101
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Gray J, Janick-Buckner D, Buckner B, Close PS, Johal GS. Light-dependent death of maize lls1 cells is mediated by mature chloroplasts. PLANT PHYSIOLOGY 2002; 130:1894-907. [PMID: 12481072 PMCID: PMC166700 DOI: 10.1104/pp.008441] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2002] [Revised: 06/25/2002] [Accepted: 08/30/2002] [Indexed: 05/18/2023]
Abstract
We reported previously the isolation of a novel cell death-suppressing gene from maize (Zea mays) encoded by the Lls1 (Lethal leaf spot-1) gene. Although the exact metabolic function of LLS1 remains elusive, here we provide insight into mechanisms that underlie the initiation and propagation of cell death associated with lls1 lesions. Our data indicate that lls1 lesions are triggered in response to a cell-damaging event caused by any biotic or abiotic agent or intrinsic metabolic imbalance--as long as the leaf tissue is developmentally competent to develop lls1 lesions. Continued expansion of these lesions, however, depends on the availability of light, with fluence rate being more important than spectral quality. Double-mutant analysis of lls1 with two maize mutants oil-yellow and iojap, both compromised photosynthetically and unable to accumulate normal levels of chlorophyll, indicated that it was the light harvested by the plant that energized lls1 lesion development. Chloroplasts appear to be the key mediators of lls1 cell death; their swelling and distortion occurs before any other changes normally associated with dying cells. In agreement with these results are indications that LLS1 is a chloroplast-localized protein whose transcript was detected only in green tissues. The propagative nature of light-dependent lls1 lesions predicts that cell death associated with these lesions is caused by a mobile agent such as reactive oxidative species. LLS1 may act to prevent reactive oxidative species formation or serve to remove a cell death mediator so as to maintain chloroplast integrity and cell survival.
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Affiliation(s)
- John Gray
- Department of Biological Sciences, The University of Toledo, Ohio 43606, USA.
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102
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Hibino T, Waditee R, Araki E, Ishikawa H, Aoki K, Tanaka Y, Takabe T. Functional characterization of choline monooxygenase, an enzyme for betaine synthesis in plants. J Biol Chem 2002; 277:41352-60. [PMID: 12192001 DOI: 10.1074/jbc.m205965200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In plants, the first step in betaine synthesis was shown to be catalyzed by a novel Rieske-type iron-sulfur enzyme, choline monooxygenase (CMO). Although CMO so far has been found only in Chenopodiaceae and Amaranthaceae, the recent genome sequence suggests the presence of a CMO-like gene in Arabidopsis, a betaine non-accumulating plant. Here, we examined the functional properties of CMO expressed in Escherichia coli, cyanobacterium, and Arabidopsis thaliana. We found that E. coli cells in which choline dehydrogenase (CDH) was replaced with spinach CMO accumulate betaine and complement the salt-sensitive phenotype of the CDH-deleted E. coli mutant. Changes of Cys-181 in spinach CMO to Ser, Thr, and Ala and His-287 to Gly, Val, and Ala abolished the accumulation of betaine. The Arabidopsis CMO-like gene was transcribed in Arabidopsis, but its protein was not detected. When the Arabidopsis CMO-like gene was expressed in E. coli, the protein was detected but was found not to promote betaine sysnthesis. Overexpression of spinach CMO in E. coli, Synechococcus sp. PCC7942, and Arabidopsis conferred resistance to abiotic stress. These facts clearly indicate that CMO, but not the CMO-like protein, could oxidize choline and that Cys-181 and His-287 are involved in the binding of Fe-S cluster and Fe, respectively.
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Affiliation(s)
- Takashi Hibino
- Graduate School of Environmental and Human Sciences and the Research Institute, Meijo University, Nagoya, 468-8502, Japan
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103
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Chen THH, Murata N. Enhancement of tolerance of abiotic stress by metabolic engineering of betaines and other compatible solutes. CURRENT OPINION IN PLANT BIOLOGY 2002; 5:250-7. [PMID: 11960744 DOI: 10.1016/s1369-5266(02)00255-8] [Citation(s) in RCA: 339] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The accumulation of compatible solutes, such as betaines, proline and sugar alcohols, is a widespread response that may protect plants against environmental stress. It is not yet fully understood how these compounds are involved in the stress tolerance of whole plants. Some plants have been genetically engineered to express enzymes that catalyze the synthesis of various compatible solutes. Some interventions have increased the tolerance of some crop plants to abiotic stress. Furthermore, analysis of such transgenic plants has begun to clarify the roles of compatible solutes in stress tolerance.
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Affiliation(s)
- Tony H H Chen
- Department of Horticulture, Oregon State University, Corvallis, Oregon, USA
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104
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Waditee R, Hibino T, Tanaka Y, Nakamura T, Incharoensakdi A, Hayakawa S, Suzuki S, Futsuhara Y, Kawamitsu Y, Takabe T, Takabe T. Functional characterization of betaine/proline transporters in betaine-accumulating mangrove. J Biol Chem 2002; 277:18373-82. [PMID: 11907031 DOI: 10.1074/jbc.m112012200] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Betaine is an important osmoprotectant in many plants, but its transport activity has only been demonstrated using a proline transporter from tomato, a betaine-nonaccumulating plant. In this study, two full-length and one partial transporter genes were isolated from betaine-accumulating mangrove Avicennia marina. Their homologies to betaine transporters from bacteria and betaine/4-aminobutyrate transporters from mammalian cells were low but were high to proline transporters from Arabidopsis and tomato. Two full-length transporters could complement the Na(+)-sensitive phenotype of the Escherichia coli mutant deficient in betT, putPA, proP, and proU. Both transporters could efficiently take up betaine and proline with similar affinities (K(m), 0.32-0.43 mm) and maximum velocities (1.9-3.6 nmol/min/mg of protein). The uptakes of betaine and proline were significantly inhibited by mono- and dimethylglycine but only partially inhibited by betaine aldehyde, choline, and 4-aminobutyrate. Sodium and potassium chloride markedly enhanced betaine uptake rates with optimum concentrations at 0.5 m, whereas sucrose showed only modest activation. The change of amino acids Thr(290)-Thr-Ser(292) in a putative periplasmic loop to Arg(290)-Gly-Arg(292) yielded the active transporter independent of salts, suggesting the positive charge induced a conformational change to the active form. These data clearly indicate that the betaine-accumulating mangrove contains betaine/proline transporters whose properties are distinct from betaine transporters of bacteria and mammalian cells.
