Breeding of blue chrysanthemums by genetic engineering

Abstract

Breeding of blue flowers in commercially important ornamental plants, such as chrysanthemum and rose, is relatively difficult by conventional breeding techniques because there are no closely-related species with blue flowers. Therefore, the creation of novel blue flowers has been attempted in various ornamental plants by using biotechnology. As a result, bluish colored carnations and roses have been produced and successfully commercialized. Our research group has also succeeded in developing technology based on genetic engineering to confer the pure blue flower color trait to chrysanthemum (Chrysanthemum morifolium). The blue coloration of the chrysanthemum was accomplished by constructing functional genes producing flavonoid 3’,5’-hydroxylase and anthocyanin 3’,5’-O-glucosyltransferase. Accumulation of 3’,5’-O-glucosylated delphinidin-based anthocyanins synthesized by the transgenes led to the development of blue color via intermolecular copigmentation with flavone glycosides present in chrysanthemum petal. Subsequently, by introducing the two genes necessary for blue petal coloration, we succeeded in conferring the blue flower color trait to various chrysanthemums with different floral shapes and color shades. Successful commercialization of blue chrysanthemums should facilitate an expansion of flower color variation, increase potential flower value, and raise new possibilities and applications for chrysanthemums. Furthermore, in vitro experiments suggested that, in addition to flavone glycosides, flavonol glycosides might have an effect on 3’,5’-O-glucosylated delphinidin-based anthocyanins as blue-coloring copigments in planta. These results indicate that the method established in chrysanthemums for the blue color development of petals by hydroxylation and glucosylation of the B-ring of anthocyanins is likely to be applicable to other ornamental plants.