Abstract
Sclerotium rolfsii, which causes southern blight in a wide variety of crops, is a devastating plant pathogen worldwide. Mycoviruses that induce hypovirulence in phytopathogenic fungi are potential biological control resources against fungal plant diseases. However, in S. rolfsii, mycoviruses are rarely reported. In a previous study, we found a hypovirulent strain carrying a diverse pattern of dsRNAs. Here, we utilized the RNA_Seq technique to detect viral sequences. Deep sequencing, RT-PCR and Sanger sequencing validation analyses revealed that this strain harbors various new viral species that show affinity to the distinctly established and proposed families Benyviridae, Endornaviridae, Fusariviridae, Hypoviridae, and Fusagraviridae. Moreover, some viral sequences that could not be assigned to any of the existing families or orders were also identified and showed similarities to the Alphavirus, Ourmiavirus, phlegivirus-like and Curvularia thermal tolerance virus-like groups. In addition, we also conducted deep sequencing analysis of small RNAs in the virus-infecting fugal strain. The results indicated that the Dicer-mediated gene silencing mechanism was present in S. rolfsii. This is the first report of viral diversity in a single S. rolfsii fungal strain, and the results presented herein might provide insight into the taxonomy and evolution of mycoviruses and be useful for the exploration of mycoviruses as biocontrol agents.
Highlights
Mycoviruses are a type of virus that infect and replicate in fungi, infecting all major taxonomic fungal groups (Ghabrial and Suzuki, 2009)
Because most of these assembled viral sequences shared less than 50% amino acid identity with the previously described mycovirus, we suggest that they are novel viruses
When exploring the polar distribution of SrHV1 and SrEV1derived virus derived small interfering RNAs (vsiRNAs), we found that the vsiRNAs in sizes of 21 and 22 nts originated from SrHV1 and Sclerotium rolfsiii endornavirus 1 (SrEV1) were heterogeneously distributed along the sense and antisense strands of the virus genomes
Summary
Mycoviruses are a type of virus that infect and replicate in fungi, infecting all major taxonomic fungal groups (Ghabrial and Suzuki, 2009). Several mycoviruses can obviously cause abnormal symptoms in the host, such as hypovirulence and debilitation, and hold great promise for exploitation as biological agents to control fungal diseases. Since Cryphonectria hypovirus 1 (CHV1) was successfully used to control chest blight disease in Europe (Nuss, 1992; Xie and Jiang, 2014; Ghabrial et al, 2015), phytopathologists have been inspired to study mycovirus-mediated hypovirulence in plant pathogenic fungi. The DNA virus Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1) was proven to possess the potential for biologically controlling sclerotinia disease under field conditions (Yu et al, 2010, 2013). Rosellinia necatrix megabirnavirus 1 has the ability to control apple white root rot disease caused by Rosellinia necatrix (Chiba et al, 2009; Liu et al, 2016). With the rare exceptions of DNA and negative-sense RNA (-ssRNA) (Liu et al, 2014), mycoviral genomes consist of double-stranded (ds) or positive-sense single-stranded
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