The RALF-FERONIA Signaling Axis: A Central Hub Integrating Plant Growth, Reproduction, and Stress Responses.

Rapid alkalinization factor (RALF) peptides represent a central class of signaling molecules in plants, regulating processes ranging from fertilization to immune responses. These diverse functions are largely mediated by a conserved receptor complex centered on FERONIA kinase (FER). This review summarizes recent advances positioning the RALF-FER signaling pathway as a major regulatory hub integrating intrinsic and extrinsic signals to coordinate growth, development, and stress adaptation. We examine how this pathway controls the polar growth of root hairs and pollen tubes, orchestrates reproductive barriers and fertilization, and modulates immune and abiotic stress signaling through mechanisms involving ROS, Ca2+, and apoplast pH. By framing this new knowledge within the broader framework of known RALF-FER mechanisms, we demonstrate how this pathway achieves high signaling specificity. Finally, we discuss critical unresolved issues and suggest future research directions in the emerging field of molecular stress physiology, highlighting the potential for manipulating this pathway for agricultural crop improvement.