JXB Advance Access published online on January 19, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erl272
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
RESEARCH PAPER |
Reproductive development and phenotypic differences in garlic are associated with expression and splicing of LEAFY homologue gaLFY
1The Robert H. Smith Institute of Plant Science and Genetics in Agriculture, The Hebrew University of Jerusalem, Faculty of Agricultural, Food, and Environmental Quality Sciences, Rehovot 76100, Israel
2Department of Ornamental Horticulture, Volcani Center, Bet Dagan 50250, Israel
To whom correspondence should be addressed. E-mail: vhrkamen{at}valcani.agri.gov.il
Received 7 September 2006; Revised 15 November 2006 Accepted 16 November 2006
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Modern garlic (Allium sativum L.) cultivars are sterile and propagated only vegetatively. The recent discovery of fertile genotypes in Central Asia and the restoration of flowering and fertility by environmental manipulations open the way for in-depth florogenetic, genetic, and molecular research in garlic. In the present work, two bolting garlic accessions were employed: #3026, developing normal flowers and seeds, and #2509, in which flowers abort at the early stages of development. Morphological studies showed transition of the apical meristems from the vegetative to the reproductive stage and inflorescence initiation in both genotypes. Low temperatures promote transition of the apex and stem elongation, but have no effect on the phenotypic expression of the inflorescence development. The initial stages of reproductive development in non-flowering #2509 plants were followed by abortion of floral primordia at the differentiation stage. A search for genes involved in the control of flowering in garlic resulted in identification of the garlic LEAFY/FLO homologue, gaLFY. Further comparative analyses of gene expression revealed two gaLFY transcripts, differing in 64 nucleotides, with clear splicing borders. The short variant transcript was identified in both genotypes throughout all development stages, whereas the long variant appears in the flowering genotype #3026 only during reproductive development. The phenotypic differences in garlic, with regard to flowering, may be associated with the efficacy of the splicing process.
Key words: Allium sativum, alternative splicing, bulbs, fertility, flowering time control, LFY
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Modern garlic (Allium sativum L.) cultivars are sterile and thus propagated only vegetatively. The lack of sexual propagation prohibits genetic studies, and severely impairs conventional breeding. Recently, fertility restoration in garlic has become a major goal of Allium researchers, and attention has been directed towards the morphological and physiological processes during florogenesis (Kamenetsky and Rabinowitch, 2001, 2002; Etoh and Simon, 2002; Simon and Jenderek, 2003). Garlic genotypes are categorized as non-bolting, semi-bolting, and bolting types (Takagi, 1990; Kamenetsky and Rabinowitch, 2001; Etoh and Simon, 2002; Kamenetsky et al., 2004a, b). In the former, the inflorescence is either not visible, or its initials abort at the early stages of differentiation. In the latter, scapes grow to their final size, but florogenesis is usually interrupted by development of topsets (bulb-like structures) in the inflorescence (Kamenetsky and Rabinowitch, 2001; Kamenetsky et al., 2004a, b). Environmental manipulations of temperature and photoperiod led to regulation of flower and/or topset development in the inflorescence, and to completion of floral development and seed production (Kamenetsky et al., 2004b). Fertility restoration thus provided evidence that flowering in garlic is controlled by a number of genetic factors encoding a cascade of processes, some of which are differentially regulated by photoperiod and temperature, and that the garlic genome contains all genes required for the flowering and seed production (Kamenetsky et al., 2004b). A thorough understanding of the genetic coding of florogenesis and its interactions with the environment should improve our knowledge of flowering processes and facilitate fertility restoration in garlic.
