The self-incompatibility (S) haplotypes of Brassica contain highly divergent and rearranged sequences of ancient origin.

Boyes, Douglas C.; Nasrallah, Mikhail E.; Vrebalov, Julia; Nasrallah, June B.

doi:10.1105/tpc.9.2.237

Cited by 115 publications

(48 citation statements)

References 43 publications

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“…Note that rearranged gene order and fractured homology often are associated with complex loci and are thought to reduce the frequency of recombination within coadapted gene complexes (Ferris and Goodenough, 1994). Similarly, structural heteromorphism at the S locus might serve to maintain the tight association of the SI specificity genes over time (Boyes et al, 1997;Casselman et al, 2000).An unexpected result of our study was the finding that the S locus occupies different chromosomal locations in Brassica and Arabidopsis spp. In Brassica, the S locus is located in a region that is syntenous with an ETR1-linked chromosomal segment of A. thaliana chromosome I (Conner et al, 1998), whereas in A. lyrata, the S locus maps to a region that corresponds to contig fragments 54 to 55 of A. thaliana chromosome IV.…”

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“…Class I consists of S haplotypes that are placed high in the dominance series and that determine a robust SI response; class II consists of S haplotypes that are recessive to class I haplotypes in pollen and that determine a relatively leaky SI response (Chen and Nasrallah, 1990;Kusaba et al, 1997). Class I and class II SRK alleles diverge by Ͼ 30%, whereas class I and class II SCR alleles are so diverged from one another (Schopfer et al, 1999) that the high number of available class I SCR sequences has not allowed the isolation of class II SCR alleles.Comparative mapping of different S haplotypes has demonstrated that they vary not only in the sequence of their SI genes but also in the order, relative orientation, and spacing of these genes (Boyes and Nasrallah, 1993;Boyes et al, 1997;Cui et al, 1999;Nasrallah, 2000;Takayama et al, 2000). This structural heteromorphism and the sequence polymorphism of SI genes exhibit trans -specific variation (Dwyer et al, 1991;Kusaba et al, 1997;Schopfer et al, 1999; Uyenoyama, 2000).…”

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Self-Incompatibility in the Genus Arabidopsis: Characterization of the S Locus in the Outcrossing A. lyrata and Its Autogamous Relative A. thaliana

Kusaba¹,

Dwyer²,

Hendershot³

et al. 2001

The Plant Cell

131

282

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As a starting point for a phylogenetic study of self-incompatibility (SI) in crucifers and to elucidate the genetic basis of transitions between outcrossing and self-fertilizing mating systems in this family, we investigated the SI system of Arabidopsis lyrata . A. lyrata is an outcrossing close relative of the self-fertile A. thaliana and is thought to have diverged from A. thaliana ‫ف‬ 5 million years ago and from Brassica spp 15 to 20 million years ago. Analysis of two S (sterility) locus haplotypes demonstrates that the A. lyrata S locus contains tightly linked orthologs of the S locus receptor kinase ( SRK ) gene and the S locus cysteine-rich protein ( SCR ) gene, which are the determinants of SI specificity in stigma and pollen, respectively, but lacks an S locus glycoprotein gene. As described previously in Brassica , the S haplotypes of A. lyrata differ by the rearranged order of their genes and by their variable physical sizes. Comparative mapping of the A. lyrata and Brassica S loci indicates that the S locus of crucifers is a dynamic locus that has undergone several duplication events since the Arabidopsis-Brassica split and was translocated as a unit between two distant chromosomal locations during diversification of the two taxa. Furthermore, comparative analysis of the S locus region of A. lyrata and its homeolog in self-fertile A. thaliana identified orthologs of the SRK and SCR genes and demonstrated that self-compatibility in this species is associated with inactivation of SI specificity genes. INTRODUCTIONSelf-incompatibility (SI) is the major outcrossing mechanism in the family Brassicaceae (de Nettancourt, 1977). Species in this family have been grouped into 19 tribes on the basis of morphological criteria (Schultz, 1936), and SI has been described in all tribes analyzed to date. When Bateman (1955) surveyed 182 species distributed in 11 tribes, he found that approximately half of these species included selfincompatible accessions. In a survey of 59 taxa in the subtribe Brassicineae of the tribe Brassiceae (which includes Brassica and Raphanus ), 50 taxa were self-incompatible (Takahata and Hinata, 1980). In all cases analyzed, SI has been shown to be controlled sporophytically by a single S (sterility) locus, with multiple alleles or variants and complex dominance relationships between alleles (Bateman, 1954(Bateman, , 1955Thompson and Taylor, 1966): in self-incompatible plants, pollen will not develop on a stigma that expresses the same S alleles as the pollen parent.Molecular analysis of the Brassica S locus region has shown that this mendelian locus is a gene complex consisting of distinct stigma-expressed and anther-expressed genes that determine SI specificity in stigma and pollen, respectively (reviewed in Nasrallah, 2000). The SRK (for S locus receptor kinase) gene (Stein et al., 1991) encodes a plasma membrane-spanning receptor serine/threonine kinase specific to the stigma epidermis (Stein et al., 1996) and is the determinant of SI specificity in the stigma (Takasaki et al., 2000). ...

