Dataset Information

Molecular population genetics of the SRK and SCR self-incompatibility genes in the wild plant species Brassica cretica (Brassicaceae).

ABSTRACT: Self-incompatibility (SI) in plants is a classic example of a trait evolving under strong frequency-dependent selection. As a consequence, population genetic theory predicts that the S locus, which controls SI, should maintain numerous alleles, display a high level of nucleotide diversity, and, in structured populations, show a lower level of among-population differentiation compared to neutral loci. Population-level investigations of DNA sequence variation at the S locus have recently been carried out in the genus Arabidopsis, largely confirming results from theoretical models of S-locus evolutionary dynamics, but no comparable studies have been done in wild Brassica species. In this study, we sequenced parts of the S-locus genes SRK and SCR, two tightly linked genes that are directly involved in the determination of SI specificity in samples from four natural populations of the wild species Brassica cretica. The amount and distribution of nucleotide diversity, as well as the frequency spectrum of putative functional haplotypes, observed at the S locus in B. cretica fit very well with expectations from theoretical models, providing strong evidence for frequency-dependent selection acting on the S locus in a wild Brassica species.

SUBMITTER: Edh K

PROVIDER: S-EPMC2651069 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Molecular population genetics of the SRK and SCR self-incompatibility genes in the wild plant species Brassica cretica (Brassicaceae).

Edh Kristina K Widén Björn B Ceplitis Alf A

Genetics 20081215 3

Self-incompatibility (SI) in plants is a classic example of a trait evolving under strong frequency-dependent selection. As a consequence, population genetic theory predicts that the S locus, which controls SI, should maintain numerous alleles, display a high level of nucleotide diversity, and, in structured populations, show a lower level of among-population differentiation compared to neutral loci. Population-level investigations of DNA sequence variation at the S locus have recently been carr ...[more]

PMID: 19087967

Similar Datasets

Project description:BackgroundMolecular lock-and-key systems are common among reproductive proteins, yet their evolution remains a major puzzle in evolutionary biology. In the Brassicaceae, the genes encoding self-incompatibility have been identified, but technical challenges currently prevent detailed analyses of the molecular interaction between the male and female components. In the present study, we investigate sequence polymorphism in the female specificity determinant SRK of Arabidopsis halleri from throughout Europe. Using a comparative approach based on published SRK sequences in A. lyrata and Brassica, we track the signature of frequency-dependent selection acting on these genes at the codon level. Using simulations, we evaluate power and accuracy of our approach and estimate the proportion of codon sites involved in the molecular interaction.ResultsWe identified several members of the S-gene family, together with 22 putative S-haplotypes. Linkage to the S-locus and the presence of a kinase domain were formally demonstrated for four and six of these haplotypes, respectively, and sequence polymorphism was extremely high. Twenty-five codons showed signs of positive selection in at least one species, and clustered significantly (but not exclusively) within hypervariable regions. We checked that this clustering was not an artifact due to variation in evolution rate at synonymous sites. Simulations revealed that the analysis was highly accurate, thus providing a reliable set of candidates for future functional analyses, but with an overall power not higher than 60 %. Assuming similar power, we infer from our results that about 23% of all codons in the S-domain may actually be involved in recognition. Interestingly, while simulations demonstrated that this comparison remained reliable even at very high levels of divergence, codons identified in Brassica had higher posterior rates of non-synonymous to synonymous substitutions than codons identified in A. halleri or A. lyrata, possibly suggesting more intense selection in Brassica.ConclusionThe signature of balancing selection can be identified reliably at the codon level even in cases of very high sequence divergence, provided that a sufficiently large set of sequences are analyzed. Altogether, our results indicate that a large proportion of codons may be involved in recognition and confirm the particular importance of hypervariable regions. The more intense signature of positive selection detected in Brassica suggests that allelic diversification in this genus was very recent, possibly following a recent demographic bottleneck.

Project description:BackgroundCrop wild relatives (CWRs) contain genetic diversity, representing an invaluable resource for crop improvement. Many of their traits have the potential to help crops to adapt to changing conditions that they experience due to climate change. An impressive global effort for the conservation of various CWR will facilitate their use in crop breeding for food security. The genus Brassica is listed in Annex I of the International Treaty on Plant Genetic Resources for Food and Agriculture. Brassica oleracea (or wild cabbage), a species native to southern and western Europe, has become established as an important human food crop plant because of its large reserves stored over the winter in its leaves. Brassica cretica Lam. (Bc) is a CWR in the brassica group and B. cretica subsp. nivea (Bcn) has been suggested as a separate subspecies. The species Bc has been proposed as a potential gene donor to brassica crops, including broccoli, cabbage, cauliflower, oilseed rape, etc. RESULTS: We sequenced genomes of four Bc individuals, including two Bcn and two Bc. Demographic analysis based on our whole-genome sequence data suggests that populations of Bc are not isolated. Classification of the Bc into distinct subspecies is not supported by the data. Using only the non-coding part of the data (thus, the parts of the genome that has evolved nearly neutrally), we find the gene flow between different Bc population is recent and its genomic diversity is high.ConclusionsDespite predictions on the disruptive effect of gene flow in adaptation, when selection is not strong enough to prevent the loss of locally adapted alleles, studies show that gene flow can promote adaptation, that local adaptations can be maintained despite high gene flow, and that genetic architecture plays a fundamental role in the origin and maintenance of local adaptation with gene flow. Thus, in the genomic era it is important to link the selected demographic models with the underlying processes of genomic variation because, if this variation is largely selectively neutral, we cannot assume that a diverse population of crop wild relatives will necessarily exhibit the wide-ranging adaptive diversity required for further crop improvement.

Dataset Information

Molecular population genetics of the SRK and SCR self-incompatibility genes in the wild plant species Brassica cretica (Brassicaceae).

Publications

Molecular population genetics of the SRK and SCR self-incompatibility genes in the wild plant species Brassica cretica (Brassicaceae).

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets