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Characterization of debilitation-associated mycovirus infecting the plant-pathogenic fungus Sclerotinia sclerotiorum

¹ Plant Pathology, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, PR China
² National Key Laboratory of Agriculture Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China
³ Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, 1405 Veterans Drive, University of Kentucky, Lexington, KY 40546-0312, USA
⁴ Department of Plant Pathology, China Agricultural University, Beijing 100092, PR China

Correspondence
Daohong Jiang
daohongjiang{at}mail.hzau.edu.cn

It was previously reported that three dsRNA segments, designated L, M and S, were isolated from Sclerotinia sclerotiorum strain Ep-1PN and that the M dsRNA segment was coincident with hypovirulence and debilitation of the fungal host. Here, the complete nucleotide sequence of the M dsRNA of 5419 nt, excluding the poly(A) tail, was determined. Sequence analysis revealed the occurrence of a single open reading frame (nt 93–5195) encoding a protein with significant similarity to the replicases of the ‘alphavirus-like’ supergroup of positive-strand RNA viruses. The M dsRNA-encoded putative replicase protein contained the conserved methyl transferase, helicase and RNA-dependent RNA polymerase (RdRp) domains characteristic of the replicases of potex-like plant viruses (flexiviruses) and Botrytis virus F (BVF), a flexuous rod mycovirus infecting the phytopathogenic fungus Botrytis cinerea. Furthermore, convincing evidence is presented showing that ascospore descendents derived from the debilitated strain Ep-1PN were devoid of dsRNA and exhibited normal colony morphology. Moreover, it was demonstrated that the debilitation phenotype was transmitted from the parental debilitated strain to its normal ascospore progeny via hyphal anastomosis. These results suggest that the M dsRNA from strain Ep-1PN is derived from the genomic RNA of a positive-strand RNA virus, which we designated Sclerotinia sclerotiorum debilitation-associated RNA virus (SsDRV). Although phylogenetic analysis of the conserved RdRp motifs verified that SsDRV is closely related to BVF and to the allexiviruses in the family Flexiviridae, SsDRV is distinct from these viruses, mainly based on the lack of coat protein and movement protein.

The GenBank/EMBL/DDBJ accession number for the sequence determined in this work is AY147260.