|FISHMAN, MAX - Cornell University|
|ZHANG, JOHNSON - Non ARS Employee|
|BRONSTEIN, PHILIP - Food Safety Inspection Service (FSIS)|
Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2017
Publication Date: 12/20/2017
Citation: Fishman, M., Zhang, J., Bronstein, P., Stodghill, P., Filiatrault, M.J. 2017. The Ca2+ induced two-component system, CvsSR regulates the Type III secretion system and the extracytoplasmic function sigma-factor AlgU in Pseudomonas syringae pv. tomato DC3000. Journal of Bacteriology. doi:10.1128/JB.00538-17.
Interpretive Summary: Bacteria must be able to respond and react to the surrounding environment, make use of available resources, and avert or counter host immune responses. Often, these abilities rely on a two-component system (TCS) composed of interacting proteins that modulate gene expression. We identified a unique previously uncharacterized TCS in P. syringae and found that it responds to the presence of calcium, which is a very important signal in the plant’s defense response. It was unknown how P. syringae responds to the presence of calcium. Here we show when the bacteria are grown in the presence of calcium, this TCS regulates expression of factors produced by the bacteria involved in disease. The link to disease makes this protein a potential candidate for disease control. Furthermore, we were able to show this TCS influences the ability of the bacteria to form cell aggregates as well as precipitate calcium. Our data suggests that these newly described functions for this TCS are important during infection and may represent novel targets for controlling disease.
Technical Abstract: Two-component systems (TCSs) of bacteria regulate many different aspects of the bacterial life cycle including pathogenesis. Most TCSs remain uncharacterized with no information about the signal(s) or regulatory targets and/or role in bacterial pathogenesis. Here, we characterize a TCS in the plant-pathogenic bacterium Pseudomonas syringae pv. tomato DC3000 (Pto) that is composed of the histidine kinase, CvsS, and the response regulator, CvsR. CvsSR is necessary for full virulence of Pto on multiple hosts. We discovered that the expression of cvsSR is induced by Ca2+ concentrations found in leaf apoplastic fluid. Thus, Ca2+ can be added to the list of signals that promote pathogenesis of Pto during host colonization. Through chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) and global transcriptome analysis (RNA-seq) we discerned the CvsR regulon. CvsR is a direct activator of the type III secretion system regulators, hrpR and hrpS, that regulates Pto virulence in a type III secretion system dependent manner. CvsR also repressed transcription of the extracytoplasmic sigma factor algU and production of alginate. Phenotypic analysis determined that CvsSR inversely regulated biofilm formation and swarming motility in a Ca2+-dependent manner. Overall, our results show that CvsSR is a key regulatory hub critical for interaction with host plants.