THE STRUCTURES OF SYRINGOLIDE-1 AND SYRINGOLIDE-2, NOVEL C-GLYCOSIDIC ELICITORS FROM PSEUDOMONAS-SYRINGAE PV TOMATO

The isolation and structure determination of two bacterial signal molecules which elicit active plant defense responses are reported. The production of these molecules by Gram-negative bacteria requires the action of a virulence gene D (avrD), cloned from Pseudomonas syringae pv. tomato. The structures of syringolide 1 (1a) and syringolide 2 (1b) are determined by a combination of NMR experiments, biosynthetic arguments, molecular modeling, and X-ray crystallography. A proposed biosynthetic scheme based on the condensation of D-xylulose with a beta-ketoalkanoic acid is presented. Further cyclization of the biosynthetic intermediates leads to C-glycosides with a novel tricyclic ring system. These are the first nonproteinaceous specific elicitors of a plant hypersensitive response.