Molecular and Biological Characterization of the First Mymonavirus Identified in Fusarium oxysporum

We characterized a negative sense single-stranded RNA mycovirus, Fusarium oxysporum mymonavirus 1 (FoMyV1), isolated from the phytopathogenic fungus Fusarium oxysporum. The genome of FoMyV1 is 10,114 nt, including five open reading frames (ORFs1-5) that are non-overlapping and linearly arranged. The largest, ORF5, encodes a large polypeptide L containing a conserved regions corresponding to Mononegavirales RNA-dependent RNA polymerase and mRNA-capping enzyme region V; the putative functions of the remaining four ORFs are unknown. The L protein encoded by ORF5 shared a high amino acid identity of 65% with that of Hubei rhabdo-like virus 4, a mymonavirus that associated with arthropods. However, the L protein of FoMyV1 also showed amino acid similarity (27-36%) with proteins of mynonaviruses that infect the phytopathogenic fungi Sclerotinia sclerotiorum and Botrytis cineaea. Phylogenetic analysis based on L protein showed that FoMyV1 is clustered with the members of the genus Hubramonavirus in the family Mymonaviridae. Moreover, we found that FoMyV1 could successfully transfer by hyphal anastomosis to a virus-free strain. FoMyV1 reduced the vegetative growth and conidium production of its fungal host but did not alter its virulence. To the best of our knowledge, this is not only the first mymonavirus described in the species F. oxysporum, but also the first Hubramonavirus species found to infect a fungus. However, the incidence of FoMyV1 infections in the tested F. oxysporum strains was only 1%.

Automated summary

We identified and characterized a mycovirus named Fusarium oxysporum mymonavirus 1 (FoMyV1) from the phytopathogenic fungus Fusarium oxysporum. The genome of FoMyV1 has a length of 10,114 nucleotides and contains five non-overlapping open reading frames (ORFs). The largest ORF encodes a polypeptide with high amino acid identity to other mymonaviruses and also shares similarity with proteins of mynonaviruses that infect other phytopathogenic fungi. Phylogenetic analysis revealed that FoMyV1 belongs to the genus Hubramonavirus in the family Mymonaviridae. FoMyV1 can be transmitted through hyphal anastomosis and affects the growth and conidium production of its fungal host.