Journal of Experimental Botany, Vol. 54, No. 380, pp. 149-156,
January 1, 2003
© 2003 Oxford University Press
Molecular mechanism of self-recognition in Brassica self-incompatibility
Received 22 May 2002; Accepted 7 August 2002
Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
1 To whom correspondence should be addressed. Fax: +81 743 72 5459. E-mail: takayama{at}bs.aist-nara.ac.jp
 |
Abstract |
|---|
 Top Abstract IntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
In most self-incompatible plant species, recognition of self-pollen is controlled by a single locus, termed the S-locus. In Brassica, genetic dissection of the S-locus has revealed the presence of three highly-polymorphic genes: S-receptor kinase (SRK), S-locus protein 11 (SP11) (also known as S-locus cysteine-rich protein; SCR) and S-locus glycoprotein (SLG). SRK encodes a membrane-spanning serine/threonine kinase that determines the S-haplotype specificity of the stigma. SP11 encodes a small cysteine-rich protein that determines the S-haplotype specificity of pollen. SLG encodes a secreted form of stigma protein similar to the extracellular domain of SRK. Recent biochemical studies have revealed that SP11 functions as the sole ligand for its cognate SRK receptor complex. Their interaction induces the autophosphorylation of SRK, which is expected to trigger the signalling cascade that results in the rejection of self-pollen. This so-called ligand–receptor complex interaction and receptor activation occur in an S-haplotype-specific manner, and this specificity is almost certainly the basis for self-pollen recognition.
Key words: Brassica, ligand, receptor, self-incompatibility, SLG, SP11, SRK.
|
Introduction |
|---|
|
TopAbstractIntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
Self-incompatibility (SI) is a widespread mechanism used by flowering plants to prevent inbreeding and thereby generate and maintain genetic diversity within a species. SI involves a self and non-self discrimination process between pollen and pistil, and has attracted considerable attention since its precise observation by Darwin (1876, 1877).
Classical genetic analysis revealed that SI recognition is, in most cases, controlled by a single multi-allelic locus, the S-locus. Pollen rejection has been postulated to occur when the same ‘S-allele’ specificity is expressed by both pollen and pistil. Molecular studies on several self-incompatible species of Brassicaceae, Solanaceae and Papaveraceae have revealed that the S-locus of these families consists of at least two polymorphic genes, one encoding the male determinant and another the female (McCubbin and Kao, 2000; Silva and Goring, 2001). This multi-gene complex at the S-locus is known to be inherited as one segregating unit and, therefore, the variants of the gene complex are now called ‘S-haplotypes.’ More than one hundred S-haplotypes are inferred to be present in B. rapa (Nou et al., 1993). The molecular interactions between the male and female determinants encoded by the same S-haplotype are expected to induce the SI response.
During the last two decades, molecular analysis of SI systems has focused on identifying and characterizing the male and female determinants of SI. Recently, both determinants have been identified in Brassica, and much progress has been made towards understanding their mechanisms of action. This review focuses on recent efforts to understand the molecular basis of self/non-self recognition between pollen and pistil in Brassica.
|
Female determinant |
|---|
|
TopAbstractIntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
Searches for the determinant of Brassica SI began with the immunological identification of an S-haplotype-specific antigen in the stigma (Nasrallah and Wallace, 1967), followed by the biochemical identification of abundant soluble glycoproteins (later named S-locus glycoproteins; SLGs) that co-segregate with S-haplotypes (Nishio and Hinata, 1977). Molecular and biochemical studies revealed the structure of SLG (Fig. 1), consisting of a cleavable signal peptide, several N-glycosylation sites, three hypervariable regions, and 12 conserved cysteine residues located towards the C-terminus (Takayama et al., 1987; Nasrallah et al., 1987). SLGs were demonstrated to be localized to the cell wall of stigma papillae at the top of the pistil (Kandasamy et al., 1989; Kishi-Nishizawa et al., 1990).
|
The identification of ZmPK1 in maize, the first identified plant receptor-like kinase (RLK) whose extracellular domain is homologous to SLG (Walker and Zhang, 1990), subsequently led to the isolation of the second S-locus gene, that of S-receptor kinase (SRK) (Stein et al., 1991). SRK consists of a signal peptide, an SLG-like predicted extracellular domain (S-domain), a transmembrane domain, and an intracellular serine/threonine kinase domain (Fig. 1).
SLG and SRK were found to exhibit a number of characteristics expected for the female determinant of SI. First, they are predominantly produced in the stigma papilla cells, which come into direct contact with pollen. Second, their expression just prior to flower opening coincides with the timing of the acquisition of SI by the stigma. Third, they exhibit allelic sequence diversity among all of the S-haplotypes examined.
