OsVIRK1 functions with OsbZIP39 to fine-tune rice defense against rice stripe virus

• The Cysteine-rich receptor-like kinase OsVIRK1 interacts with the UPR sensor OsbZIP39. • OsVIRK1 stabilizes OsbZIP39 from ubiquitin-mediated proteolysis during RSV infection. • OsbZIP39 interferes with the interaction of OsVIRK1 and RSV CP. • The Osbzip39 mutant is more susceptible to RSV accompanied by reduced expression of OsAGO18 and UPR genes. • Overexpression of OsbZIP39 promotes RSV infection and the expression of UPR genes. Cysteine-rich receptor-like kinases (CRKs) play pivotal regulatory roles in the interactions between pathogens and plants. However, the underlying regulatory mechanisms are still not fully understood. The unfolded protein response (UPR) plays a critical role in plant–virus interactions by either promoting or restricting infection. It is unclear how CRKs coordinate with the UPR to regulate the plant's response to viral infection. OsVIRK1, an RSV-induced CRK, defends rice against rice stripe virus (RSV) infection by interacting with RSV CP (coat protein) and activating CP-triggered defense gene. OsbZIP39 is a UPR sensor that regulates UPR-activated genes. In this study, we demonstrate that OsVIRK1 interacts with OsbZIP39 and promotes its stability during RSV infection. The osbzip39 mutant is more susceptible to RSV, involving a reduction in the expression of UPR genes and CP-triggered antiviral defense gene. This suggests that OsVIRK1 functions with OsbZIP39 to promote rice resistance to RSV. Interestingly, OsbZIP39 can strongly inhibit the interaction of OsVIRK1 with CP. Overexpression of OsbZIP39 promotes RSV infection and the expression of UPR genes, indicating that OsbZIP39 plays a role in fine-tuning OsVIRK1 function. Our study reveals the mechanism by which OsVIRK1/OsbZIP39 mediates antiviral defense, and establishes that the UPR sensor OsbZIP39 plays a dual role in the interaction between rice and RSV.