THE PSEUDOMONAS PHYTOTOXIN CORONATINE MIMICS OCTADECANOID SIGNALING MOLECULES OF HIGHER-PLANTS

The phytotoxic principle, coronatine, which is present in several path ovars of the plant pathogen, Pseudomonas syringae was shown to be high ly active in completely different, jasmonate-selective bioassays. At n anomolar to micromolar concentrations, coronatine induced the accumula tion of defense-related secondary metabolites in several plant cell cu ltures, induced transcript accumulation of the elicitor-responsive gen e encoding the berberine bridge enzyme of Eschscholtzia californica, a s well as the coiling response of Bryonia dioica tendrils. Biological activity critically depended upon the structure of coronatine, and sli ght modifications, such as methylation of the carboxyl moiety or reduc tion of the carbonyl group, rendered the molecules almost inactive. Co ronafacic acid, obtained by hydrolysis of coronatine, was also nearly inactive. Coronatine did not elicit the accumulation of endogenous jas monic acid in the systems analyzed. While coronafacic acid is similar in structure to jasmonic acid, we found coronatine to be a close struc tural analoye of the cyclic C18-precursor of jasmonic acid, 12-oxo-phy todienoic acid. The phytotoxic symptoms produced by coronatine can now be understood on the basis of the toxin's action as a mimic of the oc tadecanoid signalling molecules of higher plants.