One Piece at a Time: Flavonol Deglycosylation and Peroxidation in Abiotic Stressed Plants

农业领域的高温和干旱压力最终导致作物受损，并给北美带来数十亿美元的经济损失。这些压力及其对植物的有害影响预计将随着全球气候变化而加剧。这将对全球粮食安全产生负面影响，因为缺乏改进的环境压力耐受机制。通常，植物在环境胁迫下积累活性氧（ROS），导致细胞和组织损伤，限制生长发育。抗坏血酸水平的增加是氧化应激的标志反应，尽管这种代谢调节不能持续。因此，许多农业系统缺乏代谢灵活性来抵消活性氧的损害。为了提高对干旱和热联合胁迫的耐受性，有必要确定替代ROS解毒机制的生化和分子特性。我们的研究计划集中在内源性氧化应激机制发生在植物受到环境扰动；一个中心主题是研究影响植物中黄酮醇苷分布的代谢过程。黄酮醇苷是受氧化应激影响的植物的特殊代谢物，包括在高温和干旱暴露期间。黄酮醇苷几乎没有抗氧化潜力，因此假设这些化合物的降解需要产生参与抗氧化的黄酮醇苷元部分。我们之前已经确定了一种ß-葡萄糖苷酶（BGLU）活性，它可以启动植物中葡萄糖化黄酮醇的水解（例如山奈酚3-O-ß-葡萄糖苷-7- o -a-鼠李糖苷）。BGLU分解代谢物（如山奈酚7- o -a-鼠李糖苷）的短暂积累以及山奈酚在植物中转化为更小分子（如4-羟基苯甲酸酯）意味着黄酮醇通过a-鼠李糖苷酶和过氧化物酶活性持续降解。我们认为，这些a-鼠李糖苷酶和过氧化物酶活性的协同作用将提供黄酮醇苷元（如山奈酚）在非生物胁迫下解毒ROS。目的是阐明植物黄酮醇7- o -鼠李糖苷酶和黄酮醇过氧化物酶的生化特性。第二个目的是确定这些降解机制在各种非生物胁迫下黄酮醇转化和活性氧封存的功能重要性，如热旱联合胁迫。该研究将为旨在提高农业系统环境胁迫耐受性的生物技术策略提供新的生化和分子靶点。拟议的研究将为2名博士、3名硕士和3名学士提供独特的多学科研究培训机会，包括经典生物化学、分子生物学、分析化学和基因组学，这些技术技能在科学工业领域需求量很大。

Heat and drought stresses in agricultural fields culminate in damaged crops and billions of dollars in economic losses across North America. These stresses and the deleterious effects they elicit in plants are expected to intensify with global climate change. This will have negative consequences for global food security in the absence of improved environmental stress tolerance mechanisms. Typically, plants accumulate reactive oxygen species (ROS) under environmental stress, which results in cellular and tissue damage that limit growth and development. An increase in ascorbate levels is a hallmark response to oxidative stress, although this metabolic adjustment is not sustained. Thus many agricultural systems lack the metabolic flexibility to offset ROS damage. In order to improve tolerance to combined drought and heat stress, it is imperative to identify the biochemical and molecular properties of alternative ROS detoxification mechanisms. Our research program is focused on endogenous oxidative stress mechanisms that occur in plants subjected to environmental perturbations; a central theme is the study of metabolic processes that affect the distribution of flavonol glycosides in plants. Flavonol glycosides are specialized metabolites that amass in plants affected by oxidative stress, including during heat and drought exposure. Flavonol glycosides have little antioxidant potential, and thus it is postulated that degradation of these compounds is required to produce the flavonol aglycone moiety that would participate in anti-oxidation. We have previously identified a ß-glucosidase (BGLU) activity that initiates the hydrolysis of glucosylated flavonols (e.g., kaempferol 3-O-ß-glucoside-7-O-a-rhamnoside) in plants. The transient accumulation of BGLU catabolites (e.g., kaempferol 7-O-a-rhamnoside) as well as in planta conversion of kaempferol to smaller molecules (i.e., 4-hydroxybenzoate) implies continual degradation of flavonols by a-rhamnosidase and peroxidase activities. We propose that the concerted action of these a-rhamnosidase and peroxidase activities would supply flavonol aglycones (e.g., kaempferol) for ROS detoxification during abiotic stress. Our aim is to elucidate the biochemical properties of plant flavonol 7-O-a-rhamnoside a-rhamnosidases and flavonol peroxidases. A second aim is to define the functional importance of these degradative mechanisms for flavonol turnover and sequestration of ROS during various abiotic stresses, such as combined heat and drought. The research will provide new biochemical and molecular targets for biotechnology strategies aimed at improving environmental stress tolerance in agricultural systems. The proposed research will provide unique training opportunities for 2 PhD, 3 MSc and 3 BSc in multi-disciplinary research, including classical biochemistry, molecular biology, analytical chemistry, and genomics, technological skills that are in high demand within the scientific industry sector.