Abstract
Here we report a biological and molecular characterization of a novel positive-sense RNA virus isolated from a field isolate (NW10) of a filamentous phytopathogenic fungus, the white root rot fungus that is designated as Rosellinia necatrix fusarivirus 1 (RnFV1). A recently developed technology using zinc ions allowed us to transfer RnFV1 to two mycelially incompatible Rosellinia necatrix strains. A biological comparison of the virus-free and -recipient isogenic fungal strains suggested that RnFV1 infects latently and thus has no potential as a virocontrol agent. The virus has an undivided positive-sense RNA genome of 6286 nucleotides excluding a poly (A) tail. The genome possesses two non-overlapping open reading frames (ORFs): a large ORF1 that encodes polypeptides with RNA replication functions and a smaller ORF2 that encodes polypeptides of unknown function. A lack of coat protein genes was suggested by the failure of virus particles from infected mycelia. No evidence was obtained by Northern analysis or classical 5′-RACE for the presence of subgenomic RNA for the downstream ORF. Sequence similarities were found in amino-acid sequence between RnFV1 putative proteins and counterparts of a previously reported mycovirus, Fusarium graminearum virus 1 (FgV1). Interestingly, several related sequences were detected by BLAST searches of independent transcriptome assembly databases one of which probably represents an entire virus genome. Phylogenetic analysis based on the conserved RNA-dependent RNA polymerase showed that RnFV1, FgV1, and these similar sequences are grouped in a cluster distinct from distantly related hypoviruses. It is proposed that a new taxonomic family termed Fusariviridae be created to include RnFV1 and FgV1.
Highlights
An increasing number of mycoviruses have been reported from various host fungi (Urayama et al, 2010, 2014; Cai and Hillman, 2013; Chiba et al, 2013a,b; Jiang et al, 2013; Kalifa and Pearson, 2013; Kondo et al, 2013b; Nibert et al, 2014)
We report a biological and molecular characterization of a novel positive-sense RNA virus isolated from a field isolate (NW10) of a filamentous phytopathogenic fungus, the white root rot fungus that is designated as Rosellinia necatrix fusarivirus 1 (RnFV1)
Based on RNA-dependent RNA polymerase (RdRp)-based dendrograms, Sclerotinia sclerotiorum RNA virus L (SsRV-L) and Diaporthe RNA virus (DaRV) are phylogenetically related to animal and plant viruses, while Fusarium graminearum virus 1 (FgV1) is phylogenetically related to members of the family Hypoviridae
Summary
An increasing number of mycoviruses (fungal viruses) have been reported from various host fungi (Urayama et al, 2010, 2014; Cai and Hillman, 2013; Chiba et al, 2013a,b; Jiang et al, 2013; Kalifa and Pearson, 2013; Kondo et al, 2013b; Nibert et al, 2014). There are several species that have not yet been assigned to any genus or family Those viruses include Sclerotinia sclerotiorum RNA virus L (SsRV-L) (Liu et al, 2009), Fusarium graminearum virus 1 (FgV1) (Kwon et al, 2007), Sclerophthora macrospora viruses A and B (SmVA and SmVB) (Honkura et al, 1983; Yokoi et al, 1999, 2003), and Diaporthe RNA virus (DaRV) (Moleleki et al, 2003). Based on RNA-dependent RNA polymerase (RdRp)-based dendrograms, SsRV-L and DaRV are phylogenetically related to animal and plant viruses, while FgV1 is phylogenetically related to members of the family Hypoviridae
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