Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2011
Publication Date: 10/1/2011
Citation: Swingle, B.M., Markel, E.J., Maciak, C.L., Butcher, B., Myers, C., Stodghill, P., Cartinhour, S.W., Bao, Z. 2011. An ECF sigma factor mediated cell surface signaling system in Pseudomonas syringae pv. tomato DC3000 regulates gene expression in response to heterologous siderophores. Journal of Bacteriology. 193:5775-5783. Interpretive Summary: Bacteria that cause disease in plants need to sense their environments and change the way that genes are expressed in order to survive. These types of sensory systems are a very important part of how bacteria cause disease. In this report, we describe results of our study of one sensory system that was found by looking at the genome sequence of Pseudomonas syringae, an important pathogen of tomatoes. We found genes that were regulated by this system and identified several compounds that turn on this system. There are several features of the way that this system works that may be useful for understanding how bacterial pathogens respond to changes in their environment.
Technical Abstract: The diversity of regulatory systems encoded by bacteria provides an indication of the variety of stresses and interactions that these organisms encounter in nature. We have been investigating how the plant pathogen, Pseudomonas syringae pv. tomato DC3000, responds to iron limitation and have focused on the role of the iron starvation (IS) sigma factors to identify regulon members and to learn about the mechanistic details of genetic control for this class of regulators. In this report, we used chromatin immunoprecipitation paired with high throughput sequencing (ChIP-seq) as a method to screen the genome for locations associated with binding of the P. syringae IS sigma factor PSPTO_1203. We then used multiple methods to demonstrate differential regulation of two genes identified in the ChIP-seq screen and characterized the promoter elements that facilitate PSPTO_1203 dependent regulation. Additionally, we identified siderophores that induce the activity of PSPTO_1203 and used this information to characterize the functional components of the signal transduction cascade. These data suggest that this sigma factor is active in its default state, and can be deactivated by the associated TonB-dependent transducer (via the sigma regulator) in the absence of the inducing signal and imply that there is a novel type feedback regulating sigma factor activity.