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整个北美的农作物受损和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。在没有改进的环境压力容忍机制的情况下，这将对全球粮食安全产生负面影响。通常，植物在环境胁迫下积累活性氧物种(ROS)，导致细胞和组织损伤，限制生长和发育。抗坏血酸水平的增加是对氧化应激的一种标志性反应，尽管这种新陈代谢调节是不可持续的。因此，许多农业系统缺乏抵消ROS损害的代谢灵活性。为了提高植物对干旱和高温复合胁迫的耐受性，有必要对不同的ROS解毒机制进行生化和分子性质的鉴定。我们的研究计划集中在植物受到环境干扰时发生的内源性氧化应激机制；一个中心主题是研究影响植物体内黄酮醇糖苷分布的代谢过程。黄酮醇糖苷是一种特殊的代谢物，在受氧化胁迫影响的植物中积聚，包括在高温和干旱暴露期间。黄酮醇糖苷几乎没有抗氧化潜力，因此推测这些化合物需要降解才能产生参与抗氧化的黄酮醇苷元部分。我们以前已经在植物中发现了一种葡萄糖苷酶(BGLU)活性，它能启动植物中葡萄糖基黄酮醇(如山奈酚3-O-β-葡萄糖苷-7-O-a-鼠李糖苷)的水解。BGLU分解代谢物(例如山奈酚7-O-a-鼠李糖苷)的瞬时积累以及山奈酚向小分子(即4-羟基苯甲酸酯)的转化意味着α-鼠李糖苷酶和过氧化物酶活性对黄酮醇的持续降解。我们认为，这些α-鼠李糖苷酶和过氧化物酶活性的协同作用将为非生物胁迫期间的ROS解毒提供黄酮醇苷元(如山奈酚)。本研究旨在阐明植物黄酮醇7-O-a-鼠李糖苷a-鼠李糖苷酶和黄酮醇过氧化物酶的生化性质。第二个目的是确定这些降解机制在不同的非生物胁迫(如高温和干旱)中对黄酮醇的周转和ROS的封存的功能重要性。这项研究将为旨在提高农业系统环境胁迫耐受性的生物技术战略提供新的生化和分子目标。拟议的研究将为2名博士、3名硕士和3名理科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部门非常需要。

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.