Molecular Genetics of the Glutamine Synthetases in Rhizobium Species

Espı́n, Guadalupe; Moreno, Soledad; Guzmán, Josefina

doi:10.3109/10408419409113551

Cited by 17 publications

(13 citation statements)

References 31 publications

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“…Since glnII (GSII) is switched off in the root nodule, GSI is probably the only glutamine synthetase present in bacteroids (Shatters et al, 1989 ;Patriarca et al, 1992 ;Amar et al, 1994 ;Espin et al, 1994). Therefore, one could hypothesize that GlnD could play a role in the regulation pathway leading to GSI adenylylation, i.e.…”

Section: Expression Of Glnd Under Free-living and Symbiotic Conditionsmentioning

confidence: 99%

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The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation

et al. 2000

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A Rhizobium leguminosarum bv. viciae VF39 gene (glnD) encoding the uridylyltransferase/uridylyl-removing enzyme, which constitutes the sensory component of the nitrogen regulation (ntr) system, was identified, cloned and characterized. The deduced amino acid sequence contains the conserved active site motif of the nucleotidyltransferase superfamily and is highly homologous to the glnD gene products of other bacterial species. Downstream of the VF39 glnD resides an open reading frame with similarity to the Salmonella typhimurium virulence factor gene mviN. Mutation of the glnD gene abolished the ability to use nitrate as a sole nitrogen source but not glutamine. In addition, neither uridylylation of P II nor induction of the ntr-regulated glnII gene (encoding glutamine synthetase II) under ammonium deficiency could be observed in mutant strains. This strongly suggests that glnD mutants harbour a permanently deuridylylated P II protein and as a consequence are unable to activate transcription from NtrC-dependent promoters. The glnD gene itself is expressed constitutively, irrespective of the nitrogen content of the medium. A functional GlnD protein is not essential for nitrogen fixation in R. leguminosarum bv. viciae, but in situ detection of glnD expression in the symbiotic and infection zone of the root nodule and quantitative measurements suggest that at least part of the ntr system functions in symbiosis. The results also indicate that the N-terminal part of GlnD is essential for the cell, as deletions in the 5'-region of the gene appear to be lethal and mutations possibly affecting the expression of the first half of the protein have a significant effect on the vitality of the mutant strain.

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Section: Expression Of Glnd Under Free-living and Symbiotic Conditionsmentioning

confidence: 99%

“…R. leguminosarum possesses three GSs encoded by glnA (GSI), glnII (GSII) and glnT (GSIII) (Espin et al, 1994). GSI is homologous to GS from enteric bacteria and its enzymic activity is regulated by reversible adenylylation\deadenylylation (Filser et al, 1986 ;Colonna-Romano et al, 1987 ;Bravo & Mora, 1988).…”

Section: Introductionmentioning

confidence: 99%

The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation

et al. 2000

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“…Very low levels of GS activity are found in isolated N 2 -fixing SBs, and genetic manipulation indicates that none of the GS isozymes is necessary for effective symbiosis (37,54,116,192). However, a glnA glnII double mutant of S. meliloti induces normal invaded nodules (37), and GSIII activity was detected (162).…”

Section: Assimilationmentioning

confidence: 99%

“…As shown below, assimilatory GDH appears to be absent in rhizobia, while there are two GS isozymes, GSI and GSII. In some species a third GS has been identified (30,53,54,162), which in free-living rhizobia is expressed only under special conditions. Why rhizobia express more than one GS isozyme remains an unresolved question.…”

Section: Assimilationmentioning

confidence: 99%

Key Role of Bacterial NH ₄ ⁺ Metabolism in Rhizobium-Plant Symbiosis

Patriarca

Tatè

Iaccarino

2002

Microbiol Mol Biol Rev

159

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Symbiotic nitrogen fixation is carried out in specialized organs, the nodules, whose formation is induced on leguminous host plants by bacteria belonging to the family Rhizobiaceae. Nodule development is a complex multistep process, which requires continued interaction between the two partners and thus the exchange of different signals and metabolites. NH4+ is not only the primary product but also the main regulator of the symbiosis: either as ammonium and after conversion into organic compounds, it regulates most stages of the interaction, from the production of nodule inducers to the growth, function, and maintenance of nodules. This review examines the adaptation of bacterial NH4+ metabolism to the variable environment generated by the plant, which actively controls and restricts bacterial growth by affecting oxygen and nutrient availability, thereby allowing a proficient interaction and at the same time preventing parasitic invasion. We describe the regulatory circuitry responsible for the downregulation of bacterial genes involved in NH4+ assimilation occurring early during nodule invasion. This is a key and necessary step for the differentiation of N2-fixing bacteroids (the endocellular symbiotic form of rhizobia) and for the development of efficient nodules

