Khan, Sheharyar Ahmed (2025). Arbuscular mycorrhizal fungi-mediated modulation of maize secondary metabolism under drought conditions. (Thesis). Universität Bern, Bern
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Abstract
Climate change results in increased drought frequency and severity which eventually alters functioning of the ecosystem. In my thesis, I studied modulation of the maize secondary metabolism under association with arbuscular mycorrhizal fungi (AMF) when subjected to drought conditions. In the first chapter, I focused on the interactions between drought and AMF Rhizophagus irregularis (SAF22) association on benzoxazinoids (BXDs) modulation and consequences for herbivore feeding by the Spodoptera exigua larvae. We found that BXDs profile was altered both by drought and AMF. Interestingly, the herbivores gain more weight under drought stress, an effect that was minimized in the presence of AMF. In the second chapter, I investigated the role of BXDs in forming symbiotic association with the AMF, through MBOA complementation of bx1 mutant plants. We also investigated the impact of kinetic drought on the colonization efficiency. Intriguingly, MBOA was found to increase the rate of colonization in bx1 mutant plants, while kinetic drought had no impact on the rate of colonization efficiency. The third chapter focused on identifying the UDP-glucosyltransferases (UGTs) responsible for modulation of maize secondary metabolites under drought conditions. The concentrations of DIMBOA-2Glc, DIMBOA-3Glc, and HMBOA-2Glc were increased up to 40-fold in roots under drought stress. Transcriptome mining and phylogenetic analysis identified nine candidate UGTs in the UGT79, UGT91, and UGT94 families, of which two, Zm00001eb330430 (UGT94A1) and Zm00001eb111270 (UGT94A2) were highly expressed under drought. These genes were heterologously expressed in Escherichia coli cells and enzymatic assays demonstrated that both enzymes convert DIMBOA-Glc to DIMBOA-2Glc. The activity of Zm00001eb330430 (UGT94A1) was abolished by site-directed mutagenesis, confirming the functional role of the target residues. Together, these findings illustrate the role of BXDs in signalling, symbiotic associations and plant defences against biotic and abiotic factors, more investigations are needed to develop better strategies to enhance the plant’s ability to cope with various stresses. Furthermore, our findings offer new insights into the chemical adaptation of maize to environmental stress by uncovering key enzymes that were previously uncharacterized in multihexose benzoxazinoid biosynthesis pathway.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 19 August 2025 |
| Subjects: | 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: | 25 Aug 2025 16:16 |
| Last Modified: | 25 Aug 2025 16:16 |
| URI: | https://boristheses.unibe.ch/id/eprint/6620 |
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