Infection of Nigrospora nonsegmented RNA Virus 1 Has Important Biological Impacts on a Fungal Host.

Nigrospora nonsegmented RNA virus 1 (NoNRV1) has been reported previously in the fungus Nigrospora oryzae, but its biological effects on its host are unknown. In this work, we isolated a strain 9-1 of N. oryzae from a chrysanthemum leaf and identified NoNRV1 infection in the isolated strain. The genome sequence of NoNRV1 identified here is highly homologous to that of the isolate HN-21 of NoNRV1 previously reported; thus, we tentatively designated the newly identified NoNRV1 as NoNRV1-ZJ. Drug treatment with Ribavirin successfully removed NoNRV1-ZJ from the strain 9-1, which provided us with an ideal control to determine the biological impacts of NoNRV1 infection on host fungi. By comparing the virus-carrying (9-1) and virus-cured (9-1C) strains, our results indicated that infection with NoNRV1 promoted the pigmentation of the host cells, while it had no discernable effects on host growth on potato dextrose agar plates when subjected to osmotic or oxidative stress. Interestingly, we observed inhibitory impacts of virus infection on the thermotolerance of N. oryzae and the pathogenicity of the host fungus in cotton leaves. Collectively, our work provides clear evidence of the biological relevance of NoNRV1 infection in N. oryzae, including pigmentation, hypovirulence, and thermotolerance.