Insights into the Extracytoplasmic Stress Response of Xanthomonas campestris pv. campestris : Role and Regulation of σ E -Dependent Activity

Author:

Bordes Patricia12,Lavatine Laure12,Phok Kounthéa12,Barriot Roland12,Boulanger Alice34,Castanié-Cornet Marie-Pierre12,Déjean Guillaume34,Lauber Emmanuelle4,Becker Anke5,Arlat Matthieu34,Gutierrez Claude12

Affiliation:

1. Université de Toulouse, UPS, Laboratoire de Microbiologie et Génétique Moléculaires, F-31000 Toulouse, France

2. Centre National de la Recherche Scientifique, LMGM, F-31000 Toulouse, France

3. Université de Toulouse, UPS, F-31000 Toulouse, France

4. Laboratoire des Interactions Plantes Micro-Organismes, UMR CNRS-INRA 2594/441, F-31326 Castanet-Tolosan, France

5. Institute of Biology III, Faculty of Biology, University of Freiburg, D-79104 Freiburg, Germany

Abstract

ABSTRACT Xanthomonas campestris pv. campestris is an epiphytic bacterium that can become a vascular pathogen responsible for black rot disease of crucifers. To adapt gene expression in response to ever-changing habitats, phytopathogenic bacteria have evolved signal transduction regulatory pathways, such as extracytoplasmic function (ECF) σ factors. The alternative sigma factor σ E , encoded by rpoE , is crucial for envelope stress response and plays a role in the pathogenicity of many bacterial species. Here, we combine different approaches to investigate the role and mechanism of σ E -dependent activation in X. campestris pv. campestris . We show that the rpoE gene is organized as a single transcription unit with the anti-σ gene rseA and the protease gene mucD and that rpoE transcription is autoregulated. rseA and mucD transcription is also controlled by a highly conserved σ E -dependent promoter within the σ E gene sequence. The σ E -mediated stress response is required for stationary-phase survival, resistance to cadmium, and adaptation to membrane-perturbing stresses (elevated temperature and ethanol). Using microarray technology, we started to define the σ E regulon of X. campestris pv. campestris . These genes encode proteins belonging to different classes, including periplasmic or membrane proteins, biosynthetic enzymes, classical heat shock proteins, and the heat stress σ factor σ H . The consensus sequence for the predicted σ E -regulated promoter elements is GGAACTN 15-17 GTCNNA. Determination of the rpoH transcription start site revealed that rpoH was directly regulated by σ E under both normal and heat stress conditions. Finally, σ E activity is regulated by the putative regulated intramembrane proteolysis (RIP) proteases RseP and DegS, as previously described in many other bacteria. However, our data suggest that RseP and DegS are not only dedicated to RseA cleavage and that the proteolytic cascade of RseA could involve other proteases.

Publisher

American Society for Microbiology

Subject

Molecular Biology,Microbiology

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