Flowering regulation is a complicated process created by an intricate network of signalling pathways. Partial understanding of the genetics and molecular mechanisms underlying flower development was obtained by analysing genetic variations in model plants such as Arabidopsis thaliana, snapdragon (Antirrhinum majus), and corn (Zea mays), among others (Coen et al., 1990; Weigel and Nilsson, 1995; Bomblies et al., 2003; Sreekantan et al., 2004). These studies led to the identification of components within individual signalling pathways that affect flowering, and to their positioning within molecular hierarchies. The most important environmental factors controlling flowering in model species are photoperiod (Corbesier et al., 1996) and low temperatures (Michaels and Amasino, 2000). In addition, an autonomous pathway (Martinez-Zapater and Somerville, 1990; Koornneef et al., 1991) and flowering promotion by gibberellins (Wilson et al., 1992; Putterill, et al., 1995; Blazquez et al., 1998) were reported.
It was demonstrated in model plants that the transition from a vegetative to a reproductive meristem is controlled by floral meristem identity genes, followed by floral initiation, and that differentiation (organogenesis) is coded by floral homeotic genes, for example the Arabidopsis gene LEAFY (AtLFY) and its homologues in other plants (e.g. FLORICAULA and FALSIFLORA) (Weigel and Meyerowitz, 1994; Simpson et al., 1999). In Arabidopsis, LFY is expressed constitutively throughout the annual life cycle; however, its expression is rather low during vegetative growth, and rises significantly in reproductive tissues (Weigel et al., 1992; Blazquez et al., 1997). In Antirrhinum, a decline in FLO mRNA levels coincided with an arrest of reproductive development and the initiation of vegetative organs in the inflorescence (Coen et al., 1990). In Titanotrichum oldhamii, which sequentially produces flowers and bulbils in the inflorescence, reverse transcription-polymerase chain reaction (RT-PCR) studies showed a rise and decrease in the expression of the LFY/FLO homologue GFLO during normal flower development and following bulbil formation, respectively (Wang et al., 2004). The roles of LFY/FLO homologues in flower development have been demonstrated in numerous dicots (Coen et al., 1990; Weigel and Nilsson, 1995; Sreekantan et al., 2004), while little is known about the function of these meristem identity genes in monocots. Recently, LFY/FLO homologues were found in rice (Kyozuka et al., 1998) and in maize (Bomblies et al., 2003), and it was shown that these genes share conserved roles with dicots in flower and inflorescence pattern.
LEAFY is a transcription factor that affects not only inflorescence initiation but also floral organ determination. In the latter situation, LFY regulates the downstream expression of at least three genes: the meristem and floral identity gene APETALA1 (AP1) which is expressed largely in petals and sepals; the floral organ-determining gene APETALA3 (AP3), required for the development of petals and stamens; and AGAMOUS (AG), which is required for the development of stamens and carpels (Parcy et al., 1998; Busch et al., 1999; Wagner et al., 1999, 2004; Lamb et al., 2002).
Alternative splicing has recently emerged as one of the most significant generators of functional complexity in higher plants (Kazan, 2003), as it generates multiple proteins with different functions from a single gene, and thus greatly enhances the coding potential of a genome. Multiple transcripts from a single gene can result from exon skipping, mutual exclusion of exons and retention of introns, and/or selection of an alternative 5' or 3' site. Alternative splicing can affect the stability and translatability at the RNA level and produce truncated or extended proteins with altered (increased, decreased, or loss of) activity, cellular localization, and/or regulation (Smith et al., 1989; Reddy, 2004). A few examples were already reported for flowering-related genes. Thus, FCA, a promoter of the floral transition in Arabidopsis, produces four transcripts (
, ß, 
, and 
) by alternative processing (Macknight et al., 2002). Two major FLC (vernalization-associated gene, determined as a strong flowering antagonist) haplogroups (FLCA and FLCB) are associated with flowering time variation in Arabidopsis (Caicedo et al., 2004).
