Identification and characterisation of resistance gene analogues from wild Chinese Vitis species

Abstract

SummaryGenerating a collection of resistance gene analogues (RGAs) is an initial step towards the isolation of plant disease resistance genes. Based on the two conserved motifs in the nucleotide-binding site leucine-rich repeat (NBS-LRR) domain from previously cloned plant resistance genes, degenerate oligonucleotide primers were designed and used to isolate RGAs from five wild Chinese Vitis species: V. quinquangularis ‘83-4-96’, V. bashanica ‘Xunyang-8’, V. davidii ‘Tangwei’, V. yeshanensis ‘Yanshan’, and V. bryoniifolia ‘Anlin-3’. A total of 55 RGAs with uninterrupted open reading frames were obtained and further assembled within each species into 26 distinct RGAs. These RGAs were classified into six distinct families. Their deduced amino acid sequences contained the conserved motifs characteristic of NBS-LRR resistance genes. However, the sequences of the identified RGAs were very divergent from each other. The low ratio of non-synonymous to synonymous substitutions, and non-detectable recombination events within families, indicate that the NBS regions of Vitis RGAs are under purifying selection rather than diversifying selection. Furthermore, all the RGAs identified in this study were grouped into the non-Toll/Interleukin 1 receptor (TIR)-type of NBS-LRR resistance genes, based on phylogenetic analysis with other known plant R genes.