Towards Metabolic Engineering of Carotenoid Content in Sweet-orange (Citrus sinensis (L.) Osb.)
Plants have a remarkable array of biosynthetic pathways, of which many synthesize products of secondary metabolism with biotechnological and health-related importance. One of these, known as carotenoid biosynthetic pathway, leads to biosynthesis of healthpromoting compounds (i.e., beta-carotene, lycopene, lutein, zeaxanthin) which reduce the onset of chronic disease states, such as cancer, macular degeneration and cardiovascular disease. In addition, all the carotenoid species that contain a beta-ring can be converted to retinol and, thus, are precursors of vitamin A. These properties have led to intensive efforts to alter and elevate such isoprenoids in food crops (Taylor and Ramsay, 2005).
Citrus is the main fruit crop produced and consumed in the world. It contains the largest number of carotenoids found in any fruit (Franciullino et al., 2006), making citrus fruit an important target for increasing carotenoids with health-promoting properties. Carotenoid content and composition vary greatly among citrus species and growing conditions. Cryptoxanthin, violaxanthin, and antheraxanthin and their esters are the primary xanthophylls present in most citrus fruits; the hydrocarbon carotenoids, such as phytoene and lycopene, are usually present in low concentrations (Gross, 1976). To enhance nutritionally important carotenoids in citrus plants, the use of gene transfer technologies is essential since improvement of citrus plants by traditional breeding has been hampered by its reproductive biology and prolonged juvenility (Gmitter et al., 1992).
KeywordsHydrocarbon Carotenoid Kanamycin Lutein Lycopene
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