Role of 2-oxoglutarate dependent oxygenases in flavonoid metabolism

Plants are capable of producing a vast array of secondary metabolites amounting likely to more than 200,000 diverse compounds. The enormous chemical complexity and variety of structures are ensured by the selective expression of biosynthetic genes encoding enzymes such as position- 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 colorations requires several mono- and dioxygenase activities. Most dioxygenases depend on 2-oxoglutarate as a second substrate and constitute the largest group of mononuclear, non-haem ferrous iron-dependent oxidizing enzymes and the second largest enzyme family in plant genomes. So far six 2-oxoglutarate dependent dioxygenases have been assigned to flavonoid biosynthesis. Recently, this large family was grouped into three sub-families (DOXA-C) based on polypeptide sequence alignments. The vast majority of plant 2-oxoglutarate dependent dioxygenases involved in the formation of land plant secondary metabolites was classified to the DOXC sub-family which also includes those committed to flavonoids