The interplay of RALF structural and signaling functions in plant-microbe interactions

Rapid alkalinization factor (RALF) peptides are important signaling molecules binding to Catharanthus roseus receptor-like kinase 1-like (CrRLK1L)-LORELEI/LORELEI-like GPI-anchored protein complexes to regulate a plethora of physiological responses, including plant-microbe interactions. Recently, RALF peptides were demonstrated to possess additional structural functions as organizers of primary cell wall structure through binding to de-methylated pectin via Leucine-rich repeat extensin proteins. In this review, we discuss these novel findings and their possible implications for RALF-regulated plant-microbe interactions, put them into context with the well-known signaling function of RALF-CrRLK1L complexes, and address key future directions for this emerging field in molecular stress physiology and beyond.