Conditional neutrality at two adjacent NBS-LRR disease resistance loci in natural populations of Arabidopsis lyrata.
We examined patterns of nucleotide diversity at a genomic region containing two linked candidate disease resistance (NBS-LRR) genes in seven populations of the outcrossing plant Arabidopsis lyrata. In comparison with two adjacent control genes and neutral reference genes across the genome, the NBS-LRR genes exhibited elevated nonsynonymous variation and a large number of major-effect polymorphisms causing early stop codons and/or frameshift mutations. In contrast, analysis of synonymous diversity provided no evidence that the region was subject to long-term balancing selection or recent selective sweeps in any of the seven populations surveyed. Also in contrast with earlier surveys of one of these R genes, there was no evidence that the resistance genes or the major-effect mutations were subject to elevated differentiation between populations. We suggest that conditional neutrality in the absence of the corresponding pathogen, rather than long-term balancing selection or local adaptation, may in some circumstances be a significant cause of elevated functional polymorphism at R genes. In contrast with the R genes, analysis of diversity and differentiation at the flanking FERONIA locus showed high population divergence, suggesting local adaptation on this locus controlling male-female signalling during fertilization.
Gos
Gesseca
G
Department of Biology, York University, 4700 Keele Street, Toronto, ON, Canada M3J1P3.
Wright
Stephen I
SI
D017360:Arabidopsis / Q000235:genetics* / Q000276:immunology; D018388:Codon, Terminator; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D016368:Frameshift Mutation; D017343:Genes, Plant; D005828:Genetics, Population; D018745:Genome, Plant; D007113:Immunity, Innate / Q000235:genetics*; D011110:Polymorphism, Genetic; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA
D018388:Codon, Terminator; D018744:DNA, Plant