Carotenoid Biosynthesis And Regulation: More Than Meets The Eye
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Carotenoids are antioxidants synthesized almost exclusively in plants, providing pigmentation in flowers and fruits for the attraction of pollinators and seed dispersing organisms. While carotenoids are essential throughout plant development, they are also extremely important in human diets providing necessary nutrition and aiding in the prevention of various cancers, age-related diseases and macular degeneration. The elevated carotenoid content in ripe tomato fruit make them ideal sources of dietary carotenoids and a model system for discovery of how carotenoid accumulation is regulated. Recent efforts to improve nutritional quality of various crops (e.g. maize, rice and potato) by increasing carotenoid biosynthesis have proven useful, but are still limited compared to the high carotenoid content achieved in ripe tomato fruit. Breeding and transgenic efforts to enhance carotenoid content in tomato fruit have provided evidence of feedback mechanisms, which must be understood and overcome to substantially impact fruit carotenoid content. Using tomato as a model system we explored feedback mechanisms limiting the augmentation of carotenoid biosynthesis in ripening fruit with the goal of developing genetic strategies facilitating improvement of nutritional quality of tomato and other fruit and vegetable crops. Recent reports in plants, as well as animals, provide evidence that carotenoid cleavage products (apocarotenoids) play important roles as signaling molecules and logical candidates for roles in the previously mentioned feedback mechanisms. My thesis project focused on building a more complete understanding of signaling involved in ripening-associated carotenogenesis through the achievement of three specific goals: 1. Functionally characterize ZDS, a carotenoid desaturase encoding gene not yet defined by mutation, via the use of transgenic technologies; 2. develop a strategy to circumvent previously observed negative feedback regulation via overexpression of a heterologous phytoene desaturase; 3. Explore the potential for the identification of unique carotenoid derived signals through QTL mapping of ciscarotenoid associated loci in a little explored Solanum habrochaites introgression population. Upon completion, this work will provide a "tool box" for those interested in carotenoid biology and crop improvement to employ in their search for novel carotenoid catabolism pathways essential for carotenoid-derived signal production and eventual targeted manipulation of carotenoid profiles and accumulation.
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