Molecular characterization of a dsRNA totivirus infecting the sclerotial parasite Coniothyrium minitans

The complete nucleotide sequence, 4975 bp, of the double-stranded RNA (dsRNA) mycovirus infecting the sclerotial parasite Coniothyrium minitans (CmRV) was determined. Sequence analysis revealed the occurrence of two overlapping open reading frames (ORFs): the 5′-proximal large ORF (ORF1; nucleotide positions 62–2389) encodes a putative coat protein (CP) with a predicted molecular mass of 80344 Da, and the 3′-proximal ORF (ORF2, nucleotide positions 2386–4875) encodes a putative RNA dependent RNA Polymerase (RdRp) with a predicted molecular mass of 82551 Da. The tetranucleotide AUGA at nucleotide positions 2386–2389 includes the predicted start codon of ORF2, which overlaps with the stop codon for ORF1. Based on genome organization and sequence analysis encoded proteins, the virus infecting C. minitans strain Chy-1, designated C. minitans RNA virus (CmRV), belongs to the family Totiviridae. Pairwise sequence comparisons of the deduced amino acid sequences encoded by CmRV as well as phylogentic analysis indicated that it is more closely related to the totiviruses that infect filamentous fungi than to those infecting protozoa, yeast and smut fungi. The role of CmRV in the abnormal phenotype associated with a variant of C. minitans is discussed.