Honors College Thesis
 

Regulation of the Pantoea agglomerans type III secretion system by plant-exuded sugars

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https://ir.library.oregonstate.edu/concern/honors_college_theses/05742114h

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  • Pantoea agglomerans pathovar betae (Pab) is a bacterium that causes galls on the roots of beet plants, resulting in reduced marketability of beet roots and crop loss. Pab uses a type III secretion system (T3SS) to infect and cause galls on beets. The T3SS is a molecular syringe-like structure that injects proteins, termed “effectors” into plant cells. Once inside the cells, effectors target and suppress the plant’s immune signaling pathways, allowing the pathogen to avoid the host immune response. How Pab regulates the deployment of its T3SS during the infection process is poorly understood. For other T3SS-containing plant pathogens, plant-derived metabolites act as signals that induce transcription of genes encoding for T3SS regulatory proteins. In this study, we identified metabolites exuded from beet seedlings using gas chromatography-mass spectrometry (GC-MS). Among these metabolites, we identified several plant-exuded sugars. We then tested if the T3SS regulatory genes hrpXY, hrpS, and hrpL are induced by these sugars, as well as by several sugars not found in beet exudate. We found that hrpXY and hrpL were both strongly induced in response to each of the sugars we tested, regardless of whether the sugar was found in beet exudate or not. In contrast, hrpS expression was not strongly induced in response to any sugars tested. We also found that the growth of Pab was induced by the same sugars, and that the amount of growth and hrp transcription were positively correlated. The close correlation between sugar induced T3SS induction and growth suggests a potential link between rates of sugar catabolism or sugar uptake in determining the relative response of Pab to the various sugars tested.
  • Keywords: Type III Secretion System, Pantoea agglomerans, virulence, chemical signaling, gene expression, hypersensitive response and pathogenicity cluster, transcriptional reporter assay
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  • The research conducted in the completion of this thesis was partially funded by the Oregon State Agricultural Research Foundation for Continuing Researcher support.
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