Elevation of carotenoids in tomato by genetic manipulation

Transgenic tomato Lines expressing either the Erwinia uredovora phytoene sy nthase (crtB) or phytoene desaturase (crtl) gene have been produced using t he polygalacturonase (PG) or CaMV 35S promoter respectively. Over three gen erations, tomato fruits expressing the additional phytoene synthase showed increased total carotenoids approaching twofold. Ripe tomato fruits express ing crtl showed significant increases in beta -carotene (threefold) but a r eduction in the total carotenoid content (twofold). The contents of other b iosynthetically related isoprenoids, including tocopherols (vitamin E), vit amin R, ubiquinones and plastoquinones, were not altered by manipulations t o the carotenoid pathway. Detailed biochemical analysis indicates that both enzymes are targeted to the correct location and reside in active states. Increases in enzyme activity and the levels of carotenoid endproducts do no t correlate. The data suggest that enhancement of carotenoids can be achiev ed by metabolic engineering of the pathway, but intrinsic regulatory mechan isms such as feedback inhibition and metabolite channelling may limit the p otential shown by the increased enzyme activities. (C) 2001 Society of Chem ical Industry.