Evidence for Methylerythritol Pathway (MEP) Contributions to Zerumbone Biosynthesis as Revealed by Expression Analysis of Regulatory Genes and Metabolic Inhibitors Studies

Abstract

Sesquiterpenoid Zerumbone, the principal secondary metabolite in Zingiber zerumbet Smith, has been identified as the putative molecule conferring resistance against soft-rot causative, Pythium myriotylum. Metabolic precursors for sesquiterpenoid biosynthesis namely, isopentenyl diphosphate (IPP) and DMAPP, are generated either from cytosolic mevalonic acid (MVA) and/or the plastidal methylerythritol phosphate (MEP) pathway. Evaluation of expression pattern of regulatory genes of MEP and MVA pathway following P. myriotylum infection revealed that while transcripts of MVA regulatory gene, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), did not show significant changes, biphasic expression pattern was observed for MEP pathway regulatory genes, viz., 1-deoxy-D-xylulose-5-phosphate reductase (DXR) and 1-deoxy-D-xylulose-5-phosphate synthase (DXS) as well for ZzTPS (terpene synthase) and Farnesyl phosphate synthase (FPS) compared with uninfected control. Contribution of the two pathways in zerumbone biosynthesis was evaluated in axenic tissue culture raised Z. zerumbet plantlets using MVA and MEP pathway specific inhibitors, mevinolin (MEV) and fosmidomycin (FOS) respectively. Results generated by regulatory gene and metabolite analysis are informative with respect to the role of plastidial IPP pool generated via MEP pathway in zerumbone biosynthesis and the possible redirection of flux in the event of metabolic perturbations mediated by chemical inhibitors.