Flower colour and cytochromes P450

Abstract

Cytochromes P450 play important roles in biosynthesis of flavonoids and their coloured class of compounds, anthocyanins, both of which are major floral pigments. The number of hydroxyl groups on the B-ring of anthocyanidins (the chromophores and precursors of anthocyanins) impact the anthocyanin colour, the more the bluer. The hydroxylation pattern is determined by two cytochromes P450, flavonoid 30-hydroxylase (F30H) and flavonoid 30,50-hydroxylase (F3050H) and thus they play a crucial role in the determination of flower colour. F30H and F3050H mostly belong to CYP75B and CYP75A, respectively, except for the F3050Hs in Compositae that were derived from gene duplication of CYP75B and neofunctionalization. Roses and carnations lack blue/violet flower colours owing to the deficiency of F3050H and therefore lack the B-ring-trihydroxylated anthocyanins based upon delphinidin. Successful redirection of the anthocyanin biosynthesis pathway to delphinidin was achieved by expressing F3050H coding regions resulting in carnations and roses with novel blue hues that have been commercialized. Suppression of F3050H and F30H in delphinidinproducing plants reduced the number of hydroxyl groups on the anthocyanidin B-ring resulting in the production of monohydroxylated anthocyanins based on pelargonidin with a shift in flower colour to orange/red. Pelargonidin biosynthesis is enhanced by additional expression of a dihydroflavonol 4-reductase that can use the monohydroxylated dihydrokaempferol (the pelargonidin precursor). Flavone synthase II (FNSII)-catalysing flavone biosynthesis from flavanones is also a P450 (CYP93B) and contributes to flower colour, because flavones act as co-pigments to anthocyanins and can cause blueing and darkening of colour. However, transgenic plants expression of a FNSII gene yielded paler flowers owing to a reduction of anthocyanins because flavanones are precursors of anthocyanins and flavones. © 2013 The Author(s) Published by the Royal Society. All rights reserved.