Abstract
BACKGROUND: Chemotaxis to plant compounds is frequently the initial step for the colonization of plants by bacteria. Plant pathogens and plant-associated bacteria contain approximately twice as many chemoreceptors as the bacterial average does, indicating that chemotaxis is particularly important for bacteria-plant interactions. However, information on the corresponding chemoreceptors and their chemoeffectors is limited. RESULTS: We identify the chemoreceptor PacP from the phytopathogen Pectobacterium atrosepticum, which exclusively recognizes phosphorylated C3 compounds at its sCache ligand binding domain, mediating chemoattraction. Using a motif of PacP amino acid residues involved in ligand binding, we identify a chemoreceptor family, termed sCache_PC3, that is specific for phosphorylated C3 compounds. Isothermal titration calorimetry studies reveal that family members preferentially bind glycerol 3-phosphate, a key plant signaling molecule. Family members recognize glycerol 2-phosphate and glycolysis intermediates glyceraldehyde 3-phosphate, dihydroxyacetone phosphate, and 3-phosphoglycerate. This study presents the first evidence of chemoreceptors that bind phosphorylated compounds. We show that the sCache_PC3 family has evolved from an ancestral sCache domain that responds primarily to Krebs cycle intermediates. Members of the sCache_PC3 family are predominantly found in plant-associated bacteria, including many important phytopathogens belonging to the genera Brenneria, Dickeya, Musicola, Pectobacterium, and Herbaspirillum. Consistently, glycerol 3-phosphate is a signal molecule that is excreted by plants in response to stress and infection. CONCLUSIONS: Chemotaxis toward glycerol 3-phosphate may be a means for bacteria to localize stressed plants and move to infection sites. This study lays the groundwork for investigating the role of chemotaxis to phosphorylated C3 compounds in plant-bacteria interactions and virulence.