Research ArticleAGRICULTURAL ENGINEERING

Generation of blue chrysanthemums by anthocyanin B-ring hydroxylation and glucosylation and its coloration mechanism

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Science Advances  26 Jul 2017:
Vol. 3, no. 7, e1602785
DOI: 10.1126/sciadv.1602785

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Abstract

Various colored cultivars of ornamental flowers have been bred by hybridization and mutation breeding; however, the generation of blue flowers for major cut flower plants, such as roses, chrysanthemums, and carnations, has not been achieved by conventional breeding or genetic engineering. Most blue-hued flowers contain delphinidin-based anthocyanins; therefore, delphinidin-producing carnation, rose, and chrysanthemum flowers have been generated by overexpression of the gene encoding flavonoid 3′,5′-hydroxylase (F3′5′H), the key enzyme for delphinidin biosynthesis. Even so, the flowers are purple/violet rather than blue. To generate true blue flowers, blue pigments, such as polyacylated anthocyanins and metal complexes, must be introduced by metabolic engineering; however, introducing and controlling multiple transgenes in plants are complicated processes. We succeeded in generating blue chrysanthemum flowers by introduction of butterfly pea UDP (uridine diphosphate)–glucose:anthocyanin 3′,5′-O-glucosyltransferase gene, in addition to the expression of the Canterbury bells F3′5′H. Newly synthesized 3′,5′-diglucosylated delphinidin-based anthocyanins exhibited a violet color under the weakly acidic pH conditions of flower petal juice and showed a blue color only through intermolecular association, termed “copigmentation,” with flavone glucosides in planta. Thus, we achieved the development of blue color by a two-step modification of the anthocyanin structure. This simple method is a promising approach to generate blue flowers in various ornamental plants by metabolic engineering.

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