Circumstantial evidence for the involvement of SRK and SLG in SI has been obtained by the identification of self-compatible lines of Brassica carrying non-functional SRKs (Goring et al., 1993; Nasrallah et al., 1994) or exhibiting reduced levels of SLG expression (Nasrallah and Nasrallah, 1989), respectively. In order to show the function of SRK or SLG directly, a large number of transformation experiments have been performed. All ‘gain-of-function’ approaches, however, have resulted in the breakdown of SI in the transformants, most likely as a result of co-suppression between the endogenous SLG and/or SRK and the transgene. Therefore, ‘loss-of-function’ experiments were conducted using an antisense SLG gene, and it was demonstrated that the transformants became self-compatible (Shiba et al., 1995, 2000). The expression of SRK, as well as that of SLG, was suppressed in these transformants. These results suggested that SLG and/or SRK are necessary for SI, yet the precise role played by each gene remained to be determined.
Takasaki et al. succeeded with the ‘gain-of-function’ approach by introducing class-I S-haplotype SRK and SLG genes independently into Brassica plants homozygous for a class-II S-haplotype (Fig. 2; Takasaki et al., 2000). This classification of S-haplotypes is based on amino acid sequence similarities of SLG and SRK. Lesser sequence similarity between these two classes is believed to minimize the problem of co-suppression. Transgenic plants expressing S9-haplotype SRK (SRK9) acquired S9-haplotype specificity in the stigma and set a reduced number of seeds (c. 1.9 seeds/flower) compared to the stigma of non-transformants (c. 15 seeds/flower) after crossing with pollen from S9-homozygotes (S9-pollen). By contrast, transgenic plants expressing SLG9 did not display S9-haplotype specificity. When the SLG9 transgene was introduced into transgenic plants expressing SRK9 by crossing, however, the obtained progeny expressing both SLG9 and SRK9 exhibited very strong incompatibility against S9-pollen and set a reduced number of seeds (c. 0.3 seeds/flower). This number was comparable to that obtained from incompatible pollination of S9S60-heterozygotes with S9-pollen (c. 0.2 seeds/flower). These results demonstrated that SRK alone determines the S-haplotype specificity of the stigma, and that SLG acts to promote the full manifestation of the SI response through an unknown mechanism.
|
Silva et al. (2001) also found that SRK is the primary determinant of SI by introducing SRK910 into the B. napus self-compatible line. However, no enhancing role was detected for SLG910: the mean seed production for the SLG910/SRK910 double transgenic plants (1.04 seeds/flower) was not statistically different from that for the SRK910 single transgenic plants (1.22 seeds/flower). Thus, the requirement for SLG in the SI response may be variable among different S-haplotypes. In support of this view, Suzuki et al. (2000) identified two self-incompatible B. oleracea haplotypes, S18 and S60, which produced no SLG protein, yet exhibited a strong SI phenotype.
|
Male determinant |
|---|
|
TopAbstractIntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
Since the identification of the female determinant genes SLG and SRK, many efforts have been focused on identifying the male S-haplotype determinant. The male determinant was expected to exhibit the following properties: (i) being encoded by a gene located at the S-locus (close to SLG and SRK); (ii) allelic diversity among S-haplotypes; (iii) being expressed before meiosis in the pollen mother cell, or expressed later in the anther tapetum cells, as the Brassica SI is sporophytically regulated; (iv) physically interacting with SRK and/or SLG in an S-haplotype-specific manner. Starting with these assumptions, several strategies were then put into effect.
The first important clue towards the discovery of the male determinant was provided from biochemical studies. Using a band-shift assay with IEF (isoelectric focusing) gels, it was shown that the pollen coat contained a 7 kDa protein (PCP7, renamed later PCP-A1) that interacted with SLG (Doughty et al., 1993, 1998). This was determined to be a cysteine-rich basic protein belonging to a large protein family, termed PCP (pollen coat protein) family. Furthermore, using a pollination bioassay, Stephenson et al. demonstrated that the biological activity of the male determinant resided in a small basic protein fraction containing PCP-A1 (Stephenson et al., 1997). PCP-A1 itself was, however, ruled out as a candidate for the male S determinant because it was not S-haplotype-specific and not linked to the S-locus.
Using an optical biosensor (BIAcore) along with chromatographic methods, a number of pollen coat proteins that interact with SLGs have also been identified (Takayama et al., 2000a). All of them exhibited the properties of PCP family proteins, however, none of these candidates were found to be S-linked.
Based on these facts, It was decided to pursue two different molecular biological approaches to find the male determinant. First, the region of the S-locus that contains SRK and SLG was examined in order to identify genes that are expressed in the anther. To this end, a 76 kbp SRK/SLG region of the S9-haplotype of B. rapa was cloned directly using a P1-derived artificial chromosome (PAC) vector (Suzuki et al., 1997b). The complete sequencing of this region and subsequent thorough search for expressed genes using anther cDNA libraries identified 14 transcriptional units in this region. It was found that one of these genes, SP11 (S-locus protein 11; Fig. 1), was a potential candidate for the male S-determinant because it (i) encodes a small, cysteine-rich basic protein similar to PCP-A1, (ii) is located between SLG and SRK, and (iii) is expressed predominantly in the anther (Suzuki et al., 1999). Genomic DNA gel blot analyses revealed that the cDNA probe of S9-SP11 (SP11 from S9-haplotype) hybridized either very weakly or not at all to the genomic DNA of other S-haplotypes, suggesting that SP11 is a highly-polymorphic gene.
