Plant subtilases as key initiators of peptide ligand-receptor signaling

Peptide ligand-receptor signaling plays a crucial role in regulating diverse biological processes in plants. Over the past three decades, numerous peptide ligands and their corresponding receptors have been identified, and our understanding of their downstream signaling pathways and biological functions has gradually advanced. By contrast, relatively less attention has been paid to an earlier step in the signaling process: the generation of active peptide ligands. Some peptide ligands are generated through proteolytic processing of inactive precursor proteins. In recent years, significant progress has been made in identifying the proteases involved in this maturation process in flowering plants, primarily Arabidopsis thaliana. In this review, we focus on the processing proteases of peptide ligands, particularly subtilases, identified to date. We discuss recent findings on these proteases, including the approaches used for their identification, their enzymatic activities and substrate specificities, and the regulation of protease activity involved in peptide maturation. These insights deepen our understanding of how peptide ligand-receptor signaling pathways are initiated and ultimately provide important clues to the diverse physiological processes mediated by these signaling pathways.