The regulatory protein MucR binds to a short DNA region located upstream of the muc R coding region in Rhizobium meliloti

Bertram-Drogatz, P. A.; Rüberg, Silvia; Becker, Anke; Pühler, Alfred

doi:10.1007/s004380050448

Cited by 33 publications

(25 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In both Rm1021 and the expR101 strain, increasing the phosphate concentration decreases EPS II production to very low levels. Merely increasing the osmolarity of the medium has been previously shown (10) to have no significant effect on either the amount of succinoglycan produced or the expression of the exo genes. EPS II production cannot be detected in Rm1021 when the phosphate level is raised to 2 mM and in the expR101 background when the phosphate level is raised to 100 mM.…”

Section: Discussionmentioning

confidence: 99%

“…Due to its position between the two oppositely transcribed arms of the exo operon, the exoX-exoY intergenic region has been suggested to be a logical site for transcriptional regulation of the exo operon. Recent work has demonstrated that the exoX-exoY intergenic region may have sites for binding of the MucR protein, a positive regulator of succinoglycan production (10).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Environmental Regulation of Exopolysaccharide Production in Sinorhizobium meliloti

2000

View full text Add to dashboard Cite

Exopolysaccharide production by Sinorhizobium meliloti is required for invasion of root nodules on alfalfa and successful establishment of a nitrogen-fixing symbiosis between the two partners. S. meliloti wild-type strain Rm1021 requires production of either succinoglycan, a polymer of repeating octasaccharide subunits, or EPS II, an exopolysaccharide of repeating dimer subunits. The reason for the production of two functional exopolysaccharides is not clear. Earlier reports suggested that low-phosphate conditions stimulate the production of EPS II in Rm1021. We found that phosphate concentrations determine which exopolysaccharide is produced by S. meliloti. The low-phosphate conditions normally found in the soil (1 to 10 M) stimulate EPS II production, while the high-phosphate conditions inside the nodule (20 to 100 mM) block EPS II synthesis and induce the production of succinoglycan. Interestingly, the EPS II produced by S. meliloti in low-phosphate conditions does not allow the invasion of alfalfa nodules. We propose that this invasion phenotype is due to the lack of the active molecular weight fraction of EPS II required for nodule invasion. An analysis of the function of PhoB in this differential exopolysaccharide production is presented.The soil bacterium Sinorhizobium meliloti (Rhizobium meliloti) fixes nitrogen in symbiotic association with the leguminous plant Medicago sativa (alfalfa). Molecular analyses have revealed that early steps in the establishment of this symbiosis, including attraction of the bacteria to the plant and formation of the plant nodule, depend upon an exchange of small signaling molecules between the two partners (12, 27, 28). Bacterial invasion of root nodules requires exopolysaccharide production by S. meliloti (25), although the function of these exopolysaccharides in invasion is not yet clear.S. meliloti wild-type strain Rm1021 produces succinoglycan (26), a well-characterized exopolysaccharide polymer of repeating octasaccharide subunits. Each subunit consists of one galactose and seven glucose residues and is decorated with a succinyl, an acetyl, and a pyruvyl modification (2, 36, 37). Mutants of Rm1021 that fail to synthesize succinoglycan (exo mutants) form empty nodules that are devoid of bacteria and are unable to fix nitrogen (24,25). A 25-kb cluster of exo genes has been identified on the second symbiotic megaplasmid (8,9,16,17,24,35) that is required for the production of succinoglycan (14,22,25), and biosynthetic roles have been assigned to most of the gene products (38). A tetramer fraction of succinoglycan was originally assigned as the active species in nodule invasion (7, 43), but recent evidence suggests that the active fraction is a trimer of the octasaccharide subunit (19).Rm1021 also has the capacity to make a second distinct exopolysaccharide, designated EPS II (15), which is a polymer of repeating disaccharide subunits. Subunits of EPS II consist of an acetylated glucose connected to a pyruvylated galactose residue (15, 21). A 32-kb cluster of exp genes (di...

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Environmental Regulation of Exopolysaccharide Production in Sinorhizobium meliloti

2000

View full text Add to dashboard Cite

show abstract

“…Cy3-labeled DNA fragments I, Ia, II, III, or IIIa (Table 1) in various concentrations were mixed with purified (His) 6 ExpG (0.125 lg/ll) in a reaction buffer containing 50 mM Tris-HCl, pH 8.0, 100 mM NaCl, 0.1 mM MgSO 4 , 5% glycerol, 0.05 mg/ml sonicated hering testes DNA and 0.5 mg/ml bovine serum albumin and were subjected to EMSAs (Bertram-Drogatz et al, 1997;Bertram-Drogatz et al, 1998). In competition assays, protein was added to Cy3-labeled DNA fragments in the presence of various concentrations of competitor DNA fragments.…”

