Involvement of Glutaredoxin and Thioredoxin Systems in the Nitrogen-Fixing Symbiosis between Legumes and Rhizobia

Leguminous plants can form a symbiotic relationship with Rhizobium bacteria, during which plants provide bacteria with carbohydrates and an environment appropriate to their metabolism, in return for fixed atmospheric nitrogen. The symbiotic interaction leads to the formation of a new organ, the root nodule, where a coordinated differentiation of plant cells and bacteria occurs. The establishment and functioning of nitrogen-fixing symbiosis involves a redox control important for both the plant-bacteria crosstalk and the regulation of nodule metabolism. In this review, we discuss the involvement of thioredoxin and glutaredoxin systems in the two symbiotic partners during symbiosis. The crucial role of glutathione in redox balance and S-metabolism is presented. We also highlight the specific role of some thioredoxin and glutaredoxin systems in bacterial differentiation. Transcriptomics data concerning genes encoding components and targets of thioredoxin and glutaredoxin systems in connection with the developmental step of the nodule are also considered in the model system Medicago truncatula–Sinorhizobium meliloti.

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Sinorhizobium meliloti Requires a Cobalamin-Dependent Ribonucleotide Reductase for Symbiosis With Its Plant Host

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-07-10-0151 ◽

2010 ◽

Vol 23 (12) ◽

pp. 1643-1654 ◽

Cited By ~ 38

Author(s):

Michiko E. Taga ◽

Graham C. Walker

Keyword(s):

Ribonucleotide Reductase ◽

Sinorhizobium Meliloti ◽

Critical Role ◽

Methionine Synthase ◽

Nitrogen Fixing ◽

Plant Host ◽

Gene Encoding ◽

Cobalamin Biosynthesis ◽

Methionine Synthesis

Vitamin B12 (cobalamin) is a critical cofactor for animals and protists, yet its biosynthesis is limited to prokaryotes. We previously showed that the symbiotic nitrogen-fixing alphaproteobacterium Sinorhizobium meliloti requires cobalamin to establish a symbiotic relationship with its plant host, Medicago sativa (alfalfa). Here, the specific requirement for cobalamin in the S. meliloti–alfalfa symbiosis was investigated. Of the three known cobalamin-dependent enzymes in S. meliloti, the methylmalonyl CoA mutase (BhbA) does not affect symbiosis, whereas disruption of the metH gene encoding the cobalamin-dependent methionine synthase causes a significant defect in symbiosis. Expression of the cobalamin-independent methionine synthase MetE alleviates this symbiotic defect, indicating that the requirement for methionine synthesis does not reflect a need for the cobalamin-dependent enzyme. To investigate the function of the cobalamin-dependent ribonucleotide reductase (RNR) encoded by nrdJ, S. meliloti was engineered to express an Escherichia coli cobalamin-independent (class Ia) RNR instead of nrdJ. This strain is severely defective in symbiosis. Electron micrographs show that these cells can penetrate alfalfa nodules but are unable to differentiate into nitrogen-fixing bacteroids and, instead, are lysed in the plant cytoplasm. Flow cytometry analysis indicates that these bacteria are largely unable to undergo endoreduplication. These phenotypes may be due either to the inactivation of the class Ia RNR by reactive oxygen species, inadequate oxygen availability in the nodule, or both. These results show that the critical role of the cobalamin-dependent RNR for survival of S. meliloti in its plant host can account for the considerable resources that S. meliloti dedicates to cobalamin biosynthesis.

