Functional Analysis of Plant Carotenoid Dioxygenases

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This proposal addresses the functions of a class of enzymes known as carotenoid cleaving dioxygenases (CCDs). These enzymes metabolize carotenoids, creating a vast array of molecules that are economically important in the food industry as colorants and contribute to flavor. The products of these enzymes, generally known as apocarotenoids, also have biological activity in plants and animals. Important apocarotenoids include retinoids in animals, abscisic acid in plants, the major colorant and flavor compound in saffron, and the major scent volatiles in roses. Four CCD enzymes (CCD1, CCD4, CCD7 and CCD8) of unknown function have been the focus of research. Studies to date have shown that 9,10 (9',10') cleavage of diverse carotenoid substrates by CCD1 is a major source of volatiles and flavor constituents in tomato and petunia. CCD1 also plays a major role in regulating accumulation of nutritionally important carotenoids such as beta-carotene in cereal grains. Mutations in CCD7 and CCD8 cause major alterations in plant growth, particularly in the ability of the plant to make branches. Therefore, It has been concluded that CCD7 and CCD8 act together in the synthesis of a novel, and as yet unidentified, apocarotenoid hormone. The continuing work will have three key objectives: 1) An integrated, multitiered strategy aimed at identifying the biologically active compound synthesized by the CCD7/CCD8. 2) Comparative analysis of CCD7 and CCD8 function in divergent plant species. 3) Functional analysis of CCD4 with goals of defining its substrate specificity and its role in leaf development.Broader Impacts: The work has already generated material that will be fundamentally important to human nutrition, taste and aroma. A collaboration aimed at increasing carotenoid content in cereal grains that has the potential to impact the developing world has also been initiated. This research will be used as a platform to educate undergraduate and graduate students, including minority students from Fort Valley State University, an 1890 Land-Grant University.