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Li S, Wu C, Liu H, Lyu X, Xiao F, Zhao S, Ma C, Yan C, Liu Z, Li H, Wang X, Gong Z. Systemic regulation of nodule structure and assimilated carbon distribution by nitrate in soybean. FRONTIERS IN PLANT SCIENCE 2023; 14:1101074. [PMID: 36814755 PMCID: PMC9939697 DOI: 10.3389/fpls.2023.1101074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 01/13/2023] [Indexed: 06/18/2023]
Abstract
BACKGROUND The nitrate regulates soybean nodulation and nitrogen fixation systemically, mainly in inhibiting nodule growth and reducing nodule nitrogenase activity, but the reason for its inhibition is still inconclusive. METHODS The systemic effect of nitrate on nodule structure, function, and carbon distribution in soybean (Glycine max (L.) Merr.) was studied in a dual-root growth system, with both sides inoculated with rhizobia and only one side subjected to nitrate treatment for four days. The non-nodulating side was genetically devoid of the ability to form nodules. Nutrient solutions with nitrogen concentrations of 0, 100, and 200 mg L-1 were applied as KNO3 to the non-nodulating side, while the nodulating side received a nitrogen-free nutrient solution. Carbon partitioning in roots and nodules was monitored using 13C-labelled CO2. Other nodule responses were measured via the estimation of the nitrogenase activity and the microscopic observation of nodule ultrastructure. RESULTS Elevated concentrations of nitrate applied on the non-nodulating side caused a decrease in the number of bacteroids, fusion of symbiosomes, enlargement of the peribacteroid spaces, and onset of degradation of poly-β-hydroxybutyrate granules, which is a form of carbon storage in bacteroids. These microscopic observations were associated with a strong decrease in the nitrogenase activity of nodules. Furthermore, our data demonstrate that the assimilated carbon is more likely to be allocated to the non-nodulating roots, as follows from the competition for carbon between the symbiotic and non-symbiotic sides of the dual-root system. CONCLUSION We propose that there is no carbon competition between roots and nodules when they are indirectly supplied with nitrate, and that the reduction of carbon fluxes to nodules and roots on the nodulating side is the mechanism by which the plant systemically suppresses nodulation under nitrogen-replete conditions.
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Affiliation(s)
- Sha Li
- College of Resources and Environment, Northeast Agricultural University, Harbin, China
| | - Chengbin Wu
- College of Resources and Environment, Northeast Agricultural University, Harbin, China
| | - Hao Liu
- College of Agriculture, Northeast Agricultural University, Harbin, China
| | - Xiaochen Lyu
- College of Agriculture, Northeast Agricultural University, Harbin, China
| | - Fengsheng Xiao
- College of Agriculture, Northeast Agricultural University, Harbin, China
| | - Shuhong Zhao
- College of Engineering, Northeast Agricultural University, Harbin, China
| | - Chunmei Ma
- College of Agriculture, Northeast Agricultural University, Harbin, China
| | - Chao Yan
- College of Agriculture, Northeast Agricultural University, Harbin, China
| | - Zhilei Liu
- College of Resources and Environment, Northeast Agricultural University, Harbin, China
| | - Hongyu Li
- College of Agriculture, Northeast Agricultural University, Harbin, China
| | - Xuelai Wang
- College of Agriculture, Northeast Agricultural University, Harbin, China
| | - Zhenping Gong
- College of Agriculture, Northeast Agricultural University, Harbin, China
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Abstract
Rhizobia are a phylogenetically diverse group of soil bacteria that engage in mutualistic interactions with legume plants. Although specifics of the symbioses differ between strains and plants, all symbioses ultimately result in the formation of specialized root nodule organs which host the nitrogen-fixing microsymbionts called bacteroids. Inside nodules, bacteroids encounter unique conditions that necessitate global reprogramming of physiological processes and rerouting of their metabolism. Decades of research have addressed these questions using genetics, omics approaches, and more recently computational modelling. Here we discuss the common adaptations of rhizobia to the nodule environment that define the core principles of bacteroid functioning. All bacteroids are growth-arrested and perform energy-intensive nitrogen fixation fueled by plant-provided C4-dicarboxylates at nanomolar oxygen levels. At the same time, bacteroids are subject to host control and sanctioning that ultimately determine their fitness and have fundamental importance for the evolution of a stable mutualistic relationship.
