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Unformatted text preview: Carotenoid Cleavage Dioxygenase (CmCCD4a) Contributes to White Color Formation in Chrysanthemum Petals 1[OA] Akemi Ohmiya*, Sanae Kishimoto, Ryutaro Aida, Satoshi Yoshioka, and Katsuhiko Sumitomo National Institute of Floricultural Science, Fujimoto 2-1, Tsukuba, Ibaraki 3058519, Japan The white petals of chrysanthemum ( Chrysanthemum morifolium Ramat.) are believed to contain a factor that inhibits the accumulation of carotenoids. To find this factor, we performed polymerase chain reaction-Select subtraction screening and obtained a clone expressed differentially in white and yellow petals. The deduced amino acid sequence of the protein (designated CmCCD4a) encoded by the clone was highly homologous to the sequence of carotenoid cleavage dioxygenase. All the white-flowered chrysanthemum cultivars tested showed high levels of CmCCD4a transcript in their petals, whereas most of the yellow-flowered cultivars showed extremely low levels. Expression of CmCCD4a was strictly limited to flower petals and was not detected in other organs, such as the root, stem, or leaf. White petals turned yellow after the RNAi construct of CmCCD4a was introduced. These results indicate that in white petals of chrysanthemums, carotenoids are synthesized but are subsequently degraded into colorless compounds, which results in the white color. Carotenoids are 40-carbon isoprenoids with polyene chains that may contain up to 15 conjugated double bonds. More than 700 naturally occurring carotenoids have been identified (Britton et al., 2004). Carotenoids are essential for photosynthesis, and they furnish flowers and fruits with distinct colors designed to attract insects and other animals. Carotenoids also serve as precursors for the biosynthesis of the plant growth regulator abscisic acid (Schwartz et al., 1997). The chrysanthemum ( Chrysanthemum morifolium Ramat.), which has been bred for more than 2,000 years, is one of the most important ornamental flowers in theworld. Thepetalcolorof yellow-flowered cultivars originates mainly from carotenoids. Understanding the mechanism that controls carotenoid accumulation in petals will not only contribute greatly to the breeding of chrysanthemums and other flowering plants but also provide important information about the molecular evolutionary mechanisms responsible for different petal colors. Cultivated chrysanthemums are thought to have originated from hybrids between white- and yellow-flowered wild species. On the basis of an ex- periment in which white- and yellow-flowered chry- santhemums were crossed, Hattori (1991) observed that the white petal color is dominant over yellow and suggested that a single dominant gene that inhibits carotenoid accumulation may exist. The detailed func- tionofsuchagene,however,isstillunknown.Kishimoto and Ohmiya (2006) demonstrated no significant differ- ence between the expression levels of carotenoid bio- synthetic genes in white and yellow petals during the course of development. In addition, the carotenoidcourse of development....
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This note was uploaded on 08/01/2009 for the course HORT hor-11-12 taught by Professor Park during the Spring '09 term at A.T. Still University.
- Spring '09