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Understanding pathogenic success by identifying Ralstonia solanacearum’s in planta nutrient sources

Corri Hamilton: University of Wisconsin-Madison

<div>The soilborne pathogen <em>Ralstonia solanacearum (Rs) </em>causes bacterial wilt by colonizing plant xylem, causing plants to wilt and die. <em>Rs</em> reduces crop yields at every level of production from small- to large-scale farming operations. Although the xylem environment has been historically characterized as nutrient poor, xylem sap must contain food sources because <em>Rs</em> populations in wilting plants exceed 10<sup>9 </sup>CFU/g stem in tomato. Our group’s previous genomic, <em>in planta</em> transcriptomic, and xylem sap metabolomic genomic data sets offer clues about the pathogen’s carbon source utilization during disease. This work suggests that sucrose, trehalose, galactose, glucose, gluconate, and myo-inositol could fuel <em>Rs</em> growth <em>in planta</em>. However, we do not know which specific xylem sap carbon sources the pathogen uses. To identify these carbon sources, we measured virulence and competitive fitness of a suite of bacterial mutants lacking catabolic and transport genes for sucrose (<em>scrA</em>), trehalose (<em>treA</em>), galactose (Rsc2755), glucose (<em>glk</em>), gluconate (<em>gntK</em>), and myo-inositol (<em>iolG</em>). Additionally, it was previously found that <em>Rs </em>grows better in sap from infected plants, which suggested that the <em>Rs </em>manipulates host xylem carbon source content. To test the hypothesis that wilt-resistant plants withhold carbon sources from <em>Rs</em>, we compared the metabolomic profiles of xylem sap from susceptible and resistant tomato plants.</div>