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Self-Incompatibility in the Genus Arabidopsis: Characterization of the S Locus in the Outcrossing A. lyrata and Its Autogamous Relative A. thaliana

Kusaba¹,

Dwyer²,

Hendershot³

et al. 2001

The Plant Cell

131

282

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“…Sequence analysis of the S c haplotype region revealed that the region is rich in retrotransposon-like sequences, which may have been causal to the region being heteromorphic. These findings indicate that the almond S locus has been subjected to repeated rearrangements, deletions, and insertions, like the S locus of Brassicaceae (Boyes et al, 1997;Casselman et al, 2000;Kusaba et al, 2001). The structural heteromorphism is a distinctive feature of loci consisting of coadapted gene complexes in different genetic systems (Ferris and Goodenough, 1994;Brown and Casselton, 2001).…”

Section: Discussionmentioning

confidence: 99%

Structural and Transcriptional Analysis of the Self-Incompatibility Locus of Almond: Identification of a Pollen-Expressed F-Box Gene with Haplotype-Specific Polymorphism

et al. 2003

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Gametophytic self-incompatibility in Rosaceae, Solanaceae, and Scrophulariaceae is controlled by the S locus, which consists of an S-RNase gene and an unidentified "pollen S " gene. An ‫ف‬ 70-kb segment of the S locus of the rosaceous species almond, the S haplotype-specific region containing the S-RNase gene, was sequenced completely. This region was found to contain two pollen-expressed F-box genes that are likely candidates for pollen S genes. One of them, named SFB ( S haplotype-specific F-box protein), was expressed specifically in pollen and showed a high level of S haplotype-specific sequence polymorphism, comparable to that of the S-RNases. The other is unlikely to determine the S specificity of pollen because it showed little allelic sequence polymorphism and was expressed also in pistil. Three other S haplotypes were cloned, and the pollen-expressed genes were physically mapped. In all four cases, SFBs were linked physically to the S-RNase genes and were located at the S haplotype-specific region, where recombination is believed to be suppressed, suggesting that the two genes are inherited as a unit. These features are consistent with the hypothesis that SFB is the pollen S gene. This hypothesis predicts the involvement of the ubiquitin/26S proteasome proteolytic pathway in the RNase-based gametophytic self-incompatibility system.

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“…This has suggested that functional self-incompatibility requires alleles from the two loci to be similar and that recombination between the two loci is suppressed to maintain this matching (Stein et al, 1991). High sequence divergence in the region between the loci (Boyes et al, 1997) and near Petunia inflata S-loci (Coleman & Kao, 1992) support rarity of recombinational exchange, but divergence could be due to relaxed selection in these flanking regions. Sequence differences are not only a feature of S-loci, but are also found in maize intergenic regions (Sanmiguel et al, 1997).…”

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Flowering plant self-incompatibility: the molecular population genetics of Brassica S-loci

Charlesworth

Awadalla

1998

Heredity

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Self-incompatibility systems in different angiosperm families are reviewed, and the evidence that incompatibility has arisen several times is outlined. New data on the sequence polymorphism of self-incompatibility loci from two different angiosperm families are compared with results from other highly polymorphic loci, particularly MHC loci. We discuss what molecular genetic analyses of these sequences can tell us about the nature and maintenance of the polymorphism at self-incompatibility loci. We suggest that there is evidence for recombination at the Brassica selfincompatibility loci, so that it may be possible to discern regions that are particularly functionally important in the recognition reaction, even though the long-term maintenance of polymorphisms in these amino acid residues has caused the evolution of many other sequence differences between alleles.

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The self-incompatibility (S) haplotypes of Brassica contain highly divergent and rearranged sequences of ancient origin.

Cited by 115 publications

References 43 publications

Self-Incompatibility in the Genus Arabidopsis: Characterization of the S Locus in the Outcrossing A. lyrata and Its Autogamous Relative A. thaliana

Self-Incompatibility in the Genus Arabidopsis: Characterization of the S Locus in the Outcrossing A. lyrata and Its Autogamous Relative A. thaliana

Structural and Transcriptional Analysis of the Self-Incompatibility Locus of Almond: Identification of a Pollen-Expressed F-Box Gene with Haplotype-Specific Polymorphism

Flowering plant self-incompatibility: the molecular population genetics of Brassica S-loci

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