Journal Article

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

Kanhayuwa, Lakkhana, Ioly Kotta-Loizou, A. Patrick Gunning, Robert H. A. Coutts, Selin Özkan

2015

Overview

Mycoviruses generally contain dsRNA genomes but ssRNA and ssDNA examples are known. Mycovirus diversity is increasing, and here we describe a unique example that contains four dsRNA elements nominated Aspergillus fumigatus tetramycovirus-1 (AfuTmV-1). We show for the first time (to our knowledge) that both purified AfuTmV-1 and its dsRNA are infectious for protoplasts and that the virus genome is not conventionally encapsidated and has a unique organization. Separation of the genes encoding the RNA-dependent RNA polymerase enzyme responsible for copying the viral genome and an S -adenosyl methionine-dependent methyltransferase capping enzyme on different dsRNAs is also previously unreported for a mycovirus. AfuTmV-1 appears to be intermediate between dsRNA and positive-strand ssRNA viruses, as well as between encapsidated and capsidless RNA viruses. 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.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Aspergillus fumigatus / Aspergillus fumigatus - isolation & purification / Aspergillus fumigatus - virology / Biological Sciences / capping enzyme / Clone Cells / Cloning, Molecular / DNA, Complementary - genetics / double-stranded RNA / Fungi / genes / Genome, Viral / Genomes / Host-Pathogen Interactions / infectious dsRNA / methyltransferases / Microscopy, Atomic Force / Molecular Sequence Data / mycovirus / mycoviruses / positive sense, single-stranded RNA viruses / Proteins / protoplast transfection / protoplasts / Ribonucleic acid / RNA / RNA polymerase / RNA, Double-Stranded - metabolism / RNA-directed RNA polymerase / Sequence Analysis, DNA / single-stranded DNA / virus evolution / Virus Replication / Viruses / Viruses - chemistry / Viruses - genetics / Viruses - pathogenicity