A novel mycovirus from Aspergillus fumigatus contains four unique dsRNAs as its genome and is infectious as dsRNA

Abstract

We report the discovery and characterization of a double-stranded RNA (dsRNA) mycovirus isolated from the human pathogenic fungus Aspergillus fumigatus, Aspergillus fumigatus tetramycovirus-1 (AfuTmV-1), which reveals several unique features not found previously in positive-strand RNA viruses, including the fact that it represents the first dsRNA (to our knowledge) that is not only infectious as a purified entity but also as a naked dsRNA. The AfuTmV-1 genome consists of four capped dsRNAs, the largest of which encodes an RNA-dependent RNA polymerase (RdRP) containing a unique GDNQ motif normally characteristic of negative-strand RNA viruses. The third largest dsRNA encodes an S-adenosyl methionine–dependent methyltransferase capping enzyme and the smallest dsRNA a P-A-S–rich protein that apparently coats but does not encapsidate the viral genome as visualized by atomic force microscopy. A combination of a capping enzyme with a picorna-like RdRP in the AfuTmV-1 genome is a striking case of chimerism and the first example (to our knowledge) of such a phenomenon. AfuTmV-1 appears to be intermediate between dsRNA and positive-strand ssRNA viruses, as well as between encapsidated and capsidless RNA viruses.

Harbouring public good mutants within a pathogen population can increase both fitness and virulence

“…Engineering viruses that lower pathogen virulence, for example, is being investigated for control of plant diseases (Nuss, 2005; Kanhayuwa et al, 2015) and was recently developed in vitro for bacterial pathogens (Lu and Collins, 2007). Similarly, synthetic low-virulence strains have been used in animal infection models (Harrison et al, 2006; Rumbaugh et al, 2009; Pollitt et al, 2014) and suggested as a treatment of plant pathogens (Frey et al, 1994; Cleveland et al, 1990).…”

Isolation, molecular characterization and virome analysis of culturable wood fungal endophytes in esca symptomatic and asymptomatic grapevine plants

“…We also identified a virus belonging to a group of viruses still unclassified hosting tetramycoviruses. They are characterized by a multipartite genome (4-5 segments were reported) each presenting a single ORF: RNA1 encodes for the RdRp, RNA2 encodes for a Per-Arnt-Sim-rich protein, RNA3 encodes a protein with a methyltransferase domain, RNA4 and five encode for proteins of unknown function (Kanhayuwa et al, 2015;Mu et al, 2018). In addition, from the discovery of the first member of this group, a number of new viruses belonging to this clade were reported, forming now a well-supported and independent group.…”

Virus-mediated suppression of host non-self recognition facilitates horizontal transmission of heterologous viruses

“…The diversity of mycoviruses is markedly high; mycoviruses are grouped into at least twelve families with many mycoviruses remaining unclassified [27]. Aspergillus fumigatus tetramycovirus-1 appears to be an intermediate between double-stranded (ds) RNA and positive-stranded (+ss) RNA viruses, as well as between encapsidated and capsidless RNA viruses [28]. Furthermore, many novel mycoviruses were discovered frequently by deep sequencing analysis of fungal RNA samples [29].…”