Abstract
The red colors of flowers are mainly produced by two types of pigments: anthocyanins and betacyanins. Although anthocyanins are widely found as flower and fruit pigments in higher plants, betacyanins have largely replaced anthocyanins in the Caryophyllales, except in the families Caryophyllaceae and Molluginaceae. The occurrence of anthocyanins in the betacyanin-producing Caryophyllales has not been reported. Thus, these two red pigments, anthocyanins and betacyanins, have never been demonstrated to co-exist in one plant. Although this curious mutual exclusion has been examined from genetic and evolutionary perspectives, nothing is known about it at the molecular level. Thus, the evolutionary mechanism of the mutual exclusion of these two pathways remains a mystery.
Although the biosynthesis of betacyanins is poorly understood, the biosynthetic pathway of flavonoids is probably one of the best-studied examples of secondary metabolism in higher plants. To gain further insight into the diversification of red pigments in higher plants, we focus on the potential for anthocyanin biosynthesis in the Caryophyllales at the molecular level.