As a second independent approach, fluorescent differential display (FDD) was used to compare anther cDNAs from S8- and S12-haplotypes to identify genes that were specific for either S-haplotype. Using this technique, it was possible to obtain an allelic gene of SP11 from the S8-haplotype of B. rapa. After FDD analyses using 240 independent primer combinations, 26 S-haplotype-specific bands were found, which were discovered to be derived from nine independent genes after cloning and sequence analysis of each DNA band. Among these genes, one gene, S8-SP11, exhibited the characteristic features specific for SP11 (Takayama et al., 2000b).
Both S9- and S8-SP11 contain eight conserved cysteine residues and relatively conserved putative signal peptides, but most regions of the mature proteins exhibited very weak homology. Using a primer designed from the conserved signal peptide sequence, it was possible to amplify allelic SP11 genes from most of the class-I S-haplotypes. These, however, again displayed little homology in their mature protein coding regions (Watanabe et al., 2000). Recently, the authors have succeeded in identifying SP11 genes also from the class-II S-haplotypes (Shiba et al., 2002). Phylogenetic analysis revealed that the class-II SP11s form a distinct group separated from class-I SP11s, as do stigmatic SLGs and SRKs, consistent with the proposal that class-II S-haplotypes have a different origin to class-I S-haplotypes (Hinata et al., 1995). Although class-II SP11s showed relatively greater sequence similarity with each other than with class-I SP11s, their mature protein coding regions again displayed weak homology.
As the homology between these SP11 sequences was extremely low, it was necessary to demonstrate whether these genes were truly allelic. In addition to the S9-haplotype, the S-locus region of the S8- and S12-haplotypes were analysed. In these three S-haplotypes, the SP11 genes identified are all located between the SLG and SRK genes, confirming their allelic relationships (Takayama et al., 2000b). Interestingly, although these SP11 genes are located between SLG and SRK, their location relative to SLG/SRK, and their direction of transcription and the size of their introns were divergent. This divergent genomic organization of the S-locus may explain why recombination has not been detected within this region.
That SP11/SCR is the male S-determinant has been definitively established by gain-of-function experiments (Schopfer et al., 1999) and a pollination bioassay (Takayama et al., 2000b). Schopfer et al. introduced SCR6 cDNA into B. oleracea S2-homozygote plants, and showed that the transgenic plants expressing the SCR6 cDNA produced pollen of S6-haplotype specificity which was rejected by the stigmas of S6-homozygotes (S6S6-stigmas). The pollination bioassay system developed by Stephenson et al. (1997) was used to demonstrate that S9-SP11 is the male determinant of the S9-haplotype. When the recombinant S9-SP11 protein was applied to papilla cells of S9S9- and S8S8-stigmas, S9-SP11 elicited the SI response only when applied to the former (S9S9) stigmas, resulting in the inhibition of cross-pollen hydration (Takayama et al., 2000b). A gain-of-function approach was also used to confirm further the role of SP11 as the sole male determinant (Shiba et al., 2001). Pollen from transformants with S8- and S9-SP11 transgenes was shown to acquire S8- and S9-haplotype specificity, respectively (Fig. 3).
|
By contrast with the expectation that the male determinant should be expressed sporophytically in the anther, all of the PCP family proteins examined thus far exhibited a strictly gametophytic expression pattern (Doughty et al., 1998; Takayama et al., 2000a). Therefore, the temporal and spatial expression patterns of SP11 were analysed in detail. In situ hybridization of anther sections clearly demonstrated that an SP11 from class-I S-haplotype (S8-SP11) was expressed sporophytically in the tapetal cell layer at early developmental stages and also gametophytically in microspores at later developmental stages (Takayama et al., 2000b). Because the tapetal cell layer is a diploid tissue known to nourish developing pollen grains and provide the components of pollen coating, this expression pattern can easily explain the sporophytic nature of Brassica SI. Furthermore, SP11s from class-II S-haplotypes (e.g. S40-SP11 and S60-SP11) exhibited strictly sporophytic expression pattern, suggesting that the expression of SP11 in the tapetal cell layer is sufficient for SI (Shiba et al., 2002).
Next, the SP11 protein was characterized in detail in order to shed light on its activity and to examine its potential interaction with SRK and/or SLG. Immuno histochemical analysis was performed using antibodies produced against the recombinant S8-SP11 protein. The S8-SP11 protein was detected in both the tapetal cells and microspores of S8-homozygotes as was observed for S8-SP11 mRNA by in situ hybridization (S Takayama et al., unpublished results). At late developmental stages, the S8-SP11 protein was found to localize mainly in the pollen coat. To purify and characterize the S8-SP11 protein, total pollen coat protein was extracted from mature pollen grains and immunoprecipitation was carried out. MALDI-TOF-MS analysis of S8-SP11 purified from pollen under non-reducing conditions revealed a precise Mr value of 5716. This value is consistent with calculations based on the assumption that (i) S8-SP11 is present as a monomer, (ii) the predicted signal peptide is removed at the expected cleavage site, and (iii) all eight cysteine residues are oxidized to form four intramolecular disulphide bonds (Takayama et al., 2001).
