Abstract
We have reported 15 agarose gel band patterns of double-stranded RNA (dsRNA) from Trichoderma spp. We describe herein that band pattern IX in Trichoderma harzianum NFCF319, which appeared to be a single band but consisted of two dsRNAs of similar size, was identified as a novel mycovirus, designated Trichoderma harzianum partitivirus 1 (ThPV1). The larger segment (dsRNA1) of the ThPV1 genome comprised 2,289 bp and contained a single open reading frame (ORF) encoding an RNA-dependent RNA polymerase (RdRp). The smaller segment (dsRNA2) consisted of 2,245 bp with a single ORF encoding a capsid protein (CP). Evaluation of the deduced amino acid sequence and phylogenetic analysis indicated that ThPV1 is a new member of the genus Betapartitivirus in the family Partitiviridae. Curing of virus infection by single-sporing generated 31 virus-free single-spore clones. No significant differences in growth rate, conidia production, or pigmentation were observed between ThPV1-infected and -cured isogenic strains. In addition, comparison of the newly ThPV1-transmitted isolates with their ThPV1-cured parental strain showed no significant difference in colony morphology or pigmentation. However, inhibition of growth in co-cultured Pleurotus ostreatus and Rhizoctonia solani by T. harzianum was increased in ThPV1-containing strains compared with ThPV1-cured isogenic strains. Moreover, β-1,3-glucanase activity was significantly increased in the ThPV1-containing strains. However, no difference in chitinase activity was observed, suggesting that ThPV1 regulates the activity of a specific fungal enzyme.
Highlights
Mycoviruses, i.e., fungal viruses, are widespread and have been found in all major taxa of filamentous fungi and yeasts (Van Alfen, 1986; Nuss and Koltin, 1990; Wickner, 1992)
The double-stranded RNA (dsRNA) extracted from the mycelia of T. harzianum NFCF319 was resolved by 1% agarose gel electrophoresis, and distinctive bands of approximately 2.3 kb were excised (Figure 1A)
A homology search of the assembled reads suggested the presence of contigs with high similarity to the known viral sequences of RNA-dependent RNA polymerase (RdRp) and capsid protein (CP)
Summary
Mycoviruses, i.e., fungal viruses, are widespread and have been found in all major taxa of filamentous fungi and yeasts (Van Alfen, 1986; Nuss and Koltin, 1990; Wickner, 1992). The majority of characterized mycoviruses have a double-stranded RNA (dsRNA) genome, others have single-stranded RNA (ssRNA) and DNA genomes. Mycoviruses of seven families, Chrysoviridae, Endornaviridae, Megabirnaviridae, Quadriviridae, Partitiviridae, Reoviridae, and Totiviridae have dsRNA genomes, while those of six families, Alphaflexiviridae, Barnaviridae, Gammaflexiviridae, Hypoviridae, Narnaviridae, and Mymonaviridae have ssRNA genomes according to a report by the International Committee on the Taxonomy of Viruses (ICTV) in 2016 (Ghabrial et al, 2015). Using multi-omics techniques, a large number of novel mycoviruses are expected to be discovered and characterized from various fungi. Infection of fungi by many mycoviruses is asymptomatic or cryptic (Ghabrial, 1998), there are many cases of mycoviruses inducing viralspecific symptoms in the host and reduced fungal virulence, known as hypovirulence, is one of representative examples in phytopathogenic fungi (Nuss, 2005)
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