RALF Peptides, a Review

RAPID ALKALINIZATION FACTORS (RALFs) are a family of plant peptide hormones involved in development, reproduction, and response to stresses. These versatile peptides are found throughout land plants, but their molecular mechanisms of action are best understood in the model plant Arabidopsis thaliana. Known to science for more than 20 years, RALFs were initially viewed as apoplastic signaling molecules that elicit intracellular responses through their canonical membrane receptors, the Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE (CrRLK1L) family. Recently, it was shown that RALF peptides also have structural roles by binding to LEUCINE-RICH REPEAT EXTENSINS (LRXs) and pectin, forming cell wall-associated complexes. Currently the focus of state-of-the-art science, RALF peptides’ central influence on plants still leaves unanswered questions. This work is a detailed review of RALF peptides in A. thaliana, but it also encompasses the literature on other species. As new discoveries in the field are published, this review will be updated.