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

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-07, Vol.112 (29), p.9100-9105
• Main Authors: Kanhayuwa, Lakkhana, Ioly Kotta-Loizou, Selin Özkan, A. Patrick Gunning, Robert H. A. Coutts
• Format: Article
• Language: English
• Subjects: 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
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1419225112

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.