Inheritance, fine-mapping, and candidate gene analyses of resistance to soybean mosaic virus strain SC5 in soybean

Soybean mosaic virus (SMV) is one of the most devastating pathogens for soybeans in China. Among the country-wide 22 strains, SC5 dominates in Huang-Huai and Changjiang valleys. For controlling its damage, the resistance gene was searched through Mendelian inheritance study, gene fine-mapping, and candidate gene analysis combined with qRT-PCR (quantitative real-time polymerase chain reaction) analysis. The parents F-1, F-2, and RILs (recombinant inbred lines) of the cross Kefeng-1 (Resistance, R) x NN1138-2 (Susceptible, S) were used to examine the inheritance of SC5-resistance. The F-1 was resistant and the F-2 and RILs segregated in a 3R:1S and 1R:1S ratio, respectively, indicating a single dominant gene conferring the Kefeng-1 resistance. Subsequently, the genomic region conferring the resistance was found in "Bin 352-Bin353 with 500 kb" on Chromosome 2 using the phenotyping data of the 427 RILs and a high-density genetic map with 4703 bin markers. In the 500 kb genomic region, 38 putative genes are contained. The association analysis between the SNPs in a putative gene and the resistance phenotype for the 427 RILs prioritized 11 candidate genes using Chi-square criterion. The expression levels of these genes were tested by qRT-PCR. On infection with SC5, 7 out of the 11 genes had differential expression in Kefeng-1 and NN1138-2. Furthermore, integrating SNP-phenotype association analysis with qRT-PCR expression profiling analysis, Glyma02g13495 was found the most possible candidate gene for SC5-resistance. This finding can facilitate the breeding for SC5-resistance through marker-assisted selection and provide a platform to gain a better understanding of SMV-resistance gene system in soybean.