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Muthui SW, Wei L, Ochieng WA, Linda EL, Otieno DO, Nyongesa EW, Liu F, Xian L. The distinctive level of interaction between carbon and nitrogen metabolisms in the leaves of submerged macrophytes plays a key role in ammonium detoxification. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2024; 268:106840. [PMID: 38278063 DOI: 10.1016/j.aquatox.2024.106840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 01/08/2024] [Accepted: 01/12/2024] [Indexed: 01/28/2024]
Abstract
Possible ammonium detoxification mechanisms have been proposed recently, on submerged macrophytes, evidently illustrating that glutamate dehydrogenase (GDH) plays a greater role in ammonium detoxification compared to the primary glutamine synthetase/glutamate oxaloacetate transaminase (GS/GOGAT) pathway. In the current investigation, we cultured three submerged macrophytes to extreme concentrations of [NH4+-N] of up to 50 mg/L with the aim of clarifying the interaction between carbon and nitrogen metabolisms. The activities of carboxylation enzymes pyruvate orthophosphate dikinase (PPDK) and phosphoenolpyruvate carboxylase (PEPC), in lieu of Rubisco, increased almost two-fold for ammonium tolerant species P. maackianus and M. spicatum, compared with the sensitive species P. lucens. While these enzymes are well known for their central role in CO2 fixation, their inference in conferring resistance to ammonium stress has not been well elucidated before. In this study, we demonstrate that the overproduction of PEPC and PPDK led to improved photosynthesis, better ammonium assimilation and overall ammonium detoxification in M. spicatum and P. maackianus. These findings propose likelihood for the existence of a complementary ammonium detoxification pathway that targets carbon metabolism, thus, presenting a relatively efficient linkage between nitrogen and carbon metabolisms and identify candidate species for practical restoration of fresh water resources.
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Affiliation(s)
- Samuel Wamburu Muthui
- Core Botanical Gardens/Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, China; University of Chinese Academy of Sciences, Beijing, China; Sino-Africa Joint Research Centre, Chinese Academy of Sciences, Wuhan, China
| | - Li Wei
- Changjiang Water Resources and Hydropower Development Group (Hubei) Co., Ltd., Wuhan 430010, China
| | - Wyckliffe Ayoma Ochieng
- Core Botanical Gardens/Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, China; University of Chinese Academy of Sciences, Beijing, China; Sino-Africa Joint Research Centre, Chinese Academy of Sciences, Wuhan, China
| | - Elive Limunga Linda
- Hubei University, School of Resources and Environmental Science, Wuhan 430074, China
| | - Duncan Ochieng Otieno
- Core Botanical Gardens/Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, China; University of Chinese Academy of Sciences, Beijing, China; Sino-Africa Joint Research Centre, Chinese Academy of Sciences, Wuhan, China
| | - Emmanuel Waswa Nyongesa
- Core Botanical Gardens/Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, China; University of Chinese Academy of Sciences, Beijing, China; Sino-Africa Joint Research Centre, Chinese Academy of Sciences, Wuhan, China
| | - Fan Liu
- Core Botanical Gardens/Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, China
| | - Ling Xian
- Core Botanical Gardens/Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, China.
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2
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Zheng Y, Cabassa-Hourton C, Planchais S, Lebreton S, Savouré A. The proline cycle as an eukaryotic redox valve. JOURNAL OF EXPERIMENTAL BOTANY 2021; 72:6856-6866. [PMID: 34331757 DOI: 10.1093/jxb/erab361] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 07/29/2021] [Indexed: 06/13/2023]
Abstract
The amino acid proline has been known for many years to be a component of proteins as well as an osmolyte. Many recent studies have demonstrated that proline has other roles such as regulating redox balance and energy status. In animals and plants, the well-described proline cycle is concomitantly responsible for the preferential accumulation of proline and shuttling of redox equivalents from the cytosol to mitochondria. The impact of the proline cycle goes beyond regulating proline levels. In this review, we focus on recent evidence of how the proline cycle regulates redox status in relation to other redox shuttles. We discuss how the interconversion of proline and glutamate shuttles reducing power between cellular compartments. Spatial aspects of the proline cycle in the entire plant are considered in terms of proline transport between organs with different metabolic regimes (photosynthesis versus respiration). Furthermore, we highlight the importance of this shuttle in the regulation of energy and redox power in plants, through a particularly intricate coordination, notably between mitochondria and cytosol.
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Affiliation(s)
- Yao Zheng
- Sorbonne Université, UPEC, CNRS, IRD, INRAE, Institute of Ecology and Environmental Sciences of Paris (iEES), F-75005 Paris, France
| | - Cécile Cabassa-Hourton
- Sorbonne Université, UPEC, CNRS, IRD, INRAE, Institute of Ecology and Environmental Sciences of Paris (iEES), F-75005 Paris, France
| | - Séverine Planchais
- Sorbonne Université, UPEC, CNRS, IRD, INRAE, Institute of Ecology and Environmental Sciences of Paris (iEES), F-75005 Paris, France
| | - Sandrine Lebreton
- Sorbonne Université, UPEC, CNRS, IRD, INRAE, Institute of Ecology and Environmental Sciences of Paris (iEES), F-75005 Paris, France
| | - Arnould Savouré
- Sorbonne Université, UPEC, CNRS, IRD, INRAE, Institute of Ecology and Environmental Sciences of Paris (iEES), F-75005 Paris, France
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3
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Waters JK, Mawhinney TP, Emerich DW. Nitrogen Assimilation and Transport by Ex Planta Nitrogen-Fixing Bradyrhizobium diazoefficiens Bacteroids Is Modulated by Oxygen, Bacteroid Density and l-Malate. Int J Mol Sci 2020; 21:E7542. [PMID: 33066093 PMCID: PMC7589128 DOI: 10.3390/ijms21207542] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Revised: 10/09/2020] [Accepted: 10/12/2020] [Indexed: 12/23/2022] Open
Abstract
Symbiotic nitrogen fixation requires the transfer of fixed organic nitrogen compounds from the symbiotic bacteria to a host plant, yet the chemical nature of the compounds is in question. Bradyrhizobium diazoefficiens bacteroids were isolated anaerobically from soybean nodules and assayed at varying densities, varying partial pressures of oxygen, and varying levels of l-malate. Ammonium was released at low bacteroid densities and high partial pressures of oxygen, but was apparently taken up at high bacteroid densities and low partial pressures of oxygen in the presence of l-malate; these later conditions were optimal for amino acid excretion. The ratio of partial pressure of oxygen/bacteroid density of apparent ammonium uptake and of alanine excretion displayed an inverse relationship. Ammonium uptake, alanine and branch chain amino acid release were all dependent on the concentration of l-malate displaying similar K0.5 values of 0.5 mM demonstrating concerted regulation. The hyperbolic kinetics of ammonium uptake and amino acid excretion suggests transport via a membrane carrier and also suggested that transport was rate limiting. Glutamate uptake displayed exponential kinetics implying transport via a channel. The chemical nature of the compounds released were dependent upon bacteroid density, partial pressure of oxygen and concentration of l-malate demonstrating an integrated metabolism.
