||