To characterize S8-SP11 further, S8-SP11 was chemically synthesized by using both solid-phase and solution methods. When the synthetic S8-SP11 was reduced and then subjected to mild oxidation, only one major oxidized form was obtained. The disulphide linkage (C1–C8, C2–C5, C3–C6, C4–C7) of this major form was determined by analysing its proteolytic fragments using Edman degradation and mass spectrometry (S Takayama et al., unpublished results). This disulphide bond arrangement is identical to that of the plant defensin protein family, antimicrobial proteins represented by 
1-P, even though the positioning of the fourth cysteine residue is rather different. Moreover, this oxidized form of S8-SP11 was shown to be biologically active using a modified pollination bioassay system (Takayama et al., 2001). The availability of this form of S8-SP11 made it possible to perform the following stoichiometric interaction analysis.
|
Interaction between male and female determinants |
|---|
|
TopAbstractIntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
From the molecular nature of the male (SP11) and female (SRK) determinants, it was expected that they would function in a ligand–receptor relationship. To reveal this relationship experimentally, radioactive S8-SP11 was first prepared by 125I-labelling of an internal tyrosine residue. After confirming that this chemical modification had no effect on the biological activity of S8-SP11, its affinity to the stigmatic microsomal membrane was measured. 125I-labelled S8-SP11 (125I-S8-SP11) was shown to bind specifically the stigmatic microsomal membranes of the S8-homozyogote (Fig. 4a). Scatchard analysis indicated the presence of a high-affinity binding site (Kd=0.7 nM, Bmax=180 fmol mg–1 protein) and a low-affinity binding site (Kd=250 nM, Bmax=3 pmol mg–1 protein) (Fig. 4b). Both binding sites were present only in the membrane of the cognate S-haplotype, and were expected to comprise S-locus protein(s). The exact molecular nature and basis for the binding difference, however, remains to be determined (Takayama et al., 2001).
|
To identify the receptor components of 125I-S8-SP11 in the stigmatic microsomal membranes, cross-linking experiments were performed. The chemical bis[sulphosuccinimidyl] suberate effectively cross-linked 125I-S8-SP11 to two proteins that could be detected as radio labelled protein bands of 120 K and 65 K after SDS-PAGE. As the intensity of both protein bands decreased in parallel with decreasing concentrations of 125I-S8-SP11 (10–0.1 nM), these two proteins were expected to co-operate to form the single high-affinity binding site for S8-SP11. The molecular masses of these protein bands and the immunoprecipitation experiments suggested that the 120 K protein is SRK8, and that the 65 K protein is probably SLG8 (Takayama et al., 2001). However, the identity of these bands, especially that of the 65 K band, should be confirmed by other methods, because at least two SRK alleles have been shown to produce a truncated soluble form of SRK (designated eSRKs) by alternative splicing (Giranton et al., 1995; Suzuki et al., 1996), and there are many other SLG-like proteins (termed S-multigene family) shown to be expressed in the stigma (Suzuki et al., 1995, 1997a; Kai et al., 2001).
Having shown the S-haplotype-specific binding of SP11 to its cognate SRK receptor complex, it was investigated further whether this interaction results in the activation of SRK. When added to the plasma membrane of S8-stigmas at a kinetically relevant concentration, S8-SP11 but not S9-SP11 induced autophosphorylation of SRK8. This result clearly suggested that SP11 alone can activate SRK in an S-haplotype-specific manner (Takayama et al., 2001).
Kachroo et al. also reported a direct interaction between SP11 and SRK using a different approach involving tagged versions of recombinant SRK and SCR (Kachroo et al., 2001). The extracellular domain of SRK6 (eSRK6-FLAG) was expressed in tobacco leaves, and SCR (SCR-Myc-His6) was expressed in bacteria. The eSRK6-FLAG was shown to interact more strongly with SCR6-Myc-His6 than with SCR13-Myc-His6, both by ‘pull-down’ assay and ELISA. Their finding that the extracellular domain by itself possesses high-affinity SP11-binding capacity is interesting, because no interaction between SP11 and the extracellular domain of SRK expressed in insects was detected (Takayama et al., 2001). They also observed that the extracellular domain of SRK binds to a 
16 kDa pollen coat protein, which they suggested may be a dimer of SP11. This also contrasts with this study’s data, as no dimers were detected in pollen in these immunoprecipitation experiments (Takayama et al., 2001). It is difficult to make any definitive comparisons at present because of the many differences in the materials and methods used in these studies; however, these observed discrepancies need to be addressed in the future.
|
Dominant and recessive interactions between S-haplotypes |
|---|
|
TopAbstractIntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
One interesting feature of the Brassica SI system observed by Thompson and Taylor was the occurrence of some dominant and recessive interactions between S-haplotypes (Thompson and Taylor, 1966). Because Brassica exhibits sporophytic SI, the SI phenotype of pollen, as well as the stigma, is determined by relationships between the two S-haplotypes carried by its parent. The following observations have been made about dominance relationships among S-haplotypes: (i) co-dominance is common; (ii) dominance/recessiveness is frequent in pollen; (iii) dominance relationships in the stigma are different from those in the pollen; and (iv) dominance relationships are non-linear (Hatakeyama et al., 1998). Now that both male and female determinants of Brassica SI have been identified, it becomes possible to analyse the dominance relationships in connection with the expression or activities of these determinants.
