#400-14 Extracellular pectin-RALF phase separation mediates FERONIA global signaling function

Body of Abstract: The FERONIA (FER) receptor kinase–glycosylphosphatidylinositol-anchored protein LLG1 coreceptor has emerged as a key signal perception complex on the cell surface controlling myriad processes throughout the plant life cycle. Regulated by peptide ligands RALFs, FER–LLG1 controls growth, intersecting several hormone-regulated pathways. It also ensures reproductive success, mediates responses to environmental stresses and even impacts the rhizosphere microbiome to impact plant wellness. In seeking to solve the mystery of how FER–LLG1 achieves its broad and profound biological roles, we discovered a novel cell surface mechanism involving interactions between RALFs, FER, LLG1 and oligogalacturonides (OGs), cell wall-derived pectic fragments known to have active signaling roles. Our results illustrate that intrinsically disordered RALF triggers clustering and endocytosis of its cognate receptors, and FER- and LLG1-dependent endocytosis of non-cognate regulators of diverse processes, thus capable of broadly impacting downstream responses. RALF, however, remains extracellular. We demonstrate that RALF binds the cell wall polysaccharide pectin, they phase separate and recruit FER and LLG1 into pectin-RALF-FER-LLG1 condensates to initiate RALF-triggered cell surface responses. We show further that two frequently encountered environmental challenges, elevated salt and temperature, trigger RALF-pectin phase separation, promiscuous receptor clustering and massive endocytosis, and that this process is crucial for recovery from stress-induced growth attenuation. Our results suggest RALF-pectin phase separation mediates an exoskeletal mechanism to broadly activate FER‑LLG1-dependent cell surface responses to mediate the global role of FER in plant growth and survival.