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POSTERS: Molecular plant-microbe interactions

A sticky situation: elucidating the role of putative adhesins in Ralstonia solanacearum virulence
Mariama Carter - University of Wisconsin-Madison. Caitilyn Allen- University of Wisconsin-Madison, Madeline Hayes- University of Wisconsin-Madison, Devanshi Khokhani- University of Wisconsin-Madison

Attachment to host surfaces (adhesion) and to fellow cells (cohesion) are critical steps in bacterial pathogenesis. The bacterial wilt pathogen Ralstonia solanacearum (Rs) needs adhesion and cohesion at two distinct points in its life cycle: early in infection, when Rs must attach to root epidermal cells and form microcolonies, and later in infection, when Rs attaches to xylem walls and forms biofilm-like aggregates. Cell surface proteins called adhesins help bacteria stick to diverse surfaces, facilitating interactions with animal and plant hosts. An in planta transcriptomic analysis identified seven putative adhesins differentially expressed in a quorum sensing mutant (?phcA) that is locked in a low cell density (early infection) mode. Three genes were upregulated in the phcA mutant, while four were repressed. We hypothesized that the upregulated adhesins are important for virulence early in infection when Rs is at a low cell density, while the repressed adhesins are needed later in disease when Rs is at a high cell density. Targeted single and poly-mutants lacking the putative early adhesins did not attach to tomato roots as well as wild-type Rs. Consistent with the early-function hypothesis, they did not contribute to Rs virulence beyond this first critical host-pathogen interaction. These results suggest Rs strategically deploys adhesins at specific stages of disease in diverse host environments.