A novel nonsegmented double-stranded RNA mycovirus identified in the phytopathogenic fungus Nigrospora oryzae shows similarity to partitivirus-like viruses.

Nigrospora oryzae is a pathogen that can infect plants of various species. Here, we report the isolation of a novel mycovirus from N. oryzae infecting rice, as well as the complete genome sequence and genomic organization of this virus, which we have named "Nigrospora oryzae nonsegmented RNA virus 1" (NoNRV1). The genome of NoNRV1 contained two non-overlapping open reading frames (ORF1 and ORF2) potentially encoding a protein with an unknown function in ORF1 and a putative RNA-dependent RNA polymerase (RdRp) in ORF2. Homology and phylogenetic analysis revealed that NoNRV1 was most similar to the Ustilaginoidea virens nonsegmented virus 1 (UvNV-1) and distantly related to members of the virus family Partitiviridae. It is proposed that NoNRV1, together with UvNV-1 and other related viruses, might represent a novel virus taxon of mycoviruses belonging to a partitivirus-like lineage.