Clarification of Plant Octadecanoide Signaling Pathway by using the Modified Probe of Phytotoxin, Coronatine

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A phytotoxin, coronatine exhibits various biological activities induced by endogenous phytohormone-like regulators, octadecanoide/jasmonoide. Because the intensity of biological activity caused by coronatine is higher than those by octadecanoide/jasmonoide, it seems that coronatine is the most valuable probe to clarify plant octadecanoide signaling pathway.Coronafacic acid, the acid component of coranatine could be synthesized in 1-2 g scale by using the catalytic asymmetric synthesis. The modification of partial structure of coronafacic acid (reduction of conjugated double bond and/or carbonyl group) made it possible to provide chemically stable coronatine analogs, which possess various probe parts (fluorescent chromophore, photoaffinity labeling functional group, radioactive element, and biotin). Since the introduction of a linker to the coronamic acid, was achived, preparation of the affinity chromatography linked by coronatine analogs is possible.The synthesized coronatine analogs were subjected to the bioassay using rice leaves. After treatment of rice leaves with solution of coronatine analogs for 6 h, induced volatiles (terpenes) from leaves to headspace were quantitatively analyzed. Most of the coronatine analogs exhibited higher volatile-inducing activity than that caused by racemic jasmonic acid, which was used as the positive control in this assay. The activity of some coronatine analogs was higher than that of coronatine itself. Therefore, these results showed that coronatine analogs would be useful chemical probes to clarify coronatine binding protein, which might be octadecanoide/jasmonoide binding protein responsible for plant octadecanoide signaling pathway.The research on determination of coronatine binding protein is now in progress.