Molecular characterization of a novel narnavirus from the plant-pathogenic fungus Ustilaginoidea virens

Mycoviruses are viruses that infect fungi, yeasts, and oomycetes and can replicate and multiply within them. They are widely distributed in plant- and animal-pathogenic fungi. In this study, we identified a novel positive-sense single-stranded RNA (+ ssRNA) mycovirus from Ustilaginoidea virens strain Uv339, the causal agent of rice false smut (RSF), and this virus was named "Ustilaginoidea virens narnavirus 5" (UvNV5). Sequence analysis revealed that UvNV5 has a complete genome length of 2091 nt and contains a single open reading frame (ORF) (nt 131–2038) encoding a 635-amino-acid (aa) RNA-dependent RNA polymerase (RdRp) with a molecular mass of 71.8 kDa. BLASTp analysis revealed that the RdRp of UvNV5 shares only 38.22% amino acid sequence identity with that of Ustilaginoidea virens narnavirus virus 13, its closest relative. Phylogenetic analysis indicated that UvNV5 clustered within a branch alongside members of the class Amabiliviricetes. In summary, UvNV5 is a novel mycovirus of the class Amabiliviricetes that infects U. virens.