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Affiliation(s)
- Rungaroon Waditee
- Research Institute, Faculty of Science and Technology, and School of Agriculture, Meijo University, Nagoya 468-8502, Japan
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105
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Abstract
Drought and salinity are among the worst scourges of agriculture. One effective mechanism to reduce damage from these stresses is the accumulation of high intracellular levels of osmoprotectant compounds. These compounds include proline, ectoine, betaines, polyols, and trehalose and have evolved in many different organisms. Since some crop plants have low levels of these osmoprotectants or none at all, engineering osmoprotectant biosynthesis pathways is a potential way to improve stress tolerance. First-generation engineering work--much of it with single genes--has successfully introduced osmoprotectant pathways into plants that lack them naturally, and this has often improved stress tolerance. However, the engineered osmoprotectant levels are generally low and the increases in tolerance commensurately small. To get beyond trace levels of osmoprotectants and marginal tolerance increments we need to use flux measurements to diagnose what limits osmoprotectant levels in engineered plants and to use iterative cycles of engineering to overcome these limitations.
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Affiliation(s)
- Denis Rontein
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611, USA
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106
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Iba K. Acclimative response to temperature stress in higher plants: approaches of gene engineering for temperature tolerance. ANNUAL REVIEW OF PLANT BIOLOGY 2002; 53:225-45. [PMID: 12221974 DOI: 10.1146/annurev.arplant.53.100201.160729] [Citation(s) in RCA: 291] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Temperature stresses experienced by plants can be classified into three types: those occurring at (a) temperatures below freezing, (b) low temperatures above freezing, and (c) high temperatures. This review outlines how biological substances that are deeply related to these stresses, such as heat-shock proteins, glycinebetaine as a compatible solute, membrane lipids, etc., and also detoxifiers of active oxygen species, contribute to temperature stress tolerance in plants. Also presented here are the uses of genetic engineering techniques to improve the adaptability of plants to temperature stress by altering the levels and composition of these substances in the living organism. Finally, the future prospects for molecular breeding are discussed.
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Affiliation(s)
- Koh Iba
- Department of Biology, Kyushu University, Fukuoka 812-8581, Japan.
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107
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Abstract
Glycinebetaine is an osmoprotectant accumulated by barley (Hordeum vulgare) plants in response to high levels of NaCl, drought, and cold stress. Using barley seedlings in hydroponic culture, we characterized additional inducers of glycinebetaine accumulation. These included other inorganic salts (KCl, MgCl(2), LiCl, and Na(2)SO(4)), oxidants (H(2)O(2) and cumene hydroperoxide), and organic compounds (abscisic acid, polymixin B, n-butanol, salicylic acid, and aspirin). Stress symptoms brought on by high NaCl and other inducers, and not necessarily correlated with glycinebetaine accumulation, include wilting, loss of chlorophyll, and increase in thiobarbituric acid reacting substances. For NaCl, Ca(2+) ions at 10 to 20 mM decrease these stress symptoms without diminishing, or even increasing, glycinebetaine induction. Abscisic acid induces glycinebetaine accumulation without causing any of the stress symptoms. NaCl, KCl, and H(2)O(2) (but not other inducers) induce glycinebetaine at concentrations below those needed for the other stress symptoms. Mg(2+) at 10 to 20 mM induces both stress symptoms and glycinebetaine, but only at low (0.2 mM) Ca(2+). Although illumination is needed for optimal induction, a significant increase in the leaf glycinebetaine level is found in complete darkness, also.
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Affiliation(s)
- A T Jagendorf
- Plant Biology Department, Cornell University, Ithaca, New York 14853, USA.
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108
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Zhang J, Okubo A, Yamazaki S. Measurement of free choline in plant leaves by capillary electrophoresis. Biosci Biotechnol Biochem 2001; 65:2573-6. [PMID: 11791738 DOI: 10.1271/bbb.65.2573] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A low pH capillary electrophoresis (CE) was used for the measurement of free choline in plant leaves. Choline in the leaf extract was first converted to the benzoyl ester and put into CE. A well-resolved peak in the electropherogram was easily obtained. Involvement of enzymes in a two-step oxidation of choline to glycine betaine was evaluated in different plant species with the same method developed for glycine betaine and betaine aldehyde.
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Affiliation(s)
- J Zhang
- Department of Applied Biological Chemistry, The University of Tokyo, Bunkyo, Japan
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109
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Nakamura T, Nomura M, Mori H, Jagendorf AT, Ueda A, Takabe T. An isozyme of betaine aldehyde dehydrogenase in barley. PLANT & CELL PHYSIOLOGY 2001; 42:1088-92. [PMID: 11673624 DOI: 10.1093/pcp/pce136] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Betaine aldehyde dehydrogenase (BADH) is an important enzyme for Gly betaine synthesis. We isolated two types of BADH cDNAs (BBD1 and BBD2) from barley. As BBD1 contained the signal sequence (SKL) targeting to microbodies, BBD2 was more similar to previously reported genes coding for BADH in dicotyledons (chloroplast type) than those in monocotyledons (microbody type). The two barley BADH genes showed different expression patterns. The BBD1 transcript was more abundant in roots than leaves and was induced to higher levels by salt, drought and abscisic acid (ABA) treatment. BBD2 transcript was more abundant in leaves and induced by salt, drought, PEG and ABA treatment. To understand the processing of these BADH proteins, we partially purified both enzymes and determined their N-terminal sequences. Based on comparisons of the N-terminal sequences to their deduced amino acid sequence, neither BBD1 nor BBD2 is processed at the N-terminus. These results suggest that BBD2 codes for a new type of BADH, which is not localized in either chloroplasts or mitochondria.