In the present work, two bolting garlic accessions were employed: #3026, developing normal flowers and seeds, and #2509, in which topsets develop in the inflorescence and flowers abort at the early stages of development. Tests were conducted to determine whether the LFY homologue is present in garlic and how it is expressed during plant development and floral initiation.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Plant material and sampling procedures
Garlic bulbs, accessions #3026 and #2059, introduced into Israel from Kazakhstan in 1999, were obtained from the Field Gene Bank for Vegetatively Propagated Short-Day Allium spp., The Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot, Israel. Both plants produce mature bulbs under Israeli spring conditions. Each clone was propagated vegetatively from a single bulb, to guarantee genetic uniformity of the experimental stock. In June 2003, mature bulbs were harvested, cured, and stored under ambient conditions, in a roofed shed, until September. Healthy looking intact bulbs were then transferred to controlled storage for 8 weeks, at either 4 °C or 20 °C in the dark. In November, bulbs were broken and cloves were planted at the experimental farm in Rehovot, using standard agricultural practices throughout.
Phenological data, including developmental stages, number of leaves, and floral scape length, were recorded throughout the experiment. Destructive morphological analyses were performed weekly, on five randomly selected plants per treatment. Apical meristems were sampled for RNA analysis (i) during ambient storage of the parent plants (beginning of August 2003); (ii) prior to bulb storage at 4 °C or 20 °C (September 2003); (iii) at the end of 8 weeks storage, prior to planting (November 2003); (iv) following sprouting of the fourth foliage leaf (15–20 December 2003); and (v) following transition to the reproductive stage (10–15 January 2004).
Morphological studies
Developmental morphology was studied under a stereoscope (Zeiss Stemi 2000-C), and by scanning electron microscopy (SEM; JSM-35C, JEOL Japan; Kamenetsky, 1994). Prior to microscopic observation, freshly harvested plants were carefully stripped of their leaves, and the spathes removed from the developing inflorescences. Samples for SEM analysis were fixed in a 5:5:90 (by vol.) mixture of glacial acetic acid:formalin (40%):ethanol (70%), and were dehydrated in a graded ethanol series (25, 50, 75, 95, 100%). Immediately thereafter, tissues were dried using liquid CO2 in a Bio-Rad 750 critical-point dryer. Samples were then mounted on SEM stubs with double-sided tape and sputter-coated with 
10 nm of gold. SEM studies were performed with an accelerating potential of 15 kV.
Nucleic acid isolation
DNA from leaves was extracted using a Nucleon PhytoPure Genomic DNA Extraction Kit (Amersham Biosciences, Buckinghamshire, UK). An RNeasy Mini Kit (Qiagen, Hilden, Germany) was used for total RNA extraction from the apical meristem, leaves, and roots.
PCR and cloning of PCR products for sequencing
The garlic homologue of LFY was amplified by standard PCR and RT-PCR procedures (Sambrook and Russell, 2001), using the following primers: forward, 5'-GAGCTCGACGACATGATG-3' (ELDDMM); and reverse, 5'-CTTGGGCTTGTTGATGTA-3' (NKPK).
RT-PCR of garlic RNA was followed by nested PCR. The primers for RT-PCR were forward nested, 5'-ACCACTCTCTCCCACCTCTT-3'; and reverse nested, 5'-TTCGCAATCGCCTGAACCT-3'. Primers for 18S rRNA were designed from Nicotiana tabacum (GB: AJ236016 [GenBank] ): forward, 5'-AGGAATTGACGGAAGGGCAC-3'; reverse, 5'-GTGCGGCCCAGAACATCTAAG-3'.
The amplified PCR products were analysed on an agarose gel, excised, and cloned into the vector pDrive (Qiagen) for sequencing. Alignment of the deduced amino acid sequences of the putative garlic DNA and cDNAs was performed using DNAMAN software.
Southern hybridization was performed according to Sambrook and Russell (2001), using the digoxigenin-labelled gaLFY clone as a probe (Roche Diagnostics GmbH, Germany).
RNase protection assays were performed according to Zeitoune et al. (1999).
