Conservation and diversification of flavonoid metabolism in the plant kingdom

Flavonoids are by far the largest class of polyphenols with huge structural and functional diversity. However, the mystery regarding the exact evolutionary pressures which lead to the amazing diversity in plant flavonoids has yet to be completely uncovered. Here we review recent advances in understanding the conservation and diversification of flavonoid pathway from algae and early land plants to vascular plants including the model plant Arabidopsis and economically important species such as cereals, legumes, and medicinal plants. Studies on the origin and evolution of R2R3-MYB regulatory system demonstrated its highly conserved function of regulating flavonoid production in land plants and this innovation appears to have been crucial in boosting the overall levels of these compounds in land plants. Convergent evolution has occurred as different flavonoids independently which emerged in distant taxa resulting in similar defense and tolerance characteristics against environmental stresses. Future studies on an increasing number of plant species taking advantage of newly developed genomic and metabolite profiling technologies are envisaged to provide comprehensive insight into flavonoid biosynthesis as well as pathway diversification and the underlying evolutionary mechanisms.