Ching-Hong Yang,2 and
1State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193; 2Department of Biological Sciences, University of Wisconsin–Milwaukee, 53211, U.S.A.
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Accepted 8 June 2012.
Two-component systems (TCS) consisting of histidine kinases (HK) and response regulators (RR) play essential roles in bacteria to sense environmental signals and regulate cell functions. One type of RR is involved in metabolism of cyclic diguanylate (c-di-GMP), a ubiquitous bacterial second messenger. Although genomic studies predicted a large number of them existing in different bacteria, only a few have been studied. In this work, we characterized a novel TCS consisting of PdeK(PXO_01018)/PdeR(PXO_ 01019) from Xanthomonas oryzae pv. oryzae, which causes the bacterial leaf blight of rice. PdeR (containing GGDEF, EAL, and REC domains) was shown to have phosphodiesterase (PDE) activity in vitro by colorimetric assays and high-performance liquid chromatography analysis. The PDE activity of full-length PdeR needs to be triggered by HK PdeK. Deletion of pdeK or pdeR in X. oryzae pv. oryzae PXO99A had attenuated its virulence on rice. ΔpdeK and ΔpdeR secreted less exopolysaccharide than the wild type but there were no changes in terms of motility or extracellular cellulase activity, suggesting the activity of PdeK/PdeR might be specific.
© 2012 The American Phytopathological Society