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Effect of storage temperature on the development of two garlic genotypes
The two garlic clones #2509 and #3026 differ in their ability to undergo normal florogenesis (Table 1). In both genotypes, low storage temperatures significantly promote leaf elongation and transition from the vegetative to reproductive state (Table 1; Fig. 1A).
|
|
In cold-treated #3026 plants, initial inflorescence development occurred in
85–90% of the plants. The transition from the vegetative (Fig. 1B) to the reproductive stage was followed by differentiation of flower primordia in the apical meristem (Fig. 1C), which thereafter developed into normal flowers (Fig. 1D). A small number of topsets were formed in the inflorescences, irrespective of storage treatment. In plants subjected to 4 °C, florogenesis proceeded to completion, thus resulting in the development of normal flowers by the end of May (Fig. 1E) and the production of fertile seeds. In comparison, bulb storage at 20 °C resulted in only 6% of the plants with visible scapes. However, elongation of those was arrested before the final size was reached (Table 1), and the developing inflorescences were aborted within the spathe. In 94% of the plants stored at 20 °C, scape was arrested in the early stages of elongation (Fig. 1F). Initial inflorescence development occurred in 84% of the cold-treated #2509 plants. However, flowers were aborted at the early stages of their differentiation, and numerous topsets developed in the inflorescence (Fig. 1G, H). In plants stored at 20 °C, scape was arrested in the early stages of elongation.
Gene identification and expression
DNA segments from garlic accession #3026 were amplified by PCR, using primers from conserved LFY regions of homologous genes from various plants. The major PCR product (700 bp) was isolated and cloned (Fig. 2), and sequence analysis of the translation product indicated 46.7% and 61% homology to AtLFY from Arabidopsis thaliana and FLORICAULA of Antirrhinum, respectively (Fig. 3). The gene fragment isolated from garlic was thus designated gaLFY and deposited in GenBank (accession no. AY4563104).
|
|
DNA from the two garlic genotypes was cleaved with the restriction enzymes EcoRI and HindIII. Southern blot analyses using the gaLFY clone as a probe indicated the presence of a single-copy LFY homologue in both garlic clones (Fig. 4).
|
Expression of gaLFY in developing garlic plants was followed by RT-PCR (Fig. 5). A single amplified transcript was observed in cDNA of garlic accession #2509, which under our experimental conditions does not produce fully developed flowers. However, amplification of cDNA from accession #3026 (producing fertile flowers and seeds after storage at 4 °C) during the transition phase from the vegetative to reproductive state yielded two distinct bands (Fig. 5, lanes 5 and 7). The two bands were cloned, designated as ‘gaLFY short’ (gaLFYs) and ‘gaLFY long’ (gaLFYl), and their sequence analysis revealed 95% identity. The sequence of gaLFYl (570 bp) was identical to that of the corresponding sequence in garlic genomic DNA, whereas gaLFYs is shorter (506 bp) and it shows 89% identity to garlic genomic DNA, due to a 64 bp deletion between bases 161 and 225 (Fig. 6). The 64 bp deleted sequence was confirmed as an intron by the NetGene program, checking donor and acceptor sites, as well as the branch point, at a confidence level of 95%.
|
|
Spliced transcript gaLFYs appears in both genotypes during all developmental stages, whereas unspliced gaLFYl was shown only in #3026 in the transition phase from the vegetative to reproductive stage (four foliage leaves) and later at the stage of flower differentiation (eight foliage leaves) (Fig. 5).
RNA was further extracted from the inflorescences of both genotypes at the beginning of differentiation of the individual flowers, and RT-PCR was performed (Fig. 7). Both gaLFYl and gaLFYs were clearly visible in extracts from accession #3026. In #2509 plants, only the gaLFYs transcript was clearly visible. The more sensitive and size-dependent RNase protection assay demonstrated the presence of a considerable amount of both transcripts in accession #3026, in comparison with accession #2509, expressing predominantly gaLFYs (Fig. 8).
