Complete genome sequence and organization of a novel virus from the rice false smut fungus Ustilaginoidea virens

In this study, three dsRNA segments from the rice false smut fungus Ustilaginoidea virens, the causal agent of a serious disease in rice, with molecular size ranging from 1.3 to 5 Kb, were isolated and named as dsRNA-L, dsRNA-M, and dsRNA-S. The complete nucleotide sequences of dsRNA-M and dsRNA-S were determined and analyzed. The dsRNA-M putatively encodes an RNA-dependent RNA polymerase, which is similar to that of the partitiviruses in the family Partitiviridae. Although the protein encoded by dsRNA-S showed less similarity to the typical coat protein of the virus in the family Partitiviridae, the structural analysis results indicated that the dsRNA-S might function as the capsid protein. We propose that the virus is Ustilaginoidea virens partitivirus 2-Uv0901, a new member, but distantly related to the newly proposed genus Gammapartitivirus with a distinct sequence pattern of capsid protein.