Characterization of a novel botybirnavirus with a unique dsRNA infectingDidymella theifoliafrom tea plants

Abstract

AbstractDidymella theifoliaspecifically infects some local varieties ofCamellia sinensisin 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 ofD. theifoliaexhibiting 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 ofD. theifoliainfected by DtBRV1. DtBRV1 with specific molecular traits contributes useful information for a better understanding of the mycoviral community.ImportanceTea plants represent an ancient and unique plant species community cultured in China, while the mycoviruses related to the phytopathogenetic fungi infecting tea remain limited. Here, we characterized a novel botybirnavirus (tentatively named Didymella theifolia botybirnavirus1 (DtBRV1), and a specific dsRNA infectingDidymella theifoliaresponsible for a noticeable disease of tea plants. DtBRV1 contains two dsRNAs (1 and 2) encapsidated in isometric virions in size of ∼39.8 nm, while dsRNA3 is not encapsidated in the viral particles although it has a high identity with the mycoviral genomic components. Additionally, DtBRV1 coat proteins are composed of fused proteins encoded by both dsRNA-coding open reading frames most likely after cleave and fuse processing progress, which is striking unlike most mycoviruses. With some specific molecular traits, DtBRV1 and the related specific dsRNA unit expand our understanding of virus diversity, taxonomy, and evolution.