Signatures of balancing selection are maintained at disease resistance loci following mating system evolution and a population bottleneck in the genus Capsella.
BACKGROUND
Population bottlenecks can lead to a loss of variation at disease resistance loci, which could have important consequences for the ability of populations to adapt to pathogen pressure. Alternatively, current or past balancing selection could maintain high diversity, creating a strong heterogeneity in the retention of polymorphism across the genome of bottlenecked populations. We sequenced part of the LRR region of 9 NBS-LRR disease resistance genes in the outcrossing Capsella grandiflora and the recently derived, bottlenecked selfing species Capsella rubella, and compared levels and patterns of nucleotide diversity and divergence with genome-wide reference loci.


RESULTS
In strong contrast with reference loci, average diversity at resistance loci was comparable between C. rubella and C. grandiflora, primarily due to two loci with highly elevated diversity indicative of past or present balancing selection. Average between-species differentiation was also reduced at the set of R-genes compared with reference loci, which is consistent with the maintenance of ancestral polymorphism.


CONCLUSIONS
Historical or ongoing balancing selection on plant disease resistance genes is a likely contributor to the retention of ancestral polymorphism in some regions of the bottlenecked Capella rubella genome.
Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada. gos@lunenfeld.ca
Gesseca
G
Gos
Tanja
T
Slotte
Stephen I
SI
Wright
D005075:Biological Evolution; D029687:Capsella / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics; D060467:Disease Resistance; D017343:Genes, Plant; D014644:Genetic Variation; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA
D018744:DNA, Plant