GENETICALLY MODIFIED TOMATO LINES WITH ELEVATED AND ALTERED CAROTENOID COMPOSITION

Transgenic tomato lines have been produced with increased and altered carotenoid compositions. The biosynthetic steps in carotenoid formation that have been subjected to genetic engineering include phytoene synthesis and desaturation as well as lycopene cyclisation. Homozygous (T₃) lines containing an additional phytoene synthase from the bacterium Erwinia uredovora, expressed in a fruit-specific manner show increases in phytoene, lycopene and -carotene levels of 2.4, 1.8 and 2.2-fold respectively (Fraser et al., 2002). Homozygous (up to T₆) lines containing a constitutively-expressed phytoene desaturase from E. uredovora show an elevated (up to 4-fold) level of b-carotene and other xanthophylls (Römer et al. 2000). However, the total carotenoid content is reduced 2-fold. In contrast transgenic lines (up to T₃) expressing lycopene -cyclase show increased -carotene levels with no reduction in total carotene content. These genetically modified varieties have been subjected to detailed molecular and biochemical analysis at the gene, protein and enzyme-activity level as well as metabolic control analysis. Evidence for regulatory mechanisms such as feedback inhibition and metabolite channelling has been revealed.