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Affiliation(s)
| | | | - David W. Emerich
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA; (J.K.W.); (T.P.M.)
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4
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Thal B, Braun HP, Eubel H. Proteomic analysis dissects the impact of nodulation and biological nitrogen fixation on Vicia faba root nodule physiology. PLANT MOLECULAR BIOLOGY 2018; 97:233-251. [PMID: 29779088 DOI: 10.1007/s11103-018-0736-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 05/08/2018] [Indexed: 05/25/2023]
Abstract
Symbiotic nitrogen fixation in root nodules of legumes is a highly important biological process which is only poorly understood. Root nodule metabolism differs from that of roots. Differences in root and nodule metabolism are expressed by altered protein abundances and amenable to quantitative proteome analyses. Differences in the proteomes may either be tissue specific and related to the presence of temporary endosymbionts (the bacteroids) or related to nitrogen fixation activity. An experimental setup including WT bacterial strains and strains not able to conduct symbiotic nitrogen fixation as well as root controls enables identification of tissue and nitrogen fixation specific proteins. Root nodules are specialized plant organs housing and regulating the mutual symbiosis of legumes with nitrogen fixing rhizobia. As such, these organs fulfill unique functions in plant metabolism. Identifying the proteins required for the metabolic reactions of nitrogen fixation and those merely involved in sustaining the rhizobia:plant symbiosis, is a challenging task and requires an experimental setup which allows to differentiate between these two physiological processes. Here, quantitative proteome analyses of nitrogen fixing and non-nitrogen fixing nodules as well as fertilized and non-fertilized roots were performed using Vicia faba and Rhizobium leguminosarum. Pairwise comparisons revealed altered enzyme abundance between active and inactive nodules. Similarly, general differences between nodules and root tissue were observed. Together, these results allow distinguishing the proteins directly involved in nitrogen fixation from those related to nodulation. Further observations relate to the control of nodulation by hormones and provide supportive evidence for the previously reported correlation of nitrogen and sulfur fixation in these plant organs. Additionally, data on altered protein abundance relating to alanine metabolism imply that this amino acid may be exported from the symbiosomes of V. faba root nodules in addition to ammonia. Data are available via ProteomeXchange with identifier PXD008548.
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Affiliation(s)
- Beate Thal
- Institut für Pflanzengenetik, Leibniz Universität Hannover, Herrenhäuser Str. 2, 30419, Hanover, Germany
| | - Hans-Peter Braun
- Institut für Pflanzengenetik, Leibniz Universität Hannover, Herrenhäuser Str. 2, 30419, Hanover, Germany
| | - Holger Eubel
- Institut für Pflanzengenetik, Leibniz Universität Hannover, Herrenhäuser Str. 2, 30419, Hanover, Germany.
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5
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Valentine AJ, Kleinert A, Benedito VA. Adaptive strategies for nitrogen metabolism in phosphate deficient legume nodules. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2017; 256:46-52. [PMID: 28167037 DOI: 10.1016/j.plantsci.2016.12.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 12/17/2016] [Accepted: 12/19/2016] [Indexed: 05/23/2023]
Abstract
Legumes play a significant role in natural and agricultural ecosystems. They can fix atmospheric N2 and contribute the fixed N to soils and plant N budgets. In legumes, the availability of P does not only affect nodule development, but also N acquisition and metabolism. For legumes as an important source of plant proteins, their capacity to metabolise N during P deficiency is critical for their benefits to agriculture and the natural environment. In particular for farming, rock P is a non-renewable source of which the world has about 60-80 years of sustainable extraction of this P left. The global production of legume crops would be devastated during a scarcity of P fertiliser. Legume nodules have a high requirement for mineral P, which makes them vulnerable to soil P deficiencies. In order to maintain N metabolism, the nodules have evolved several strategies to resist the immediate effects of P limitation and to respond to prolonged P deficiency. In legumes nodules, N metabolism is determined by several processes involving the acquisition, assimilation, export, and recycling of N in various forms. Although these processes are integrated, the current literature lacks a clear synthesis of how legumes respond to P stress regarding its impact on N metabolism. In this review, we synthesise the current state of knowledge on how legumes maintain N metabolism during P deficiency. Moreover, we discuss the potential importance of two additional alterations to N metabolism during P deficiency. Our goals are to place these newly proposed mechanisms in perspective with other known adaptations of N metabolism to P deficiency and to discuss their practical benefits during P deficiency in legumes.
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Affiliation(s)
- Alex J Valentine
- Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa.
