Expression of Allene Oxide Cyclase from Pharbitis nil upon Theobroxide Treatment

In previous reports we have reported that theobroxide induces characteristic accumulation of allene oxide cyclase (AOC; EC 5.3.99.6) protein and jasmonic acid (JA) in Pharbitis nil. In the present study, PnAOC, an AOC gene from Pharbitis nil was cloned. Immunofluorescence assays indicated that the AOC protein is located in the chloroplast of vascular bundles in Pharbitis nil leaves. The PnAOC cDNA sequence lacking the chloroplast signal peptide was successfully expressed in Escherichia coli, and a gas chromatography-mass spectrum assay suggested the relative AOC activity of the recombinant PnAOC protein in comparison with Arabidopsis AOC2. Interestingly, a biphasic expression of PnAOC was induced by theobroxide, which is consistent with the accumulation patterns of AOC protein and JA. All these results indicate that AOC is the primary target of theobroxide regulation and suggest that feedback regulation of PnAOC by JA occurs upon theobroxide treatment in Pharbitis nil.