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
The discovery of the fertile genotypes in Central Asia in the 1980s (Etoh, 1985; Etoh and Simon, 2002), the restoration of flowering and fertility in bolting plants by environmental manipulations (Kamenetsky et al., 2004b), and the recent acquisitions of new variations in bolting and blooming (Table 1; Fig. 1; Etoh and Simon, 2002; Jenderek and Hannan, 2004; Kamenetsky et al., 2004a) open the way for in-depth florogenetic, genetic, and molecular research in garlic.
Morphological studies of two bolting genotypes showed transition of the apical meristems from the vegetative to the reproductive stage following the formation of a specific number of leaves. However, the initial stages of reproductive development in #2059 plants were followed by abortion of floral primordia already at the differentiation phase. In contrast, florogenesis in #3026 plants proceeded normally, and fertile flowers and seeds were produced. As with other geophytes (De Hertogh and Le Nard, 1993), florogenesis in garlic is promoted by low temperatures and a long photoperiod. Hence, scape elongation occurred only in a few (6%) of the #3026 plants treated at 20 °C, followed by inflorescence abortion (Table 1; Fig. 1; Kamenetsky et al., 2004b). Cold treatment promoted transition to the reproductive stage already at the physiological age of 6–7 leaves, whereas plants stored under non-inductive 20 °C underwent such a transition much later, at an older physiological age of 12–14 leaves, most probably when the autonomous pathway became operational, when the photoperiod became sufficiently long, or both (Table 1), as suggested for Arabidopsis (Simpson and Dean, 2002). It is therefore concluded that in both accessions, low temperatures promoted transition of the apex and stem elongation, but did not affect topset formation. These results indicate a strong genetic control and minimum or no effect of storage treatment on the phenotypic expression of flower and topset differentiation.
A search for genes involved in the control of flowering in garlic resulted in identification of a fragment of a gene designated gaLFY, homologous to LFY and FLO (Fig. 3; Coen et al., 1990; Weigel et al., 1992). The temporal accumulation of LFY is often associated with determining florogenesis (Weigel and Nilsson, 1995; Blazquez et al., 1997), while mutations or down-regulation of LFY and its homologues lead to a reversion in flower determination and the development of vegetative shoots (Coen et al., 1990; Weigel et al., 1992; Molinero-Rosales et al., 1999; Wang et al., 2004). In garlic, Southern blot analysis revealed only one copy of gaLFY in the genome of garlic in both accessions (Fig. 4), but further comparative analyses of gene expression using RT–PCR revealed two gaLFY transcripts: gaLFYl and gaLFYs. The two transcripts were amplified, and sequence analysis clearly indicated that gaLFY has an intron–exon border. LFY transcripts from Arabidopsis are known to undergo splicing (e.g. GenBank accession no. AF466800); however, to the best of our knowledge, this is the first evidence of alternative splicing of an LFY homologue.
Strong evidence is available to support the fact that alternative splicing plays a major role in the regulation of gene expression in plants, and that it has functional significance in the transition from the vegetative to the reproductive phase (Macknight et al., 1997; Eckardt, 2002; Kazan, 2003). Yet the nature and exact role of these processes in floral regulation is not clear. For instance, FCA and FLC, known to be involved in the flowering process (Simpson et al., 1999), were recently reported to be alternatively spliced (Eckardt, 2002; Caicedo et al., 2004). In garlic, spliced transcript gaLFYs is continuously present in all tissues of the plant, while the second unspliced transcript gaLFYl accumulates mainly during flower differentiation (Figs 5, 7). In both studied garlic accessions, splicing of gaLFY transcripts occurs throughout the vegetative phase. During reproductive development, splicing is partially inhibited and accumulation of the unspliced form (gaLFYl) was observed (Fig. 8). The two studied genotypes differ in the expression of the unspliced variant gaLFYl: it was strongly expressed in the flowering accession during both inflorescence initiation and flower differentiation, but not in the genotype #2509, in which differentiating flowers were aborted. It can be concluded that, of the two gaLFY transcripts, flower differentiation is associated with accumulation of the unspliced gaLFYl variant of the LFY homologue and presumably the phenotypic differences, with regard to flowering, are associated with the efficacy of the splicing process.
