Present addresses: Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, Eng. Bldg. #.4, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan;
Sinorhizobium meliloti CpdR1 is critical for co-ordinating cell cycle progression and the symbiotic chronic infection
Article first published online: 7 JUL 2009
© 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Ltd
Volume 73, Issue 4, pages 586–600, August 2009
How to Cite
Kobayashi, H., De Nisco, N. J., Chien, P., Simmons, L. A. and Walker, G. C. (2009), Sinorhizobium meliloti CpdR1 is critical for co-ordinating cell cycle progression and the symbiotic chronic infection. Molecular Microbiology, 73: 586–600. doi: 10.1111/j.1365-2958.2009.06794.x
- Issue published online: 7 AUG 2009
- Article first published online: 7 JUL 2009
- Accepted 29 June, 2009.
ATP-driven proteolysis plays a major role in regulating the bacterial cell cycle, development and stress responses. In the nitro -fixing symbiosis with host plants, Sinorhizobium meliloti undergoes a profound cellular differentiation, including endoreduplication of the ome. The regulatory mechanisms governing the alterations of the S. meliloti cell cycle in planta are largely unknown. Here, we report the characterization of two cpdR homologues, cpdR1 and cpdR2, of S. meliloti that encode single-domain response regulators. In Caulobacter crescentus, CpdR controls the polar localization of the ClpXP protease, thereby mediating the regulated proteolysis of key protein(s), such as CtrA, involved in cell cycle progression. The S. meliloti cpdR1-null mutant can invade the host cytoplasm, however, the intracellular bacteria are unable to differentiate into bacteroids. We show that S. meliloti CpdR1 has a polar localization pattern and a role in ClpX positioning similar to C. crescentus CpdR, suggesting a conserved function of CpdR proteins among α-proteobacteria. However, in S. meliloti, free-living cells of the cpdR1-null mutant show a striking morphology of irregular coccoids and aberrant DNA replication. Thus, we demonstrate that CpdR1 mediates the co-ordination of cell cycle events, which are critical for both the free-living cell division and the differentiation required for the chronic intracellular infection.