CHAPTER 15: Role of 2-Oxoglutarate-Dependent Oxygenases in Flavonoid Metabolism

Plants are capable of producing a vast array of secondary metabolites, probably amounting to more than 200 000 diverse compounds. The enormous chemical complexity and variety of these structures are enabled by the selective expression of biosynthetic genes encoding for enzymes such as regio- and stereospecific oxygenases and hydroxylases. Many of these enzymes are rather labile and access has been gained in recent years only by reverse genetics. For example, the extensively studied biosynthesis of flavonoids, which form the third largest group of phytochemicals and are responsible for peculiar tissue colourations, requires several mono- and dioxygenase activities. Most plant dioxygenases depend on 2-oxoglutarate (2OG) as a substrate and constitute the largest group of mononuclear, non-haem ferrous ion-dependent oxidizing enzymes and the second largest enzyme family in plant genomes. So far six 2OG-dependent dioxygenases have been assigned to flavonoid biosynthesis. Recently, this family has been grouped into three subfamilies (DOXA-C) based on polypeptide sequence alignments. The vast majority of plant 2OG-dependent dioxygenases involved in the formation of land plant secondary metabolites were classified to the DOXC subfamily, including those committed to flavonoid biosynthesis.