Abstract
The complete sequence and genome organization of a novel Endornavirus from the hypovirulent strain GD-2 of Rhizoctonia solani AG-1 IA, the causal agent of rice sheath blight, were identified using a deep sequencing approach and it was tentatively named as Rhizoctonia solani endornavirus 1 (RsEV1). It was composed of only one segment that was 19,936 bp in length and was found to be the longest endornavirus genome that has been reported so far. The RsEV1 genome contained two open reading frames (ORFs): ORF1 and ORF2. ORF1 contained a glycosyltransferase 1 domain and a conserved RNA-dependent RNA polymerase domain, whereas ORF2 encoded a conserved hypothetical protein. Phylogenetic analysis revealed that RsEV1 was phylogenetically a new endogenous RNA virus. A horizontal transmission experiment indicated that RsEV1 could be transmitted from the host fungal strain GD-2 to a virulent strain GD-118P and resulted in hypovirulence in the derivative isogenic strain GD-118P-V1. Metabolomic analysis showed that 32 metabolites were differentially expressed between GD-118P and its isogenic hypovirulent strain GD-118P-V1. The differential metabolites were mainly classified as organic acids, amino acids, carbohydrates, and the intermediate products of energy metabolism. Pathway annotation revealed that these 32 metabolites were mainly involved in pentose and glucuronate interconversions and glyoxylate, dicarboxylate, starch, and sucrose metabolism, and so on. Taken together, our results showed that RsEV1 is a novel Endornavirus, and the infection of virulent strain GD-118P by RsEV1 caused metabolic disorders and resulted in hypovirulence. The results of this study lay a foundation for the biocontrol of rice sheath blight caused by R. solani AG1-IA.
Highlights
Mycoviruses are widespread in almost all major groups of Kingdom Fungi, and an increasing number of novel mycoviruses have been reported [1,2,3,4]
Our results showed that Rhizoctonia solani endornavirus 1 (RsEV1) is a novel Endornavirus, and the infection of virulent strain GD-118P by RsEV1 caused metabolic disorders and resulted in hypovirulence
Some mycoviruses are known to cause phenotypic alterations, including hypovirulence and debilitation of their fungal hosts [3,5], which may be exploited as biological control agents against fungal diseases, e.g., the +ssRNA mycovirus Cryphonectria hypovirus 1 (CHV1) against Cryphonectria
Summary
Mycoviruses (fungal viruses) are widespread in almost all major groups of Kingdom Fungi, and an increasing number of novel mycoviruses have been reported [1,2,3,4]. The presence of most mycoviruses in fungi does not cause any visible abnormal symptoms (cryptic infections) for their fungal hosts. Viruses 2019, 11, 178 parasitica [5] and the ssDNA mycovirus Sclerotinia sclerotiorum hypovirulence-associated DNA virus. Endornaviruses rely on vertical transmission through infected pollen and ova and do not move from cell to cell because of the lack of movement proteins [8]. In fungal hosts, they transmit vertically via spores and horizontally via hyphal anastomosis [9,10,11]. Most endornaviruses do not cause any apparent symptoms in their hosts
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