Evaluation of Transgenic Tomato Plants Expressing an Additional Phytoene Synthase in a Fruit-Specific Manner

• Published in: Proceedings of the National Academy of Sciences - PNAS 2002-01, Vol.99 (2), p.1092-1097
• Main Authors: Fraser, Paul D., Romer, Susanne, Shipton, Cathie A., Mills, Philippa B., Kiano, Joy W., Misawa, Norihiko, Drake, Rachel G., Schuch, Wolfgang, Bramley, Peter M.
• Format: Article
• Language: English
• Subjects: Alkyl and Aryl Transferases - genetics; b-carotene; Bacteria; Biological Sciences; Carotenoids; Carotenoids - metabolism; crtB gene; CRTB protein; Diphosphates; Enzyme activity; Enzymes; Erwinia uredovora; Fruits; Gene Expression; Genes, Bacterial; Genetic engineering; Geranylgeranyl-Diphosphate Geranylgeranyltransferase; lutein; lycopene; Lycopersicon esculentum; Pectobacterium carotovorum - enzymology; Pectobacterium carotovorum - genetics; phytoene; Plants; Plants, Genetically Modified; Plastids; plastoquinone; Ripening; Solanum lycopersicum - enzymology; Solanum lycopersicum - genetics; Solanum lycopersicum - metabolism; Terpenoids; Tissue Distribution; Tomatoes; Transgenic plants; ubiquinone
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.241374598

Phytoene synthase from the bacterium Erwinia uredovora (crtB) has been overexpressed in tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig). Fruit-specific expression was achieved by using the tomato polygalacturonase promoter, and the CRTB protein was targeted to the chromoplast by the tomato phytoene synthase-1 transit sequence. Total fruit carotenoids of primary transformants (T0) were 2-4-fold higher than the controls, whereas phytoene, lycopene, β-carotene, and lutein levels were increased 2.4-, 1.8-, and 2.2-fold, respectively. The biosynthetically related isoprenoids, tocopherols plastoquinone and ubiquinone, were unaffected by changes in carotenoid levels. The progeny (T1and T2generations) inherited both the transgene and phenotype. Determination of enzyme activity and Western blot analysis revealed that the CRTB protein was plastid-located and catalytically active, with 5-10-fold elevations in total phytoene synthase activity. Metabolic control analysis suggests that the presence of an additional phytoene synthase reduces the regulatory effect of this step over the carotenoid pathway. The activities of other enzymes in the pathway (isopentenyl diphosphate isomerase, geranylgeranyl diphosphate synthase, and incorporation of isopentenyl diphosphate into phytoene) were not significantly altered by the presence of the bacterial phytoene synthase.