Discovery of a small peptide from combinatorial libraries that can activate the plant immune system by a jasmonic...

Plants defend themselves by using an innate immune system that is activated in response to a variety of molecules derived from pathogens. These molecules have provided profound insights into the mechanisms of pathogen recognition and subsequent signaling pathways in plants. In the present study, we screened a combinatorial random hexapeptide library for peptides that activate the plant immune system, by using a cell-based high-throughput screening system in which H(2)O(2) generation was monitored. We discovered a novel small peptide (YGIHTH-amide, PIP-1) that triggered H(2)O(2) production in tobacco and tomato cells, but not in Arabidopsis cells. PIP-1 induced significant levels of phytoalexin biosynthesis and defense-related gene expression in tobacco cells; this is likely to be activated by a jasmonic acid pathway.