| | - Aleysia Kleinert
- Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa
| | - Vagner A Benedito
- Division of Plant & Soil Sciences, 3425 New Agricultural Sciences Building, West Virginia University, P.O. Box 6108, Morgantown, WV 26506-6108, USA
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Iyer B, Rajput MS, Jog R, Joshi E, Bharwad K, Rajkumar S. Organic acid mediated repression of sugar utilization in rhizobia. Microbiol Res 2016; 192:211-220. [PMID: 27664739 DOI: 10.1016/j.micres.2016.07.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 07/20/2016] [Accepted: 07/25/2016] [Indexed: 01/17/2023]
Abstract
Rhizobia are a class of symbiotic diazotrophic bacteria which utilize C4 acids in preference to sugars and the sugar utilization is repressed as long as C4 acids are present. This can be manifested as a diauxie when rhizobia are grown in the presence of a sugar and a C4 acid together. Succinate, a C4 acid is known to repress utilization of sugars, sugar alcohols, hydrocarbons, etc by a mechanism termed as Succinate Mediated Catabolite Repression (SMCR). Mechanism of catabolite repression determines the hierarchy of carbon source utilization in bacteria. Though the mechanism of catabolite repression has been well studied in model organisms like E. coli, B. subtilis and Pseudomonas sp., mechanism of SMCR in rhizobia has not been well elucidated. C4 acid uptake is important for effective symbioses while mutation in the sugar transport and utilization genes does not affect symbioses. Deletion of hpr and sma0113 resulted in the partial relief of SMCR of utilization of galactosides like lactose, raffinose and maltose in the presence of succinate. However, no such regulators governing SMCR of glucoside utilization have been identified till date. Though rhizobia can utilize multitude of sugars, high affinity transporters for many sugars are yet to be identified. Identifying high affinity sugar transporters and studying the mechanism of catabolite repression in rhizobia is important to understand the level of regulation of SMCR and the key regulators involved in SMCR.
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Affiliation(s)
- Bhagya Iyer
- Institute of Science, Nirma University, Ahmedabad, Gujarat, India
| | | | - Rahul Jog
- Institute of Science, Nirma University, Ahmedabad, Gujarat, India; Environmental Molecular Biology Laboratory, Division of Biosphere, Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Hokkaido, Japan
| | - Ekta Joshi
- Institute of Science, Nirma University, Ahmedabad, Gujarat, India
| | - Krishna Bharwad
- Institute of Science, Nirma University, Ahmedabad, Gujarat, India
| | - Shalini Rajkumar
- Institute of Science, Nirma University, Ahmedabad, Gujarat, India.
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Magadlela A, Vardien W, Kleinert A, Steenkamp ET, Valentine AJ. Variable P supply affects N metabolism in a legume tree, Virgilia divaricata, from nutrient-poor Mediterranean-type ecosystems. FUNCTIONAL PLANT BIOLOGY : FPB 2016; 43:287-297. [PMID: 32480461 DOI: 10.1071/fp15262] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 11/11/2015] [Indexed: 06/11/2023]
Abstract
Virgilia divaricata Adamson is a forest margin legume that is known to invade the N- and P-poor soils of the mature fynbos, implying that it tolerates variable soil N and P levels. It is not known how the legume uses inorganic N from soil and atmospheric sources under variable P supply. Little is known about how P deficiency affects the root nodule metabolic functioning of V. divaricata and the associated energy costs of N assimilation. This study aimed to determine whether P deficiency affects the metabolic status of roots and nodules, and the impact on the routes of N assimilation in V. divaricata.V. divaricata had reduced biomass, plant P concentration and biological nitrogen fixation during P deficiency. Based on adenylate data, P-stressed nodules maintained their P status better than P-stressed roots. V. divaricata was able to alter C and N metabolism differently in roots and nodules under P stress. This was achieved via internal P cycling by possible replacement of membrane phospholipids with sulfolipids and galactolipids, and increased reliance on the pyrophosphate (PPi)-dependent metabolism of sucrose via UDP-glucose (UDPG) and to fructose-6-phosphate (Fru-6-P). P-stressed roots mostly exported ureides as organic N and recycled amino acids via deaminating glutamate dehydrogenase. In contrast, P-stressed nodules largely exported amino acids. Compared with roots, nodules showed more P conservation during low P supply. The roots and nodules of V. divaricata metabolised N differently during P stress, meaning that these organs may contribute differently to the success of this plant in soils from forest to fynbos.
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Affiliation(s)
- Anathi Magadlela
- Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa
| | - Waafeka Vardien
- Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa
| | - Aleysia Kleinert
- Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa
| | - Emma T Steenkamp
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria 0002, South Africa
| | - Alexander J Valentine
- Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa
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8
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Abstract
Rhizobia are bacteria in the α-proteobacterial genera Rhizobium, Sinorhizobium, Mesorhizobium, Azorhizobium and Bradyrhizobium that reduce (fix) atmospheric nitrogen in symbiotic association with a compatible host plant. In free-living and/or symbiotically associated rhizobia, amino acids may, in addition to their incorporation into proteins, serve as carbon, nitrogen or sulfur sources, signals of cellular nitrogen status and precursors of important metabolites. Depending on the rhizobia-host plant combination, microsymbiont amino acid metabolism (biosynthesis, transport and/or degradation) is often crucial to the establishment and maintenance of an effective nitrogen-fixing symbiosis and is intimately interconnected with the metabolism of the plant. This review summarizes past findings and current research directions in rhizobial amino acid metabolism and evaluates the genetic, biochemical and genome expression studies from which these are derived. Specific sections deal with the regulation of rhizobial amino acid metabolism, amino acid transport, and finally the symbiotic roles of individual amino acids in different plant-rhizobia combinations.
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9
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Salt tolerance of nitrogen fixation in Medicago ciliaris is related to nodule sucrose metabolism performance rather than antioxidant system. Symbiosis 2010. [DOI: 10.1007/s13199-010-0073-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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10
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Tcherkez G. Natural 15N/ 14N isotope composition in C 3 leaves: are enzymatic isotope effects informative for predicting the 15N-abundance in key metabolites? FUNCTIONAL PLANT BIOLOGY : FPB 2010; 38:1-12. [PMID: 32480857 DOI: 10.1071/fp10091] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Accepted: 10/24/2010] [Indexed: 06/11/2023]
Abstract
Although nitrogen isotopes are viewed as important tools for understanding plant N acquisition and allocation, the current interpretation of natural 15N-abundances (δ15N values) is often impaired by substantial variability among individuals or between species. Such variability is likely to stem from the fact that 15N-abundance of assimilated N is not preserved during N metabolism and redistribution within the plant; that is, 14N/15N isotope effects associated with N metabolic reactions are certainly responsible for isotopic shifts between organic-N (amino acids) and absorbed inorganic N (nitrate). Therefore, to gain insights into the metabolic origin of 15N-abundance in plants, the present paper reviews enzymatic isotope effects and integrates them into a metabolic model at the leaf level. Using simple steady-state equations which satisfactorily predict the δ15N value of amino acids, it is shown that the sensitivity of δ15N values to both photorespiratory and N-input (reduction by nitrate reductase) rates is quite high. In other words, the variability in δ15N values observed in nature might originate from subtle changes in metabolic fluxes or environment-driven effects, such as stomatal closure that in turn changes v0, the Rubisco-catalysed oxygenation rate.