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Requirement of Fra proteins for communication channels between cells in the filamentous nitrogen-fixing cyanobacteriumAnabaenasp. PCC 7120

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1512232112 ◽

2015 ◽

Vol 112 (32) ◽

pp. E4458-E4464 ◽

Cited By ~ 16

Author(s):

Amin Omairi-Nasser ◽

Vicente Mariscal ◽

Jotham R. Austin ◽

Robert Haselkorn

Keyword(s):

Electron Tomography ◽

Atmospheric Nitrogen ◽

Channel Formation ◽

Nitrogen Fixing ◽

Vegetative Cells ◽

Metabolite Exchange ◽

Minor Part ◽

A Minor ◽

Pcc 7120

The filamentous nitrogen-fixing cyanobacteriumAnabaenasp. PCC 7120 differentiates specialized cells, heterocysts, that fix atmospheric nitrogen and transfer the fixed nitrogen to adjacent vegetative cells. Reciprocally, vegetative cells transfer fixed carbon to heterocysts. Several routes have been described for metabolite exchange within the filament, one of which involves communicating channels that penetrate the septum between adjacent cells. Severalfragene mutants were isolated 25 y ago on the basis of their phenotypes: inability to fix nitrogen and fragmentation of filaments upon transfer from N+ to N− media. Cryopreservation combined with electron tomography were used to investigate the role of threefragene products in channel formation. FraC and FraG are clearly involved in channel formation, whereas FraD has a minor part. Additionally, FraG was located close to the cytoplasmic membrane and in the heterocyst neck, using immunogold labeling with antibody raised to the N-terminal domain of the FraG protein.

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Novel Genes and Regulators That Influence Production of Cell Surface Exopolysaccharides inSinorhizobium meliloti

Journal of Bacteriology ◽

10.1128/jb.00501-17 ◽

2017 ◽

Vol 200 (3) ◽

Cited By ~ 5

Author(s):

Melanie J. Barnett ◽

Sharon R. Long

Keyword(s):

Cell Surface ◽

Biofilm Formation ◽

Sinorhizobium Meliloti ◽

Developmental Process ◽

Root Nodules ◽

Critical Role ◽

Nitrogen Fixing ◽

Symbiotic Interaction ◽

Content Type ◽

Mutant Phenotypes

ABSTRACTSinorhizobium melilotiis a soil-dwelling alphaproteobacterium that engages in a nitrogen-fixing root nodule symbiosis with leguminous plants. Cell surface polysaccharides are important both for adapting to stresses in the soil and for the development of an effective symbiotic interaction. Among the polysaccharides characterized to date, the acidic exopolysaccharides I (EPS-I; succinoglycan) and II (EPS-II; galactoglucan) are particularly important for protection from abiotic stresses, biofilm formation, root colonization, and infection of plant roots. Previous genetic screens discovered mutants with impaired EPS production, allowing the delineation of EPS biosynthetic pathways. Here we report on a genetic screen to isolate mutants with mucoid colonial morphologies that suggest EPS overproduction. Screening with Tn5-110, which allows the recovery of both null and upregulation mutants, yielded 47 mucoid mutants, most of which overproduce EPS-I; among the 30 unique genes and intergenic regions identified, 14 have not been associated with EPS production previously. We identified a new protein-coding gene,emmD, which may be involved in the regulation of EPS-I production as part of the EmmABC three-component regulatory circuit. We also identified a mutant defective in EPS-I production, motility, and symbiosis, where Tn5-110 was not responsible for the mutant phenotypes; these phenotypes result from a missense mutation inrpoAcorresponding to the domain of the RNA polymerase alpha subunit known to interact with transcription regulators.IMPORTANCEThe alphaproteobacteriumSinorhizobium meliloticonverts dinitrogen to ammonium while inhabiting specialized plant organs termed root nodules. The transformation ofS. melilotifrom a free-living soil bacterium to a nitrogen-fixing plant symbiont is a complex developmental process requiring close interaction between the two partners. As the interface between the bacterium and its environment, theS. meliloticell surface plays a critical role in adaptation to varied soil environments and in interaction with plant hosts. We isolated and characterizedS. melilotimutants with increased production of exopolysaccharides, key cell surface components. Our diverse set of mutants suggests roles for exopolysaccharide production in growth, metabolism, cell division, envelope homeostasis, biofilm formation, stress response, motility, and symbiosis.