For most plant species, only one FLO/LFY homologue was reported to be involved in the regulation of florogenesis. Recently, however, two LFY homologues were isolated from apple floral buds (AFL1 and AFL2; Wada et al., 2002), Eucalyptus (ELF1 and ELF2; Southerton et al., 1998), and maize (zfl1 and zfl2; Bomblies et al., 2003). In Eucalyptus, one gene is expressed in the developing floral organs in a pattern similar to LFY, while the other appears to be inactive (Southerton et al., 1998). Similarly to the two gaLFY transcripts, AFL1 is only expressed in floral buds of apple during transition from vegetative to reproductive growth, whereas AFL2 was detected in all tissues of the plant (Wada et al., 2002). gaLFY, on the other hand, seems to be a single-copy gene (Fig. 4), but two LFY products are generated by alternative splicing. Presumably, different plants apply different strategies in their evolutionary track, i.e. coding for the various LFY forms by multicopy genes or by alternative splicing.
|
Acknowledgements |
|---|
This work was supported by the Minerva Otto Warburg Center for Plant Biotechnology. We thank the Wolfson Foundation for the use of facilities contributed to the Robert H. Smith Plant Science Institute. We also acknowledge the helpful discussions with Dr A. Samach (The Hebrew University of Jerusalem) and Dr Michel Zaccai (University of Ben Gurion) during this study. Sequences generated during the course of this work were deposited with GenBank, accession nos AY672745 [GenBank] , AY563104 [GenBank] , and AY563105 [GenBank] .
|
Footnotes |
|---|
* Authorship is shared equally.
|
Abbreviations |
|---|
RT-PCR, reverse transcription–polymerase chain reaction; SEM, scanning electron microscopy.
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Blazquez MA, Soowal LN, Lee Y, Weigel D. (1997) LEAFY expression and flower initiation in Arabidopsis. Development 124 3835–3844.[Abstract]
Blazquez MA, Green R, Nilsson O, Sussman MR, Weigel D. (1998) Gibberellins promote flowering of Arabidopsis by activating the LEAFY promoter. The Plant Cell 10 791–800.
Bomblies K, Wang RL, Ambrose BA, Schmidt RJ, Meeley RB, Doebly J. (2003) Duplicate FLORICAULA/LEAFY homologs zfl1 and zfl2 control inflorescence architecture and flower patterning in maize. Development 130 2385–2395.
Busch MA, Bombiles K, Weigel D. (1999) Activation of a floral homeotic gene in Arabidopsis. Science 285 585–587.
Caicedo AL, Stinchcombe JR, Olsen KM, Schmitt J, Purugganan MD. (2004) Epistatic interaction between Arabidopsis FRI and FLC flowering time genes generates a latitudinal cline in a life history trait. Proceedings of the National Academy of Sciences, USA 101 15670–15675.
Coen ES, Romero JM, Doyle S, Elliott R, Murphy G, Carpenter R. (1990) Floricaula: a homeotic gene required for flower development in Antirrhinum majus. Cell 63 1311–1322.[CrossRef][Web of Science][Medline]
Corbesier L, Gadisseur I, Silvestre G, Jacqmard A, Bernier G. (1996) Design in Arabidopsis thaliana of a synchronous system of floral induction by one long day. The Plant Journal 9 947–952.[CrossRef][Web of Science][Medline]
De Hertogh AA and Le Nard M. (1993) Physiological and biochemical aspects of flower bulbs. In De Hertogh AA and Le Nard M (Eds.). The physiology of flower bulbsAmsterdam Elsevier pp. 53–69.
Eckardt NA. (2002) Alternative splicing and the control of flowering time. The Plant Cell 14 743–747.
Etoh T. (1985) Studies on the sterility in garlic, Allium sativum L. Memoirs of the Faculty of Agriculture, Kagoshima University 21 77–132.
