Molecular characterization of a novel double-stranded RNA virus infecting the entomopathogenic fungus Metarhizium brunneum.

There are four dsRNAs segments present in the entomopathogenic fungus Metarhizium brunneum strain RCEF0766. The genomic segments dsRNA1 and dsRNA3 are of a novel virus, "Metarhizium brunneum bipartite mycovirus 1" (MbBV1), while dsRNA2 and dsRNA4 are the components of the Metarhizium brunneum partitivirus 2 (MbPV2), a member in genus Gammapartitivirus of the family Partitiviridae based on molecular analysis and RT-PCR. This suggests that the strain RCEF0766 was co-infected by two different mycoviruses. The complete genome sequence of MbBV1 was elucidated by high-throughput sequencing and RLM-RACE. MbBV1 consists of two dsRNAs (1987 and 1642 bp) encode open-reading frames (ORFs). The ORF1 in dsRNA 1 encode is a putative RNA-dependent RNA polymerase (RdRp) with the molecular weight of 68.08 kDa, while ORF2 in dsRNA 2 encodes a hypothetical protein with the molecular weight of 33.07 kDa. The deduced proteins of ORF1 and ORF2 have the highest identity to those of Erysiphe necator-associated bipartite virus 1 (76.88% and 65.30%). Based on the amino acid sequence of RdRp, MbBV1 is phylogenetically clustered together with the unassigned mycoviruses and represents a distinct lineage. Our study proposes that MbBV1 is a novel mycovirus with bisegmented dsRNA genomes and should be considered a new member of the unassigned group.