A bacterial protein Rhp-PSP inhibits plant viral proliferation through endoribonuclease activity1

Plant virus causes massive crop losses globally. However, there is currently no effective measure to control plant viral disease. Previously, we identify an antiviral protein Rhp-PSP, produced by the bacterial Rhodopseudomonas palustris strain JSC-3b. In this study, we discover that the antiviral activity of Rhp-PSP relies on its endoribonuclease activity. Convert the arginine (R) residue at position 129 onto alanine (A) abolish its endoribonuclease activity on coat protein (CP) RNA of tobacco mosaic virus (TMV), consequentially, compromised the antiviral activity of Rhp-PSP. Further investigation demonstrates that, the mutant Rhp-PSPR129A is unable to form the homotrimer as the wild type, indicating the importance of quaternary junction for the endoribonuclease activity. Overexpression of Rhp-PSP in Nicotiana benthamiana significantly enhances the resistance against TMV of seedlings, while expression of Rhp-PSPR129A did not, confirming that endoribonuclease activity is responsible for the antiviral activity of Rhp-PSP. In addition, foliar spray of Rhp-PSP solution on tomato and pepper plants significantly reduces the disease index of viral diseases, indicating that Rhp-PSP shows potential to develop antiviral agent in practice.