Metabolic engineering of the mevalonate and non-mevalonate isopentenyl diphosphate-forming pathways for the production of health-promoting isoprenoids in tomato

The genetic manipulation of both the mevalonic acid (MVA) and methylerythritol-4-phosphate (MEP) pathways, leading to the formation of isopentenyl diphosphate (IPP), has been achieved in tomato using 3-hydroxymethylglutaryl CoA (hmgr-1) and 1-deoxy-D-xylulose-5-phosphate synthase (dxs) genes, respectively. Transgenic plants containing an additional hmgr-1 from Arabidopsis thaliana, under the control of the cauliflower mosaic virus (CaMV) 35S constitutive promoter, contained elevated phytosterols (up to 2.4-fold), but IPP-derived isoprenoids in the plastid were unaltered. Transgenic lines containing a bacterial dxs targeted to the plastid with the tomato dxs transit sequence resulted in an increased carotenoid content (1.6-fold), which was inherited in the next generation. Phytoene and beta-carotene exhibited the greatest increases (2.4- and 2.2-fold, respectively). Extra-plastidic isoprenoids were unaffected in these lines. These data are discussed with respect to the regulation, compartmentalization and manipulation of isoprenoid biosynthetic pathways and their relevance to plant biotechnology.