Hatakeyama et al. investigated whether the female determinant of SRK was directly involved in determining the dominance relationships in the stigma using five S-homozygotes carrying an SRK9 transgene (Hatakeyama et al., 2001). They showed that the dominance relationship between the SRK9 transgene and each of the endogenous S-haplotypes was identical to that between the S9-haplotype and the respective endogenous S-haplotype. Furthermore, in the S8-homozygote carrying the SRK9 transgene, in which the S8-phenotype in the stigma was masked by the presence of SRK9, the mRNA level of SRK9 was found to be much lower than that of SRK8. These results suggested that the dominant/recessive relationship between S-haplotypes in the stigma was determined by the female determinant of SRK itself, but not as a result of its relative mRNA level. Is it determined post-transcriptionally by SRK protein level? Are the two SRK competing differently for a limited pool of components of the SRK-mediated signalling pathway? Further studies are necessary to understand fully the molecular mechanism of the dominance relationships in the stigma.
Regarding dominance relationships in pollen, it has long been suggested that the class-II S-haplotypes are generally recessive to the class-I S-haplotypes, although the mechanism that underpins this is unknown (Nasrallah and Nasrallah, 1993; Hatakeyama et al., 1998). Recently, it was found that the dominant/recessive relationship between class-I and class-II S-haplotypes in pollen was determined by the male determinant of SP11 itself, and as a result of its relative mRNA level (Shiba et al., 2002). That is the mRNA of SP11 of the class-II S-haplotype, detected predominantly in the anther tapetum of homozygotes, was not detected in the heterozygotes of class I and class II S-haplotypes. A similar phenomenon was observed between two SCR genes identified in Arabidopsis lyrata, a wild self-incompatible crucifer (Kusaba et al., 2002). Molecular dissection of this newly found gene silencing system remains a challenge for the future.
|
Conclusions and perspectives |
|---|
|
TopAbstractIntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
Considerable knowledge about the mechanisms of self-pollen recognition in Brassica self-incompatibility has been obtained from the extensive studies described here. It is now known that the Brassica S-locus contains three genes: SLG, SRK, and SP11 (Fig. 5). SP11 is mainly expressed in anther tapetum cells and the protein accumulates in the pollen coat during the maturation of pollen. Following pollination, SP11 penetrates the papilla cell wall and binds to the SRK receptor complex on the papilla cell membrane. This binding induces autophosphorylation of SRK, which is expected to trigger the signalling cascade that results in the rejection of self-pollen. This ligand–receptor complex interaction and receptor activation occur in an S-haplotype-specific manner, and this specificity is almost certainly the basis for self-pollen recognition in Brassica.
|
Now that the molecular basis of self-pollen recognition, the first step of the self-incompatibility response, has been established, the next phase of research must be the characterization of downstream signalling pathway(s). Autophosphorylation of SRK induced by the cognate SP11 presumably causes subsequent phosphorylation of intracellular substrates of SRK. ARC1 (arm-repeat-containing protein 1) is the only candidate identified thus far for such intracellular substrates. ARC1 is specifically expressed in the stigma and becomes phosphorylated in vitro on binding to the cytosolic domain of SRK (Gu et al., 1998). Importantly, suppression of ARC1 expression by an antisense transgene resulted in the partial breakdown of SI, confirming that ARC1 is a positive effector of SI signalling (Stone et al., 1999). However, the precise role of ARC1 in the signal transduction remains to be determined.
Two thioredoxin-h proteins, THL1/2, were shown to interact with a conserved cysteine at the transmembrane domain of SRK in a phosphorylation-independent manner (Bower et al., 1996; Muzzurco et al., 2001). In vitro phosphorylation experiments demonstrated that THL1 negatively regulates SRK activity in the absence of an ‘activating’ component of the pollen coat (presumably SP11/SCR) (Cabrillac et al., 2001). The next important demonstration should be the direct interaction of THL1/2 and SRK in vivo.
A naturally occurring self-compatible line, B. rapa var. yellow sarson, has a recessive mutation in the MOD gene (Hinata and Okazaki, 1986), which was once suggested to encode an aquaporin-like protein, MIP-MOD (Ikeda et al., 1997). However, recent analysis suggested that MIP-MOD is not likely to be MOD itself (Fukai et al., 2001). The identification of the true MOD would provide a promising clue to SI signalling.
