Abstract

Bacterial pathogens threaten crop production worldwide, which highlights the need to understand plant and pathogen interactions. Studies on plant-pathogen interactions typically focus on a single host and pathogen. However, bacteria exist in complex microbial communities, not alone. There are few studies that examine the mechanisms behind multi-pathogen infections which renders a gap in our understanding of the subsequent implications on agriculture. In this dissertation, I use in vitro plate assays with RNA-sequencing and in planta assays to investigate the interactions between two cotton bacterial pathogens, Xanthomonas citri pv. malvaearum (Xcm) and Pseudomonas syringae (Ps). In vitro plate assays demonstrate that the bacteria can interact outside their host and that Xcm can prompt directional movement in Ps. RNA-sequencing along with studying genetic mutants revealed that iron-sensing in Ps plays a role in this interaction, and that the movement is independent of typical movement appendages, flagella and Type-4 pili. For in planta interactions, sequential infiltrations and microscopy suggest that both bacteria can colocalize in cotton and that a cotton defense response, once initiated by Xcm first, is effective against Ps. I also explore the presence of genetic resistance to either pathogen in cotton by screening a diversity panel of 253 accessions. This screen revealed that cotton lacks resistance to Ps. Sixty-one accessions showed strong resistance responses to Xcm. This work expands our broad understanding of how bacteria can interact and, more specifically, the interaction dynamics between Ps and Xcm and the potential implications in cotton. Washington

Committee Chair

Rebecca Bart

Committee Members

Barbara Kunkel, Christina Stallings, Blake Meyers, Rachel Penczykowski

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Plant & Microbial Biosciences)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

12-20-2023

Language

English (en)

Author's ORCID

https://orcid.org/0000-0002-6019-5124

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