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Affiliation(s)
- T Nakamura
- Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601 Japan
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110
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Martensen I, Schauer R, Shaw L. Cloning and expression of a membrane-bound CMP-N-acetylneuraminic acid hydroxylase from the starfish Asterias rubens. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:5157-66. [PMID: 11589708 DOI: 10.1046/j.0014-2956.2001.02446.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The sialic acid N-glycolylneuraminic acid (Neu5Gc) is synthesized by the action of CMP-Neu5Ac hydroxylase. The enzyme from various mammals has been purified, characterized and sequenced by cDNA cloning. Although functional sequence motifs can be postulated from comparisons with several enzymes, no global homologies to any other proteins have been found. The unusual characteristics of this hydroxylase raise questions about its evolution. As echinoderms are phylogenetically the oldest organisms possessing Neu5Gc, they represent a starting point for investigations on the origin of this enzyme. Despite many similarities with its mammalian counterpart, CMP-Neu5Ac hydroxylase from the starfish A. rubens exhibits fundamental differences, most notably its association with a membrane and a requirement for high ionic strength. In order to shed light on the structural basis for these differences, the primary structure of CMP-Neu5Ac hydroxylase from A. rubens has been determined by PCR and cDNA-cloning techniques, using initial sequence information from the mouse enzyme. The complete assembled cDNA contained an ORF coding for a protein of 653 amino acids with a molecular mass of 75 kDa. The deduced amino-acid sequence exhibited a high degree of homology with the mammalian enzyme, although the C-terminus was some 60 residues longer. This extension consists of a terminal hydrophobic region, which may mediate membrane-binding, and a preceding hydrophilic sequence which probably serves as a hinge or linker. The identity of the ORF was confirmed by expression of active CMP-Neu5Ac hydroxylase in E. coli at low temperatures.
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Affiliation(s)
- I Martensen
- Biochemisches Institut, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Germany
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111
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Meng YL, Wang YM, Zhang B, Nii N. Isolation of a choline monooxygenase cDNA clone from Amaranthus tricolor and its expressions under stress conditions. Cell Res 2001; 11:187-93. [PMID: 11642403 DOI: 10.1038/sj.cr.7290085] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Plants synthesize the osmoprotectant glycine betaine (GB) via choline-->betaine aldehyde-->glycine betaine[1]. Two enzymes are involved in the pathway, choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH). A full length CMO cDNA (1,643bp) was cloned from Amaranthus tricolor. The open reading frame encoded a 442-amino acid polypeptide, which showed 69% identity with CMOs in Spinacia oleracea L. and Beta vulgaris L. DNA gel blot analysis indicated the presence of one copy of CMO gene in the A. tricolor genome. The expressions of CMO and BADH proteins in A.tricolor leaves significantly increased under salinization, drought and heat stress (42 degrees C), as determined by immunoblot analysis, but did not respond to cold stress (4 degrees C), or exogenous ABA application. The increase of GB content in leaves was parallel to CMO and BADH contents.
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Affiliation(s)
- Y L Meng
- Faculty of Agriculture, Meijo University, Nagoya, Aichi, Japan
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112
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Schmidt CL, Shaw L. A comprehensive phylogenetic analysis of Rieske and Rieske-type iron-sulfur proteins. J Bioenerg Biomembr 2001; 33:9-26. [PMID: 11460929 DOI: 10.1023/a:1005616505962] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The Rieske iron-sulfur center consists of a [2Fe-2S] cluster liganded to a protein via two histidine and two cysteine residues present in conserved sequences called Rieske motifs. Two protein families possessing Rieske centers have been defined. The Rieske proteins occur as subunits in the cytochrome bc1 and cytochrome b6f complexes of prokaryotes and eukaryotes or form components of archaeal electron transport systems. The Rieske-type proteins encompass a group of bacterial oxygenases and ferredoxins. Recent studies have uncovered several new proteins containing Rieske centers, including archaeal Rieske proteins, bacterial oxygenases, bacterial ferredoxins, and, intriguingly, eukaryotic Rieske oxygenases. Since all these proteins contain a Rieske motif, they probably form a superfamily with one common ancestor. Phylogenetic analyses have, however, been generally limited to similar sequences, providing little information about relationships within the whole group of these proteins. The aim of this work is, therefore, to construct a dendrogram including representatives from all Rieske and Rieske-type protein classes in order to gain insight into their evolutionary relationships and to further define the phylogenetic niches occupied by the recently discovered proteins mentioned above.
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Affiliation(s)
- C L Schmidt
- Institut für Biochemie der Medizinischen Universität Lübeck, Germany.
