From roots to reproduction: the multifaceted roles of rapid alkalinization factor and epidermal patterning factor...

In plants, peptides play an irreplaceable role as intercellular communication molecules, triggering signal transduction by activating plasma membrane-localized receptors. Of specific interest here are the cysteine-rich peptides (CRPs), which are well-characterized for their disulfide bonds that enhance structural stability and functional specificity. Although the first CRP, systemin, was identified over three decades ago, our understanding of the evolutionary trajectories, functional diversity, and underlying mechanisms of CRPs remains limited. This review focuses on two main families of CRPs: the Rapid Alkalinization Factor (RALF) and the Epidermal Patterning Factor (EPF)/EPF-Like peptides. We thus explore the diverse and, so far, identified signalling pathways in which the peptides have a pivotal function. We organize our tour by providing a comprehensive overview of the discovery of peptides, structural diversity, and biological functions. Particularly, emphasis is placed on their roles in plant growth, development, reproduction, defence against biotic and abiotic stresses, and plant-bacteria symbiosis.