Résumé
Precursor feeding experiments have shown that the terpene moiety biosynthesis is the most rate-limiting step of terpenoid indole alkaloids (TIA) produced by Catharanthus roseus suspension cells. The biosynthesis of TIA terpene moiety is strictly regulated by hormones: auxin inhibits, jasmonate stimulates and cytokinin and ethylene enhance their biosynthesis. Biochemical analyses coupled to molecular approaches have outlined a regulatory cross-talk between two metabolite pathways leading to the biosynthesis of terpene precursors. Terpenes derivatives produced through the mevalonic acid (MVA) pathway regulate the activity of the 2-C-methyl-d-erythritol 4-phosphate (MEP) non-mevalonate pathway producing the precursor of the TIA terpene moiety. This cross-talk involves regulatory prenylated proteins and acts on the regulation of the expression of early steps of monoterpenoid biosynthesis (ESMB) genes. The expression of the genes involved in the TIA terpene moiety biosynthesis is regulated in part by a general TIA transcription factor, ORCA3, and other unidentified transcription factors. This review sums up the essential information obtained at the metabolic, physiological, biochemical and molecular levels of regulation of TIA terpene moiety biosynthesis in C. roseus. We propose a synthetic scheme of the general regulatory network emerging from these experimental data, and discuss the related hypothesis and prospect in elucidating other key events involved in the regulation of TIA terpene moiety biosynthesis.