Résumé
The Arabidopsis cytochrome P450 CYP94C1 is involved in the metabolism of jasmonates, a family of phytohormones implicated in plant development and responses to bioagressors. It has been shown to down-regulate the level of the active hormone jasmonoyl-isoleucine (JA-Ile) by catalyzing its successive oxidation into hydroxyl (12OH-JA-Ile) and carboxyl (12COOH-JA-Ile) derivatives. The systematic investigation of this enzymatic reaction in vitro reported here revealed the formation of a third oxidized product: UPLC-MS/MS data matched a possible aldehyde, an intermediate form between 12OH-JA-Ile and 12COOH-JA-Ile. To confirm the presence of an aldehyde group, the extracted metabolite from incubations were derivatized with methoxyamine, an agent known to target carbonyl functions specifically. UPLC-MS/MS analysis after derivatization confirmed the presence of 12-oxojasmonoyl-isoleucine (12CHO-JA-Ile). Methanolic extracts from Arabidopsis leaves were then investigated after wounding, a treatment that triggers the accumulation of JA-Ile and its oxidized derivatives. The 12CHO-JA-Ile produced a significant signal with the same order of magnitude than the other oxidized forms. This study illustrates the underestimated potential of chemical derivatization for rapid metabolite identification in modern metabolomics and enriches our knowledge of the jasmonates family.