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Brear EM, Day DA, Smith PMC. Iron: an essential micronutrient for the legume-rhizobium symbiosis. FRONTIERS IN PLANT SCIENCE 2013; 4:359. [PMID: 24062758 PMCID: PMC3772312 DOI: 10.3389/fpls.2013.00359] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Accepted: 08/26/2013] [Indexed: 05/19/2023]
Abstract
Legumes, which develop a symbiosis with nitrogen-fixing bacteria, have an increased demand for iron. Iron is required for the synthesis of iron-containing proteins in the host, including the highly abundant leghemoglobin, and in bacteroids for nitrogenase and cytochromes of the electron transport chain. Deficiencies in iron can affect initiation and development of the nodule. Within root cells, iron is chelated with organic acids such as citrate and nicotianamine and distributed to other parts of the plant. Transport to the nitrogen-fixing bacteroids in infected cells of nodules is more complicated. Formation of the symbiosis results in bacteroids internalized within root cortical cells of the legume where they are surrounded by a plant-derived membrane termed the symbiosome membrane (SM). This membrane forms an interface that regulates nutrient supply to the bacteroid. Consequently, iron must cross this membrane before being supplied to the bacteroid. Iron is transported across the SM as both ferric and ferrous iron. However, uptake of Fe(II) by both the symbiosome and bacteroid is faster than Fe(III) uptake. Members of more than one protein family may be responsible for Fe(II) transport across the SM. The only Fe(II) transporter in nodules characterized to date is GmDMT1 (Glycine max divalent metal transporter 1), which is located on the SM in soybean. Like the root plasma membrane, the SM has ferric iron reductase activity. The protein responsible has not been identified but is predicted to reduce ferric iron accumulated in the symbiosome space prior to uptake by the bacteroid. With the recent publication of a number of legume genomes including Medicago truncatula and G. max, a large number of additional candidate transport proteins have been identified. Members of the NRAMP (natural resistance-associated macrophage protein), YSL (yellow stripe-like), VIT (vacuolar iron transporter), and ZIP (Zrt-, Irt-like protein) transport families show enhanced expression in nodules and are expected to play a role in the transport of iron and other metals across symbiotic membranes.
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Affiliation(s)
- Ella M. Brear
- School of Biological Sciences, The University of SydneySydney, NSW, Australia
| | - David A. Day
- School of Biological Sciences, Flinders UniversityBedford Park, Adelaide, SA, Australia
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Davies MJ, Mathieu C, Puppo A. Leghemoglobin: Properties and Reactions. ADVANCES IN INORGANIC CHEMISTRY 1998. [DOI: 10.1016/s0898-8838(08)60154-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Abstract
Infection of legume roots or stems with soil bacteria of the Rhizobiaceae results in the formation of nodules that become symbiotic nitrogen-fixing organs. Within the infected cells of these nodules, bacteria are enveloped in a membrane of plant origin, called the peribacteroid membrane (PBM), and divide and differentiate to form nitrogen-fixing bacteroids. The organelle-like structure comprised of PBM and bacteroids is termed the symbiosome, and is the basic nitrogen-fixing unit of the nodule. The major exchange of nutrients between the symbiotic partners is reduced carbon from the plant, to fuel nitrogenase activity in the bacteroid, and fixed nitrogen from the bacteroid, which is assimilated in the plant cytoplasm. However, many other metabolites are also exchanged. The metabolic interaction between the plant and the bacteroids is regulated by a series of transporters and channels on the PBM and the bacteroid membrane, and these form the focus of this review.