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113
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Hibino T, Meng YL, Kawamitsu Y, Uehara N, Matsuda N, Tanaka Y, Ishikawa H, Baba S, Takabe T, Wada K, Ishii T, Takabe T. Molecular cloning and functional characterization of two kinds of betaine-aldehyde dehydrogenase in betaine-accumulating mangrove Avicennia marina (Forsk.) Vierh. PLANT MOLECULAR BIOLOGY 2001; 45:353-63. [PMID: 11292080 DOI: 10.1023/a:1006497113323] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Glycinebetaine is an important osmoprotectant in bacteria, plants, and animals, but only little information is available on the synthesis of glycinebetaine in tree plants. Among four mangrove species, glycinebetaine could be detected only in Avicennia marina. Pinitol was the main osmoprotectant in the other three species. The level of glycinebetaine in A. marina increased under high salinity. Betaine-aldehyde dehydrogenase (BADH) was detected in all four species, but choline monooxygenase could not be detected. A cDNA library was constructed from the leaves of A. marina. Two kinds of BADH cDNAs were isolated, one homologous to the spinach chloroplast BADH, and the other with unique residues SKL at the end of C-terminus. The BADH transcription levels of the former were higher than those of the latter. The levels of the former BADH increased at high salinity whereas those of the latter were independent of salinity. BADHs were expressed in Escherichia coli and purified. Two kinds of A. marina BADHs exhibited similar kinetic and stability properties, but were significantly different from those of spinach BADH. A. marina BADHs efficiently catalyzed the oxidation of betainealdehyde, but not the oxidation of omega-aminoaldehydes and were more stable at high temperature than the spinach BADH.
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MESH Headings
- Aldehyde Oxidoreductases/genetics
- Aldehyde Oxidoreductases/metabolism
- Amino Acid Sequence
- Betaine/metabolism
- Betaine-Aldehyde Dehydrogenase
- Calcium Chloride/pharmacology
- Carbohydrate Metabolism
- Cloning, Molecular
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- Dose-Response Relationship, Drug
- Enzyme Stability
- Gene Expression Regulation, Enzymologic/drug effects
- Gene Expression Regulation, Plant/drug effects
- Hot Temperature
- Isoenzymes/genetics
- Molecular Sequence Data
- Osmolar Concentration
- Oxidation-Reduction/drug effects
- Oxygenases/metabolism
- Plant Leaves/drug effects
- Plant Leaves/enzymology
- Plant Leaves/genetics
- Plants, Medicinal/enzymology
- Plants, Medicinal/genetics
- Plants, Medicinal/metabolism
- Potassium Chloride/pharmacology
- Proline/metabolism
- RNA, Messenger/drug effects
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Sodium Chloride/pharmacology
- Species Specificity
- Spinacia oleracea/enzymology
- Substrate Specificity
- Tissue Distribution
- gamma-Aminobutyric Acid/metabolism
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Affiliation(s)
- T Hibino
- Faculty of Science & Technology, Meijo University, Nagoya, Aichi, Japan
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114
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Nuccio ML, McNeil SD, Ziemak MJ, Hanson AD, Jain RK, Selvaraj G. Choline import into chloroplasts limits glycine betaine synthesis in tobacco: analysis of plants engineered with a chloroplastic or a cytosolic pathway. Metab Eng 2000; 2:300-11. [PMID: 11120642 DOI: 10.1006/mben.2000.0158] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The biosynthesis of the osmoprotectant glycine betaine (GlyBet) is a target for metabolic engineering to enhance stress resistance in crops. Certain plants synthesize GlyBet in chloroplasts via a two-step oxidation of choline (Cho). In previous work, a chloroplastic GlyBet synthesis pathway was inserted into tobacco (which lacks GlyBet) by expressing spinach choline monooxygenase (CMO). The transformants had low CMO enzyme activity, and produced little GlyBet (less than or = 70 nmol g(-1) fresh wt). In this study, transformants with up to 100-fold higher CMO activity showed no further increase in GlyBet. In contrast, tobacco expressing a cytosolic GlyBet synthesis pathway accumulated significantly more GlyBet (430 nmol g(-1) fresh wt), suggesting that subcellular localization influences pathway flux. Modeling of the labeling kinetics of Cho metabolites observed when [14C]Cho was supplied to engineered plants demonstrated that Cho import into chloroplasts indeed limits the flux to GlyBet in the chloroplastic pathway. A high-activity Cho transporter in the chloroplast envelope may therefore be an integral part of the GlyBet synthesis pathway in species that accumulate GlyBet naturally, and hence a target for future engineering.
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Affiliation(s)
- M L Nuccio
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611-0690, USA
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115
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Hasegawa PM, Bressan RA, Zhu JK, Bohnert HJ. PLANTCELLULAR ANDMOLECULARRESPONSES TOHIGHSALINITY. ACTA ACUST UNITED AC 2000; 51:463-499. [PMID: 15012199 DOI: 10.1146/annurev.arplant.51.1.463] [Citation(s) in RCA: 1659] [Impact Index Per Article: 69.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Plant responses to salinity stress are reviewed with emphasis on molecular mechanisms of signal transduction and on the physiological consequences of altered gene expression that affect biochemical reactions downstream of stress sensing. We make extensive use of comparisons with model organisms, halophytic plants, and yeast, which provide a paradigm for many responses to salinity exhibited by stress-sensitive plants. Among biochemical responses, we emphasize osmolyte biosynthesis and function, water flux control, and membrane transport of ions for maintenance and re-establishment of homeostasis. The advances in understanding the effectiveness of stress responses, and distinctions between pathology and adaptive advantage, are increasingly based on transgenic plant and mutant analyses, in particular the analysis of Arabidopsis mutants defective in elements of stress signal transduction pathways. We summarize evidence for plant stress signaling systems, some of which have components analogous to those that regulate osmotic stress responses of yeast. There is evidence also of signaling cascades that are not known to exist in the unicellular eukaryote, some that presumably function in intercellular coordination or regulation of effector genes in a cell-/tissue-specific context required for tolerance of plants. A complex set of stress-responsive transcription factors is emerging. The imminent availability of genomic DNA sequences and global and cell-specific transcript expression data, combined with determinant identification based on gain- and loss-of-function molecular genetics, will provide the infrastructure for functional physiological dissection of salt tolerance determinants in an organismal context. Furthermore, protein interaction analysis and evaluation of allelism, additivity, and epistasis allow determination of ordered relationships between stress signaling components. Finally, genetic activation and suppression screens will lead inevitably to an understanding of the interrelationships of the multiple signaling systems that control stress-adaptive responses in plants.