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Affiliation(s)
- Guillaume Tcherkez
- Institut de Biologie des Plantes, CNRS UMR 8618, Université Paris-Sud 11, 91405 Orsay Cedex, France. Email
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11
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An alternative succinate (2-oxoglutarate) transport system in Rhizobium tropici is induced in nodules of Phaseolus vulgaris. J Bacteriol 2009; 191:5057-67. [PMID: 19502401 DOI: 10.1128/jb.00252-09] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The rhizobial DctA permease is essential for the development of effective nitrogen-fixing bacteroids, which was correlated with its requirement for growth on C(4)-dicarboxylates. A previously described dctA mutant of Rhizobium tropici CIAT899, strain GA1 (dctA), however, was unexpectedly still able to grow on succinate as a sole carbon source but less efficiently than CIAT899. Like other rhizobial dctA mutants, GA1 was unable to grow on fumarate or malate as a carbon source and induced the formation of ineffective nodules. We report an alternative succinate uptake system identified by Tn5 mutagenesis of strain GA1 that was required for the remaining ability to transport and utilize succinate. The alternative uptake system required a three-gene cluster that is highly characteristic of a dctABD locus. The predicted permease-encoding gene had high sequence similarity with open reading frames encoding putative 2-oxoglutarate permeases (KgtP) of Ralstonia solanacearum and Agrobacterium tumefaciens. This analysis was in agreement with the requirement for this gene for optimal growth on and induction by 2-oxoglutarate. The permease-encoding gene of the alternative system was also designated kgtP in R. tropici. The dctBD-like genes in this cluster were found to be required for kgtP expression and were designated kgtSR. Analysis of a kgtP::lacZ transcriptional fusion indicated that a kgtSR-dependent promoter of kgtP was specifically induced by 2-oxoglutarate. The expression of kgtPp was found in bacteroids of nodules formed with either CIAT899 or GA1 on roots of Phaseolus vulgaris. Results suggested that 2-oxoglutarate might be transported or conceivably exported in nodules induced by R. tropici on roots of P. vulgaris.
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12
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White JP, Prell J, Ramachandran VK, Poole PS. Characterization of a {gamma}-aminobutyric acid transport system of Rhizobium leguminosarum bv. viciae 3841. J Bacteriol 2009; 191:1547-55. [PMID: 19103927 PMCID: PMC2648222 DOI: 10.1128/jb.00926-08] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Accepted: 12/09/2008] [Indexed: 12/29/2022] Open
Abstract
Spontaneous mutants of Rhizobium leguminosarum bv. viciae 3841 were isolated that grow faster than the wild type on gamma-aminobutyric acid (GABA) as the sole carbon and nitrogen source. These strains (RU1736 and RU1816) have frameshift mutations (gtsR101 and gtsR102, respectively) in a GntR-type regulator (GtsR) that result in a high rate of constitutive GABA transport. Tn5 mutagenesis and quantitative reverse transcription-PCR showed that GstR regulates expression of a large operon (pRL100242 to pRL100252) on the Sym plasmid that is required for GABA uptake. An ABC transport system, GtsABCD (for GABA transport system) (pRL100248-51), of the spermidine/putrescine family is part of this operon. GtsA is a periplasmic binding protein, GtsB and GtsC are integral membrane proteins, and GtsD is an ATP-binding subunit. Expression of gtsABCD from a lacZ promoter confirmed that it alone is responsible for high rates of GABA transport, enabling rapid growth of strain 3841 on GABA. Gts transports open-chain compounds with four or five carbon atoms with carboxyl and amino groups at, or close to, opposite termini. However, aromatic compounds with similar spacing between carboxyl and amino groups are excellent inhibitors of GABA uptake so they may also be transported. In addition to the ABC transporter, the operon contains two putative mono-oxygenases, a putative hydrolase, a putative aldehyde dehydrogenase, and a succinate semialdehyde dehydrogenase. This suggests the operon may be involved in the transport and breakdown of a more complex precursor to GABA. Gts is not expressed in pea bacteroids, and gtsB mutants are unaltered in their symbiotic phenotype, suggesting that Bra is the only GABA transport system available for amino acid cycling.
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Affiliation(s)
- J P White
- University of Reading, United Kingdom
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13
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White J, Prell J, James EK, Poole P. Nutrient sharing between symbionts. PLANT PHYSIOLOGY 2007; 144:604-14. [PMID: 17556524 PMCID: PMC1914197 DOI: 10.1104/pp.107.097741] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2007] [Accepted: 04/30/2007] [Indexed: 05/15/2023]
Affiliation(s)
- James White
- School of Biological Sciences, University of Reading, Whiteknights Reading RG6 6AJ, United Kingdom
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14
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Fox MA, White JP, Hosie AHF, Lodwig EM, Poole PS. Osmotic upshift transiently inhibits uptake via ABC transporters in gram-negative bacteria. J Bacteriol 2006; 188:5304-7. [PMID: 16816205 PMCID: PMC1539945 DOI: 10.1128/jb.00262-06] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
ATP-binding cassette transporters from several rhizobia and Salmonella enterica serovar Typhimurium, but not secondarily coupled systems, were inhibited by high concentrations (100 to 500 mM) of various osmolytes, an effect reversed by the removal of the osmolyte. ABC systems were also inactivated in isolated pea bacteroids, probably due to the obligatory use of high-osmolarity isolation media. Measurement of nutrient cycling in isolated pea bacteroids is impeded by this effect.
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Affiliation(s)
- M A Fox
- School of Biological Sciences, University of Reading, Whiteknights, P.O. Box 228, Reading RG6 6AJ, United Kingdom.
