Flavonoid and flavonol glycoside metabolism in Arabidopsis

The molecular genetic analysis of Arabidopsis promises to add greatly to our understanding of secondary product pathways and their biological roles. This review focuses on flavonoid metabolism in Arabidopsis, a particularly relevant pathway for such analysis because it is so highly conserved in plants. Several of the biosynthetic enzymes of the phenylpropanoid and flavonoid pathways have been cloned and/or mapped to specific loci. Recent advances concerning the regulation of anthocyanin metabolism by light and by possible transcriptional activators (Myc- and Myb-like elements) are discussed as well as the possible roles of flavonols in cold acclimation, ultraviolet light protection and male fertility. The use of HPLC profiling for the discovery of additional metabolic and regulatory mutants is described. The identification of the major flavonol glycosides in wild-type Arabidopsis is given and the partial characterization of two new flavonol glycoside mutants discussed. The biochemical genetics for flavonol glycoside formation in soybean is presented as an example, and the high degree of specificity of the glycosyl transferases and the interesting diversity of the resulting flavonol glycosides are discussed. Hypotheses regarding the potential biological activities of the flavonoid conjugates and the possible regulatory roles of highly aglycone-specific glucosidases are presented.