Identification and structure of a family of syringolin variants: Unusual cyclic peptides from Pseudomonas syringae pv. syringae that elicit defense responses in rice

Pseudomonas syringae pv. syringae is recognized by the non-host plant Oryza sativa which reacts with defense responses leading to induced resistance t owards the rice blast fungus Pyricularia oryzae. We have previously shown t hat syringolin, a novel and unusual peptide secreted by P. syringae pv. syr ingae under appropriate conditions, is one of the molecular determinants by which rice plants can perceive the non-host pathogen. Here we show that sy ringolin is a member of a family of related compounds. We have isolated syr ingolin variants B to F and determined their structure using mass and NMR s pectroscopic methods. These variants, which differ from each other by vario us modifications, are all able to induce defense responses upon application onto rice leaves.