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Title:Metabolomic profiling of C4 grass responses to environmental stress
Author(s):Wedow, Jessica Marie
Director of Research:Ainsworth, Elizabeth A
Doctoral Committee Chair(s):Ainsworth, Elizabeth A
Doctoral Committee Member(s):Briskin, Donald P; Clough, Steven J; Marshall-Colon, Amy
Department / Program:Plant Biology
Discipline:Plant Biology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Metabolomics, C4, ozone, carbon dioxide, temperature
Abstract:Over half of the world’s grass species, including some of the most productive food and energy crops, use C4 photosynthesis. However, the responses of C4 crops to global atmospheric change, specifically rising carbon dioxide ([CO2]) and ozone ([O3]) concentrations, have been examined disproportionately less than responses of C3 crops. This thesis uses metabolomics approaches, along with integrated ‘omic’ technologies, to achieve a greater understanding of C4 grass responses to abiotic stresses associated with global atmospheric change. Rising temperatures will have a significant effect on major food and forage crops across the globe. Although the impact is expected to be greatest in tropical regions, the impacts of climate change have been poorly studied in those regions. In Chapter 2, Guinea grass (Panicum maximum Jacq.) was exposed to the individual and combined effects of elevated [CO2] and temperature, and transcript and metabolite profiles were examined. Samples were collected at a combined Free Air CO2 Enrichment and Temperature Controlled Enhancement (Trop-T-FACE) facility in Sao Paulo, Brazil. Field transcriptomics and metabolomics revealed that elevated temperature and [CO2] altered transcript and metabolite profiles associated with an environmental response, secondary metabolism and stomatal function. These metabolic responses were consistent with greater growth and leaf area production under elevated temperature. The tropical C4 grass had an unpredicted response to global climate change, with canopy warming during a cool growing season, enhancing growth and alleviating stress. Tropospheric O3 is the most damaging air pollutant to crops. Exposure to O3 causes oxidative stress to vegetative and reproductive tissues which can affect the abundance of transcripts, proteins and metabolites, leading to accelerated senescence and decreased yield. In Chapter 3, two diverse maize (Zea mays) inbred lines and the hybrid cross were exposed to season-long elevated [O3] (~100 ppb) in the field based FACE facility modified for O3. The metabolomic profile of leaves was sampled over the course of leaf senescence to achieve an understanding of the biochemical response during this developmental stage. The hybrid line, B73 x Mo17, showed an acceleration of chlorophyll loss under elevated [O3] accompanied by a significant change in the metabolite profile. In contrast, the metabolite profile of the two inbred lines (B73 and Mo17) was not different in ambient and elevated [O3] treatments. Levels of secondary metabolites were increased in B73 x Mo17 leaves as they aged and to a significantly greater degree in elevated [O3] stress. Untargeted metabolomic profiling revealed that inbred and hybrid lines of maize differ in key metabolic responses to elevated O3 pollution. The specific reactive oxygen species initially formed after O3 exposure and the antioxidants involved in apoplastic detoxification vary among plant species and even genotypes within a species. Very little is known about how C4 grasses respond to acute O3 exposure. In Chapter 4, maize and foxtail millet (Setaria viridis) were exposed to an acute O3 dose (200 – 400 nL L-1) for 24 hours. Leaf material from the youngest fully expanded leaf was taken for nuclear magnetic resonance (NMR) for identification of antioxidants and additional metabolites, and electron paramagnetic resonance (EPR) for ROS identification. EPR results showed the concentration of hydroxyl and superoxide radicals in leaves were higher after acute O3 exposure. Untargeted metabolomics performed with 1H-NMR showed altered amino acid content following initial O3 exposure, especially isoleucine and alanine. These experiments established the potential for EPR analysis of O3 response in live tissues and lay the foundation for further work to identify the specific molecular signature of the initial O3 response. This dissertation research provides insight into the metabolomic mechanisms behind the response of C4 grasses to elevated [CO2], temperature, and [O3]. Metabolomics approaches can be used for high-throughput phenotyping of diverse metabolites and their responses to stress. While field metabolomics can be challenging, the results identified novel metabolic pathways of response to global atmospheric change.
Issue Date:2020-03-30
Type:Thesis
URI:http://hdl.handle.net/2142/108095
Rights Information:Copyright 2020 Jessica Wedow
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05


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