SCIENCES DU VEGETAL

Plant adaptation in nature relies on the appropriate response to symbiotic and pathogenic microbes. Chitin is an important component of the mycorrhizal fungi cell wall and a major microbe-associated molecular pattern (MAMP), which can activate pattern recognition receptors and trigger plant immunity. How MAMP-triggered immunity is suppressed by symbiotic fungi to establish symbiosis remains elusive. Here, we found that the CO4 (Chitotetraose) symbiotic receptor OsMYR1 cannot only initiate symbiotic signaling but also can repress rice immunity by depleting the receptor-like kinase OsCERK1, thereby preventing the formation of the immunity complex OsCERK1–OsCEBiP. We propose that receptor competition for OsCERK1 in rice underlies a switch that discerns defense and symbiotic signals.