Etoh T and Simon PW. (2002) Diversity, fertility and seed production of garlic. In Rabinowitch HD and Currah L (Eds.). Allium crop sciences: recent advancesWallingford, UK CAB International pp. 101–117.
Jenderek MM and Hannan RM. (2004) Variation in reproductive characteristics and seed production in the USDA garlic germplasm collection. HortScience 39 485–488.
Kamenetsky R. (1994) Life cycle, flower initiation, and propagation of the desert geophyte Allium rothii. International Journal of Plant Science 155 597–605.[CrossRef]
Kamenetsky R and Rabinowitch HD. (2001) Floral development in bolting garlic. Sexual Plant Reproduction 13 235–241.[CrossRef][Web of Science]
Kamenetsky R and Rabinowitch HD. (2002) Florogenesis. In Rabinowitch HD and Currah L (Eds.). Allium crop sciences: recent advancesWallingford, UK CAB International pp. 31–58.
Kamenetsky R, Shafir IL, Baizerman M, Khassanov F, Kik C, Rabinowitch HD. (2004a) Garlic (Allium sativum L.) and its wild relatives from Central Asia: evaluation for fertility potential. Acta Horticulturae 637 83–91.
Kamenetsky R, Shafir IL, Zemah H, Barzilay A, Rabinowitch HD. (2004b) Environmental control of garlic growth and florogenesis. Journal of the American Society for Horticultural Science 129 144–151.
Kazan K. (2003) Alternative splicing and proteome diversity in plants: the tip of the iceberg has just emerged. Trends in Plant Science 8 468–471.[CrossRef][Web of Science][Medline]
Koornneef M, Hanhart CJ, Van Der Veen JH. (1991) A genetic and physiological analysis of late flowering mutants in Arabidopsis thaliana. Molecular and General Genetics 229 57–66.
Kyozuka J, Konishi S, Nemoto K, Izawa T, Shimamoto K. (1998) Down-regulation of RFL, the FLO/LFY homolog of rice, accompanied with panicle branch initiation. Proceedings of the National Acadeny of Sciences, USA 95 1979–1982.
Lamb RS, Hill TA, Tan OK, Irish VF. (2002) Regulation of APETALA3 floral homeotic gene expression by meristem identity genes. Development 129 2079–2086.
Macknight R, Bancroft I, Page T, et al. (1997) FCA, a gene controlling flowering time in Arabidopsis, encodes a protein containing RNA-binding domains. Cell 89 737–745.[CrossRef][Web of Science][Medline]
Macknight R, Duroux M, Laurie R, Dijkwel P, Simpson G, Dean C. (2002) Functional significance of the alternative transcript processing of the Arabidopsis floral promoter FCA. The Plant Cell 14 877–888.
Martinez-Zapater JM and Somerville CR. (1990) Effect of light quality and vernalization on late-flowering mutants of Arabidopsis thaliana. Plant Physiology 92 770–776.
Michaels SD and Amasino RM. (2000) Memories of winter: vernalization and the competence to flower. Plant, Cell and Environment 23 1145–1153.[CrossRef]
Molinero-Rosales N, Jamilena M, Zurita S, Gomez P, Capel J, Lozano R. (1999) FALSIFLORA, the tomato orthologue of FLORICAULA and LEAFY, controls flowering time and floral meristem identity. The Plant Journal 20 685–693.[CrossRef][Web of Science][Medline]
Parcy F, Nilsson O, Busch MA, Lee I, Weigel D. (1998) A genetic framework for floral patterning. Nature 395 561–588.[CrossRef][Medline]
Putterill J, Robson F, Lee K, Simon R, Coupland G. (1995) The CONSTANS gene of Arabidopsis promotes flowering and encodes a protein showing similarities to zinc finger transcription factors. Cell 80 847–857.[CrossRef][Web of Science][Medline]
Reddy ASN. (2004) Plant serine/arginine-rich proteins and their role in pre-mRNA splicing. Trends in Plant Science 9 541–547.[CrossRef][Web of Science][Medline]
Sambrook J and Russell DW. (2001) Molecular cloning: a laboratory manualCold Spring Harbor, NY Cold Spring Harbor Laboratory Press.
