Characterization of three novel betapartitiviruses co-infecting the phytopathogenic fungus Rhizoctonia solani

In this study, we isolated and characterized seven dsRNA elements, designed as dsRNA-1 to 7, from a Rhizoctonia solani strain. Sequence analysis indicated that there were at least three novel mycoviruses co-infected in this fungal strain, termed Rhizoctonia solani partitivirus 6 (RsPV6), Rhizoctonia solani partitivirus 7 (RsPV7), and Rhizoctonia solani partitivirus 8 (RsPV8), respectively. RsPV6 contained three dsRNA segments, dsRNA-1, 6 and 7. DsRNA-1 encoded a RNA-dependent RNA polymerase (RdRp), whereas the proteins encoded by dsRNA-6 and 7 showed no detectable sequence similarity with any known viral proteins in the database. RsPV7 had the genome segments of dsRNA-2 and 5, encoding proteins of RdRp and capsid protein, respectively. RsPV8 containing the genomes of dsRNA-3 and 4 also encoded a RdRp and a protein with unknown function. RdRp-based phylogenetic analysis revealed that all the three viruses were phylogenetically related to members of the genus Betapartitivirus in the family Partitiviridae. In addition, the three viruses could be horizontal co-transmitted via hyphal contact between R. solani strains and cause no apparent phenotypic alteration to their fungal host. These findings provided new insights into the virus taxonomy of the family Partitiviridae and expanded our understanding of viral diversity in R. solani fungus.