Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2011
Publication Date: 6/1/2011
Citation: Wang, D., Korban, S.S., Pusey, P.L., Zhao, Y. 2011. Characterization of the RcsC sensor kinase from Erwinia amylovora and other enterobacteria. Phytopathology. 101:710-716. Interpretive Summary: Fire blight, a destructive disease of apple and pear trees, is caused by the bacterium, Erwinia amylovora. One of the main factors allowing this organism to cause fire blight is its production of a mucilaginous substance known as amylovoran. This slimy substance has multiple functions, including the plugging of plant vascular tissues. The present study significantly contributes to our understanding of the genetic regulation and signaling mechanisms in bacterial cells that result in the production of amylovoran. The new information could lead to the development of effective strategies for controlling the fire blight disease.
Technical Abstract: RcsC is a hybrid sensor kinase which contains a sensor domain, a histidine kinase domain and a receiver domain. We have previously demonstrated that, while the Erwinia amylovora rcsC mutant produces more amylovoran than the wild type strain in vitro, the mutant remains avirulent on both immature pear fruits and apple plants. In this study, we have comparatively characterized the Erwinia RcsC and its homologs from various enterobacteria. Results demonstrate that expression of Erwinia rcsC gene suppresses amylovoran production in various amylovoran over-producing wild type (WT) and mutant strains, thus suggesting presence of a net phosphatase activity of Erwinia RcsC. Findings have also demonstrated that rcsC homologs from other enterobacteria could not rescue amylovoran production of the Erwinia rcsC mutant in vitro. However, virulence of the Erwinia rcsC mutant is partially restored by rcsC homologs from Pantoea stewartii, Yersinia pestis, and Salmonella enterica, but not from Escherichia coli on apple shoots. Domain swapping experiments indicated that replacement of the E. coli RcsC sensor domain by those of Erwinia and Yersinia partially restore virulence of the Erwinia rcsC mutant; whereas, chimeric constructs containing the sensor domain of E. coli RcsC could not rescue virulence of the Erwinia rcsC mutant on apple. Interestingly, only chimeric constructs containing the histidine kinase and receiver domain of Erwinia RcsC are fully capable of rescuing amylovoran production. These results suggest that the sensor domain of RcsC may be important in regulating bacterial virulence; whereas, the histidine kinase and receiver domain of RcsC may be responsible for amylovoran production in vitro.