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

Professor

Abstract

An optimal microbiome is important for plant health and can prime subsequent plant immune responses to enhance stress resilience. However, the molecular mechanisms that dynamically drive host-microbiome interactions and subsequent induced systemic resistance (ISR) responses in plants under elevated environmental temperatures remain underexplored. To address this major knowledge gap, this thesis further investigated Canadian soil-inhabiting rhizobacteria that had been previously shown to activate ISR in tomato (Solanum lycopersicum) plants. Specifically, this study characterized the in vitro physiology of these rhizobacterial strains under different temperatures, including growth, phosphate solubilization abilities and direct anti- pathogenic capabilities. Temperature-sensitivity of these parameters were largely species- dependent, with an observed distinction between Bacillus and Pseudomonas proliferation in various rhizosphere fractions. In situ, bacterial proliferation of a Gram-positive Bacillus velezensis strain and Gram-negative Pseudomonas defensor WCS374 was monitored in the rhizosphere and on the rhizoplane of tomato plants at two temperatures. It was determined that the rhizobacterial competency and the host plant’s epiphytic recruitment of microbes were species-dependent, and not significantly influenced by the temperature changes within the experimental parameters. Finally, gene expression analyses by RT-qPCR revealed that Bacillus and Pseudomonas did not significantly influence the expression of defence hormone-related gene expression in the tomato phyllosphere (i.e., aboveground parts of the plant). Overall, this thesis demonstrates the effect of temperature on plant interactions with, and responses to, rhizosphere microbiota. This research lays the foundation for future investigations of these experimental ISR- inducing rhizobacterial strains and is vital to potentially advance the development of microbiome-based technologies facing global warming.

Convocation Year

2023

Convocation Season

Fall

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Available for download on Wednesday, February 05, 2025

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