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Affiliation(s)
- Paul M. Hasegawa
- Center for Plant Environmental Stress Physiology, 1165 Horticulture Building, Purdue University, West Lafayette, Indiana 47907-1165; e-mail: , Departments of 1 Plant Sciences and 2Biochemistry, University of Arizona, Tucson, Arizona 85721; e-mail:
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116
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Nuccio ML, Ziemak MJ, Henry SA, Weretilnyk EA, Hanson AD. cDNA cloning of phosphoethanolamine N-methyltransferase from spinach by complementation in Schizosaccharomyces pombe and characterization of the recombinant enzyme. J Biol Chem 2000; 275:14095-101. [PMID: 10799484 DOI: 10.1074/jbc.275.19.14095] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The N-methylation of phosphoethanolamine is the committing step in choline biogenesis in plants and is catalyzed by S-adenosyl-L-methionine:phosphoethanolamine N-methyltransferase (PEAMT, EC ). A spinach PEAMT cDNA was isolated by functional complementation of a Schizosaccharomyces pombe cho2(-) mutant and was shown to encode a protein with PEAMT activity and without ethanolamine- or phosphatidylethanolamine N-methyltransferase activity. The PEAMT cDNA specifies a 494-residue polypeptide comprising two similar, tandem methyltransferase domains, implying that PEAMT arose by gene duplication and fusion. Data base searches suggested that PEAMTs with the same tandem structure are widespread among flowering plants. Size exclusion chromatography of the recombinant enzyme indicates that it exists as a monomer. PEAMT catalyzes not only the first N-methylation of phosphoethanolamine but also the two subsequent N-methylations, yielding phosphocholine. Monomethyl- and dimethylphosphoethanolamine are detected as reaction intermediates. A truncated PEAMT lacking the C-terminal methyltransferase domain catalyzes only the first methylation. Phosphocholine inhibits both the wild type and the truncated enzyme, although the latter is less sensitive. Salinization of spinach plants increases PEAMT mRNA abundance and enzyme activity in leaves by about 10-fold, consistent with the high demand in stressed plants for choline to support glycine betaine synthesis.
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Affiliation(s)
- M L Nuccio
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611, USA
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117
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Huang J, Hirji R, Adam L, Rozwadowski KL, Hammerlindl JK, Keller WA, Selvaraj G. Genetic engineering of glycinebetaine production toward enhancing stress tolerance in plants: metabolic limitations. PLANT PHYSIOLOGY 2000; 122:747-56. [PMID: 10712538 PMCID: PMC58910 DOI: 10.1104/pp.122.3.747] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/1999] [Accepted: 10/29/1999] [Indexed: 04/14/2023]
Abstract
Glycinebetaine (betaine) affords osmoprotection in bacteria, plants and animals, and protects cell components against harsh conditions in vitro. This and a compelling body of other evidence have encouraged the engineering of betaine production in plants lacking it. We have installed the metabolic step for oxidation of choline, a ubiquitous substance, to betaine in three diverse species, Arabidopsis, Brassica napus, and tobacco (Nicotiana tabacum), by constitutive expression of a bacterial choline oxidase gene. The highest levels of betaine in independent transgenics were 18.6, 12.8, and 13 micromol g(-1) dry weight, respectively, values 10- to 20-fold lower than the levels found in natural betaine producers. However, choline-fed transgenic plants synthesized substantially more betaine. Increasing the choline supplementation further enhanced betaine synthesis, up to 613 micromol g(-1) dry weight in Arabidopsis, 250 micromol g(-1) dry weight in B. napus, and 80 micromol g(-1) dry weight in tobacco. These studies demonstrate the need to enhance the endogenous choline supply to support accumulation of physiologically relevant amounts of betaine. A moderate stress tolerance was noted in some but not all betaine-producing transgenic lines based on relative shoot growth. Furthermore, the responses to stresses such as salinity, drought, and freezing were variable among the three species.
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Affiliation(s)
- J Huang
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan, Canada
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118
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Holmström KO, Somersalo S, Mandal A, Palva TE, Welin B. Improved tolerance to salinity and low temperature in transgenic tobacco producing glycine betaine. JOURNAL OF EXPERIMENTAL BOTANY 2000; 51:177-85. [PMID: 10938824 DOI: 10.1093/jexbot/51.343.177] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Glycine betaine is an osmoprotectant found in many organisms, including bacteria and higher plants. The bacterium Escherichia coli produces glycine betaine by a two-step pathway where choline dehydrogenase (CDH), encoded by betA, oxidizes choline to betaine aldehyde which is further oxidized to glycine betaine by the same enzyme. The second step, conversion of betaine aldehyde into glycine betaine, can also be performed by the second enzyme in the pathway, betaine aldehyde dehydrogenase (BADH), encoded by betB. Transformation of tobacco (Nicotiana tabacum), a species not accumulating glycine betaine, with the E. coli genes for glycine betaine biosynthesis, resulted in transgenic plants accumulating glycine betaine. Plants producing CDH were found to accumulate glycine betaine as did F1 progeny from crosses between CDH- and BADH-producing lines. Plants producing both CDH and BADH generally accumulated higher amounts of glycine betaine than plants producing CDH alone, as determined by 1H NMR analysis. Transgenic tobacco lines accumulating glycine betaine exhibited increased tolerance to salt stress as measured by biomass production of greenhouse-grown intact plants. Furthermore, experiments conducted with leaf discs from glycine betaine-accumulating plants indicated enhanced recovery from photoinhibition caused by high light and salt stress as well as improved tolerance to photoinhibition under low temperature conditions. In conclusion, introduction of glycine betaine production into tobacco is associated with increased stress tolerance probably partly due to improved protection of the photosynthetic apparatus.
