Molecular characterization of two mitoviruses co-infecting a hypovirulent isolate of the plant pathogenic fungus Sclerotinia sclerotiorum [corrected].

The complete nucleotide sequences of two double-stranded RNA (dsRNA) segments, isolated from the same hypovirulent strain (KL-1) of Sclerotinia sclerotiorum, were determined. Sequence analysis showed that dsRNAs 1 to be 2513 nts long and is A-U rich (61.7%). Excluding the poly(A) tail, dsRNAs2 is 2421 nts long and its AU content is 53.1%. The 5' and 3'-terminal sequences of the positive-strand of each dsRNA could be folded into predicted stable stem-loop structures. Mitochondrial codon usage revealed that each dsRNA has a single large open reading frame coding for a protein containing RNA-dependent RNA polymerase conserved motifs. Furthermore, dsRNAs 1 and 2 share sequence similarities with other mitoviruses. These results suggest that dsRNAs 1 and 2 represent two distinct new mitoviruses, designated Sclerotinia sclerotiorum mitovirus 1 (SsMV1/KL-1) and SsMV2/KL-1, respectively. The hypovirulence traits of strain KL-1 and the two mitoviruses could be co-transmitted to a virus-free virulent strain via hyphal anastomosis.