Carbon and water relations traits as targets for adapting C3 plants to future elevated carbon dioxide and drought conditions

Quebedeaux, Jennifer Camille

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https://hdl.handle.net/2142/115571 Copy

Description

Title

Carbon and water relations traits as targets for adapting C3 plants to future elevated carbon dioxide and drought conditions

Author(s)

Quebedeaux, Jennifer Camille

Issue Date

2022-04-18

Director of Research (if dissertation) or Advisor (if thesis)

Leakey, Andrew DB

Doctoral Committee Chair(s)

Leakey, Andrew DB

Committee Member(s)

• Ort, Donald R
• Bollero, German A
• Brooks, Matthew D

Department of Study

Plant Biology

Discipline

Plant Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Elevated carbon dioxide
• Photosynthesis
• Carbon metabolism
• Water use efficiency

Abstract

The atmospheric CO2 concentration ([CO2]) is higher now than at any time in the last 20 million years and is projected to continue rising. Precipitation patterns are also projected to become more extreme. Thus, climate change poses a significant challenge to global agriculture. This thesis employs the use of genetic modifications to better understand and to make plants better equipped to face these challenges. Growing C3 plants at elevated [CO2] can cause photosynthesis to produce sugars more efficiently—providing an experimental system to investigate the importance of phloem loading strategy and capacity in plant responses to elevated [CO2]. First, we hypothesized that species with different phloem loading strategies are differentially adapted to high mesophyll sucrose concentrations and may have fundamentally different photosynthetic responses to elevated [CO2]. Over three field seasons, five species with apoplastic loading, passive loading, or polymer trapping were grown at ambient and elevated [CO2] using mini-Free-Air CO2 Enrichment (FACE). Our results indicated that in contrast to our hypothesis, there was little difference in photosynthetic response to elevated [CO2] among these species. Variation in growth form was confounded with phloem loading strategy, thus, a phylogenetically controlled comparative analysis may be required to fully assess the hypothesis. Second, we hypothesized that plants could have insufficient sugar export capacity from the photosynthetic source to sink tissues under conditions of high carbon availability. This is suggested by feedback inhibition of photosynthetic capacity at elevated [CO2]. To overcome this potential limitation, soybean was transformed to express an additional proton/sucrose symporter in the phloem companion cells. Experiments were conducted at the Soybean Free Air Concentration Enrichment (SoyFACE) facility over three field seasons to test how increasing sucrose transport capacity in soybean impacts photosynthesis and crop yield. We found that the expression of an additional sucrose transporter did not consistently alter sucrose transport capacity and ultimately affect photosynthesis and yield in our field experiment. However, this modification may need to be combined with other approaches to maximize the benefits of improved photosynthetic efficiency at elevated [CO2]. Despite knowledge of how plants respond to elevated [CO2], the genes involved in regulating these processes are largely unknown. A soybean transcriptomics experiment identified a GATA transcription factor, involved in carbon and nitrogen metabolism, as responsive to elevated [CO2]. We hypothesized that this gene plays a previously unrecognized role in responding to elevated [CO2]. Wildtype and a T-DNA insertion line of Arabidopsis thaliana for GNC (GATA, Nitrate Inducible, Carbon Metabolism Involved) were grown under three treatment combinations: sustained ambient [CO2], sustained elevated [CO2], and transient elevated [CO2] to assess their physiology, biochemistry, and transcriptome changes. Plants lacking GNC had significantly smaller CO2 fertilization effects on photosynthesis and biomass production than WT in elevated [CO2] and transfer [CO2]. This chapter provides a case study of a transcription factor that regulated plant responses to elevated [CO2]. Further characterization of the function of GNC in regulating response to elevated [CO2] will be valuable and offers a promising avenue for engineering complex traits related to environmental stresses. In chapter 4, transgenic wheat was designed to alter expression of a gene involved in stomatal development. Several studies have shown that reducing stomatal density can lead to greater water use efficiency. Optimizing these increases without unwanted trade-offs in photosynthetic carbon gain and biomass production have not been addressed. Using optical topometry, gas exchange, and tunable-diode laser absorption spectroscopy, we sought to gain a better understanding of the interactions between stomatal and mesophyll processes. Even though there was an inconsistent presence of the phenotype, we observed a tradeoff in stomatal density and pore width that could be explored in future studies. Furthermore, our measurements of mesophyll conductance provide evidence for the influence of CO2, which could be useful in better understanding this limitation to photosynthesis. This dissertation describes several approaches to modify plants to better take on a changing climate. The primary goal of this research is to advance understanding of crop responses to future conditions and provide strategies that have potential to improve crops to meet those demands.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Jennifer Quebedeaux

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