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POSTERS: Molecular plant-microbe interactions

Characterizing the role Ralstonia solanacearum’s catabolic pathways play in pathogenesis in the xylem & root tomato environment
Corri Hamilton - University of Wisconsin-Madison. April MacIntyre- University of Wisconsin-Madison, Olivia Steidl- University of Wisconsin-Madison, Caitilyn Allen- University of Wisconsin-Madison

The soilborne pathogen Ralstonia solanacearum (Rs) causes bacterial wilt disease by colonizing plant
xylem vessels, triggering wilt and death. Rs affects over 200 species, including tomato. Although xylem sap
has been considered nutrient poor, Rs populations in wilting plants surpass 109 CFU/g of stem and ex vivo
sap from infected plants supports bacterial growth. Previous genomic, transcriptomic, and metabolomic
analyses offered clues about the pathogen’s carbon sources during infection. These datasets suggested Rs
can use dozens of carbon sources at low cell densities, as in soil or very early disease. However, once the
bacterium is established in host xylem, a major regulatory switch limits its available carbon sources to some
present in xylem sap like sucrose, glucose, fructose, and myo-inositol. We tested the hypothesis that Rs
has adapted to use a narrow set of carbon sources abundant in host xylem sap during disease. Using
bacterial mutants lacking specific catabolic pathways, plant virulence assays, and quantitative
metabolomics of xylem sap, we defined the link between xylem sap composition and virulence in the Rs tomato
pathosystem. These studies showed that sucrose is the most important carbon source for the
pathogen when it is growing in tomato stems. Overall, the sugars that were important in xylem colonization
were not needed for successful root colonization and vice versa. The contribution of each carbon source to
Rs fitness aligned with infection stage.