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Journal of Bacteriology, July 2009, p. 4372-4382, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.00376-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Role of Quorum Sensing in Sinorhizobium meliloti-Alfalfa Symbiosis{triangledown} ,{dagger}

Nataliya Gurich and Juan E. González*

Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75080-0688

Received 18 March 2009/ Accepted 17 April 2009

The ExpR/Sin quorum-sensing system of the gram-negative soil bacterium Sinorhizobium meliloti plays an important role in the establishment of symbiosis with its host plant Medicago sativa. A mutant unable to produce autoinducer signal molecules (sinI) is deficient in its ability to invade the host, but paradoxically, a strain lacking the quorum-sensing transcriptional regulator ExpR is as efficient as the wild type. We compared the whole-genome expression profile of the wild-type strain with strains missing one of the quorum-sensing regulatory components to identify genes controlled by the ExpR/Sin system throughout the different phases of the bacterial growth cycle, as well as in planta. Our analyses revealed that ExpR is a highly versatile regulator with a unique ability to show different regulatory capabilities in the presence or absence of an autoinducer. In addition, this study provided us with insight into the plant invasion defect displayed by the autoinducer mutant. We also discovered that the ExpR/Sin quorum-sensing system is repressed after plant invasion. Therefore, quorum sensing plays a crucial role in the regulation of many cell functions that ensures the successful invasion of the host and is inactivated once symbiosis is established.

* Corresponding author. Mailing address: RL11, Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, TX 75080-0688. Phone: (972) 883-2526. Fax: (972) 883-2409. E-mail: jgonzal{at}utdallas.edu

{triangledown} Published ahead of print on 24 April 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, July 2009, p. 4372-4382, Vol. 191, No. 13
0021-9193/09/$08.00+0     doi:10.1128/JB.00376-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Chen, E. J., Fisher, R. F., Perovich, V. M., Sabio, E. A., Long, S. R. (2009). Identification of Direct Transcriptional Target Genes of ExoS/ChvI Two-Component Signaling in Sinorhizobium meliloti. J. Bacteriol. 191: 6833-6842 [Abstract] [Full Text]  
  • Morris, J., Gonzalez, J. E. (2009). The Novel Genes emmABC Are Associated with Exopolysaccharide Production, Motility, Stress Adaptation, and Symbiosis in Sinorhizobium meliloti. J. Bacteriol. 191: 5890-5900 [Abstract] [Full Text]  


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