Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Christian Danve M. Castroverde

Advisor Role

Supervisor

Abstract

Studies conducted on the model plant-pathogen system Arabidopsis thaliana-Pseudomonas syringae pv. tomato (Pst) showed that elevated temperature suppresses the pathogen-induced production of salicylic acid (SA), which is a key plant defence hormone. This increased host vulnerability at higher temperatures is due to downregulated expression of CALMODULIN BINDING PROTEIN 60-LIKE G (CBP60g) and SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1), which encode master regulators of SA production. Collectively, these previous studies only focused on one natural accession of Arabidopsis called Columbia-0 (Col-0). However, the intraspecific variation in Arabidopsis immunity phenotypes under elevated temperature remains unknown. To fill this critical knowledge gap, my MSc thesis research focused on evaluating the natural variation in the Arabidopsis immune system by studying different accessions. I have identified temperature-resilient and -sensitive Arabidopsis accessions based on disease resistance to the pathogen Pseudomonas syringae (Pst DC3000). I found that temperature-sensitive or -resilient disease resistance did not correlate with sequence polymorphisms in bHLH059, a recently discovered SA regulator at non-stress temperatures. In agreement, bhlh059 mutants exhibited temperature-sensitive defences at warm temperature, suggesting that bHLH059 does not regulate immune suppression at elevated temperature. To further elucidate temperature-resilient immunity, I measured SA hormone levels in representative accessions and found very low SA levels in both representative temperature-sensitive and temperature-resilient accessions. Finally, I performed gene expression analysis of CBP60g and SARD1, and determined that the different temperature-resilient accessions showed varied gene expression profiles that did not always correspond with their pathogen resilience. Collectively, this thesis described the intraspecific diversity of Arabidopsis immune responses under warm temperatures, which is bHLH059-independent but potentially mediated by CBP60g and SARD1. Uncovering the molecular mechanisms underlying temperature-modulated defence responses will help predict how plants may respond to climate change and provide foundational knowledge on potentially engineering disease-resistant and climate-resilient crops.

Convocation Year

2023

Convocation Season

Fall

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Available for download on Thursday, February 13, 2025

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