Degree

Doctor of Philosophy (PhD)

Department

Department of Biological Sciences

Document Type

Dissertation

Abstract

Schrenkiella parvula is an extremophyte model closely related to Arabidopsis thaliana and Brassica crops. Its natural habitat includes shores of saline lakes in the Irano-Turanian region. It has adapted to grow in soils rich in multiple salts including Na+ and K+. I have investigated the genetic basis for high K+ tolerance in plants using S. parvula as a stress tolerant model compared to the premier plant model, Arabidopsis thaliana which is highly sensitive to salt stresses using physiological, ionomic, transcriptomic, and metabolomic approaches. Under high K+ stress, root system architecture changes significantly compared to control conditions, and the growth perturbation in A. thaliana is more pronounced than the effect observed for S. parvula. Notably, A. thaliana was unable to maintain the macro and micro-nutrient homeostasis while S. parvula remained unaffected despite the increased accumulation of K+ in its tissues. I identified metabolites and their associated pathways that responded to high K+ stress and deduced metabolic pathways that were differently regulated in the two models. Using methods in comparative transcriptomics, I identified corresponding genetic pathways associated with the highly affected metabolic pathways during high K+ stress. The S. parvula transcriptome showed a more targeted and refined response to high K+ stress by adjusting only a few genes in selected pathways, whereas A. thaliana showed signatures of transcriptional mismanagement with sweeping changes involving all major hormone response pathways. S. parvula was able to maintain primary metabolite pools critical to mount defenses against oxidative and osmotic stresses through transcriptional coordination of nitrogen uptake and assimilation coupled to photosynthesis. However, in A. thaliana, excess K+ stress induced nitrogen starvation and A. thaliana was unable to transcriptionally decouple decreased K-uptake from decreased N-uptake leading to depletion of antioxidants and osmoprotectants and the subsequent activation of autophagy pathway.

Date

7-17-2021

Committee Chair

Dassanayake, Maheshi

Available for download on Tuesday, July 12, 2022

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