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，并在北美造成数十亿美元的经济损失。随着全球气候变化，这些压力及其在植物中引起的有害影响预计将加剧。在缺乏更好的环境压力耐受机制的情况下，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（ROS），这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标志性反应，尽管这种代谢调节并不持续。因此，许多农业系统缺乏代谢的灵活性，以抵消ROS的损害。为了提高植物对干旱和高温胁迫的耐受性，确定活性氧解毒机制的生化和分子特性是非常必要的。我们的研究项目集中在受到环境扰动的植物中发生的内源性氧化应激机制;一个中心主题是影响植物中黄酮醇糖苷分布的代谢过程的研究。黄酮醇糖苷是在受氧化应激影响的植物中积累的专门代谢物，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的降解需要产生参与抗氧化的黄酮醇苷元部分。我们先前已经鉴定了β-葡糖苷酶（BGLU）活性，其引发葡糖基化黄酮醇的水解（例如，山奈酚3-O-α-葡糖苷-7-O-α-鼠李糖苷）。BGLU催化剂的瞬时积累（例如，山奈酚7-O-α-鼠李糖苷）以及山奈酚在植物中转化为更小的分子（即，4-羟基苯甲酸酯）意味着黄酮醇被α-鼠李糖苷酶和过氧化物酶活性持续降解。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提供黄酮醇苷元（例如，山奈酚）在非生物胁迫期间用于ROS解毒。本文旨在阐明植物黄酮醇7-O-α-鼠李糖苷α-鼠李糖苷酶和黄酮醇过氧化物酶的生化性质。第二个目的是确定功能的重要性，这些降解机制黄酮醇营业额和封存的活性氧在各种非生物胁迫，如高温和干旱相结合。这项研究将为旨在提高农业系统环境胁迫耐受力的生物技术战略提供新的生物化学和分子目标。拟议的研究将为2名博士，3名硕士和3名理学学士提供独特的培训机会，包括经典生物化学，分子生物学，分析化学和基因组学等多学科研究，这些技术技能在科学工业部门中需求量很大。

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.