Molecular characterization of a novel fusarivirus infecting the plant-pathogenic fungus Nigrospora sphaerica

Here, we describe a novel mycovirus, tentatively designated as “Nigrospora sphaerica fusarivirus 2”(NsFV2), which was isolated from the phytopathogenic fungus Nigrospora sphaerica strain HNXX-Ns20. NsFV2 has a single-stranded positive-sense RNA (+ ssRNA) genome of 6,156 nucleotides, excluding the poly(A) tail, and contains two putative open reading frames (ORFs). The ORF1 encodes a large polypeptide of 1,509 amino acid (aa) containing a conserved RNA-dependent RNA polymerase (RdRp) domains and a viral helicase domain. The ORF1-encoded polypeptide shares 29.40-68.48% sequence identity with other fusariviruses and shares the highest sequence identity (68.48%) with Nigrospora sphaerica fusarivirus 1 (NsFV1) .The small ORF2 encodes a polypeptide with 483 a and contains a conserved chromosome segregation ATPase (Smc) domain. Multiple sequence alignments and phylogenetic analysis based on the ORF1-encoded polypetide indicated that NsFV2 should be new member of the genus Alphafusarivirus of family Fusariviridae .