A novel monopartite dsRNA virus isolated from the phytopathogenic fungus Ustilaginoidea virens and ancestrally related to a mitochondria-associated dsRNA in the green alga Bryopsis

•UvNV-1 belongs to a new taxon that is yet to be established.•+1 ribosomal frameshifting was used in UvNV-1 expression.•HGT from viruses to cells might have occurred in UvNV-1.•HVT from the cytoplasm to the mitochondria might have occurred in UvNV-1.•Based on biological analysis, UvNV-1 seemed to be cryptic to its host.

In this study, we describe a novel mycovirus isolated from Ustilaginoidea virens, which was designated Ustilaginoidea virens nonsegmented virus 1 (UvNV-1). The sequence analysis revealed that UvNV-1 has two open reading frames (ORFs). ORF1 encodes an unknown protein, which is similar to the hypothetical protein BN7_5177 of Wickerhamomyces ciferrii. ORF2 encodes a putative RNA-dependent RNA polymerase (RdRp), which is most closely related to Bryopsis mitochondria-associated dsRNA (BDRM) and is likely expressed by a +1 ribosomal frameshift within the sequence CCC_UUU_CGA. The phylogenetic analysis of the RdRp of UvNV-1 showed that UvNV-1 represents a new virus taxon of mycoviruses with a partitivirus-like lineage that is classified into the family of picorna-like viruses. Based on northern hybridization, UvNV-1 was found to be common to U. virens from different geographic locations in China. The biological comparison of virus-free and infected fungal strains revealed that UvNV-1 is likely to be cryptic to its host.