The flavonoid pathway leading to anthocyanin biosynthesis has been well-characterized in a number of model systems, including maize, petunia, snapdragon and, more recently, Arabidopsis. Genetic approaches have identified many of the regulatory and structural genes required for the synthesis of these important plant pigments. In all species examined to date, control of the flavonoid pathway is known to occur, at least in part, at the level of transcription. In addition, there is evidence for regulation of this pathway at the level of the biosynthetic enzymes. Of particular interest to my research group is the possibility that flavonoid enzymes are organized as a multi-enzyme complex. This type of metabolic organization offers the potential not only for enhancing the efficiency of flavonoid biosynthesis, but also for regulating the flux of intermediates into branch pathways leading to anthocyanins and other endproducts. We have recently demonstrated specific interactions between flavonoid enzymes in Arabidopsis using co-immunoprecipitation, affinity chromatography, and two-hybrid analysis. Immunocytochemistry is providing further evidence for the co-localization of these enzymes at specific subcellular sites in root cells, consistent with biological roles of some flavonoids in auxin transport and the wound response. Additional approaches, including the expression of scFv antibodies in transgenic plants and homology modeling of the structures of various flavonoid enzymes, are being used to identify protein domains involved in the assembly and positioning of this system within the cell. Analysis of a series of Arabidopsis mutants has also provided evidence that intermediates in flavonoid biosynthesis function in a feedback control system. Our studies indicate that plants use a diversity of mechanisms to control the synthesis of flavonoid products, including anthocyanins.

Key words: Arabidopsis, chalcone isomerase, chalcone synthase, flavonoid