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Bioactive Cytokinins Are Selectively Secreted by Sinorhizobium meliloti Nodulating and Nonnodulating Strains

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-02-13-0054-r ◽

2013 ◽

Vol 26 (10) ◽

pp. 1225-1231 ◽

Cited By ~ 27

Author(s):

Anna Kisiala ◽

Carole Laffont ◽

R. J. Neil Emery ◽

Florian Frugier

Keyword(s):

Sinorhizobium Meliloti ◽

Root Nodule ◽

System Development ◽

Lateral Roots ◽

Extracellular Polysaccharide ◽

Bacterial Strains ◽

Symbiotic Interaction ◽

Root System Development ◽

Liquid Chromatography Tandem Mass ◽

Meliloti Strain

Bacteria present in the rhizosphere of plants often synthesize phytohormones, and these signals can consequently affect root system development. In legumes, plants adapt to nitrogen starvation by forming lateral roots as well as a new organ, the root nodule, following a symbiotic interaction with bacteria collectively referred to as rhizobia. As cytokinin (CK) phytohormones were shown to be necessary and sufficient to induce root nodule organogenesis, the relevance of CK production by symbiotic rhizobia was questioned. In this study, we analyzed quantitatively, by liquid chromatography-tandem mass spectrometry, the production of 25 forms of CK in nine rhizobia strains belonging to four different species. All bacterial strains were able to synthesize a mix of CK, and bioactive forms of CK, such as iP, were notably found to be secreted in bacterial culture supernatants. Use of a mutant affected in extracellular polysaccharide (EPS) production revealed a negative correlation of EPS production with the ability to secrete CK. In addition, analysis of a nonnodulating Sinorhizobium meliloti strain revealed a similar pattern of CK production and secretion when compared with a related nodulating strain. This indicates that bacterially produced CK are not sufficient to induce symbiotic nodulation.

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Identification of New Potential Regulators of the Medicago truncatula—Sinorhizobium meliloti Symbiosis Using a Large-Scale Suppression Subtractive Hybridization Approach

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-20-3-0321 ◽

2007 ◽

Vol 20 (3) ◽

pp. 321-332 ◽

Cited By ~ 28

Author(s):

Laurence Godiard ◽

Andreas Niebel ◽

Fabienne Micheli ◽

Jérôme Gouzy ◽

Thomas Ott ◽

...

Keyword(s):

Signal Transduction ◽

Suppression Subtractive Hybridization ◽

Medicago Truncatula ◽

Large Scale ◽

Sinorhizobium Meliloti ◽

Zinc Finger Protein ◽

Gene Clusters ◽

Subtractive Hybridization ◽

Symbiotic Interaction ◽

Genes Encoding

We set up a large-scale suppression subtractive hybridization (SSH) approach to identify Medicago truncatula genes differentially expressed at different stages of the symbiotic interaction with Sinorhizobium meliloti, with a particular interest for regulatory genes. We constructed 7 SSH libraries covering successive stages from Nod factor signal transduction to S. meliloti infection, nodule organogenesis, and functioning. Over 26,000 clones were differentially screened by two rounds of macroarray hybridizations. In all, 3,340 clones, corresponding to genes whose expression was potentially affected, were selected, sequenced, and ordered into 2,107 tentative gene clusters, including 767 MtS clusters corresponding to new M. truncatula genes. In total, 52 genes encoding potential regulatory proteins, including transcription factors (TFs) and other elements of signal transduction cascades, were identified. The expression pattern of some of them was analyzed by quantitative reverse-transcription polymerase chain reaction in wild-type and in Nod¯ M. truncatula mutants blocked before or after S. meliloti infection. Three genes, coding for TFs of the bHLH and WRKY families and a C2H2 zinc-finger protein, respectively, were found to be upregulated, following S. meliloti inoculation, in the infection-defective mutant lin, whereas the bHLH gene also was expressed in the root-hair-curling mutant hcl. The potential role of these genes in early symbiotic steps is discussed.

