Abstract
Infection by diverse mycoviruses is a common phenomenon in Sclerotinia sclerotiorum. In this study, the full genome of a single-stranded RNA mycovirus, tentatively named Hubei sclerotinia RNA virus 1 (HuSRV1), was determined in the hypovirulent strain 277 of S. sclerotiorum. The HuSRV1 genome is 4492 nucleotides (nt) long and lacks a poly (A) tail at the 3ˊ- terminus. Sequence analyses showed that the HuSRV1 genome contains four putative open reading frames (ORFs). ORF1a was presumed to encode a protein with a conserved protease domain and a transmembrane domain. This protein is 27% identical to the P2a protein encoded by the subterranean clover mottle virus. ORF1b encodes a protein containing a conserved RNA-dependent RNA polymerase (RdRp) domain, which may be translated into a fusion protein by a -1 ribosome frameshift. This protein is 45.9% identical to P2b encoded by the sowbane mosaic virus. ORF2 was found to encode a putative coat protein, which shares 23% identical to the coat protein encoded by the olive mild mosaic virus. ORF3 was presumed to encode a putative protein with an unknown function. Evolutionary relation analyses indicated that HuSRV1 is related to members within Sobemovirus, but forms a unique phylogenetic branch, suggesting that HuSRV1 represents a new member within Solemoviridae. HuSRV1 virions, approximately 30 nm in diameter, were purified from strain 277. The purified virions were successfully introduced into virulent strain Ep-1PNA367, resulting in a new hypovirulent strain, which confirmed that HuSRV1 confers hypovirulence on S. sclerotiorum.
Highlights
Destructive crop diseases are caused by plant pathogenic fungi globally, making disease control for sustainable agriculture a constant and costly challenge [1,2]
A367-Hubei sclerotinia RNA virus 1 (HuSRV1). (a) Colony morphology of strains Ep-1PNA367, 277 and A367-HuSRV1 grown for 7 days on potato dextrose agar (PDA) at 20 ◦ C. (b) Growth rates of strains Ep-1PNA367, 277, and A367-HuSRV1. (c) Pathogenicity assay of three strains on detached rapeseed leaves at 48 hpi, 20 ◦ C, and approximate 100% relative humidity. (d) Comparison of lesion diameters produced by these strains on detached rapeseed leaves
The first open reading frames (ORFs) (ORF1a) was found to encode predicted protein P1a (612 aa) with a predicted molecular mass of 65.82 kDa, and 27% identical to the P2a protein encoded by the subterranean clover mottle virus (GenBank accession number NP_715628)
Summary
Destructive crop diseases are caused by plant pathogenic fungi globally, making disease control for sustainable agriculture a constant and costly challenge [1,2]. Fungicides are widely used to control fungal diseases, but a large number of crops pose a difficulty with obtaining disease-resistant cultivars, and the increased application of fungicides carries a serious threat to human health and the environment. Some mycoviruses are natural promising agents known to control fungal diseases through the induction of hypovirulence [3,4,5]. They are prevalent in all major groups of phytopathogenic fungi [3].
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