RNA-seq Analysis of Rhizoctonia solani AG-4HGI Strain BJ-1H Infected by a New Viral Strain of Rhizoctonia solani Partitivirus 2 Reveals a Potential Mechanism for Hypovirulence.

Rhizoctonia solani partitivirus 2 (RsPV2), in the genus Alphapartitivirus , confers hypovirulence on R . solani AG-1-IA, the causal agent of rice sheath blight. In this study, a new strain of RsPV2 obtained from R . solani AG-4HGI strain BJ-1H, the causal agent of black scurf on potato, wasidentified and designated as Rhizoctonia solani partitivirus 2 strain BJ-1H (RsPV2-BJ). An RNA sequencing analysis of strain BJ-1H and the virus RsPV2-BJ-free strain BJ-1H-VF derived from strain BJ-1H was conducted to investigate the potential molecular mechanism of hypovirulence induced by RsPV2-BJ. In total, 14,319 unigenes were obtained, and 1,341 unigenes were identified as differentially expressed genes (DEGs), with 570 DEGs being down-regulated and 771 being up-regulated. Notably, several up-regulated DEGs were annotated to cell wall degrading enzymes, including β-1,3-glucanases. Strain BJ-1H exhibited increased expression of β-1,3-glucanase after RsPV2-BJ infection, suggesting that cell wall autolysis activity in R . solani AG-4HGI strain BJ-1H might be promoted by RsPV2-BJ, inducing hypovirulence in its host fungus R . solani AG-4HGI. To the best of our knowledge, this is the first report on the potential mechanism of hypovirulence induced by a mycovirus in R . solani .