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Affiliation(s)
- Michael K. Udvardi
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra ACT, 0200, Australia
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Bacteroids from soybean root nodules: respiration and N
2
-fixation in flow-chamber reactions with oxyleghaemoglobin. ACTA ACUST UNITED AC 1997. [DOI: 10.1098/rspb.1990.0001] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Suspensions of bacteroids prepared from root nodules of glasshouse-grown soybeans were studied in a stirred chamber supplied with variable flows of solutions containing dissolved air, oxyleghaemoglobin and various energy sources. In experiments of up to 6 h duration, several steady states were established in which frequent measurements were made of the concentration of free, dissolved O
2
in the range 5–200 nM and of rates of O
2
consumption, CO
2
efflux and N
2
fixation. The principal findings were: (i) bacteroids were capable of efficient N
2
fixation without the supply of exogenous energy sources when respiring at 10–50 nM free O
2
. This endogenous respiration was enhanced after periods of supply of succinate or malate. (ii) Exogenous energy sources were of three types, those that were poorly utilized (glucose), those that enhanced endogenous respiration and supported efficient N
2
fixation (glutamate, 2-oxoglutarate) and succinate and malate, which promoted respiration but supported N
2
fixation inefficiently or in some circumstances inhibited it. It is proposed that succinate and malate act primarily to increase endogenous reserves that become the principal source of reducing power for N
2
fixation, (iii) Bacteroids have a terminal oxidase system with very high apparent affinity for O
2
(
s
0.5
≈ 5–8 nM) and complex kinetics (plots of
v
against
s
are sigmoidal;
n
app
> 1.8). This system was active with endogenous substrates and when glutamate or 2-oxoglutarate were supplied. With succinate or malate, respiration appeared to be the sum of endogenous activity plus O
2
consumption by a system with lower affinity for O
2
(
K
s
= 38 nM) and simple kinetics (
n
app
≈ 1). (iv) During the first hour of reactions there were changes in O
2
demand and oscillations in O
2
demand and CO
2
efflux followed supply or withdrawal of exogenous substrates. It is proposed that these changes are examples of phenotypic plasticity in these symbiotic bacteria.
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Gabel C, Maier RJ. Oxygen-dependent transcriptional regulation of cytochrome aa3 in Bradyrhizobium japonicum. J Bacteriol 1993; 175:128-32. [PMID: 8380149 PMCID: PMC196105 DOI: 10.1128/jb.175.1.128-132.1993] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Cytochrome aa3 is one of two terminal oxidases expressed in free-living Bradyrhizobium japonicum but not symbiotically in bacteroids. Difference spectra (dithionite reduced minus ferricyanide oxidized) for membranes from cells incubated with progressively lower O2 concentrations showed a concomitant decrease in the A603, the absorption peak characteristic of cytochrome aa3. The level of N,N,N',N'-tetramethyl-p-phenylenediamine oxidase activity, a measure of cytochrome aa3 activity, was also found to depend on the O2 level. Dot blots of total RNA isolated from cells grown at various O2 levels were probed with a fragment of the coxA gene from B. japonicum; a sixfold reduction in transcription from the highest (250 microM) to the lowest (12.5 microM) O2 concentration was observed. Bacteroids had even less coxA message, approximately 19% that in the 12.5 microM O2-incubated cells. Primer extension analysis established the transcription initiation site of the coxA gene at 72 bases upstream of the putative translational start codon. Sequence analysis of the region upstream of the transcription initiation site revealed no homology with previously reported B. japonicum promoters.
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Affiliation(s)
- C Gabel
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218
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9
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O'Brian MR, Maier RJ. Molecular aspects of the energetics of nitrogen fixation in Rhizobium-legume symbioses. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 974:229-46. [PMID: 2659085 DOI: 10.1016/s0005-2728(89)80239-7] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- M R O'Brian
- Department of Biology, Johns Hopkins University, Baltimore, MD 21218
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Vandenbosch KA, Newcomb EH. The occurrence of leghemoglobin protein in the uninfected interstitial cells of soybean root nodules. PLANTA 1988; 175:442-451. [PMID: 24221924 DOI: 10.1007/bf00393063] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/1988] [Accepted: 05/03/1988] [Indexed: 06/02/2023]
Abstract
The distribution of leghemoglobin (Lb) in resin-embedded root nodules of soybean (Glycine max (L.) Merr.) was investigated using immunogold labeling. Using anti-Lb immunoglobulin G and protein A-gold, Lb or its apoprotein was detected both in cells infected by Bradyrhizobium japonicum and in uninfected interstitial cells. Leghemoglobin was present in the cytoplasm, exclusive of the organelles, and in the nuclei of both cell types. In a comparison of the density of labeling in adjacent pairs of infected and uninfected cells, Lb was found to be about four times more concentrated in infected cells. This is the first report of Lb in uninfected cells of any legume nodule; it raises the possibility that this important nodule-specific protein may participate in mediating oxygen flow to host plant organelles throughout the infected region of the nodule.
