Strategies for enhancement of bioactive flavonol glycosides in plants

黄酮醇（如槲皮素）是众所周知的植物化学物质。它们与人类饮食的结合可以防止与慢性疾病（包括阿尔茨海默氏症）相关的破坏性自由基的积累。大约5%的65岁以上的加拿大人被诊断患有某种形式的痴呆症。黄酮醇提供了一种预防措施，以抵消加拿大每年用于治疗这些疾病的330亿美元。在人类饮食中，黄酮醇不像它们的糖苷那样容易获得，糖苷往往在植物（如洋葱、羽衣甘蓝、西兰花）和水果（如苹果、葡萄、辣椒、番茄）组织中占主导地位。在植物中，黄酮醇作为一种或多种糖的缀合物存在，包括单糖苷、二糖苷和双糖苷（例如槲皮素3-O-ß-葡萄糖苷-7- o -a-鼠李糖苷）。这些化合物在植物中的生理作用尚不清楚，但有证据表明它们与生长、环境胁迫和植物与昆虫的相互作用有关。植物黄酮醇双糖苷的积累是对环境扰动的响应，包括UV-B光、寒冷、营养缺乏，并依赖于生物合成途径的转录调节。包括食品在内的植物中的黄酮醇保存并不完全依赖于生物合成过程，因为每天损失1-35%是典型的，包括在采后处理期间。提高黄酮醇双糖苷的水平可以通过最小化其在植物中的降解来实现，这一过程鲜为人知。

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.