Molecular characterization of a novel mycotombus‑like virus isolated from the phytopathogenic fungus Nigrospora oryzae

In this study, we identified a new mycotombus-like mycovirus from the phytopathogenic fungus Nigrospora oryzae, which was tentatively designated as "Nigrospora oryzae umbra-like virus 1" (NoULV1). The complete genome of NoULV1 is 3,381 nt long, containing two open reading frames (ORF1 and ORF2). ORF1 encodes a hypothetical protein with an unknown function, while ORF2 encodes an RNA-dependent RNA polymerase (RdRp) with a conserved RdRp domain containing a metal-binding ‘GDN’ triplet in motif C, which is distinct from the ‘GDD’ motif found in most + ssRNA mycoviruses. A homology search revealed that the RdRp encoded by ORF2 was similar to the RdRp of umbra-like mycoviruses. Phylogenetic analysis based on the RdRp indicated that NoULV1 was grouped into a clade together with umbra-like mycoviruses belonging to the proposed family “Mycotombusviridae”.