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SPECIAL SESSION: Pathogen Adaptation to the Plant Vascular System

Metabolic requirements for colonization of the tomato xylem niche.
Tiffany Lowe-Power - UC Berkeley.

The xylem is classically considered to be nutrient-poor, and yet plant pathogenic Ralstonia can grow to high cell density in this niche, reaching over 1010 CFU per gram tomato stem. To investigate Ralstonia’s metabolic adaptations to growth in the xylem, we developed an ex vivo xylem sap model. Initial experiments revealed that filter-sterilized xylem sap from Ralstonia-infected tomato plants supported the bacteria’s growth better than sap from healthy plants, suggesting that sap is enriched in nutrients during disease. Using an untargeted extracellular metabolomic (“exometabolomic”) approach, we found that wilt disease changes the chemical composition of xylem sap by enriching it in dozens of metabolites including eight metabolites that support Ralstonia’s growth as a sole carbon or nitrogen source. To identify which nutrients are preferentially consumed by Ralstonia during growth in xylem sap, we analyzed the exometabolome of filter-sterilized sap after a 3 hr incubation with Ralstonia or an equal volume of water. This revealed that Ralstonia preferentially consumed glucose, gluconate, 3-hydroxybutyrate, and proline. To functionally test which of these metabolites supports Ralstonia’s growth in intact tomato xylem and ex vivo xylem sap, we are adapting a barcoded transposon-site sequencing approach to Ralstonia.