Multiple Genetic Controls on Rhizobium meliloti syrA, a Regulator of Exopolysaccharide Abundance

Corresponding author: Sharon R. Long, Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, fa.srl{at}forsythe.stanford.edu (E-mail).

Communicating editor: J. CHORY

Exopolysaccharides (EPS) are produced by a wide assortment of bacteria including plant pathogens and rhizobial symbionts. Rhizobium meliloti mutants defective in EPS production fail to invade alfalfa nodules. Production of EPS in R. meliloti is likely controlled at several levels. We have characterized a new gene of this regulatory circuit. syrA was identified by its ability to confer mucoid colony morphology and by its ability to suppress the colonial phenotype of an exoD mutant. Here we show that syrA encodes a 9-kD hydrophobic protein that has sequence similarity to two other EPS regulatory proteins: ExoX of Rhizobium NGR234 and R. meliloti, and Psi of R. leguminosarum bv. phaseoli. The syrA transcription start site lies 522 nucleotides upstream of a non-canonical TTG start codon. The syrA promoter region is similar to the promoter region of the nodulation regulatory protein, nodD3. We found that in free-living bacteria, syrA expression is activated by the regulatory locus, syrM, but not by nodD3. In planta, syrM is not required for expression of syrA. Instead, expression of the nitrogen fixation (nifHDKE) genes upstream of syrA plays a role. Specific and distinct sets of genetic controls may operate at different times during nodule invasion.

This article has been cited by other articles:

				D. H. Keating Sinorhizobium meliloti SyrA Mediates the Transcriptional Regulation of Genes Involved in Lipopolysaccharide Sulfation and Exopolysaccharide Biosynthesis J. Bacteriol., March 15, 2007; 189(6): 2510 - 2520. [Abstract] [Full Text] [PDF]

				C. Bobik, E. Meilhoc, and J. Batut FixJ: a Major Regulator of the Oxygen Limitation Response and Late Symbiotic Functions of Sinorhizobium meliloti J. Bacteriol., July 1, 2006; 188(13): 4890 - 4902. [Abstract] [Full Text] [PDF]

				K. E. Gibson, G. R. Campbell, J. Lloret, and G. C. Walker CbrA Is a Stationary-Phase Regulator of Cell Surface Physiology and Legume Symbiosis in Sinorhizobium meliloti. J. Bacteriol., June 1, 2006; 188(12): 4508 - 4521. [Abstract] [Full Text] [PDF]

				A. N. Bittner and V. Oke Multiple groESL Operons Are Not Key Targets of RpoH1 and RpoH2 in Sinorhizobium meliloti. J. Bacteriol., May 1, 2006; 188(10): 3507 - 3515. [Abstract] [Full Text] [PDF]

				L. Luo, S.-Y. Yao, A. Becker, S. Ruberg, G.-Q. Yu, J.-B. Zhu, and H.-P. Cheng Two New Sinorhizobium meliloti LysR-Type Transcriptional Regulators Required for Nodulation J. Bacteriol., July 1, 2005; 187(13): 4562 - 4572. [Abstract] [Full Text] [PDF]

				M. J. Barnett, C. J. Toman, R. F. Fisher, and S. R. Long A dual-genome Symbiosis Chip for coordinate study of signal exchange and development in a prokaryote-host interaction PNAS, November 23, 2004; 101(47): 16636 - 16641. [Abstract] [Full Text] [PDF]

				P. H. Kaufusi, L. S. Forsberg, P. Tittabutr, and D. Borthakur Regulation of exopolysaccharide synthesis in Rhizobium sp. strain TAL1145 involves an alternative sigma factor gene, rpoH2 Microbiology, October 1, 2004; 150(10): 3473 - 3482. [Abstract] [Full Text] [PDF]

				R. M. Mitra and S. R. Long Plant and Bacterial Symbiotic Mutants Define Three Transcriptionally Distinct Stages in the Development of the Medicago truncatula/Sinorhizobium meliloti Symbiosis Plant Physiology, February 1, 2004; 134(2): 595 - 604. [Abstract] [Full Text] [PDF]

				F. Barloy-Hubler, D. Capela, M. J. Barnett, S. Kalman, N. A. Federspiel, S. R. Long, and F. Galibert High-Resolution Physical Map of the Sinorhizobium meliloti 1021 pSyma Megaplasmid J. Bacteriol., February 15, 2000; 182(4): 1185 - 1189. [Abstract] [Full Text]

				D. J. Gage and S. R. Long alpha -Galactoside Uptake in Rhizobium meliloti: Isolation and Characterization of agpA, a Gene Encoding a Periplasmic Binding Protein Required for Melibiose and Raffinose Utilization J. Bacteriol., November 1, 1998; 180(21): 5739 - 5748. [Abstract] [Full Text]