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Novel Victorivirus from a Pakistani Isolate of Alternaria alternata Lacking a Typical Translational Stop/Restart Sequence Signature

1
Institute of Plant Science and Resources, Okayama University, Chuou 2-20-1, Kurashiki, Okayama 710-0046, Japan
2
Crop Diseases Research Institute, National Agricultural Research Centre, Park Road, Islamabad 45500, Pakistan
*
Authors to whom correspondence should be addressed.
Viruses 2019, 11(6), 577; https://doi.org/10.3390/v11060577
Received: 4 June 2019 / Revised: 19 June 2019 / Accepted: 21 June 2019 / Published: 25 June 2019
(This article belongs to the Section Viruses of Plants, Fungi and Protozoa)
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Abstract

The family Totiviridae currently contains five genera Totivirus, Victorivirus, Leishmavirus, Trichomonasvirus, and Giardiavirus. Members in this family generally have a set of two-open reading frame (ORF) elements in their genome with the 5′-proximal ORF (ORF1) encoding a capsid protein (CP) and the 3′-proximal one (ORF2) for RNA-dependent RNA polymerase (RdRp). How the downstream open reading frames (ORFs) are expressed is genus-specific. All victoriviruses characterized thus far appear to use the stop/restart translation mechanism, allowing for the expression of two separate protein products from bicitronic genome-sized viral mRNA, while the totiviruses use a −1 ribosomal frame-shifting that leads to a fusion product of CP and RdRp. We report the biological and molecular characterization of a novel victorivirus termed Alternaria alternata victorivirus 1 (AalVV1) isolated from Alternaria alternata in Pakistan. The phylogenetic and molecular analyses showed AalVV1 to be distinct from previously reported victoriviruses. AalVV1 appears to have a sequence signature required for the −1 frame-shifting at the ORF1/2 junction region, rather than a stop/restart key mediator. By contrast, SDS–polyacrylamide gel electrophoresis and peptide mass fingerprinting analyses of purified virion preparations suggested the expression of two protein products, not a CP-RdRp fusion product. How these proteins are expressed is discussed in this study. Possible effects of infection by this virus were tested in two fungal species: A. alternata and RNA silencing proficient and deficient strains of Cryphonectria parasitica, a model filamentous fungus. AalVV1 showed symptomless infection in all of these fungal strains, even in the RNA silencing deficient C. parasitica strain. View Full-Text
Keywords: mycovirus; victorivirus; Totiviridae; dsRNA; stop/restart translation; pseudoknot structure; Alternaria alternata; Cryphonectria parasitica; Indian subcontinent mycovirus; victorivirus; Totiviridae; dsRNA; stop/restart translation; pseudoknot structure; Alternaria alternata; Cryphonectria parasitica; Indian subcontinent
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Jamal, A.; Sato, Y.; Shahi, S.; Shamsi, W.; Kondo, H.; Suzuki, N. Novel Victorivirus from a Pakistani Isolate of Alternaria alternata Lacking a Typical Translational Stop/Restart Sequence Signature. Viruses 2019, 11, 577.

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