Flavones and flavone synthases

• Published in: Phytochemistry (Oxford) 2005-10, Vol.66 (20), p.2399-2407
• Main Authors: Martens, Stefan, Mithöfer, Axel
• Format: Article
• Language: English
• Subjects: Antineoplastic Agents - pharmacology; Antioxidants - pharmacology; Biological and medical sciences; Chemical constitution; Cytochrome P-450 Enzyme System - genetics; Cytochrome P-450 Enzyme System - metabolism; Enzymes; Evolution, Molecular; Flavone synthases; Flavones; Flavonoids; Flavonoids - chemistry; Flavonoids - metabolism; Flavonoids - pharmacology; FNS; Fundamental and applied biological sciences. Psychology; Genetic Engineering - methods; Humans; Medicine, Chinese Traditional; Metabolism; Mixed Function Oxygenases - genetics; Mixed Function Oxygenases - metabolism; Nutritional Physiological Phenomena; Plant physiology and development; Plants - metabolism; Plants, Genetically Modified
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2005.07.013

Flavones represent one of the largest subgroups within the flavonoids. Two independently evolved and mechanistically different enzymes can convert the precursors, flavanones, into flavones. Various biological activities of flavones in plants and in human nutrition and health make them valuable targets for metabolic engineering. Within the secondary metabolite class of flavonoids which consist of more than 9000 known structures, flavones define one of the largest subgroups. Their natural distribution is demonstrated for almost all plant tissues. Various flavone aglyca and their O- or C-glycosides have been described in the literature. The diverse functions of flavones in plants as well as their various roles in the interaction with other organisms offer many potential applications, not only in plant breeding but also in ecology, agriculture and human nutrition and pharmacology. In this context, the antioxidative activity of flavones, their use in cancer prevention and treatment as well as the prevention of coronary heart disease should be emphasized. The therapeutic potential of flavones makes these compounds valuable targets for drug design, including recombinant DNA approaches. The biosynthesis of flavones in plants was found to be catalyzed by two completely different flavo ne synthase proteins (FNS), a unique feature within the flavonoids. The first, FNS I, a soluble dioxygenase, was only described for members of the Apiaceae family so far. The second, FNS II, a membrane bound cytochrome P450 enzyme, has been found in all other flavone accumulating tissues. This phenomenon is particularly of interest from the evolutionary point of view concerning the flavone biosynthesis and functions in plants. Recently, FNS I and FNS II genes have been cloned from a number of plant species. This now enables detailed biochemical and molecular characterizations and also the development of direct metabolic engineering strategies for modifications of flavone synthesis in plants to improve their nutritional and/or biopharmaceutical value.