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15
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Prell J, Poole P. Metabolic changes of rhizobia in legume nodules. Trends Microbiol 2006; 14:161-8. [PMID: 16520035 DOI: 10.1016/j.tim.2006.02.005] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2005] [Revised: 02/06/2006] [Accepted: 02/21/2006] [Indexed: 12/01/2022]
Abstract
Bacteria have evolved a wide variety of metabolic strategies to cope with varied environments. Some are specialists and only able to survive in restricted environments; others are generalists and able to cope with diverse environmental conditions. Rhizobia (e.g. Rhizobium, Sinorhizobium, Bradyrhizobium, Mesorhizobium and Azorhizobium species) can survive and compete for nutrients in soil and the plant rhizosphere but can also form a beneficial symbiosis with legumes in a highly specialized plant cell environment. Inside the legume-root nodule, the bacteria (bacteroids) reduce dinitrogen to ammonium, which is secreted to the plant in exchange for a carbon and energy source. A new and challenging aspect of nodule physiology is that nitrogen fixation requires the cycling of amino acids between the bacteroid and plant. This review aims to summarize the metabolic plasticity of rhizobia and the importance of amino acid cycling.
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Affiliation(s)
- Juergen Prell
- School of Biological Sciences, University of Reading, UK, RG6 6AJ
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Kumar S, Bourdès A, Poole P. De novo alanine synthesis by bacteroids of Mesorhizobium loti is not required for nitrogen transfer in the determinate nodules of Lotus corniculatus. J Bacteriol 2005; 187:5493-5. [PMID: 16030244 PMCID: PMC1196047 DOI: 10.1128/jb.187.15.5493-5495.2005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Deletion of both alanine dehydrogenase genes (aldA) in Mesorhizobium loti resulted in the loss of AldA enzyme activity from cultured bacteria and bacteroids but had no effect on the symbiotic performance of Lotus corniculatus plants. Thus, neither indeterminate pea nodules nor determinate L. corniculatus nodules export alanine as the sole nitrogen secretion product.
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Affiliation(s)
- Shalini Kumar
- School of Animal and Microbial Sciences, University of Reading, Whiteknights, P.O. Box 228, Reading RG6 6AJ, United Kingdom
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17
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Ramírez M, Graham MA, Blanco-López L, Silvente S, Medrano-Soto A, Blair MW, Hernández G, Vance CP, Lara M. Sequencing and analysis of common bean ESTs. Building a foundation for functional genomics. PLANT PHYSIOLOGY 2005. [PMID: 15824284 DOI: 10.1104/pp.104.054999.gumes] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Although common bean (Phaseolus vulgaris) is the most important grain legume in the developing world for human consumption, few genomic resources exist for this species. The objectives of this research were to develop expressed sequence tag (EST) resources for common bean and assess nodule gene expression through high-density macroarrays. We sequenced a total of 21,026 ESTs derived from 5 different cDNA libraries, including nitrogen-fixing root nodules, phosphorus-deficient roots, developing pods, and leaves of the Mesoamerican genotype, Negro Jamapa 81. The fifth source of ESTs was a leaf cDNA library derived from the Andean genotype, G19833. Of the total high-quality sequences, 5,703 ESTs were classified as singletons, while 10,078 were assembled into 2,226 contigs producing a nonredundant set of 7,969 different transcripts. Sequences were grouped according to 4 main categories, metabolism (34%), cell cycle and plant development (11%), interaction with the environment (19%), and unknown function (36%), and further subdivided into 15 subcategories. Comparisons to other legume EST projects suggest that an entirely different repertoire of genes is expressed in common bean nodules. Phaseolus-specific contigs, gene families, and single nucleotide polymorphisms were also identified from the EST collection. Functional aspects of individual bean organs were reflected by the 20 contigs from each library composed of the most redundant ESTs. The abundance of transcripts corresponding to selected contigs was evaluated by RNA blots to determine whether gene expression determined by laboratory methods correlated with in silico expression. Evaluation of root nodule gene expression by macroarrays and RNA blots showed that genes related to nitrogen and carbon metabolism are integrated for ureide production. Resources developed in this project provide genetic and genomic tools for an international consortium devoted to bean improvement.
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Affiliation(s)
- Mario Ramírez
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado 66210 Cuernavaca, Morelos, Mexico
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18
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Ramírez M, Graham MA, Blanco-López L, Silvente S, Medrano-Soto A, Blair MW, Hernández G, Vance CP, Lara M. Sequencing and analysis of common bean ESTs. Building a foundation for functional genomics. PLANT PHYSIOLOGY 2005; 137:1211-27. [PMID: 15824284 PMCID: PMC1088315 DOI: 10.1104/pp.104.054999] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2004] [Revised: 01/21/2005] [Accepted: 01/30/2005] [Indexed: 05/18/2023]
Abstract
Although common bean (Phaseolus vulgaris) is the most important grain legume in the developing world for human consumption, few genomic resources exist for this species. The objectives of this research were to develop expressed sequence tag (EST) resources for common bean and assess nodule gene expression through high-density macroarrays. We sequenced a total of 21,026 ESTs derived from 5 different cDNA libraries, including nitrogen-fixing root nodules, phosphorus-deficient roots, developing pods, and leaves of the Mesoamerican genotype, Negro Jamapa 81. The fifth source of ESTs was a leaf cDNA library derived from the Andean genotype, G19833. Of the total high-quality sequences, 5,703 ESTs were classified as singletons, while 10,078 were assembled into 2,226 contigs producing a nonredundant set of 7,969 different transcripts. Sequences were grouped according to 4 main categories, metabolism (34%), cell cycle and plant development (11%), interaction with the environment (19%), and unknown function (36%), and further subdivided into 15 subcategories. Comparisons to other legume EST projects suggest that an entirely different repertoire of genes is expressed in common bean nodules. Phaseolus-specific contigs, gene families, and single nucleotide polymorphisms were also identified from the EST collection. Functional aspects of individual bean organs were reflected by the 20 contigs from each library composed of the most redundant ESTs. The abundance of transcripts corresponding to selected contigs was evaluated by RNA blots to determine whether gene expression determined by laboratory methods correlated with in silico expression. Evaluation of root nodule gene expression by macroarrays and RNA blots showed that genes related to nitrogen and carbon metabolism are integrated for ureide production. Resources developed in this project provide genetic and genomic tools for an international consortium devoted to bean improvement.
