Determination of the complete genomic sequence and molecular biological analysis ofSoybean mosaic virus

Soybean mosaic virus (SMV; Potyvirus, Potyviridae) is a plant pathogenic virus that infects many commercially important plants worldwide, including soybean, and impairs their production and quality. SMV can be classified into strains based on differences in virulence. Many of these strains have been sequenced; however, only a few complete genomic sequences of virus strains and isolates from soybean grown in China have been reported. In this study, the complete genomic sequences of three SMV isolates of different virulence from plants in China were determined and compared with the sequences of 54 other SMV strains and isolates. Genomic nucleotide diversity analysis and the Neutrality Test showed that the sequence of the 5′ untranslated regions (5′UTR) of the virus genome-linked protein (VPg) and first protein (P1) genes had been altered by negative selection pressure. Phylogenetic analyses indicated that sequence variation in the cytoplasmic inclusion (CI) cistron of the virus was correlated closely with the level of virulence and with the source of the virus isolate. The CI gene was found to be crucial for classification and characterization of the SMV strains, and may be a determining factor in the level of SMV virulence.