Ogi, Vera (2024). Population Genomics of Benzoxazinoid Resistance in Entomopathogenic Nematodes. (Thesis). Universität Bern, Bern
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Abstract
The increasing global population and the need for enhanced food production present significant challenges to modern agriculture. Traditional methods, such as expanding arable land and extensive use of chemical pesticides, are no longer viable due to biodiversity conservation concerns and the negative impacts of chemicals on ecosystems. This has led to the exploration of alternative pest control strategies, including the use of entomopathogenic nematodes (EPNs). These nematode-bacterium symbiotic complexes can infect and kill insect pests and have been used in agricultural biocontrol for decades. However, their generalist nature limits their effectiveness against specialist pests such as the western corn rootworm (WCR), Diabrotica virgifera virgifera, which sequesters maize-derived benzoxazinoids (BXs) to defend itself from natural enemies, including EPNs. In this thesis, we used Heterorhabditis bacteriophora as an EPN model to explore the evolutionary, ecological, and genomic factors that influence its ability to overcome the plant defense compounds BXs. The thesis first provides a literature review of EPN adaptations to environmental stressors, and highlights the underlying genetic and biochemical mechanisms. Chapter 1 reports a de-novo chromosome-scale assembly and annotation of the H. bacteriophora genome. It reveals the unique genomic features that distinguish EPNs from other nematodes, and provides insights into their unique adaptations for insect parasitism. Annex I further explores the chromosomal structure of H. bacteriophora, uncovering the presence of holocentric chromosomes despite unusual transposable element distribution. Chapter 2 focusses on the interaction between H. bacteriophora and its bacterial symbiont Photorhabdus, examining the genomic and phylogenetic differences between susceptible and resistant EPN isolates exposed to BXs. Population genomics revealed regions of the EPN genome associated with BX resistance. Chapter 3 presents a large-scale experimental evolution study where EPN isolates were exposed to BX-sequestering WCR larvae. The results showed a rapid evolution of BX resistance in previously susceptible isolates, and identified key genetic loci associated with this resistance. This work advances the understanding of EPNs as biocontrol agents, providing novel insights into their genomic architecture and their potential for overcoming plant chemical defenses. These findings offer valuable avenues for improving the precision and efficacy of EPNs in agricultural pest management.
| Item Type: | Thesis |
|---|---|
| Dissertation Type: | Cumulative |
| Date of Defense: | 19 December 2024 |
| Subjects: | 500 Science > 570 Life sciences; biology 500 Science > 580 Plants (Botany) |
| Institute / Center: | 08 Faculty of Science > Department of Biology > Institute of Plant Sciences (IPS) |
| Depositing User: | Hammer Igor |
| Date Deposited: | 21 Feb 2025 13:48 |
| Last Modified: | 21 Feb 2025 17:09 |
| URI: | https://boristheses.unibe.ch/id/eprint/5846 |
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