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

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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.