CAR modulates plasma membrane nano-organization and immune signaling downstream of RALF1-FERONIA signaling pathway

Summary The receptor-like kinase (RLK) FERONIA (FER) senses peptide ligands in the plasma membrane (PM), modulates plant growth and development, and integrates biotic and abiotic stress signaling for downstream adaptive response. However, the molecular interplay of these diverse processes is largely unknown. Here, we show that FER, the receptor of Rapid Alkalinization Factor 1 (RALF1), physically interacts with C2 domain ABA–related (CAR) proteins to control the nano-organization of the PM in Arabidopsis . During this process, the RALF1–FER pathway upregulates CAR protein translation, and then more CAR proteins are recruited to PM. This acts as a rapid feedforward loop to stabilize PM liquid-ordered phase. FER interacts with and phosphorylates CARs, and reducing their lipid-binding ability, which breaks the feedback regulation CAR activity at latter time point. Similar to FER mutant, pentuple car14569 mutants inhibit flg22-induced FLS2-BAK1 immune complex formation, which depends on the integrity of nanodomains. Together, we propose that the FER-CAR module controls the formation of the PM nano-organization during RALF signaling through a self-contained amplifying loop including both positive and negative feedbacks.