Simon PW and Jenderek MM. (2003) Flowering, seed production, and the genesis of garlic breeding. Plant Breeding Reviews 23 211–244.
Simpson GG and Dean C. (2002) Arabidopsis, the Rosetta stone of flowering time? Science 296 285–289.
Simpson GG, Gendall AR, Dean C. (1999) When to switch to flowering. Annual Review of Cell and Developmental Biology 99 519–550.[CrossRef]
Smith CWJ, Patton JG, Nadal-Ginard B. (1989) Alternative splicing in the control of gene expression. Annual Review of Genetics 23 527–577.[CrossRef][Web of Science][Medline]
Southerton SG, Strauss SH, Olive MR, Harcourt RL, Decroocq V, Zhu X, Llewellyn DJ, Peacock WJ, Dennis ES. (1998) Eucalyptus has a functional equivalent of the Arabidopsis floral meristem identity gene LEAFY. Plant Molecular Biology 37 897–910.[CrossRef][Web of Science][Medline]
Sreekantan L, Clemens J, McKenzie MJ, Lenton JR, Croker SJ, Jameson PE. (2004) Flowering genes in Metrosideros fit a broad herbaceous model encompassing Arabidopsis and Antirrhinum. Physiologia Plantarum 121 163–173.[CrossRef][Medline]
Takagi H. (1990) Garlic Allium sativum L. In Rabinowitch HD and Brewster JL (Eds.). Onions and allied cropsBoca Raton, FL CRC Press Vol. III pp. 109–157.
Wada M, Cao QF, Kotoda N, Soejima J, Masuda T. (2002) Apple has two orthologues of FLORICAULA/LEAFY involved in flowering. Plant Molecular Biology 49 567–577.[CrossRef][Web of Science][Medline]
Wagner D, Sablowski RW, Meyerowitz EM. (1999) Transcriptional activation of APETALA1 by LEAFY. Science 285 582–584.
Wagner D, Wellmer F, Dilks K, William D, Smith MR, Kumar PP, Reichmann JL, Greenland AJ, Meyerowitz EM. (2004) Floral induction in tissue culture: a system for the analysis of LEAFY-dependent gene regulation. The Plant Journal 39 273–282.[CrossRef][Web of Science][Medline]
Wang CN, Möller M, Cronk QCB. (2004) Altered expression of GFLO, the Gesneriaceae homologue of FLORICAULA/LEAFY, is associated with the transition to bulbil formation in Titanotrichum oldhamii. Development, Genes and Evolution 3 122–127.[CrossRef]
Weigel D, Alvarez J, Smyth DR, Yanofsky MF, Meyerowitz EM. (1992) LEAFY controls floral meristem identity in Arabidopsis. Cell 69 843–859.[CrossRef][Web of Science][Medline]
Weigel D and Meyerowitz EM. (1994) The ABCs of floral homeotic genes. Cell 78 203–209.[CrossRef][Web of Science][Medline]
Weigel D and Nilsson O. (1995) A developmental switch sufficient for flower initiation in diverse plants. Nature 377 495–500.[CrossRef][Medline]
Wilson RN, Heckman JW, Somerville CR. (1992) Gibberellin is required for flowering in Arabidopsis thaliana under short days. Plant Physiology 100 403–408.
Zeitoune S, Livneh O, Kuzuetzova L, Stram Y, Sela I. (1999) T7 RNA polymerase drives transcription of a reporter gene from T7 promoter, but engenders post-transcriptional silencing of expression. Plant Science 141 59–65.[CrossRef]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  Compiled by, F. Tooke, T. Chiurugwi, and N. Battey Flowering Newsletter bibliography for 2007 J. Exp. Bot., July 18, 2008; (2008) ern109v1. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||