Characterization of a novel botybirnavirus with a unique dsRNA infecting Didymella theifolia from tea plants

Didymella theifolia specifically infects some local varieties of Camellia sinensis in China, representing a unique fungal species, and characterization of the mycoviruses related to this fungal species is attractive. Three double-stranded RNAs (dsRNAs; dsRNAs 1, 2 and 3 with sizes of 6338, 5910 and 727 bp, respectively) were identified in an avirulent strain CJP4-1 of D. theifolia exhibiting normal growth and morphologies. Characterization of the dsRNAs 1 and 2 revealed that they are genomic components of a novel botybirnavirus, tentatively named Didymella theifolia botybirnavirus 1 (DtBRV1), and encapsidated in isometric virions with a size of ~39.8 nm in diameter. It is worth noting that dsRNA3 shares no detectable identity with those sequences deposited in NCBI database, while a high identity (36.58% and 40.93%) with the left regions of dsRNAs 1 and 2, but is not encapsidated in DtBRV1 particles, suggesting it is a unique dsRNA unit that is not a DtBRV1 component or a satellite and its taxonomic classification remains unclear. SDS-polyacrylamide gel electrophoresis in combination with peptide mass fingerprint analysis revealed that DtBRV1 capsid protein consisting of polypeptides encoded by the left regions of both genomic components. DtBRV1 is efficiently vertically transmitted through conidia while difficult in horizontal transmission from strain CJP4-1 to other strains. DtBRV1 has no effects on fungal growth and virulence as accessed with the transfectants of virulent strain JYC1-6 of D. theifolia infected by DtBRV1. DtBRV1 with specific molecular traits contributes useful information for a better understanding of the mycoviral community.