Abstract
Chrysanthemum (Chrysanthemum × morifolium) is one of the most important ornamental plants in the world. They are typically used as cut flowers or potted plants. Chrysanthemum can exhibit red, purple, pink, yellow and white flowers, but lack bright red and blue flowers. In this study, we identified two chrysanthemum cultivars, C × morifolium ‘LPi’ and C × morifolium ‘LPu’, that only accumulate flavonoids in their ligulate flowers. Next, we isolated seven anthocyanin biosynthesis genes, namely CmCHS, CmF3H, CmF3’H, CmDFR, CmANS, CmCHI and Cm3GT in these cultivars. RT-PCR and qRT-PCR analyses showed that CmF3′H was the most important enzyme required for cyanidin biosynthsis. To rebuild the delphinidin pathway, we downregulated CmF3’H using RNAi and overexpressed the Senecio cruentus F3′5′H (PCFH) gene in chrysanthemum. The resultant chrysanthemum demonstrated a significantly increased content of cyanidin and brighter red flower petals but did not accumulate delphinidin. These results indicated that CmF3′H in chrysanthemum is important for anthocyanin accumulation, and Senecio cruentus F3′5′H only exhibited F3′H activity in chrysanthemum but did not rebuild the delphinidin pathway to form blue flower chrysanthemum.
Highlights
Flower colour is determined on the basis of flavonoids, carotenoids and betalains [1]
We found that the expression of genes encoding enzymes of anthocyanin biosynthesis is regulated in ray florets among the 4 chrysanthemum cultivars with different colours
In chrysanthemum ray florets, the red colour has been contributed for carotenoids, or combined with red or magenta anthocyanins [8], which was according to our study, the pigments of LPi and LPu were cyanidian
Summary
Flower colour is determined on the basis of flavonoids, carotenoids and betalains [1]. Anthocyanins, a group of secondary metabolites belonging to the flavonoid family, demonstrate a wide range of orange to red and purple to blue flowers, which can attract pollinators and, importantly, protect against damage from UV irradiation. The anthocyanin biosynthesis pathway (ABP) is a branch of the flavonoid biosynthesis pathway that is derived from the phenylpropanoid biosynthesis pathway. The ABP begins with the formation of chalcones by the chalcone synthase enzyme (CHS). Chalcone isomerase (CHI) converts chalcone into naringenin [4]. Naringenin is hydroxylated at the 3′ position of its central ring by flavanone 3-hydroxylase (F3H) to produce dihydrokaempferol (DHK). DHK can be further hydroxylated at the 3′ position or at both the 3′ and 5′
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