Molecular Characterization Of Two Novel Mycoviruses Co-infecting Rhizoctonia Oryzae-sativae Strain 40-1

Viruses that infect fungi are called mycoviruses. They are present in all the major of fungi known so far base on their appurtenance of virus-like particles and unencapsidated dsRNA. They behave like microorganism and have the ability to reproduce in the pathogen they cause disease. Rhizoctonia genus is one of the different major of fungi, which causes an important damage to plant production but also can disturb the system of their development. The full-length cDNA sequence of a double stranded RNA (dsRNA) segment was determined and isolated from the filamentous phytopathogenic fungus Rhizoctonia oryzae-sativae strain 40-1. The sequence analyses of the positive-strand RNA using the mitochondrial genetic code revealed that the presence of one large open reading frame (ORF) with 3096 nts long encoded an RNA-dependent RNA polymerase (RdRp). RdRp showed 31% acid amine similarity to Rhizophagus sp. RF1 mitovirus, and 28～44% to other mitoviruses. The 5’ and 3’-untranslated regions (UTRs) could be folded into stable stem-loop secondary structures, and the inverted terminal complimentary sequence potentially forms a panhandle structure. Thus, this Rhizoctonia oryzae-sativae mitovirus confer a new member to the genus mitovirus of the family Narnaviridae and was designated as Rhizoctonia oryzae-sativae mitovirus 1 (RoMV1). Phylogenetic analysis revealed that mitovirus RdRp are also related to RdRp-like genes from plant mitochondrial genomes evolutionarily. The RdRp protein of RoMV1 contains the six conserved acid amine sequence motifs (I-VI) as previously reported for mitoviruses. Two double-strained RNAs of a new member of the genus partitivirus was also determined and isolated from R. oryzae-sativae strain 40-1. The first segment of partitivirus dsRNA (full length of 2186bp) potentially encodes for the conserved motifs RNA-dependent RNA polymerase (RdRp) and the second segment with a partial length of 1014bp encodes for the viral Coat Protein (CP). Putative RdRp showed a similarity of 70% acid amine to Amasya cherry disease-associated mycovirus and designated this partitivirus as Rhozoctonia oryzae-sativae partitivirus 1 (RoPV1). Multiply alignment reveals that RdRp region of RoMV1 showed 24～69% identity to other members of family Partitiviridae. Partial acid amine sequence of coat protein showed 28% identity to Diuris pendunculata cryptic virus. These members (Diuris pendunculata cryptic virus and Amasya cherry disease-associated mycovirus) of family Partiviridae have plant as their host, which can explore the evolution of mycovirus ecologically. In summary, this is the first study to report mitovirus and partitivirus genomes sequence in R. oryzae-sativae.