|WU, MINGDE - Huazhong Agricultural University|
|DENG, YUE - Huazhong Agricultural University|
|ZHOU, ZILIANG - Huazhong Agricultural University|
|HE, GUOYUAN - Huazhong Agricultural University|
|LI, GUOQING - Huazhong Agricultural University|
Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2016
Publication Date: 6/22/2016
Citation: Wu, M., Deng, Y., Zhou, Z., He, G., Chen, W., Li, G. 2016. Characterization of three mycoviruses co-infecting the plant pathogenic fungus Sclerotinia nivalis. Virus Research. 223:28-38.
Interpretive Summary: Mycoviruses, viruses that live in fungi, are ubiquitous, and have a wide range of effects on their host fungi. Some mycoviruses have no obvious effect and cause no visible changes in morphology, growth rate and pathogenicity on their host fungi. However, some mycoviruses have detrimental effect on fungi and make their host fungi less virulent in causing plant diseases, causing hypovirulence. Mycoviruses that cause hypovirulence have the potential to be biocontrol agents. Sclerotinia species are a group of fungi causing serious diseases such as white mold of many economically important crops. Control of Sclerotinia disease is difficult because of persistence of the pathogen and lack of adequate resistance in host plants. Mycoviruses in Sclerotinia could offer an alternative in integrated management of Sclerotinia diseases. During studying the plant pathogen S. nivalis, one strain of the pathogen was found to be co-infected by three mycoviruses. This study was aimed at characterizing the three mycoviruses. Through genomic analysis, one of the three mycoviruses was found to be a victorivirus, designated as Sclerotinia nivalis victorivirus 1 (SnVV1). The other two mycoviruses belonged to mitoviruses, named as Sclerotinia nivalis mitovirus 1 (SnMV1) and Sclerotinia nivalis mitovirus 2 (SnMV2). All the three mycoviruses would be horizontally transmitted. This is the first report of mycoviruses infecting S. nivalis. Co-infection by these three mycoviruses had no apparent effects on growth and pathogenicity of S. nivalis.
Technical Abstract: Two dsRNAs of approximately 6.0- and 3.0-kb in length were detected in strain SsSn-1 of Sclerotinia nivalis. Genomic analysis showed that the 6.0-kb dsRNA was a victorivirus, named as Sclerotinia nivalis victorivirus 1 (SnVV1). The genome of SnVV1 is 5162 bp in length containing two large open reading frames (ORFs), ORF1 and ORF2. ORF1 was deduced to encode a coat protein (CP) showing homology to CPs of viruses belonging to the family Totiviridae. The stop codon of ORF1 overlaped with the start codon of ORF2 in the tetranucleotide sequence AUGA. ORF2 was predicted to encode for a RNA-dependent RNA polymerase (RdRp) that is very similar to the RdRps of victoriviruses. The 3.0-kb dsRNA consisted of two species of mitoviruses, named as Sclerotinia nivalis mitovirus 1 (SnMV1) and Sclerotinia nivalis mitovirus 2 (SnMV2). The genomes of SnMV1 and SnMV2 were 2720 nt and 2583 nt in length, respectively. Both mitoviruses were AU-rich and deduced to contain a major large ORF encoding a mitoviral RdRp with fungal mitochondrial codon usages. SnMV1 was most closely related to Sclerotinia sclerotiorum mitovirus 4/NZ1 (SsMV4/NZ1) and shared 76.5% and 80.1% identity with SsMV4/NZ1 for nucleotide and RdRp sequences, respectively. In addition, the nucleotide and RdRp sequences of SnMV2 were 90.6% and 95.9% identical to the nucleotide and RdRp sequences of Sclerotinia sclerotiorum mitovirus 3/NZ1 (SsMV3/NZ1), respectively. Considering its low nucleotide and RdRp sequence identities with other mitoviruses, SnMV1 might be a new virus species in the genus Mitovirus, whereas SnMV2 is possibly a strain of SsMV3. Both SnMV1 and SnMV2 were transmitted to a recipient virus-free colony faster than SnVV1. Co-infection by these three mycoviruses had no apparent effects on growth and pathogenicity of S. nivalis.