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“…Functional duplication has been found previously in R. tropici (22,32), and indeed reiteration is not uncommon in members of the Rhizobiaceae (18,37). Therefore, the presence of two functional P i stress-inducible P i transport systems in CIAT899 is not without precedent.…”

Section: Discussionmentioning

confidence: 89%

Characterization of Two Inducible Phosphate Transport Systems in Rhizobium tropici

Botero

Al-Niemi

McDermott

2000

Appl Environ Microbiol

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Rhizobium tropici forms nitrogen-fixing nodules on the roots of the common bean (Phaseolus vulgaris).Like other legume-Rhizobium symbioses, the bean-R. tropici association is sensitive to the availability of phosphate (P i ). To better understand phosphorus movement between the bacteroid and the host plant, P i transport was characterized in R. tropici. We observed two P i transport systems, a high-affinity system and a low-affinity system. To facilitate the study of these transport systems, a Tn5B22 transposon mutant lacking expression of the high-affinity transport system was isolated and used to characterize the low-affinity transport system in the absence of the high-affinity system. The K m and V max values for the low-affinity system were estimated to be 34 ؎ 3 M P i and 118 ؎ 8 nmol of P i ⅐ min ؊1 ⅐ mg (dry weight) of cells ؊1 , respectively, and the K m and V max values for the high-affinity system were 0.45 ؎ 0.01 M P i and 86 ؎ 5 nmol of P i ⅐ min ؊1 ⅐ mg (dry weight) of cells ؊1 , respectively. Both systems were inducible by P i starvation and were also shock sensitive, which indicated that there was a periplasmic binding-protein component. Neither transport system appeared to be sensitive to the proton motive force dissipator carbonyl cyanide m-chlorophenylhydrazone, but P i transport through both systems was eliminated by the ATPase inhibitor N,N-dicyclohexylcarbodiimide; the P i transport rate was correlated with the intracellular ATP concentration. Also, P i movement through both systems appeared to be unidirectional, as no efflux or exchange was observed with either the wild-type strain or the mutant. These properties suggest that both P i transport systems are ABC type systems. Analysis of the transposon insertion site revealed that the interrupted gene exhibited a high level of homology with kdpE, which in several bacteria encodes a cytoplasmic response regulator that governs responses to low potassium contents and/or changes in medium osmolarity.Nitrogen fixation in legume nodules involves a complex exchange of nutrients between the plant and bacteroids. This exchange involves transport across the bacteroid membrane and the plant-derived envelope surrounding the bacteroid, the peribacteroid membrane. In its simplest terms, this symbiosis is often viewed as an exchange of reduced carbon for reduced nitrogen. However, it is clear that optimum nodule function also involves a balanced flow of other nutrients (33). One nutrient that has been shown to be important for this symbiosis is phosphorus. Low phosphorus availability in soils is common and limits legume production worldwide; however, phosphorus metabolism in this plant-microbe interaction has not been well characterized. Given the significant metabolic activity of bacteroids, the phosphorus supply may be critical for optimum symbiotic functioning of bacteroids, and understanding the mechanisms by which bacteroids acquire phosphorus should provide useful information concerning phosphorus exchange between the symbionts and phosphorus flow in ...

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Molecular Genetics of the Glutamine Synthetases in Rhizobium Species

Cited by 17 publications

References 31 publications

The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation

The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation

Key Role of Bacterial NH ₄ ⁺ Metabolism in Rhizobium-Plant Symbiosis

Characterization of Two Inducible Phosphate Transport Systems in Rhizobium tropici

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Molecular Genetics of the Glutamine Synthetases in Rhizobium Species

Cited by 17 publications

References 31 publications

The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation

The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation

Key Role of Bacterial NH 4 + Metabolism in Rhizobium-Plant Symbiosis

Characterization of Two Inducible Phosphate Transport Systems in Rhizobium tropici

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Key Role of Bacterial NH ₄ ⁺ Metabolism in Rhizobium-Plant Symbiosis