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Affiliation(s)
- K O Holmström
- Department of Plant Biology, Uppsala Genetic Center, Swedish University of Agricultural Sciences, Uppsala, Sweden
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119
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Sakamoto A, Murata N. Genetic engineering of glycinebetaine synthesis in plants: current status and implications for enhancement of stress tolerance. JOURNAL OF EXPERIMENTAL BOTANY 2000; 51:81-88. [PMID: 10938798 DOI: 10.1093/jexbot/51.342.81] [Citation(s) in RCA: 141] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Metabolic acclimation via the accumulation of compatible solutes is regarded as a basic strategy for the protection and survival of plants in extreme environments. Certain plants accumulate significant amounts of glycinebetaine (betaine), a compatible quaternary amine, in response to high salinity, cold and drought. It is likely that betaine is involved in the protection of macrocomponents of plant cells, such as protein complexes and membranes, under stress conditions. Genetic engineering of the biosynthesis of betaine from choline has been the focus of considerable attention as a potential strategy for increasing stress tolerance in stress-sensitive plants that are incapable of synthesizing this compatible/protective solute. Three distinct pathways for the synthesis of betaine have been identified in spinach, Escherichia coli and Arthrobacter globiformis, and various genes and cDNAs for the proteins involved are available. Moreover, each of the pathways has been exploited to a greater or lesser extent in efforts to convert betaine-deficient plants to betaine accumulators. In this review, the potential of several recent examples of transgenic approaches to the enhancement of stress tolerance in plants is summarized and discussed.
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Affiliation(s)
- A Sakamoto
- National Institute for Basic Biology, Okazaki, Japan
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120
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McNeil SD, Nuccio ML, Hanson AD. Betaines and related osmoprotectants. Targets for metabolic engineering of stress resistance. PLANT PHYSIOLOGY 1999; 120:945-50. [PMID: 10444077 PMCID: PMC1539222 DOI: 10.1104/pp.120.4.945] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Affiliation(s)
- SD McNeil
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611, USA
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121
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Bourgis F, Roje S, Nuccio ML, Fisher DB, Tarczynski MC, Li C, Herschbach C, Rennenberg H, Pimenta MJ, Shen TL, Gage DA, Hanson AD. S-methylmethionine plays a major role in phloem sulfur transport and is synthesized by a novel type of methyltransferase. THE PLANT CELL 1999; 11:1485-1498. [PMID: 10449582 DOI: 10.2307/3870977] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
All flowering plants produce S-methylmethionine (SMM) from Met and have a separate mechanism to convert SMM back to Met. The functions of SMM and the reasons for its interconversion with Met are not known. In this study, by using the aphid stylet collection method together with mass spectral and radiolabeling analyses, we established that l-SMM is a major constituent of the phloem sap moving to wheat ears. The SMM level in the phloem ( approximately 2% of free amino acids) was 1.5-fold that of glutathione, indicating that SMM could contribute approximately half the sulfur needed for grain protein synthesis. Similarly, l-SMM was a prominently labeled product in phloem exudates obtained by EDTA treatment of detached leaves from plants of the Poaceae, Fabaceae, Asteraceae, Brassicaceae, and Cucurbitaceae that were given l-(35)S-Met. cDNA clones for the enzyme that catalyzes SMM synthesis (S-adenosylMet:Met S-methyltransferase; EC 2.1.1.12) were isolated from Wollastonia biflora, maize, and Arabidopsis. The deduced amino acid sequences revealed the expected methyltransferase domain ( approximately 300 residues at the N terminus), plus an 800-residue C-terminal region sharing significant similarity with aminotransferases and other pyridoxal 5'-phosphate-dependent enzymes. These results indicate that SMM has a previously unrecognized but often major role in sulfur transport in flowering plants and that evolution of SMM synthesis in this group involved a gene fusion event. The resulting bipartite enzyme is unlike any other known methyltransferase.
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Affiliation(s)
- F Bourgis
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611-0690, USA
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122
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Bourgis F, Roje S, Nuccio ML, Fisher DB, Tarczynski MC, Li C, Herschbach C, Rennenberg H, Pimenta MJ, Shen TL, Gage DA, Hanson AD. S-methylmethionine plays a major role in phloem sulfur transport and is synthesized by a novel type of methyltransferase. THE PLANT CELL 1999; 11:1485-98. [PMID: 10449582 PMCID: PMC144290 DOI: 10.1105/tpc.11.8.1485] [Citation(s) in RCA: 191] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
All flowering plants produce S-methylmethionine (SMM) from Met and have a separate mechanism to convert SMM back to Met. The functions of SMM and the reasons for its interconversion with Met are not known. In this study, by using the aphid stylet collection method together with mass spectral and radiolabeling analyses, we established that l-SMM is a major constituent of the phloem sap moving to wheat ears. The SMM level in the phloem ( approximately 2% of free amino acids) was 1.5-fold that of glutathione, indicating that SMM could contribute approximately half the sulfur needed for grain protein synthesis. Similarly, l-SMM was a prominently labeled product in phloem exudates obtained by EDTA treatment of detached leaves from plants of the Poaceae, Fabaceae, Asteraceae, Brassicaceae, and Cucurbitaceae that were given l-(35)S-Met. cDNA clones for the enzyme that catalyzes SMM synthesis (S-adenosylMet:Met S-methyltransferase; EC 2.1.1.12) were isolated from Wollastonia biflora, maize, and Arabidopsis. The deduced amino acid sequences revealed the expected methyltransferase domain ( approximately 300 residues at the N terminus), plus an 800-residue C-terminal region sharing significant similarity with aminotransferases and other pyridoxal 5'-phosphate-dependent enzymes. These results indicate that SMM has a previously unrecognized but often major role in sulfur transport in flowering plants and that evolution of SMM synthesis in this group involved a gene fusion event. The resulting bipartite enzyme is unlike any other known methyltransferase.
