Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada.
BMC Evol Biol. 2012 Aug 21;12:152. doi: 10.1186/1471-2148-12-152.
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.
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.
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.
种群瓶颈会导致疾病抗性基因座的变异丢失，这可能对种群适应病原体压力的能力产生重要影响。或者，当前或过去的平衡选择可以维持高多样性，从而在瓶颈种群的基因组中保持高度的多态性保留异质性。我们对异交的荠菜（Capsella grandiflora）和最近衍生的、瓶颈的自交种荠菜（Capsella rubella）中 NBS-LRR 疾病抗性基因的 LRR 区部分进行了测序，并将核苷酸多样性和分化水平与基因组参考位点进行了比较。
与参考位点形成鲜明对比的是，C. rubella 和 C. grandiflora 之间抗性基因座的平均多样性相当，主要是由于两个具有高度升高多样性的基因座，表明过去或现在存在平衡选择。与参考位点相比，在一组 R 基因中，种间平均分化也降低了，这与祖先多态性的维持一致。
植物疾病抗性基因的历史或正在进行的平衡选择可能是瓶颈期 C. rubella 基因组某些区域保留祖先多态性的原因之一。
