Maturing peptides open for communication.

Two decades after the discovery of systemin, the first plant peptide shown to be involved in cell to cell communication (Pearce et al., 1991), plant peptide research is coming of age, and is ready for cross-talk with older research fields in plant science. This issue of JXB illustrates that plant peptide signalling is of crucial importance for all aspects of plant growth and development. Plants respond to peptides produced by pathogens, they use peptide signalling to reinforce defence responses, and peptides exert signalling functions in both aboveand belowground organs, in vegetative and reproductive tissues. The PEPTIDE issue presents the initial characterization of recently identified peptide families, and highlights current knowledge on receptor interactions, downstream signalling modules, feedback loops, and target genes for a selection of exogenous and endogenous peptides involved in defence and development. With the overall aim of understanding the molecular mechanisms behind the biological processes in which peptide signalling is involved, plant peptide research follows three major routes: detection and functional characterization of new peptide families; genetic, molecular, and biochemical identification of receptors of peptide ligands and their signalling networks; and characterization of downstream factors and targets of peptide-controlled signalling pathways. I would like to acknowledge the first European Workshop on Peptide Signalling in Plants which was arranged in January this year in Oslo; the workshop reflected the current status of plant peptide research and many of the topics covered in this issue.