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Affiliation(s)
- F Bourgis
- Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611-0690, USA
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123
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124
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Nuccio ML, Russell BL, Nolte KD, Rathinasabapathi B, Gage DA, Hanson AD. The endogenous choline supply limits glycine betaine synthesis in transgenic tobacco expressing choline monooxygenase. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 1998; 16:487-96. [PMID: 9881168 DOI: 10.1046/j.1365-313x.1998.00316.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Certain plants produce glycine betaine (GlyBet) in the chloroplast by a two-step oxidation of choline. Introducing GlyBet accumulation into plants that lack it is a well-established target for metabolic engineering because GlyBet can lessen damage from osmotic stress. The first step in GlyBet synthesis is catalyzed by choline mono-oxygenase (CMO), a stromal enzyme with a Rieske-type [2Fe-2S] center. The absence of CMO is the primary constraint on GlyBet production in GlyBet-deficient plants such as tobacco, but the endogenous choline supply is also potentially problematic. To investigate this, we constructed transgenic tobacco plants that constitutively express a spinach CMO cDNA. The CMO protein was correctly compartmented in chloroplasts and was enzymatically active, showing that its [2Fe-2S] cluster had been inserted. Salinization increased CMO protein levels, apparently via a post-transcriptional mechanism, to as high as 10% of that in salinized spinach. However, the GlyBet contents of CMO+ plants were very low (0.02-0.05 mumol g-1 fresh weight) in both unstressed and salinized conditions. Experiments with [14C]GlyBet demonstrated that this was not due to GlyBet catabolism. When CMO+ plants were supplied in culture with 5 mM choline or phosphocholine, their choline and GlyBet levels increased by at least 30-fold. The choline precursors mono- and dimethylethanolamine also enhanced choline and GlyBet levels but ethanolamine did not, pointing to a major constraint on flux to choline at the first methylation step in its synthesis. The extractable activity of the enzyme mediating this step in tobacco was only 3% that of spinach. We conclude that in GlyBet-deficient plants engineered with choline-oxidizing genes, the size of the free choline pool and the metabolic flux to choline need to be increased to attain GlyBet levels as high as those in natural accumulators.
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Affiliation(s)
- M L Nuccio
- Horticultural Sciences Department, University of Florida, Gainesville, USA
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125
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Østeras M, Boncompagni E, Lambert A, Dupont L, Poggi MC, Le Rudulier D. Isolation and molecular characterization of theSinorhizobium meliloti bet locus encoding glycine betaine biosynthesis. J Biosci 1998. [DOI: 10.1007/bf02936139] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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126
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Stress responses ofBacillus subtilis to high osmolarity environments: Uptake and synthesis of osmoprotectants. J Biosci 1998. [DOI: 10.1007/bf02936138] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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127
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Strøm AR. Osmoregulation in the model organismEscherichia coli: genes governing the synthesis of glycine betaine and trehalose and their use in metabolic engineering of stress tolerance. J Biosci 1998. [DOI: 10.1007/bf02936137] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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128
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Osterås M, Boncompagni E, Vincent N, Poggi MC, Le Rudulier D. Presence of a gene encoding choline sulfatase in Sinorhizobium meliloti bet operon: choline-O-sulfate is metabolized into glycine betaine. Proc Natl Acad Sci U S A 1998; 95:11394-9. [PMID: 9736747 PMCID: PMC21653 DOI: 10.1073/pnas.95.19.11394] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Glycine betaine is a potent osmoprotectant accumulated by Sinorhizobium meliloti to cope with osmotic stress. The biosynthesis of glycine betaine from choline is encoded by an operon of four genes, betICBA, as determined by sequence and mutant analysis. The betI and betC genes are separated by an intergenic region containing a 130-bp mosaic element that also is present between the betB and betA genes. In addition to the genes encoding a presumed regulatory protein (betI), the betaine aldehyde dehydrogenase (betB), and the choline dehydrogenase (betA) enzymes also found in Escherichia coli, a new gene (betC) was identified as encoding a choline sulfatase catalyzing the conversion of choline-O-sulfate and, at a lower rate, phosphorylcholine, into choline. Choline sulfatase activity was absent from betC but not from betB mutants and was shown to be induced indifferently by choline or choline-O-sulfate as were the other enzymes of the pathway. Unlike what has been shown in other bacteria and plants, choline-O-sulfate is not used as an osmoprotectant per se in S. meliloti, but is metabolized into glycine betaine. S. meliloti also can use this compound as the sole carbon, nitrogen, and sulfur source for growth and that depends on a functional bet locus. In conclusion, choline-O-sulfate and phosphorylcholine, which are found in higher plants and fungi, appear to be substrates for glycine betaine biosynthesis in S. meliloti.
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Affiliation(s)
- M Osterås
- Laboratoire de Biologie Végétale et Microbiologie, Centre National de la Recherche Scientifique Equipe en Restructuration 590, Université de Nice-Sophia Antipolis, 06108 Nice Cedex, France
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129
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Gollub M, Schauer R, Shaw L. Cytidine monophosphate-N-acetylneuraminate hydroxylase in the starfish Asterias rubens and other echinoderms. Comp Biochem Physiol B Biochem Mol Biol 1998; 120:605-15. [PMID: 9787821 DOI: 10.1016/s0305-0491(98)10058-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The sialic acid N-glycolylneuraminic acid (Neu5Gc) is synthesised by an NADH-dependent hydroxylase which acts on CMP-N-acetylneuraminic acid (CMP-Neu5Ac). Although Neu5Gc is the predominant sialic acid in many echinoderms, little is known about the hydroxylase from organisms of this phylum. We show here that in contrast to the mammalian enzyme, the hydroxylase from various echinoderms is predominantly membrane-bound and exhibits optimal activity in the presence of 100 mM NaCl. A detailed characterisation of the hydroxylase from echinoderms was performed using fractionated gonads of the starfish Asterias rubens. Solubilisation using detergents led to an inactivation of the hydroxylase. However, the solubilised enzyme was reactivated by the addition of cytochrome b5 reductase together with the amphiphilic or soluble form of cytochrome b5. Although these latter proteins were only available from a mammalian source, the high affinity of the hydroxylase for cytochrome b5 suggests that, as with the mammalian enzyme, these electron carriers participate in the catalytic cycle of the hydroxylase from A. rubens in vivo. The relevance of these results to the interaction between cytochrome b5 and the hydroxylase is discussed.
