Chemoreceptor family in plant-associated bacteria responds preferentially to the plant signal molecule glycerol 3-phosphate

Plant pathogens and plant-associated bacteria contain about twice as many chemoreceptors as the bacterial average, indicating that chemotaxis is particularly important for bacteria-plant interactions. However, information on the corresponding chemoreceptors is limited. In this study, we identified the chemoreceptor PacP from the phytopathogenPectobacterium atrosepticum, which exclusively recognized C3 phosphorylated compounds at its sCache ligand binding domain, mediating chemoattraction. Using a motif of PacP amino acid residues involved in ligand binding, we identified a chemoreceptor family, termed sCache_PC3, that was specific for C3 phosphorylated compounds. Isothermal titration calorimetry studies revealed that family members preferentially bound glycerol 3-phosphate, a key plant signaling molecule. Additionally, family members recognized 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 respond primarily to Krebs cycle intermediates. Members of the sCache_PC3 family were mainly found in bacteria that interact with plants, including many important plant pathogens such asBrenneria, Dickeya, Musicola, Pectobacterium,andHerbaspirillum. Glycerol 3-phosphate is a signal molecule that is excreted by plants in response to stress and infection. Chemotaxis towards this molecule may thus be a means for bacteria to localize stressed plants and move to infection sites. This study lays the groundwork for investigating the functional importance of chemotaxis to phosphorylated C3 compounds in plant-bacteria interactions and virulence.