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Affiliation(s)
- K A Vandenbosch
- Department of Botany, University of Wisconsin, 53706, Madison, WI, USA
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Giannakis C, Nicholas DJ, Wallace W. Utilization of nitrate by bacteroids of Bradyrhizobium japonicum in the soybean root nodule. PLANTA 1988; 174:51-58. [PMID: 24221417 DOI: 10.1007/bf00394873] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/1987] [Accepted: 09/28/1987] [Indexed: 06/02/2023]
Abstract
Bacteroids of Bradyrhizobium japonicum strain CB1809, unlike CC705, do not have a high level of constitutive nitrate reductase (NR; EC 1.7.99.4) in the soybean (Glycine max. Merr.) nodule. Ex planta both strains have a high activity of NR when cultured on 5 mM nitrate at 2% O2 (v/v). Nitrite reductase (NiR) was active in cultured cells of bradyrhizobia, but activity with succinate as electron donor was not detected in freshly-isolated bacteroids. A low activity was measured with reduced methyl viologen. When bacteroids of CC705 were incubated with nitrate there was a rapid production of nitrite which resulted in repression of NR. Subsequently when NiR was induced, nitrite was utilized and NR activity recovered. Nitrate reductase was induced in bacteroids of strain CB1809 when they were incubated in-vitro with nitrate or nitrite. Increase in NR activity was prevented by rifampicin (10 μg· ml(-1)) or chloramphenicol (50 μg·ml(-1)). Nitrite-reductase activity in bacteroids of strain CB1809 was induced in parallel with NR. When nitrate was supplied to soybeans nodulated with strain CC705, nitrite was detected in nodule extracts prepared in aqueous media and it accumulated during storage (1°C) and on further incubation at 25°C. Nitrite was not detected in nodule extracts prepared in ethanol. Thus nitrite accumulation in nodule tissue appears to occur only after maceration and although bacteroids of some strains of B. japonicum have a high level of a constitutive NR, they do not appear to reduce nitrate in the nodule because this anion does not gain access to the bacteroid zone. Soybeans nodulated with strains CC705 and CB1809 were equally sensitive to nitrate inhibition of N2 fixation.
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Affiliation(s)
- C Giannakis
- Department of Agricultural Biochemistry, Waite Agricultural Research Institute, University of Adelaide, 5064, Glen Osmond, S.A., Australia
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Bergersen FJ, Trinchant JC. Flux of O2 affects apparent optimal concentrations of O2 in suspensions of bacteria respiring microaerobically. J Theor Biol 1985. [DOI: 10.1016/s0022-5193(85)80008-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Robertson JG, Wells B, Bisseling T, Farnden KJF, Johnston AWB. Immuno-gold localization of leghaemoglobin in cytoplasm in nitrogen-fixing root nodules of pea. Nature 1984. [DOI: 10.1038/311254a0] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
An NADH: (acceptor) oxidoreductase from the cytosol of soybean root nodules was purified by ammonium sulfate fractionation, hydroxylapatite adsorption, and Sephacryl S-200 Superfine chromatography. The native molecular weight of the reductase was found to be 100,000 by analytical gel filtration and 83,000 by equilibrium ultracentrifugation. The subunit molecular weight was 54,000 as determined by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. The pI of the enzyme was 5.5. With ferric leghemoglobin (Lb) as the substrate, nearly identical initial velocities were obtained using either CO or O2 to ligate the enzymatically produced ferrous leghemoglobin. With CO as the ligand in the reaction, the product of the enzyme-catalyzed, NADH-dependent reduction of ferric Lb was spectrally identified as LbCO. Initial velocity was a linear function of increasing enzyme concentration. NADPH was only 31% as effective an electron donor as NADH as determined by initial velocity. The Michaelis constants (Km) for ferric Lba and NADH were 9.5 and 18.8 microM, respectively. Myoglobin, Lba, Lbc1, Lbc2, Lbc3, and Lbd were reduced at similar rates by the reductase. At pH 5.2, acetate-bound ferric Lb and nicotinate-bound ferric Lb were reduced by the enzyme at 83 and 5%, respectively, of rates observed in the absence of these ligands. The rate of enzymatic reduction of ferric Lb was constant between pH 6.5 and 7.6 but increased approximately threefold at pH 5.2. The results indicate that the NADH: (acceptor) oxidoreductase could be identified as a ferric Lb reductase.
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