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Affiliation(s)
- Mario Ramírez
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado 66210 Cuernavaca, Morelos, Mexico
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19
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Lodwig EM, Hosie AHF, Bourdès A, Findlay K, Allaway D, Karunakaran R, Downie JA, Poole PS. Amino-acid cycling drives nitrogen fixation in the legume-Rhizobium symbiosis. Nature 2003; 422:722-6. [PMID: 12700763 DOI: 10.1038/nature01527] [Citation(s) in RCA: 269] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2002] [Accepted: 02/25/2003] [Indexed: 11/08/2022]
Abstract
The biological reduction of atmospheric N2 to ammonium (nitrogen fixation) provides about 65% of the biosphere's available nitrogen. Most of this ammonium is contributed by legume-rhizobia symbioses, which are initiated by the infection of legume hosts by bacteria (rhizobia), resulting in formation of root nodules. Within the nodules, rhizobia are found as bacteroids, which perform the nitrogen fixation: to do this, they obtain sources of carbon and energy from the plant, in the form of dicarboxylic acids. It has been thought that, in return, bacteroids simply provide the plant with ammonium. But here we show that a more complex amino-acid cycle is essential for symbiotic nitrogen fixation by Rhizobium in pea nodules. The plant provides amino acids to the bacteroids, enabling them to shut down their ammonium assimilation. In return, bacteroids act like plant organelles to cycle amino acids back to the plant for asparagine synthesis. The mutual dependence of this exchange prevents the symbiosis being dominated by the plant, and provides a selective pressure for the evolution of mutualism.
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Affiliation(s)
- E M Lodwig
- School of Animal and Microbial Sciences, University of Reading, Whiteknights, PO Box 228, Reading RG6 6AJ, UK
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20
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Abstract
One of the paradigms of symbiotic nitrogen fixation has been that bacteroids reduce N2 to ammonium and secrete it without assimilation into amino acids. This has recently been challenged by work with soybeans showing that only alanine is excreted in 15N2 labelling experiments. Work with peas shows that the bacteroid nitrogen secretion products during in vitro experiments depend on the experimental conditions. There is a mixed secretion of both ammonium and alanine depending critically on the concentration of bacteroids and ammonium concentration. The pathway of alanine synthesis has been shown to be via alanine dehydrogenase, and mutation of this enzyme indicates that in planta there is likely to be mixed secretion of ammonium and alanine. Alanine synthesis directly links carbon catabolism and nitrogen assimilation in the bacteroid. There is now overwhelming evidence that the principal carbon sources of bacteroids are the C4-dicarboxylic acids. This is based on labelling and bacteroid respiration data, and mutation of both the dicarboxylic acid transport system (dct) and malic enzyme. L-malate is at a key bifurcation point in bacteroid metabolism, being oxidized to oxaloacetate and oxidatively decarboxylated to pyruvate. Pyruvate can be aminated to alanine or converted to acetyl-CoA where it either enters the TCA cycle by condensation with oxaloacetate or forms polyhydroxybutyrate (PHB). Thus regulation of carbon and nitrogen metabolism are strongly connected. Efficient catabolism of C4-dicarboxylates requires the balanced input and removal of intermediates from the TCA cycle. The TCA cycle in bacteroids may be limited by the redox state of NADH/NAD+ at the 2-ketoglutarate dehydrogenase complex, and a number of pathways may be involved in bypassing this block. These pathways include PHB synthesis, glutamate synthesis, glycogen synthesis, GABA shunt and glutamine cycling. Their operation may be critical in maintaining the optimum redox poise and carbon balance of the TCA cycle. They can also be considered to be overflow pathways since they act to remove or add electrons and carbon into the TCA cycle. Optimum operation of the TCA cycle has a major impact on nitrogen fixation.
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Affiliation(s)
- P Poole
- Division of Microbiology, School of Animal and Microbial Sciences, University of Reading, UK
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21
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Allaway D, Lodwig EM, Crompton LA, Wood M, Parsons R, Wheeler TR, Poole PS. Identification of alanine dehydrogenase and its role in mixed secretion of ammonium and alanine by pea bacteroids. Mol Microbiol 2000; 36:508-15. [PMID: 10792736 DOI: 10.1046/j.1365-2958.2000.01884.x] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
N2-fixation by Rhizobium-legume symbionts is of major ecological and agricultural importance, responsible for producing a substantial fraction of the biosphere's nitrogen. On the basis of 15N-labelling studies, it had been generally accepted that ammonium is the sole secretion product of N2-fixation by the bacteroid and that the plant is responsible for assimilating it into amino acids. However, this paradigm has been challenged in a recent 15N-labelling study showing that soybean bacteroids only secrete alanine. Hitherto, nitrogen secretion has only been assessed from in vitro 15N-labelling studies of isolated bacteroids. We show that both ammonium and alanine are secreted by pea bacteroids. The in vitro partitioning between them will depend on whether the system is open or closed, as well as the ammonium concentration and bacteroid density. To overcome these limitations we identified and mutated the gene for alanine dehydrogenase (aldA) and demonstrate that AldA is the primary route for alanine synthesis in isolated bacteroids. Bacteroids of the aldA mutant fix nitrogen but only secrete ammonium at a significant rate, resulting in lower total nitrogen secretion. Peas inoculated with the aldA mutant are green and healthy, demonstrating that ammonium secretion by bacteroids can provide sufficient nitrogen for plant growth. However, plants inoculated with the mutant are reduced in biomass compared with those inoculated with the wild type. The labelling and plant growth studies suggest that alanine synthesis and secretion contributes to the efficiency of N2-fixation and therefore biomass accumulation.
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Affiliation(s)
- D Allaway
- School of Animal and Microbial Sciences, and Department of Soil Science, University of Reading, Reading, UK RG6 6AJ
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22
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Waters JK, Hughes BL, Purcell LC, Gerhardt KO, Mawhinney TP, Emerich DW. Alanine, not ammonia, is excreted from N2-fixing soybean nodule bacteroids. Proc Natl Acad Sci U S A 1998; 95:12038-42. [PMID: 9751786 PMCID: PMC21761 DOI: 10.1073/pnas.95.20.12038] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Symbiotic nitrogen fixation, the process whereby nitrogen-fixing bacteria enter into associations with plants, provides the major source of nitrogen for the biosphere. Nitrogenase, a bacterial enzyme, catalyzes the reduction of atmospheric dinitrogen to ammonium. In rhizobia-leguminous plant symbioses, the current model of nitrogen transfer from the symbiotic form of the bacteria, called a bacteroid, to the plant is that nitrogenase-generated ammonia diffuses across the bacteroid membrane and is assimilated into amino acids outside of the bacteroid. We purified soybean nodule bacteroids by a procedure that removed contaminating plant proteins and found that alanine was the major nitrogen-containing compound excreted. Bacteroids incubated in the presence of 15N2 excreted alanine highly enriched in 15N. The ammonium in these assays neither accumulated significantly nor was enriched in 15N. The results demonstrate that a transport mechanism rather than diffusion functions at this critical step of nitrogen transfer from the bacteroids to the plant host. Alanine may serve only as a transport species, but this would permit physiological separation of the transport of fixed nitrogen from other nitrogen metabolic functions commonly mediated through glutamate.