Preliminary analysis of the Arabidopsis genome indicated the presence of over 340 RLKs (The Arabidopsis Genome Initiative, 2000), which are expected to play crucial roles in all aspect of the plant life cycle, including cell proliferation, development, hormone perception, disease resistance, fertilization, and abscission. However, with some exceptions, such as CLV1, BRI1, and FLS2, most of them are ‘orphan receptors’ with unknown ligands (Torii, 2000). Moreover, the signalling molecules working downstream of these RLKs are almost entirely unknown. Therefore, the SI signalling system in Brassica would be an excellent model for the study of the RLK-mediated signalling pathway, and new findings on this system should have important implications for current general understanding of how plant cells communicate.
|
Acknowledgements |
|---|
We apologize to all those whose work in this field could not be cited because of limited space. We are grateful to Emeritus Professor Kokichi Hinata at Tohoku University, and Dr Masao Watanabe at Iwate University for their helpful discussion. Work in the authors’ laboratory was supported in part by Grants-in-Aid for Special Research on Priority Areas (B) (11238025), for Scientific Research (B) (14360066), and for Exploratory Research (14658224) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, by a grant from the Research for the Future Program (JSPS-RFTF 00L01605) from the Japan Society for the Promotion of Science, and by a grant from the Mitsubishi Foundation.
|
References |
|---|
|
TopAbstractIntroductionFemale determinantMale determinantInteraction between male and...Dominant and recessive...Conclusions and perspectivesReferences |
|---|
Bower MS, Matias DD, Fernandes-Carvalho E, Mazzurco M, Gu T, Rothstein S, Goring DR. 1996. Two members of the thioredoxin-h family interact with the kinase domain of a Brassica S locus receptor kinase. The Plant Cell 8, 1641–1650.[Abstract]
Cabrillac D, Cock JM, Dumas C, Gaude T. 2001. The S-locus receptor kinase is inhibited by thioredoxins and activated by pollen coat proteins. Nature 410, 220–223.[CrossRef][Medline]
Darwin C. 1876. Effects of cross- and self-fertilization in the vegetable kingdoms. New York: Appleton.
Darwin C. 1877. Different forms of flowers on plants of the same species. London: John Murray.
Doughty J, Dixon S, Hiscock SJ, Willis AC, Parkin IAP, Dickinson HG. 1998. PCP-A1, a defensin-like Brassica pollen coat protein that binds the S locus glycoprotein, is the product of gametophytic gene expression. The Plant Cell 10, 1333–1347.
Doughty J, Hedderson F, McCubbin A, Dickinson HG. 1993. Interaction between a coating-borne peptide of the Brassica pollen grain and stigmatic S (self-incompatibility)-locus-specific glycoproteins. Proceedings of the National Academy of Sciences, USA 90, 467–471.
Fukai E, Nishio T, Nasrallah ME. 2001. Molecular genetic analysis of the candidate gene for MOD, a locus required for self-incompatibility in Brassica rapa. Molecular Genetics and Genomics 265, 519–525.[CrossRef][Web of Science][Medline]
Giranton J-L, Ariza MJ, Dumas C, Cock JM, Gaude T. 1995. The S locus receptor kinase gene encodes a soluble glycoprotein corresponding to the SRK extracellular domain in Brassica oleracea. The Plant Journal 8, 827–834.[Web of Science][Medline]
Goring DR, Glavin TL, Schafer U, Rothstein SJ. 1993. An S receptor kinase gene in self-compatible Brassica napus has a 1-bp deletion. The Plant Cell 5, 531–539.[Abstract]
Gu T, Mazzurco M, Sulaman W, Matias DD, Goring DR. 1998. Binding of an arm repeat protein to the kinase domain of the S-locus receptor kinase. Proceedings of the National Academy of Sciences, USA 95, 382–387.
Hatakeyama K, Takasaki T, Suzuki G, Nishio T, Watanabe M, Isogai A, Hinata K. 2001. The S receptor kinase gene determines dominance relationships in stigma expression of self-incompatibility in Brassica. The Plant Journal 26, 69–76.[CrossRef][Web of Science][Medline]
Hatakeyama K, Watanabe M, Takasaki T, Ojima K, Hinata K. 1998. Dominance relationships between S-alleles in self-incompatible Brassica campestris L. Heredity 80, 241–247.[CrossRef]
Hinata K, Okazaki K. 1986. Role of stigma in the expression of self-incompatibility in crucifers in view of genetic analysis. In: Mulcahy DL, Mulcahy GB, Ottariano E, eds. Biotechnology and ecology of pollen. New York: Springer-Verlag, 185–190.
Hinata K, Watanabe M, Yamakawa S, Satta Y, Isogai A. 1995. Evolutionary aspects of the S-related genes of the Brassica self-incompatibility system: synonymous and non-synonymous base substitutions. Genetics 140, 1099–1104.[Abstract]
Ikeda S, Nasrallah JB, Dixit R, Preiss S, Nasrallah ME. 1997. An aquaporin-like gene required for the Brassica self-incompatibility response. Science 276, 1564–1566.
Kachroo A, Schopfer CR, Nasrallah ME, Nasrallah JB. 2001. Allele-specific receptor-ligand interactions in Brassica self-incompatibility. Science 293, 1824–1826.
