Involvement of CCD4 in Determining Petal Color

Abstract

In chrysanthemums (Chrysanthemum morifolium Ramat.), white petal color is dominant over yellow and is postulated to arise from a single dominant gene that inhibits carotenoid formation. By differential screening, we identified a gene that is expressed specifically in white petals of chrysanthemum. The gene is highly homologous to carotenoid cleavage dioxygenase 4 (CCD4) and was designated CmCCD4a. Suppression of CmCCD4a expression by RNA interference in white-flowered strains resulted in the formation of yellow petals. Flower color mutants with increased levels of carotenoids showed decreased levels of CmCCD4a expression. The results indicate that CmCCD4a is the single dominant gene encoding an enzyme that inhibits carotenoid accumulation in chrysanthemum petals by catalyzing degradation of carotenoids. Although CmCCD4a has been shown to catalyze the conversion of β-carotene to β-ionone in vivo, its catalytic product(s) in planta has not been identified. Involvement of CCD4 in controlling carotenoid content was also examined in petals of white-flowered Ipomoea nil and carnation (Dianthus caryophyllus L.). The results showed that low levels of carotenoids in petals of these plants were not caused by degradation but by low rates of biosynthesis.