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Title:Identification of chromosomes in hexaploid bread wheat (Triticum aestivum l.) Associated with natural or safener-induced tolerance to halauxifen-methyl
Author(s):Obenland, Olivia Augusta
Advisor(s):Riechers, Dean E
Contributor(s):Moose, Stephen P; Rayburn, A. Lane; Bollero, Germán A; Kolb, Frederic L
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Triticum aestivum
Herbicide Metabolism
Abstract:Wheat (Triticum aestivum L.) is one of the most widely cultivated crops globally, and like many other crops, herbicides are utilized for weed control in order to minimize yield loss. While several effective herbicides are labelled for wheat, the application rates and application time frames are often limited in order to avoid injury and yield loss. Synthetic auxin herbicides are generally applied prior to the jointing stage of wheat to avoid injury or reduced yields. Introducing a transgene to increase crop tolerance or extend the herbicide application time-frame is not a viable option due to concerns of pollen flow between wheat and a closely related weedy relative, jointed goatgrass (Aegilops cylindrica). An alternative to transgenes is the use of herbicide safeners, which are a group of chemicals that confer herbicide tolerance by inducing the expression and/or activity of herbicide-detoxifying enzymes, such as cytochrome P450-dependent monooxygenases (P450s), glutathione S-transferases (GSTs), and ATP-binding cassette (ABC) transport proteins. Safeners are easily integrated with herbicide application practices because they are typically mixed with the herbicide and utilized in post-emergence applications to wheat. While safeners have been prevalent in agriculture for decades, knowledge of how safeners induce the expression of these enzymes is still limited. Previous research indicated that genes encoding 12-oxophytodienoic acid reductases (OPRs) exhibited increased expression after treatments of the wheat safener, cloquintocet-mexyl (CM). There are two isoforms of these enzymes (OPRI and OPRII) but only OPRII isoforms participate in jasmonate (JA) biosynthesis, which are a class of oxidized lipids (oxylipins) that mediate plant responses to biotic and abiotic stresses. Based on these previous findings, my current hypothesis is that safeners utilize an oxylipin-mediated signaling pathway to induce the expression of genes encoding herbicide-detoxifying enzymes. Similarly, little is known about the herbicide-detoxifying enzymes that confer natural tolerance to synthetic auxin herbicides in wheat. Like other common monocot crop species, wheat displays a natural tolerance to synthetic auxin herbicides. While it is established P450s play a pivotal role in the natural tolerance of monocot species towards synthetic auxin herbicides, a specific P450 associated with synthetic auxin metabolism has not been characterized in wheat. In the present study I focused on the newer synthetic auxin herbicide, halauxifen-methyl (HM). Chapter 1 of this thesis includes a literature review of alien substitution and aneuploid lines of wheat, the possible role of OPRs mediating the safener response, synthetic auxin herbicide mode of action, and specifically the arylpicolinic acid class of synthetic auxin herbicides. Chapter 2 examines the results of wheat alien substitution lines and aneuploid lines in response to treatments of HM and CM. These lines lack specified wheat chromosomes and were used to identify the chromosomes of wheat associated with genes that confer natural or safener-induced HM tolerance. Results indicate that lines lacking chromosomes 5A or 5B display reduced tolerance to HM relative to unaltered wheat, indicating that chromosomes 5A and 5B possess genes needed for natural HM tolerance in wheat. Chapter 3 describes a reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) expression analysis of wheat OPR genes (TaOPRs) in CM-treated wheat. Of the three TaOPRs examined in the study, a TaOPR gene located on the long arm of chromosome 6D (TaOPR6DL) displayed the highest expression levels in all safener-treated tissues relative to unsafened controls, with the highest fold induction approximately 128-fold in the shoot meristematic region. Fold inductions for the other TaOPR genes were not as high with other fold inductions peaking around 20-fold and 6-fold for the TaOPRs located on the short arm of 2B (TaOPR2BS; 20-fold) and the long arm of 7D (TaOPR7DL; 6-fold), respectively. The highest fold inductions for all genes were observed at 6 hours after treatment (HAT) but were transient in nature, as evidenced by lower fold inductions at 12 HAT. Since CM is a prosafener, it is possible that bioactivation of the parent ester and translocation of the free acid may influence these expression patterns in wheat leaves. Chapter 4 summarizes the discussion and conclusions from Chapters 2 and 3 and identifies future research goals for identifying candidate genes that govern natural or safener-induced HM tolerance and validating their functions.
Issue Date:2020-04-28
Rights Information:Copyright 2020 Olivia Obenland
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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