Kai N, Suzuki G, Watanabe M, Isogai A, Hinata K. 2001. Sequence comparisons among dispersed members of the Brassica S multigene family in an S9 genome. Molecular Genetics and Genomics 265, 526–534.[CrossRef][Web of Science][Medline]
Kandasamy MK, Paolillo DJ, Faraday CD, Nasrallah JB, Nasrallah ME. 1989. The S-locus specific glycoproteins of Brassica accumulate in the cell wall of developing stigma papillae. Developmental Biology 134, 462–472.[CrossRef][Web of Science][Medline]
Kishi-Nishizawa N, Isogai A, Watanabe M, Hinata K, Yamakawa S, Shojima S, Suzuki A. 1990. Ultrastructure of papillar cells in Brassica campestris revealed by liquid helium rapid-freezing and substitution-fixation method. Plant and Cell Physiology 31, 1207–1219.
Kusaba M, Tung C-W, Nasrallah ME, Nasrallah JB. 2002. Monoallelic expression and dominance interactions in anthers of self-incompatible Arabidopsis lyrata. Plant Physiology 128, 17–20.
McCubbin AG, Kao T-h. 2000. Molecular recognition and response in pollen and pistil interactions. Annual Review of Cell and Developmental Biology 16, 333–364.[CrossRef][Web of Science][Medline]
Muzzurco M, Sulaman W, Elina H, Cock JM, Goring DR. 2001. Further analysis of the interactions between the Brassica S receptor kinase and three interacting proteins (ARC1, THL1 and THL2) in the yeast two-hybrid system. Plant Molecular Biology 45, 365–376.[CrossRef][Web of Science][Medline]
Nasrallah JB, Kao T-h, Chen C-H, Goldberg ML, Nasrallah ME. 1987. Amino-acid sequence of glycoproteins encoded by three alleles of the S locus of Brassica oleracea. Nature 326, 617–619.[CrossRef]
Nasrallah JB, Nasrallah ME. 1989. The molecular genetics of self-incompatibility in Brassica. Annual Review of Genetics 23, 121–139.[CrossRef][Web of Science][Medline]
Nasrallah JB, Nasrallah ME. 1993. Pollen–stigma signalling in the sporophytic self-incompatibility response. The Plant Cell 5, 1325–1335.
Nasrallah JB, Rundle SJ, Nasrallah ME. 1994. Genetic evidence for the requirement of the Brassica S-locus receptor kinase gene in the self-incompatibility response. The Plant Journal 5, 373–384.
Nasrallah ME, Wallace DH. 1967. Immunogenetics of self-incompatibility in Brassica oleracea L. Heredity 22, 519–527.
Nishio T, Hinata K. 1977. Analysis of S-specific proteins in stigma of Brassica oleracea L. by isoelectric focusing. Heredity 38, 391–396.
Nou IS, Watanabe M, Isogai A, Hinata K. 1993. Comparison of S-alleles and S-glycoproteins between two wild populations of Brassica campestris in Turkey and Japan. Sexual Plant Reproduction 6, 79–86.
Schopfer CR, Nasrallah ME, Nasrallah JB. 1999. The male determinant of self-incompatibility in Brassica. Science 286, 1697–1700.
Shiba H, Hinata K, Suzuki A, Isogai A. 1995. Breakdown of self-incompatibility in Brassica by the antisense RNA of SLG gene. Proceedings of the Japan Academy 71, Series B, 81–83.
Shiba H, Iwano M, Entani T et al. 2002. The dominance of alleles controlling self-incompatibility in Brassica pollen is regulated at the RNA level. The Plant Cell 14, 491–504.
Shiba H, Kimura N, Takayama S, Hinata K, Suzuki A, Isogai A. 2000. Alteration of the self-incompatibility phenotype in Brassica by transformation of the antisense SLG gene. Bioscience, Biotechnology, and Biochemistry 64, 1016–1024.[CrossRef][Medline]
Shiba H, Takayama S, Iwano M, et al. 2001. A pollen coat protein, SP11/SCR, determines the pollen S-specificity in the self-incompatibility of Brassica species. Plant Physiology 125, 2095–2103.
Silva NF, Goring DR. 2001. Mechanisms of self-incompatibility in flowering plants. Cellular and Molecular Life Sciences 58, 1988–2007.[CrossRef][Web of Science][Medline]
Silva NF, Stone SL, Christie LN, Sulaman W, Nazarian KAP, Burnett LA, Arnoldo MA, Rothstein SJ, Goring DR. 2001. Expression of the S receptor kinase in self-compatible Brassica napus cv. Westar leads to the allele-specific rejection of self-incompatible Brassica napus pollen. Molecular Genetics and Genomics 265, 552–559.[CrossRef][Web of Science][Medline]
Stein JC, Howlett B, Boyes DC, Nasrallah ME, Nasrallah JB. 1991. Molecular cloning of a putative receptor protein kinase gene encoded at the self-incompatibility locus of Brassica oleracea. Proceedings of the National Academy of Sciences, USA 88, 8816–8820.
