Degree

Doctor of Philosophy (PhD)

Department

Biological Sciences

Document Type

Dissertation

Abstract

How plants adapt to salt stress has been a central question in plant biology for decades. Yet we have not been able to fully understand the molecular networks and genetic mechanisms underlying this complex trait. Most of the genetic work on salinity stress has focused on understanding salt stress responses in the leading, yet a salt-sensitive model Arabidopsis thaliana. With the recent availability of genomes for wild-relatives of A. thaliana, we can now investigate how naturally salt adapted plants may have evolved modified or novel molecular networks to adapt to salt stress. Therefore, my research utilizes a comparative approach between A. thaliana and its stress adapted wild relatives to investigate the genomic and evolutionary mechanisms of salt stress adaptation.

The overall goal of the project is to broaden the current understanding on salt stress tolerance mechanisms. To achieve this, I used two extremophyte models, Schrenkiella parvula and Eutrema salsugineum, which are closely related to the salt sensitive model, A. thaliana. As S. parvula is a more recently introduced research model plant, I first investigated the physiological and structural changes in its traits throughout its life cycle in response to salt stress. This provided a series of traits that are likely to play important roles in the extremophilic lifestyle of S. parvula. S. parvula can maintain the relative water content during exposure to salt, sustain or enhance growth, and complete reproduction. Second, I investigated the changes in elemental, metabolic and gene expression profiles of both extremophytes in comparison to A. thaliana. In this work, I found that the difference in Na+ accumulation gave rise to divergent responses in metabolic and transcriptomic profiles, revealing different pre-adaptation strategies in the extremophytes. E. salsugineum showed enrichment of amino acids and sugars at the basal level. Many of these metabolites function as organic osmolytes against osmotic stress and antioxidants against oxidative stress under salinity stress. S. parvula maintained low Na+ accumulation and induced amino acid and sugar abundance to mitigate the adverse effect of excess Na+. A. thaliana accumulated excess Na+ at a much higher level compared to its extremophyte relatives.

In summary, I have assessed the salinity tolerance mechanisms in the extremophytes using comparative ionomics, metabolomics, and transcriptomics. My work adds to the established genomic and transcriptomic work done on S. parvula and E. salsugineum. This will provide a broader view of how S. parvula and E. salsugineum respond to excess Na+ differently from A. thaliana. The findings from this study will further expand the current knowledge on salt-stress tolerance mechanisms we can adapt when designing future crops that show resilient growth during high salinity stress.

Date

11-5-2021

Committee Chair

Dassanayake, Maheshi

Available for download on Wednesday, November 02, 2022

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