Abstract
Ustilaginoidea virens, the causal agent of rice false smut, is one of the most devastating grain diseases that causes loss of yield in most rice-growing areas worldwide. In this study, we performed a dsRNA screen to isolate mycoviruses from 35 U. virens strains. The results revealed that 34 of the tested isolates were infected by various dsRNA elements, displaying highly viral diversity and mixed infections. We characterized a 5.3 kbp dsRNA from a typical isolate containing dsRNA segments with sizes ranging from 0.5 to 5.3 kbp. Sequence analysis of its genomic properties indicated that it is a novel victorivirus, named Ustilaginoidea virens RNA virus 5 (UvRV5), that belongs to the family Totiviridae. RT-PCR detection was performed and indicated that not all the dsRNA bands that were 5.3 kbp in size contained UvRV5. Moreover, the genetic relatedness of all the U. virens strains was estimated according to phylogenetic analysis of the partial intergenic spacer region (IGS) sequences. However, concordance was not found between the dsRNA profiles and the IGS-based genetic relatedness of their host fungi.
Highlights
Ustilaginoidea virens, which was first reported in the Tirunelveli district of Tamil Nadu State in India, is the causal agent of false smut disease in rice [1]
We reported a novel mycovirus, designated Ustilaginoidea virens RNA virus 5 (UvRV5), from a U. virens strain and investigated whether there is a correlation between double-stranded RNA (dsRNA) profiles and the genetic relationship of their host fungi
It is reasonable to consider that the dsRNA mycoviruses infecting U. virens might be transmissible among isolates of the fungal host given that the dispersal processes of U. virens is very effective, which might provide a contiguous environment for different isolates
Summary
Ustilaginoidea virens, which was first reported in the Tirunelveli district of Tamil Nadu State in India, is the causal agent of false smut disease in rice [1]. A Ustilaginoidea virens partitivirus 3 (UvPV3), formerly named UvPV2 [21], and an unassigned virus named Ustilaginoidea virens non-segmented virus (UvNV-1), which is closely related to Bryopsis mitochondria-associated dsRNA, have been reported [22]. These findings indicate that U. virens has a repertoire of mycoviruses with substantial numbers and high diversity from which we can gain insights into the evolution and ecology of viruses as well as gain a better understanding of mycovirus-host interactions. We reported a novel mycovirus, designated Ustilaginoidea virens RNA virus 5 (UvRV5), from a U. virens strain and investigated whether there is a correlation between dsRNA profiles and the genetic relationship of their host fungi
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