Stephenson AG, Doughty J, Dixon S, Elleman C, Hiscock S, Dickinson HG. 1997. The male determinant of self-incompatibility in Brassica oleracea is located in the pollen coating. The Plant Journal 12, 1351–1359.[CrossRef][Web of Science]
Stone SL, Arnoldo M, Goring DR. 1999. A breakdown of Brassica self-incompatibility in ARC1 antisense transgenic plants. Science 286, 1729–1731.
Suzuki G, Kai N, Hirose T, Fukui K, Nishio T, Takayama S, Isogai A, Watanabe M, Hinata K. 1999. Genomic organization of the S locus: identification and characterization of genes in SLG/SRK region of S9 haplotype of Brassica campestris (syn. rapa). Genetics 153, 391–400.
Suzuki G, Watanabe M, Kai N, Matsuda N, Toriyama K, Takayama S, Isogai A, Hinata K. 1997a. Three members of the S multigene family are linked to the S locus of Brassica. Molecular and General Genetics 256, 257–264.
Suzuki G, Watanabe M, Toriyama K, Isogai A, Hinata K. 1997b. Direct cloning of the Brassica S locus by using a P1-derived artificial chromosome (PAC) vector. Gene 199, 133–137.[CrossRef][Web of Science][Medline]
Suzuki G, Watanabe M, Toriyama K, Isogai A, Hinata K. 1996. Expression of SLG9 and SRK9 genes in transgenic tobacco. Plant and Cell Physiology 37, 866–869.
Suzuki G, Watanabe M, Toriyama K, Isogai A, Hinata K. 1995. Molecular cloning of members of S-multigene family in self-incompatible Brassica campestris L. Plant and Cell Physiology 36, 1273–1280.
Suzuki T, Kusaba M, Matsushita M, Okazaki K, Nishio T. 2000. Characterization of Brassica S-haplotypes lacking S-locus glycoprotein. FEBS Letters 482, 102–108.[CrossRef][Web of Science][Medline]
Takasaki T, Hatakeyama K, Suzuki G, Watanabe M, Isogai A, Hinata K. 2000. The S receptor kinase determines self-incompatibility in Brassica stigma. Nature 403, 913–916.[CrossRef][Medline]
Takayama S, Isogai A, Tsukamoto C, Ueda Y, Hinata K, Okazaki K, Suzuki A. 1987. Sequences of S-glycoproteins, products of Brassica campestris self-incompatibility locus. Nature 326, 102–105.[CrossRef][Web of Science]
Takayama S, Shiba H, Iwano M, Asano K, Hara M, Che F-S, Watanabe M, Hinata K, Isogai A. 2000a. Isolation and characterization of pollen coat proteins of Brassica campestris that interact with S-locus-related glycoprotein 1 involved in pollen-stigma adhesion. Proceedings of the National Academy of Sciences, USA 97, 3765–3770.
Takayama S, Shiba H, Iwano M, Shimosato H, Che F-S, Kai N, Watanabe M, Suzuki G, Hinata K, Isogai A. 2000b. The pollen determinant of self-incompatibility in Brassica campestris. Proceedings of the National Academy of Sciences, USA 97, 1920–1925.
Takayama S, Shimosato H, Shiba H, Funato M, Che F-S, Watanabe M, Iwano M, Isogai A. 2001. Direct ligand–receptor complex interaction controls Brassica self-incompatibility. Nature 413, 534–538.[CrossRef][Medline]
The Arabidopsis Genome Initiative. 2000. Analysis of the genome sequence of the flowering plant Arabidopsis thaliana. Nature 408, 796–815.[CrossRef][Medline]
Thompson KF, Taylor JP. 1966. Non-linear dominance relationships between S alleles. Heredity 21, 345–362.
Torii KU. 2000. Receptor kinase activation and signal transduction in plants: an emerging picture. Current Opinion in Plant Biology 3, 361–367.[CrossRef][Web of Science][Medline]
Walker JC, Zhang R. 1990. Relationship of a putative receptor protein kinase from maize to the S-locus glycoproteins of Brassica. Nature 345, 743–746.[CrossRef][Medline]
Watanabe M, Ito A, Takada Y et al. 2000. Highly divergent sequences of the pollen self-incompatibility (S) gene in class-I S haplotypes of Brassica campestris (syn. rapa) L. FEBS Letters 473, 139–144.[CrossRef][Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  H. Shimosato, N. Yokota, H. Shiba, M. Iwano, T. Entani, F.-S. Che, M. Watanabe, A. Isogai, and S. Takayama Characterization of the SP11/SCR High-Affinity Binding Site Involved in Self/Nonself Recognition in Brassica Self-Incompatibility PLANT CELL, January 1, 2007; 19(1): 107 - 117. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Mishima, S. Takayama, K.-i. Sasaki, J.-g. Jee, C. Kojima, A. Isogai, and M. Shirakawa Structure of the Male Determinant Factor for Brassica Self-incompatibility J. Biol. Chem., September 19, 2003; 278(38): 36389 - 36395. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||