Section: Emsa Analysismentioning

confidence: 99%

Specific binding of the regulatory protein ExpG to promoter regions of the galactoglucan biosynthesis gene cluster of Sinorhizobium meliloti - a combined molecular biology and force spectroscopy investigation

Bartels

Baumgarth

Anselmetti

et al. 2003

Journal of Structural Biology

View full text Add to dashboard Cite

Specific protein-DNA interaction is fundamental for all aspects of gene transcription. We focus on a regulatory DNA-binding protein in the Gram-negative soil bacterium Sinorhizobium meliloti 2011, which is capable of fixing molecular nitrogen in a symbiotic interaction with alfalfa plants. The ExpG protein plays a central role in regulation of the biosynthesis of the exopolysaccharide galactoglucan, which promotes the establishment of symbiosis. ExpG is a transcriptional activator of exp gene expression. We investigated the molecular mechanism of binding of ExpG to three associated target sequences in the exp gene cluster with standard biochemical methods and single molecule force spectroscopy based on the atomic force microscope (AFM). Binding of ExpG to expA1, expG-expD1, and expE1 promoter fragments in a sequence specific manner was demonstrated, and a 28 bp conserved region was found. AFM force spectroscopy experiments confirmed the specific binding of ExpG to the promoter regions, with unbinding forces ranging from 50 to 165 pN in a logarithmic dependence from the loading rates of 70-79 000 pN/s. Two different regimes of loading rate-dependent behaviour were identified. Thermal off-rates in the range of k off ¼ ð1:2 AE 1:0Þ Â 10 À3 s À1 were derived from the lower loading rate regime for all promoter regions. In the upper loading rate regime, however, these fragments exhibited distinct differences which are attributed to the molecular binding mechanism.

show abstract

“…Expression of expE, expA, and expD is required for the structural biosynthesis of EPS II, while expG-expC encodes both a transcriptional regulator, ExpG, and a glycosyl transferase, ExpC (4,48). In the absence of quorum sensing, MucR, a homolog of the Agrobacterium tumefaciens RosR, represses EPS II biosynthesis through direct interactions with the promoter regions of expE, expA, and expD via its zinc finger DNAbinding domain (10,36,56). However, an intact ExpR/Sin quorum-sensing system significantly increases expression of the entire exp gene family, allowing for the production of EPS II in both high-molecular-weight (HMW) and low-molecularweight (LMW) fractions (24,34).…”

mentioning

confidence: 99%

Complex Regulation of Symbiotic Functions Is Coordinated by MucR and Quorum Sensing in Sinorhizobium meliloti

Mueller

Gonzalez

2011

J Bacteriol

View full text Add to dashboard Cite

In Sinorhizobium meliloti, the production of exopolysaccharides such as succinoglycan and exopolysaccharide II (EPS II) enables the bacterium to invade root nodules on Medicago sativa and establish a nitrogen-fixing symbiosis. While extensive research has focused on succinoglycan, less is known concerning the regulation of EPS II or the mechanism by which it mediates entrance into the host plant. Previously, we reported that the ExpR/Sin quorum-sensing system is required to produce the symbiotically active low-molecular-weight fraction of this exopolysaccharide. Here, we show that this system induces EPS II production by increasing expression of the expG-expC operon, encoding both a transcriptional regulator (ExpG) and a glycosyl transferase (ExpC). ExpG derepresses EPS II production at the transcriptional level from MucR, a RosR homolog, while concurrently elevating expression of expC, resulting in the synthesis of the low-molecular-weight form. While the ExpR/Sin system abolishes the role of MucR on EPS II production, it preserves a multitude of other quorumsensing-independent regulatory functions which promote the establishment of symbiosis. In planktonic S. meliloti, MucR properly coordinates a diverse set of bacterial behaviors by repressing a variety of genes intended for expression during symbiosis and enhancing the bacterial ability to induce root nodule formation. Quorum sensing precisely modulates the functions of MucR to take advantage of both the production of symbiotically active EPS II as well as the proper coordination of bacterial behavior required to promote symbiosis.

show abstract

The regulatory protein MucR binds to a short DNA region located upstream of the muc R coding region in Rhizobium meliloti

Cited by 33 publications

References 51 publications

Environmental Regulation of Exopolysaccharide Production in Sinorhizobium meliloti

Environmental Regulation of Exopolysaccharide Production in Sinorhizobium meliloti

Specific binding of the regulatory protein ExpG to promoter regions of the galactoglucan biosynthesis gene cluster of Sinorhizobium meliloti - a combined molecular biology and force spectroscopy investigation

Complex Regulation of Symbiotic Functions Is Coordinated by MucR and Quorum Sensing in Sinorhizobium meliloti

Contact Info

Product

Resources

About