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Sinorhizobium meliloti Mutants Deficient in Phosphatidylserine Decarboxylase Accumulate Phosphatidylserine and Are Strongly Affected during Symbiosis with Alfalfa

Journal of Bacteriology ◽

10.1128/jb.00610-08 ◽

2008 ◽

Vol 190 (20) ◽

pp. 6846-6856 ◽

Cited By ~ 14

Author(s):

Miguel Angel Vences-Guzmán ◽

Otto Geiger ◽

Christian Sohlenkamp

Keyword(s):

Sinorhizobium Meliloti ◽

Minimal Medium ◽

Root Nodule ◽

Membrane Lipids ◽

Nodule Formation ◽

Deficient Mutant ◽

Nitrogen Fixing ◽

Wild Type ◽

Root Nodule Symbiosis ◽

Nodule Symbiosis

ABSTRACT Sinorhizobium meliloti contains phosphatidylglycerol, cardiolipin, phosphatidylcholine, and phosphatidylethanolamine (PE) as major membrane lipids. PE is formed in two steps. In the first step, phosphatidylserine synthase (Pss) condenses serine with CDP-diglyceride to form phosphatidylserine (PS), and in the second step, PS is decarboxylated by phosphatidylserine decarboxylase (Psd) to form PE. In this study we identified the sinorhizobial psd gene coding for Psd. A sinorhizobial mutant deficient in psd is unable to form PE but accumulates the anionic phospholipid PS. Properties of PE-deficient mutants lacking either Pss or Psd were compared with those of the S. meliloti wild type. Whereas both PE-deficient mutants grew in a wild-type-like manner on many complex media, they were unable to grow on minimal medium containing high phosphate concentrations. Surprisingly, the psd-deficient mutant could grow on minimal medium containing low concentrations of inorganic phosphate, while the pss-deficient mutant could not. Addition of choline to the minimal medium rescued growth of the pss-deficient mutant, CS111, to some extent but inhibited growth of the psd-deficient mutant, MAV01. When the two distinct PE-deficient mutants were analyzed for their ability to form a nitrogen-fixing root nodule symbiosis with their alfalfa host plant, they behaved strikingly differently. The Pss-deficient mutant, CS111, initiated nodule formation at about the same time point as the wild type but did form about 30% fewer nodules than the wild type. In contrast, the PS-accumulating mutant, MAV01, initiated nodule formation much later than the wild type and formed 90% fewer nodules than the wild type. The few nodules formed by MAV01 seemed to be almost devoid of bacteria and were unable to fix nitrogen. Leaves of alfalfa plants inoculated with the mutant MAV01 were yellowish, indicating that the plants were starved for nitrogen. Therefore, changes in lipid composition, including the accumulation of bacterial PS, prevent the establishment of a nitrogen-fixing root nodule symbiosis.

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LEGHEMOGLOBIN: THE ROLE OF HEMOGLOBIN IN THE NITROGEN-FIXING LEGUME ROOT NODULE

Annals of the New York Academy of Sciences ◽

10.1111/j.1749-6632.1975.tb41519.x ◽

1975 ◽

Vol 244 (1 The Biologica) ◽

pp. 28-34 ◽

Cited By ~ 10

Author(s):

Jonathan B. Wittenberg ◽

C. A. Appleby ◽

F. J. Bergersen ◽

G. L. Turner

Keyword(s):

Root Nodule ◽

Nitrogen Fixing

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Exopolysaccharide II Is Relevant for the Survival of Sinorhizobium meliloti under Water Deficiency and Salinity Stress

Molecules ◽

10.3390/molecules25214876 ◽

2020 ◽

Vol 25 (21) ◽

pp. 4876

Author(s):

Emiliano Primo ◽

Pablo Bogino ◽

Sacha Cossovich ◽

Emiliano Foresto ◽

Fiorela Nievas ◽

...

