Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2010
Publication Date: 10/18/2010
Publication URL: http://hdl.handle.net/10113/49244
Citation: Campbell, R., Ducreux, L.J.M., Morris, W.L., Morris, J.A., Suttle, J.C., Ramsay, G., Bryan, G.J., Hedley, P.E., Taylor, M.A. 2010. The metabolic and developmental roles of carotenoid cleavage dioxygenase4 from potato. Plant Physiology. 154:656-664. Interpretive Summary: Carotenoids are an important class of naturally occurring pigments that serve critical roles in both human nutrition and plant development. In humans, carotenoids and their derivatives fulfill numerous roles including serving as antioxidants and pro-vitamins. In plants, carotenoids are also antioxidants but recent evidence has demonstrated that they also serve as precursors to several important signaling molecules that regulate critical aspects of plant development. In this paper, the role of a carotenoid metabolizing enzyme (CCD4) in controlling potato tuber carotenoid content and development were determined using biochemical and molecular techniques. A gene encoding CCD4 was cloned from potato tuber tissues and was shown to be expressed in all parts of the potato plant. CCD4 expression was inversely proportional to total tuber carotenoid content suggesting that the enzyme encoded by this gene regulates total tuber carotenoid levels. Genetic manipulation of CCD4 expression demonstrated that significant (2-3 fold) elevations of tuber carotenoids occurred in tubers with reduced expression of CCD4. Genetic manipulation of CCD4 expression also resulted in several changes in tuber size and shape suggesting an additional role for this gene in tuber growth and development.
Technical Abstract: The factors that regulate storage organ carotenoid content remain to be fully elucidated despite the nutritional and economic importance of this class of compound. Recent findings suggest that carotenoid pool size is determined at least in part, by the activity of carotenoid cleavage dioxygenases. The aim of this study was to investigate whether CCD4 activity affects potato tuber carotenoid content. Microarray analysis revealed elevated expression of the potato CCD4 gene in mature tubers from white-fleshed cultivars compared with higher carotenoid yellow-fleshed tubers. The expression level of the potato CCD4 gene was down-regulated using an RNAi approach in stable transgenic lines. Down-regulation in tubers resulted in an increased carotenoid content, two- to three-fold higher than in control plants. The increase in carotenoid content was mainly due to elevated violaxanthin content, implying that this carotenoid may act as the in vivo substrate. Although transcript level was also reduced in plant organs other than tubers, such as leaves, stems and flowers, there was no change in carotenoid content in these organs. As well as changes in tuber carotenoid content, tubers from RNAi lines exhibited phenotypes such as heat sprouting, formation of chain tubers and an elongated shape. These results suggest that the product of the CCD4 reaction may be an important factor in tuber heat responses.