Pathogen effector induced interaction of the resistance protein Cf-4-SOBIR1 complex with BAK1 initiates endocytosis-regulated plant immunity

CS-21.3 - The plant immune system is activated by receptors that detect infectious pathogens. Cf receptor-like proteins (RLPs) induce immunity against Cladosporium fulvum , a fungus causing tomato leaf mold isease. Using live-cell imaging, we find that Cf-4, in complex with SUPPRESSOR OF BIR1-1 (SOBIR1), localizes at the plasma membrane. Upon elicitation with the matching C. fulvum effector Avr4, the receptor complex is recruited to ARA7/ARA6 late endosomes, providing a mechanism to regulate the number of active receptors at the plasma membrane. Furthermore, we discovered that the Cf-4-SOBIR1 complex behaves like a two-component RLK that interacts with the co-receptor BRI1-ASSOCIATED KINASE 1 (BAK1) upon its activation by Avr4. Importantly, BAK1 is required both for Avr4-triggered Cf-4-SOBIR1 endocytosis and plant defense. Our observations indicate that Cf-4 immune signaling is initiated by the formation of at least a tripartite receptor complex. These findings provide a significant contribution to elucidating how RLPs, lacking a cytoplasmic signaling domain, initiate immune responses upon ligand perception. Currently, we are examining in detail how the Cf-4-SOBIR1 couple interacts with BAK1 upon activation, the involvement of the Cf-4YxxF putative endocytic motif, and the clathrin dependency of Cf-4 endocytosis.