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Front Microbiol. 2014 Jul 18;5:360. doi: 10.3389/fmicb.2014.00360. eCollection 2014.

A novel single-stranded RNA virus isolated from a phytopathogenic filamentous fungus, Rosellinia necatrix, with similarity to hypo-like viruses.

Author information

1
Group of Plant/Microbe Interactions, Institute of Plant Science and Resources, Okayama University Kurashiki, Okayama, Japan.
2
Apple Research Division, National Institute of Fruit Tree Science, National Agricultural Research Organization (NARO) Morioka, Iwate, Japan.

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.

KEYWORDS:

Rosellinia necatrix; fusarivurs; hypovirus; novel mycovirus; ssRNA virus; transcriptome shotgun assembly

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