The Receptor Kinase FERONIA–CAR Axis Regulates Proper Lipid Order Formation And Its Preliminary Function To Response RALF Signaling

The majority of plants grow fixedly on the land and can not leave their soil and environment for almost their whole life.Therefore,how plants adapt to the changeable environment and survive is an important scientific question.As one of the most important“guardrails” of plant cells,cell membrane provides a stable intracellular environment,which makes it possible for cells to perceive the external environment and respond to them.There are many proteins reside on the cell membrane,among which receptor like protein kinase(RLK)is one of the most important members.RLKs senses external signals through the multiple extracellular ligands,and then transmits the signals to the intracellular kinase domain through phosphorylation.Finally,by recruiting downstream interacting proteins,the signals are amplified and transmitted to the whole cell,enabling the cell to respond to the environment.However,environmental cues are very complex,and sometimes cells need to process multiple external signals at the same time,which requires proteins on the membrane to coordinated response of signals at the same time.Previous studies focus on how the downstream proteins rapidly transmit signals after sensing signals,while ignoring membranes integrate and allocate various receptor protein kinases and anchor proteins on the membrane.Therefore,it is largely unknow about signal integration events on the membrane.FERONIA(FER)is a receptor kinase from the Catharanthus roseus receptor-like kinase1-like(Cr RLK1L)family.While it was discovered nearly two decades ago for its role in fertilization,this receptor kinase has recently attracted much attention.Indeed,FERONIA turned out to be involved in a plethora of signaling pathways including cell growth,cell wall sensing,innate immunity,energy and RNA metabolism,stress adaptation,morphogenesis,mechanosensing,among others.However,the molecular bases behind FERONIA’s multiple,fundamental but tissue-specific functions remain a puzzle and an area of both intense scrutiny and scientific debates.Based on the above background,a series of studies were conducted on how extracellular signals regulate signal integration events on the membrane,and the following conclusions were drawn:(1)We used a multidisciplinary strategy to obtain a complete mechanistic dataset on the function of CAR proteins in FERONIA signaling.To this end,we combined high-resolution microscopy,particle tracking and lipid order analyses,with molecular genetics tools,biochemical interactions,mapping of phosphorylation sites and translation dynamics,and uncovered that multiple CAR proteins act downstream of FER during innate immunity.We show that the perception of the RALF1 ligand by FER triggers the upregulation of CAR proteins translation.In turn,CAR proteins directly and specifically interact with the kinase –cytosolic–domain of FER.At the cell surface,CAR proteins,likely via their lipid binding domains,modulate lipid order and thus impinge on the membrane nano-organization.FER then phosphorylates CAR proteins to triggers their membrane dissociation.(2)Our study provides an unprecedented analysis of the dynamic regulation triggered by FERONIA signaling.Importantly,we describe multiple feedback mechanisms which promote the rapid transmission of extracellular signals to intracellular and mediates the regulation of plant growth and immunity.(3)We propose that the FER-CAR module controls the dynamics of the plasma membrane nano-organization during RALF signaling through a self-contained amplifying loop including both positive and negative feedbacks.These findings provide a paradigm for studying the environmental responsive membrane organization.(4)FERONIA has recently emerged as a potential target for crop improvement and protection due to its versatile function in plants growth,development and multiple stress responses.Our work put the function of FERONIA in regulating the plasma membrane nanoorganization as one of the core mechanisms likely involved in many of the FERONIA responses,notably through the regulation of immunoreceptor kinase(e.g.FLS2 and BAK1)at the cell surface.We thus believe that the RALF-FER-CAR pathway has the potential to serve as a general mechanism that modulates plasma membrane compartmentalization and signaling in plants.