Update: Twenty years of progress in physiological and biochemical investigation of RALF peptides (Plant Physiol)

RALFs (Rapid Alkalinzation Factors) were one of the first types of signaling peptides identified in plants, and as their name suggests they were shown to induce an increase in the pH (i.e., alkalinization) of culture medium, through inducing phosphorylation of a plasma-membrane proton pump. There are more than 30 RALF-encoding genes in Arabidopsis, and also evidence that RALF-like sequences are present in some phytopathogenic fungi and bacteria. Blackburn et al. review the history of research into these important peptide signals, their receptors, and their biological functions. Key questions include how do the different peptides interact with closely related receptors, and what determines the specificity of these interactions and downstream functions. (Summary by Mary Williams) Plant Physiol. 10.1104/pp.19.01310