Keyword(s):

Sinorhizobium Meliloti ◽

Protective Role ◽

Environmental Stressors ◽

Saline Stress ◽

Symbiotic Association ◽

Atmospheric Nitrogen ◽

Water Deficiency ◽

Wild Type ◽

Induced Stress

Sinorhizobium meliloti is a soil bacterium of great agricultural importance because of its ability to fix atmospheric nitrogen in symbiotic association with alfalfa (Medicago sativa) roots. We looked into the involvement of exopolysaccharides (EPS) in its survival when exposed to different environmental stressors, as well as in bacteria–bacteria and bacteria–substrate interactions. The strains used were wild-type Rm8530 and two strains that are defective in the biosynthesis of EPS II: wild-type Rm1021, which has a non-functional expR locus, and mutant Rm8530 expA. Under stress by water deficiency, Rm8530 remained viable and increased in number, whereas Rm1021 and Rm8530 expA did not. These differences could be due to Rm8530′s ability to produce EPS II. Survival experiments under saline stress showed that viability was reduced for Rm1021 but not for Rm8530 or Rm8530 expA, which suggests the existence of some regulating mechanism dependent on a functional expR that is absent in Rm1021. The results of salinity-induced stress assays regarding biofilm-forming capacity (BFC) and autoaggregation indicated the protective role of EPS II. As a whole, our observations demonstrate that EPS play major roles in rhizobacterial survival.

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Why Should Nodule Cysteine-Rich (NCR) Peptides Be Absent From Nodules of Some Groups of Legumes but Essential for Symbiotic N-Fixation in Others?

Frontiers in Agronomy ◽

10.3389/fagro.2021.654576 ◽

2021 ◽

Vol 3 ◽

Author(s):

J. Allan Downie ◽

Eva Kondorosi

Keyword(s):

Nitrogen Fixation ◽

Terminal Differentiation ◽

N Fixation ◽

Nitrogen Fixing ◽

Bacterial Differentiation ◽

Genes Encoding

In nitrogen-fixing nodules of legumes such as pea (Pisum) and Medicago spp. the plant induces terminal differentiation in the rhizobial endosymbionts by targeting nodule-specific cysteine-rich defensin-like peptides into the bacteria. However, in nodules of other legumes such as soybean and Lotus spp. terminal bacterial differentiation does not occur; these legumes lack genes encoding equivalent peptides controlling rhizobial development. Here, we review the effects of some of these peptides on rhizobia and address the question as to how and why such peptides may have evolved to enslave rhizobia and become essential for nitrogen fixation in some clades of legumes but not in others.

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Identification of Sinorhizobium melilotiGenes Regulated during Symbiosis

Journal of Bacteriology ◽

10.1128/jb.182.13.3632-3637.2000 ◽

2000 ◽

Vol 182 (13) ◽

pp. 3632-3637 ◽

Cited By ~ 25

Author(s):

Didier Cabanes ◽

Pierre Boistard ◽

Jacques Batut

Keyword(s):

Sinorhizobium Meliloti ◽

Sequence Similarity ◽

Pyruvate Dehydrogenase Complex ◽

Surface Protein ◽

Symbiotic Interaction ◽

High Sequence Similarity ◽

Copper Transporter ◽

Genes Encoding ◽

A Cell ◽

Arbitrarily Primed Pcr

ABSTRACT RNA fingerprinting by arbitrarily primed PCR was used to isolateSinorhizobium meliloti genes regulated during the symbiotic interaction with alfalfa (Medicago sativa). Sixteen partial cDNAs were isolated whose corresponding genes were differentially expressed between symbiotic and free-living conditions. Thirteen sequences corresponded to genes up-regulated during symbiosis, whereas three were instead repressed during establishment of the symbiotic interaction. Seven cDNAs corresponded to known or predictednif and fix genes. Four presented high sequence similarity with genes not yet identified in S. meliloti, including genes encoding a component of the pyruvate dehydrogenase complex, a cell surface protein component, a copper transporter, and an argininosuccinate lyase. Finally, five cDNAs did not exhibit any similarity with sequences present in databases. A detailed expression analysis of the nine non-nif-fix genes provided evidence for an unexpected variety of regulatory patterns, most of which have not been described so far.

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