Xanthomonas type III effector XopN targets scaffold protein OsRACK1B to suppress rice immunity

Bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzicola (Xoc), is a major bacterial disease that poses a substantial threat to rice production. Although Xoc deploys a variety of effectors to subvert host defenses, the mechanistic basis of how these effectors modulate plant immune signaling remains largely unclear. Here, we show that XopN suppresses rice immune responses and physically interacts with the rice scaffold protein OsRACK1B. Notably, OsRACK1B expression is induced following Xoc infection in a type III secretion system (T3SS)-independent manner. Functional analyses indicate that OsRACK1B overexpression enhances Xoc resistance, whereas loss-of-function mutants exhibit heightened susceptibility. This increased susceptibility is characterized by compromised immunity, including reduced callose deposition, diminished reactive oxygen species (ROS) accumulation, and attenuated expression of defense-related genes such as OsPBZ1 and OsPAL1. Furthermore, we demonstrate that XopN competes with OsRap2.6 for binding to OsRACK1B, thereby disrupting the formation of the OsRACK1B-OsRap2.6 immune complex. These findings reveal a novel virulence strategy in Xoc and identify promising gene targets for developing disease-resistant rice varieties.