Comparative Sequence Analysis to Identify Rsv3 Gene Encoding Resistance to Soybean Mosaic Virus.

Soybean mosaic virus (SMV) causes one of the most destructive viral diseases in soybean worldwide, with significant yield reductions and deficiencies in seed quality. The disease can be effectively managed through the deployment of single-dominant resistance genes known as Rsv genes that confer resistance to different strains of SMV. Three genes (Rsv1, Rsv3, and Rsv4) that confer resistance to different strains of SMV have been reported. The Rsv3 gene confers extreme resistance to the most virulent strain groups of SMV (G5-G7). The genetic mapping analysis of Rsv3 locus (154 kb) has revealed presence of a family of closely related Coiled-Coil Nucleotide Binding-Leucine Rich Repeat (CC-NB-LRR) encoding genes. Most characterized resistance genes in plants are of NB-LRR type, which are constitutively expressed at low levels in host cell to detect pathogen at any given time in order to initiate host defense response. Moreover, these genes have high sequence similarity due to extensive gene duplication, and variations in different allelic forms that enable differential recognition specificity. In this study, we performed comparative sequence analyses to identify polymorphisms in the Rsv3gene candidates between resistant and susceptible lines, followed by candidate gene expression estimation. Our analyses have identified a candidate with gene sequence homologous among different Rsv3-containing SMV resistant lines. We have assembled coding region of this candidate gene using transcriptome sequencing, and verified several polymorphisms in different resistance lines. These findings provide strong evidence for this candidate to be a resistance conferring gene, Rsv3.