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Date of Award

Spring 5-15-2023

Author's School

School of Engineering & Applied Science

Author's Program

Chemical Engineering

Degree Name

Bachelor of Science




The interaction between the plant pathogen Pseudomonas syringae strain PtoDC3000 and one of its hosts, Arabidopsis thaliana, is used as a model to help us better understand bacterial pathogenesis in plants. PtoDC3000 is a Gram-negative bacterium that causes disease in the cruciferous family of plants, which includes A. thaliana as well as many important crop plants such as broccoli, cabbage, and cauliflower. This bacterium enters the leaf tissue through natural openings, such as stomata, and wounds. Once in the extracellular space of the leaf it is able to further multiply by suppressing basal host defense responses using the Type III protein secretion system (T3SS) that delivers virulence proteins directly into host cells. Auxin, including indole-3-acetic acid (IAA), is a class of plant hormones that is important for plant growth and development. Previous research in the Kunkel lab found that PtoDC3000 responds to IAA to promote infection in the plant (Kunkel and Harper, 2018). The mechanism by which PtoDC3000 senses and responds to IAA is unclear, and thus this project aims to identify genes involved in the PtoDC3000 IAA response. Several genes implicated in regulating PtoDC3000 auxin response were identified in a screen for mutants that failed to induce wildtype (wt) levels of PSPTO_4297 (aur1), a gene strongly induced by auxin. One of the genes identified from the screening, amgS, was pursued further because it is predicted to encode a two-component sensor kinase protein important in envelope stress. In-culture gene expression assays were conducted to check if other auxin-responsive genes were misregulated in the mutant background; various auxin-responsive genes, including aur1 and genes involved in regulation of the T3SS, were found to be misregulated in the amgS mutant. The mutant was also found to have a growth defect in-planta and to have delayed expression of the T3SS in-planta. Future investigation will involve characterizing the role of amgS in the envelope stress response in PtoDC3000.


Barbara Kunkel

Additional Advisors

Janie Brennan, Yinjie Tang

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