Molecular characterization of a novel chrysovirus isolated from the phytopathogenic fungus Fusarium commune

In this study, a novel double-stranded RNA (dsRNA) mycovirus was isolated from the phytopathogenic fungus Fusarium commune, the causal agent of tobacco root rot, and designated "Fusarium commune chrysovirus 1" (FcCV1). The complete genome of FcCV1 consists of five dsRNA fragments with lengths of 3670 bp, 3242 bp, 2866 bp, 2829 bp, and 1258 bp, designated as dsRNA1 to dsRNA5 according to their size. Each of these five dsRNA segments contains a single open reading frame (ORF), designated ORF1 to ORF5, with strictly conserved termini in their 5′ and 3′ untranslated regions. Notably, ORF1 encodes a potential RNA-dependent RNA polymerase (RdRp) comprising 1151 amino acids (aa), which exhibits the highest sequence identity (56.14%) with the RdRp of Tolypocladium cylindrosporum virus 2 (TcV2). ORF2, ORF3, and ORF5 encode hypothetical proteins of unknown function, displaying amino acid sequence similarity to proteins encoded by different dsRNAs of chrysoviruses. ORF4 encodes a predicted coat protein (CP). Phylogenetic analysis based on RdRp sequences placed FcCV1 within the genus Betachrysovirus of the family Chrysoviridae. This is the first report of a novel chrysovirus infecting F. commune.