Plant peptide hormones: three decades of discovery and emerging paradigms.

Peptide hormones have reshaped our understanding of intercellular signaling in plants. Once considered absent in plants, peptide-based signaling pathways emerged as key regulators of plant growth, development, environmental responses, and immunity. A paradigm shift occurred with the discoveries of systemin and phytosulfokine (PSK) in the 1990s, as well as the identification of receptor-like kinases regulating important biological processes. Over the past 3 decades, a repertoire of peptide hormone families has been expanded enormously, with deeper understandings of peptide modifications, cleavage, modes of action, receptor binding, and signal transduction. In this review, I highlight selected peptide hormone families-- systemin, PSK, INFLORESCENCE DEFICIENT IN ABSCISSION (IDA)/IDA-LIKES, CLAVATA3/EMBRYO SURROUNDING REGION, and EPIDERMAL PATTERNING FACTORs (EPF)/EPF-LIKES-- and discuss how individual discoveries of the peptides and their cognate receptors have shaped emerging concepts in plant peptide signaling. To celebrate this Centennial Issue, emphasis will be given to contributions published in Plant Physiology. Finally, I discuss how expanding genomic resources and advanced technologies will accelerate the discovery and engineering of peptide signaling pathways to enhance plant resilience.