Strategies for enhancement of bioactive flavonol glycosides in plants

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Flavonols (e.g. quercetin) are well known phytochemicals. Their incorporation in the human diet may prevent accumulation of damaging radicals associated with chronic diseases including Alzheimer's. Approximately 5% of Canadians over the age of 65 are diagnosed with some form of dementia. Flavonols offer a preventative measure to offset the $33 billion spent annually to treat these disorders in Canada. In the human diet, flavonols are not as available as their glycosides, forms which tend to predominate across vegetative (e.g. onion, kale, broccoli) and fruit (e.g. apple, grape, pepper, tomato) tissues. In plants, flavonols exists as conjugates of one or more sugars, including monoglycosides, diglycosides and bisglycosides (e.g. quercetin 3-O-ß-glucoside-7-O-a-rhamnoside). The physiological roles of these compounds in plants are not yet clear, but evidence suggests they are linked to growth, environmental stress, and plant-insect interactions. Plant accumulation of flavonol bisglycosides occurs in response to environmental perturbations, including UV-B light, chilling, nutrient deficiencies, and is dependent upon transcriptional regulation of the biosynthetic pathway. Flavonol preservation in plants, including foodstuffs, is not solely dependent upon biosynthetic processes as losses on the order of 1-35% per day are typical, including during postharvest handling. Enhanced levels of flavonol bisglycosides may be achieved by minimizing their degradation in planta, processes that are little understood. ***Over the past 6 years, my laboratory has established the biochemical evidence for the loss of flavonol bisglycosides and their related molecules from plants. Our current research focuses on characterizing this catabolism in Arabidopsis thaliana, a model plant for flavonol biochemistry due to the availability of genetic mutants. A highlight of our research includes the identification of an enzymatic component, specifically a ß-glucosidase, as a possible first step in the loss of these bioactive compounds. We are interested in elucidation of the complete flavonol bisglycoside catabolism pathway in plants. Our laboratory uses cutting edge analytical chemistry platforms together with physiology, classical biochemistry and biotechnology to identify the genes/enzymes associated with the turnover of these important small molecules. In addition to providing unique training opportunities for students in biochemistry, molecular biology and analytical chemistry, this research aims to enhance knowledge of plant flavonol catabolism. Moreover, this novel research provides potential tools for genetic engineering and molecular breeding strategies targeting flavonol biofortification in economically important crop plants.***********