Bluer than blue: regulation of delphinidin branch anthocyanins in Vaccinium berries

Vaccinium berries include several economically important cultivated and wild species such as blueberries, cranberries, bilberries and lingonberries. These species are recognized for the various health beneficial properties, which are generally linked to the high yields and the complex profile of flavonoids in the berries, including anthocyanin, proanthocyanidin, and flavonol classes of flavonoids. Anthocyanins are one of the main pigments in plants contributing to the characteristic reddish to bluish colours in flowers and fruits. Most important anthocyanins are glucosides of six common aglycons: cyanidins, delphinidins, pelargonidins, petunidins, peonidins and malvidins. Of these, delphinidin branch anthocyanins, namely delphinidins, petunidins, and malvidins are responsible of bluish colours in blue Vaccinium berries. The biosynthesis of anthocyanins has been intensively studied, and the structural enzyme genes responsible of the specific steps of the pathway have been characterised also in diverse Vaccinium species. For the delphinidin branch, flavanone 3’5’ hydroxylase (F3’5’H) is the key enzyme for the branching point towards bluish anthocyanins. Our recent results both from controlled and field experiments have revealed new information on the key regulators controlling the different branches of the anthocyanin biosynthesis in blue-coloured berries. Transcriptome analyses combined with metabolite results have identified signaling routes leading to increase in delphinidin branch anthocyanins. Our results show that the anthocyanin composition in blue Vaccinium berries could be modified by specific environmental factors.