Recombination and selection at Brassica self-incompatibility loci

Area of Science:

• Plant reproductive biology
• Molecular evolution
• Population genetics

Background:

• Self-incompatibility (SI) in Brassica is controlled by the S-locus, involving SLG and SRK genes.
• High genetic diversity exists at SLG and SRK, with ancient origins and hypervariable regions.
• Previous hypotheses suggested suppressed recombination in the S-locus region to maintain haplotype integrity.

Purpose of the Study:

• To investigate the occurrence of intragenic recombination within the SLG gene in Brassica species.
• To analyze patterns of nucleotide diversity within SLG and SRK genes to infer recombination and selection.
• To test whether hypervariable regions are under balancing selection.

Main Methods:

• Analysis of linkage disequilibrium within the SLG gene using published coding sequences from two Brassica species.
• Examination of synonymous nucleotide diversity patterns within SLG and SRK genes.
• Comparison of nucleotide diversity between domains of the SRK gene.

Main Results:

• Evidence suggests that intragenic recombination has occurred in the evolutionary history of SLG alleles.
• Patterns of synonymous nucleotide diversity support recombination within both SLG and SRK genes, and between SRK domains.
• Clusters of linkage disequilibrium in SLG indicate hypervariable regions are maintained by balancing selection.

Conclusions:

• Intragenic recombination has played a role in the evolution of Brassica self-incompatibility genes.
• Hypervariable regions within SLG and SRK are likely under balancing selection, contributing to SI diversity.
• These findings necessitate re-evaluation of functional inferences based solely on sequence diversity patterns.