Functional characterization of the methyl-accepting chemotaxis proteins RS10830 and RS10815 in Xanthomonas oryzae pv. oryzicola.

Xanthomonas oryzae pv. oryzicola (Xoc) causes the economically important leaf streak disease in rice. Chemotaxis plays a role in the entry and colonization of some phytopathogens within the host. However, the physiological function and ligand specificity of Xoc methyl-accepting chemotaxis proteins (MCPs) are not well defined. In this study, we show that the transmembrane MCP ACU12_RS10830 (RS10830) binds L-malic acid and L-tartaric acid, whereas the transmembrane MCP ACU12_RS10815 (RS10815) binds ethanolamine, methylamine, ethylamine, ethylenediamine, amylamine, and tyramine, to elicit attractant responses. The chemotactic responses mediated by the sensory domains of RS10830 and RS10815 were also observed for the chimeric receptors in Escherichia coli. Furthermore, the RS10830 and RS10815-mediated positive chemotaxis of Xoc RS105 correlated with the promoting effects of their ligands on bacterial growth and virulence in rice. To the best of our knowledge, this is the first report on the function of Xoc MCPs in virulence and signaling molecules of the Xoc chemotaxis system. RS10830 is the first L-tartaric acid-binding MCP reported in bacteria.