This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dupont, L. Articles by Le Rudulier, D. Search for Related Content PubMed PubMed Citation Articles by Dupont, L. Articles by Le Rudulier, D.

The Sinorhizobium meliloti ABC Transporter Cho Is Highly Specific for Choline and Expressed in Bacteroids from Medicago sativa Nodules

Unité Interactions Plantes-Microorganismes et Santé Végétale, UMR6192 CNRS-INRA-Université de Nice Sophia Antipolis, Centre INRA Agrobiotech, Sophia Antipolis, France

Received 2 April 2004/ Accepted 9 June 2004

In Sinorhizobium meliloti, choline is the direct precursor of phosphatidylcholine, a major lipid membrane component in the Rhizobiaceae family, and glycine betaine, an important osmoprotectant. Moreover, choline is an efficient energy source which supports growth. Using a PCR strategy, we identified three chromosomal genes (choXWV) which encode components of an ABC transporter: ChoX (binding protein), ChoW (permease), and ChoV (ATPase). Whereas the best homology scores were obtained with components of betaine ProU-like systems, Cho is not involved in betaine transport. Site-directed mutagenesis of choX strongly reduced (60 to 75%) the choline uptake activity, and purification of ChoX, together with analysis of the ligand-binding specificity, showed that ChoX binds choline with a high affinity (K_D, 2.7 µM) and acetylcholine with a low affinity (K_D, 145 µM) but binds none of the betaines. Uptake competition experiments also revealed that ectoine, various betaines, and choline derivatives were not effective competitors for Cho-mediated choline transport. Thus, Cho is a highly specific high-affinity choline transporter. Choline transport activity and ChoX expression were induced by choline but not by salt stress. Western blotting experiments with antibodies raised against ChoX demonstrated the presence of ChoX in bacteroids isolated from nitrogen-fixing nodules obtained from Medicago sativa roots. The choX mutation did not have an effect on growth under standard conditions, and neither Nod nor Fix phenotypes were impaired in the mutant, suggesting that the remaining choline uptake system(s) still present in the mutant strain can compensate for the lack of Cho transporter.

This article has been cited by other articles:

• Chen, C., Beattie, G. A. (2007). Characterization of the Osmoprotectant Transporter OpuC from Pseudomonas syringae and Demonstration that Cystathionine-{beta}-Synthase Domains Are Required for Its Osmoregulatory Function. J. Bacteriol. 189: 6901-6912 [Abstract] [Full Text]  
• Mauchline, T. H., Fowler, J. E., East, A. K., Sartor, A. L., Zaheer, R., Hosie, A. H. F., Poole, P. S., Finan, T. M. (2006). Mapping the Sinorhizobium meliloti 1021 solute-binding protein-dependent transportome. Proc. Natl. Acad. Sci. USA 103: 17933-17938 [Abstract] [Full Text]  
• Alloing, G., Travers, I., Sagot, B., Le Rudulier, D., Dupont, L. (2006). Proline Betaine Uptake in Sinorhizobium meliloti: Characterization of Prb, an Opp-Like ABC Transporter Regulated by both Proline Betaine and Salinity Stress.. J. Bacteriol. 188: 6308-6317 [Abstract] [Full Text]  
• Fox, M. A., White, J. P., Hosie, A. H. F., Lodwig, E. M., Poole, P. S. (2006). Osmotic Upshift Transiently Inhibits Uptake via ABC Transporters in Gram-Negative Bacteria.. J. Bacteriol. 188: 5304-5307 [Abstract] [Full Text]  
• Sugiyama, A., Shitan, N., Sato, S., Nakamura, Y., Tabata, S., Yazaki, K. (2006). Genome-wide analysis of ATP-binding cassette (ABC) proteins in a model legume plant, Lotus japonicus: comparison with Arabidopsis ABC protein family. DNA Res 13: 205-228 [Abstract] [Full Text]  
• Terasaka, K., Blakeslee, J. J., Titapiwatanakun, B., Peer, W. A., Bandyopadhyay, A., Makam, S. N., Lee, O. R., Richards, E. L., Murphy, A. S., Sato, F., Yazaki, K. (2005). PGP4, an ATP Binding Cassette P-Glycoprotein, Catalyzes Auxin Transport in Arabidopsis thaliana Roots. Plant Cell 17: 2922-2939 [Abstract] [Full Text]