During the past 20 years, biochemical, genetic, and bioinformatic analyses have identified more than a dozen secreted peptide hormones in plants. These peptide hormones have proven to be functionally more diverse than anticipated. The number of functionally characterized peptide hormones now exceeds the number of classical plant hormones and constitute one of the largest research areas in plant biology. Because a number of uncharacterized genes encoding small secreted peptides have been identified in Arabidopsis, unraveling the signal transduction pathways mediated by secreted peptides is currently one of the most exciting targets. This review series covers recent topics in peptide hormone research in plants.
