RALF-FER, a master ligand‒receptor pair in plant health

Pathogens deliver many effector proteins into the plant apoplast, which helps plants evade pattern recognition receptor (PRR)-mediated surveillance by camouflaging or blocking PRR-triggered signaling. Plants must prioritize immunity or growth and development according to the presence or absence of pathogen-derived effectors. Crosstalk exists between PRR immune signaling pathways and growth and development pathways. A typical example is the signaling pathway of the receptor kinase FERONIA (FER), a core element of a global signaling network. FER interacts with its coreceptors and different Rapid Alkalinization Factor (RALF) peptide ligands to function in various growth and developmental processes and respond to pathogens. Studies on the roles of host FERs in different plant species and those of RALFs derived from both hosts and pathogens are beginning to flourish. Here, we focus on recent advances in FER and RALF in plant‒pathogen interactions, with an emphasis on the mechanisms underlying these interactions. We also present a brief outlook to highlight challenges and perspectives for future research on how to utilize the RALF-FER pair or its related signaling elements as targets to improve crop resistance to pathogens.