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Affiliation(s)
- J K Waters
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
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23
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Walshaw DL, Wilkinson A, Mundy M, Smith M, Poole PS. Regulation of the TCA cycle and the general amino acid permease by overflow metabolism in Rhizobium leguminosarum. MICROBIOLOGY (READING, ENGLAND) 1997; 143 ( Pt 7):2209-2221. [PMID: 9245810 DOI: 10.1099/00221287-143-7-2209] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Mutants of Rhizobium leguminosarum were selected that were altered in the uptake activity of the general amino acid permease (Aap). The main class of mutant maps to sucA and sucD, which are part of a gene cluster mdh-sucCDAB, which codes for malate dehydrogenase (mdh), succinyl-CoA synthetase (sucCD) and components of the 2-oxoglutarate dehydrogenase complex (sucAB). Mutation of either sucC or sucD prevents expression of 2-oxoglutarate dehydrogenase (sucAB). Conversely, mutation of sucA or sucB results in much higher levels of succinyl-CoA synthetase and malate dehydrogenase activity. These results suggest that the genes mdh-sucCDAB may constitute an operon. suc mutants, unlike the wild-type, excrete large quantities of glutamate and 2-oxoglutarate. Concomitant with mutation of sucA or sucD, the intracellular concentration of glutamate but no 2-oxoglutarate was highly elevated, suggesting that 2-oxoglutarate normally feeds into the glutamate pool. Elevation of the intracellular glutamate pool appeared to be coupled to glutamate excretion as part of an overflow pathway for regulation of the TCA cycle. Amino acid uptake via the Aap of R. leguminosarum was strongly inhibited in the suc mutants, even though the transcription level of the aap operon was the same as the wild-type. This is consistent with previous observations that the Aap, which influences glutamate excretion in R. leguminosarum, has uptake inhibited when excretion occurs. Another class of mutant impaired in uptake by the Aap is mutated in polyhydroxybutyrate synthase (phaC). Mutants of succinyl-CoA synthetase (sucD) or 2-oxoglutarate dehydrogenase (sucA) form ineffective nodules. However, mutants of aap, which are unable to grow on glutamate as a carbon source in laboratory culture, show wild-type levels of nitrogen fixation. This indicates that glutamate is not an important carbon and energy source in the bacteroid. Instead glutamate synthesis, like polyhydroxybutyrate synthesis, appears to be a sink for carbon and reductant, formed when the 2-oxoglutarate dehydrogenase complex is blocked. This is in accord with previous observations that bacteroids synthesize high concentrations of glutamate. Overall the data show that the TCA cycle in R. leguminosarum is regulated by amino acid excretion and polyhydroxybutyrate biosynthesis which act as overflow pathways for excess carbon and reductant.
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Affiliation(s)
- David L Walshaw
- School of Animal and Microbial Sciences, University of Reading, Whiteknights PO Box 228, Reading RG6 6AJ, UK
| | - Adam Wilkinson
- School of Animal and Microbial Sciences, University of Reading, Whiteknights PO Box 228, Reading RG6 6AJ, UK
| | - Mathius Mundy
- School of Animal and Microbial Sciences, University of Reading, Whiteknights PO Box 228, Reading RG6 6AJ, UK
| | - Mary Smith
- School of Animal and Microbial Sciences, University of Reading, Whiteknights PO Box 228, Reading RG6 6AJ, UK
| | - Philip S Poole
- School of Animal and Microbial Sciences, University of Reading, Whiteknights PO Box 228, Reading RG6 6AJ, UK
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24
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Haaker H, Szafran M, Wassink H, Klerk H, Appels M. Respiratory control determines respiration and nitrogenase activity of Rhizobium leguminosarum bacteroids. J Bacteriol 1996; 178:4555-62. [PMID: 8755884 PMCID: PMC178223 DOI: 10.1128/jb.178.15.4555-4562.1996] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The relationship between the O2 input rate into a suspension of Rhizobium leguminosarum bacteroids, the cellular ATP and ADP pools, and the whole-cell nitrogenase activity during L-malate oxidation has been studied. It was observed that inhibition of nitrogenase by excess O2 coincided with an increase of the cellular ATP/ADP ratio. When under this condition the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) was added, the cellular ATP/ADP ratio was lowered while nitrogenase regained activity. To explain these observations, the effects of nitrogenase activity and CCCP on the O2 consumption rate of R. leguminosarum bacteroids were determined. From 100 to 5 microM O2, a decline in the O2 consumption rate was observed to 50 to 70% of the maximal O2 consumption rate. A determination of the redox state of the cytochromes during an O2 consumption experiment indicated that at O2 concentrations above 5 microM, electron transport to the cytochromes was rate-limiting oxidation and not the reaction of reduced cytochromes with oxygen. The kinetic properties of the respiratory chain were determined from the deoxygenation of oxyglobins. In intact cells the maximal deoxygenation activity was stimulated by nitrogenase activity or CCCP. In isolated cytoplasmic membranes NADH oxidation was inhibited by respiratory control. The dehydrogenase activities of the respiratory chain were rate-limiting oxidation at O2 concentrations (if >300 nM. Below 300 nM the terminal oxidase system followed Michaelis-Menten kinetics (Km of 45 +/- 8 nM). We conclude that (i) respiration in R. leguminosarum bacteroids takes place via a respiratory chain terminating at a high-affinity oxidase system, (ii) the activity of the respiratory chain is inhibited by the proton motive force, and (iii) ATP hydrolysis by nitrogenase can partly relieve the inhibition of respiration by the proton motive force and thus stimulate respiration at nanomolar concentrations of O2.
