Peptides and the regulation of plant homeostasis

Homeostasis defines the property of living organisms to keep a stable internal environment despite considerable external fluctuations, and this process is of considerable importance to plants as they are trapped unmoving in their changing surroundings. In addition to plant hormones, signaling peptides also have role(s) in maintaining plant homeostasis. Plant natriuretic peptides (PNPs) modulate ion channels and water uptake and have been implicated as compounds important in maintaining homeostasis. PNP and molecular mimics produced by pathogens modulate photosynthesis and the chloroplast proteome, thus indicating that PNP has widespread effects on homeostasis and could be considered a prototype homeostatic peptide. We propose that other peptides such as phytosulfokines (PSKs) and rapid alkalinization factors (RALFs) that have recognized roles in development and defense also have functions in plant homeostasis.