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Affiliation(s)
- H Haaker
- Department of Biochemistry, Agricultural University, Wageningen, The Netherlands
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25
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Malate, Aspartate and Proton Exchange Between Rhizobium Leguminosarvm Symbiosomes and Its Symbiotic Partner Pisum Sativum. ACTA ACUST UNITED AC 1995. [DOI: 10.1007/978-94-011-0379-4_67] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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26
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Alfano JR, Kahn ML. Isolation and characterization of a gene coding for a novel aspartate aminotransferase from Rhizobium meliloti. J Bacteriol 1993; 175:4186-96. [PMID: 8320232 PMCID: PMC204848 DOI: 10.1128/jb.175.13.4186-4196.1993] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Aspartate aminotransferase (AAT) is an important enzyme in aspartate catabolism and biosynthesis and, by converting tricarboxylic acid cycle intermediates to amino acids, AAT is also significant in linking carbon metabolism with nitrogen metabolism. To examine the role of AAT in symbiotic nitrogen fixation further, plasmids encoding three different aminotransferases from Rhizobium meliloti 104A14 were isolated by complementation of an Escherichia coli auxotroph that lacks three aminotransferases. pJA10 contained a gene, aatB, that coded for a previously undescribed AAT, AatB. pJA30 encoded an aromatic aminotransferase, TatA, that had significant AAT activity, and pJA20 encoded a branched-chain aminotransferase designated BatA. Genes for the latter two enzymes, tatA and batA, were previously isolated from R. meliloti. aatB is distinct from but hybridizes to aatA, which codes for AatA, a protein required for symbiotic nitrogen fixation. The DNA sequence of aatB contained an open reading frame that could encode a protein 410 amino acids long and with a monomer molecular mass of 45,100 Da. The amino acid sequence of aatB is unusual, and AatB appears to be a member of a newly described class of AATs. AatB expressed in E. coli has a Km for aspartate of 5.3 mM and a Km for 2-oxoglutarate of 0.87 mM. Its pH optimum is between 8.0 and 8.5. Mutations were constructed in aatB and tatA and transferred to the genome of R. meliloti 104A14. Both mutants were prototrophs and were able to carry out symbiotic nitrogen fixation.
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Affiliation(s)
- J R Alfano
- Institute of Biological Chemistry, Washington State University, Pullman 99164-6340
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27
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Watson RJ, Rastogi VK. Cloning and nucleotide sequencing of Rhizobium meliloti aminotransferase genes: an aspartate aminotransferase required for symbiotic nitrogen fixation is atypical. J Bacteriol 1993; 175:1919-28. [PMID: 8096210 PMCID: PMC204262 DOI: 10.1128/jb.175.7.1919-1928.1993] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
In Rhizobium meliloti, an aspartate aminotransferase (AspAT) encoded within a 7.3-kb HindIII fragment was previously shown to be required for symbiotic nitrogen fixation and aspartate catabolism (V. K. Rastogi and R.J. Watson, J. Bacteriol. 173:2879-2887, 1991). A gene coding for an aromatic aminotransferase located within an 11-kb HindIII fragment was found to complement the AspAT deficiency when overexpressed. The genes encoding these two aminotransferases, designated aatA and tatA, respectively, have been localized by subcloning and transposon Tn5 mutagenesis. Sequencing of the tatA gene revealed that it encodes a protein homologous to an Escherichia coli aromatic aminotransferase and most of the known AspAT enzymes. However, sequencing of the aatA gene region revealed two overlapping open reading frames, neither of which encoded an enzyme with homology to the typical AspATs. Polymerase chain reaction was used to selectively generate one of the candidate sequences for subcloning. The cloned fragment complemented the original nitrogen fixation and aspartate catabolism defects and was shown to encode an AspAT with the expected properties. Sequence analysis showed that the aatA protein has homology to AspATs from two thermophilic bacteria and the eukaryotic tyrosine aminotransferases. These aminotransferases form a distinct class in which only 13 amino acids are conserved in comparison with the well-known AspAT family. DNA homologous to the aatA gene was found to be present in Agrobacterium tumefaciens and other rhizobia but not in Klebsiella pneumoniae or E. coli.
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Affiliation(s)
- R J Watson
- Plant Research Centre, Agriculture Canada, Ottawa, Ontario
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28
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Udvardi MK, Kahn ML. Isolation and analysis of a cDNA clone that encodes an alfalfa (Medicago sativa) aspartate aminotransferase. MOLECULAR & GENERAL GENETICS : MGG 1991; 231:97-105. [PMID: 1753949 DOI: 10.1007/bf00293827] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have isolated an alfalfa leaf cDNA clone that encodes aspartate aminotransferase (AAT, EC 2.6.1.1) by direct complementation of an Escherichia coli aspartate auxotroph with a plasmid cDNA library. DNA sequence analysis of the recombinant plasmid, pMU1, revealed that a 1514 bp cDNA was inserted in the correct orientation and in-frame with the start of the lacZ coding sequence in the vector, pUC18. The resulting fusion protein is predicted to be 424 amino acids in length with a molecular weight of 46387 Daltons. The cDNA-encoded protein has a characteristic pyridoxal phosphate attachment site motif and has substantial amino acid sequence homology to both animal and bacterial AATs. Plasmid pMU1 encodes an AAT with a Km for aspartate of 3.3 mM, a Km for 2-oxoglutarate of 0.28 mM, and a pH optimum between 8.0 and 8.5. Several lines of evidence including Western blot analysis, the isoelectric point of the encoded protein, and the effect of pH on the activity of the fusion protein, suggest that the cDNA encodes the isozyme AAT-1 rather than AAT-2. Northern blot analysis showed that the aat-1 clone hybridized to a 1.6 kb transcript present in alfalfa leaves, roots and nodules. The relative concentrations of aat-1 mRNA in these tissues were 1:2:5, respectively. Thus, transcription of aat-1 appears to be induced during nodule development. Southern blot analysis suggested that AAT-1 in alfalfa is encoded by either a single-copy gene or a small, multigene family.
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Affiliation(s)
- M K Udvardi
- Institute of Biological Chemistry, Washington State University, Pullman 99164-6340
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