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Affiliation(s)
- M Gollub
- Biochemisches Institut der Christian-Albrechts-Universität zu Kiel, Germany
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130
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Hare PD, Cress WA, Van Staden J. Dissecting the roles of osmolyte accumulation during stress. PLANT, CELL AND ENVIRONMENT 1998; 21:535-553. [PMID: 0 DOI: 10.1046/j.1365-3040.1998.00309.x] [Citation(s) in RCA: 483] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
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131
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Abstract
A common effect of many environmental stresses is to cause oxidative damage; consequently, the antioxidant system is being intensively investigated. The use of transgenic plants to probe the role of the antioxidant system continues to be an important approach. The uncharted area of signal transduction in relation to oxidative stress is beginning to attract attention. Studies of drought response at the cellular level have focused on the role of compatible solutes (osmolytes) in acclimation to water stress. Information on signal transduction processes during drought is beginning to appear. As with the antioxidant system, there is increasing use of metabolic engineering in transgenic plants to introduce exotic compatible solutes. It is concluded that these potentially have a use in understanding, or even improving, drought resistance; however, there is a need for the assessment of stress tolerance of transgenics to be carried out at a more sophisticated level and for a critical analysis of the relevance for crop yield of the genes currently being manipulated.
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Affiliation(s)
- N Smirnoff
- Department of Biological Sciences University of Exeter Hatherly Laboratories Prince of Wales Road, Exeter, EX4 4PS, UK
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132
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Russell BL, Rathinasabapathi B, Hanson AD. Osmotic stress induces expression of choline monooxygenase in sugar beet and amaranth. PLANT PHYSIOLOGY 1998; 116:859-65. [PMID: 9489025 PMCID: PMC35146 DOI: 10.1104/pp.116.2.859] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/1997] [Accepted: 10/22/1997] [Indexed: 05/18/2023]
Abstract
Choline monooxygenase (CMO) catalyzes the committing step in the synthesis of glycine betaine, an osmoprotectant accumulated by many plants in response to salinity and drought. To investigate how these stresses affect CMO expression, a spinach (Spinacia oleracea L., Chenopodiaceae) probe was used to isolate CMO cDNAs from sugar beet (Beta vulgaris L., Chenopodiaceae), a salt- and drought-tolerant crop. The deduced beet CMO amino acid sequence comprised a transit peptide and a 381-residue mature peptide that was 84% identical (97% similar) to that of spinach and that showed the same consensus motif for coordinating a Rieske-type [2Fe-2S] cluster. A mononuclear Fe-binding motif was also present. When water was withheld, leaf relative water content declined to 59% and the levels of CMO mRNA, protein, and enzyme activity rose 3- to 5-fold; rewatering reversed these changes. After gradual salinization (NaCl:CaCl2 = 5.7:1, mol/mol), CMO mRNA, protein, and enzyme levels in leaves increased 3- to 7-fold at 400 mM salt, and returned to uninduced levels when salt was removed. Beet roots also expressed CMO, most strongly when salinized. Salt-inducible CMO mRNA, protein, and enzyme activity were readily detected in leaves of Amaranthus caudatus L. (Amaranthaceae). These data show that CMO most probably has a mononuclear Fe center, is inducibly expressed in roots as well as in leaves of Chenopodiaceae, and is not unique to this family.
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Affiliation(s)
- B L Russell
- Horticultural Sciences Department, University of Florida, Gainesville 32611, USA
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133
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Russell BL, Rathinasabapathi B, Hanson AD. Osmotic stress induces expression of choline monooxygenase in sugar beet and amaranth. PLANT PHYSIOLOGY 1998; 116:859-865. [PMID: 9489025 DOI: 10.2307/4278159] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Choline monooxygenase (CMO) catalyzes the committing step in the synthesis of glycine betaine, an osmoprotectant accumulated by many plants in response to salinity and drought. To investigate how these stresses affect CMO expression, a spinach (Spinacia oleracea L., Chenopodiaceae) probe was used to isolate CMO cDNAs from sugar beet (Beta vulgaris L., Chenopodiaceae), a salt- and drought-tolerant crop. The deduced beet CMO amino acid sequence comprised a transit peptide and a 381-residue mature peptide that was 84% identical (97% similar) to that of spinach and that showed the same consensus motif for coordinating a Rieske-type [2Fe-2S] cluster. A mononuclear Fe-binding motif was also present. When water was withheld, leaf relative water content declined to 59% and the levels of CMO mRNA, protein, and enzyme activity rose 3- to 5-fold; rewatering reversed these changes. After gradual salinization (NaCl:CaCl2 = 5.7:1, mol/mol), CMO mRNA, protein, and enzyme levels in leaves increased 3- to 7-fold at 400 mM salt, and returned to uninduced levels when salt was removed. Beet roots also expressed CMO, most strongly when salinized. Salt-inducible CMO mRNA, protein, and enzyme activity were readily detected in leaves of Amaranthus caudatus L. (Amaranthaceae). These data show that CMO most probably has a mononuclear Fe center, is inducibly expressed in roots as well as in leaves of Chenopodiaceae, and is not unique to this family.
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Affiliation(s)
- B L Russell
- Horticultural Sciences Department, University of Florida, Gainesville 32611, USA
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134
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Caliebe A, Grimm R, Kaiser G, Lübeck J, Soll J, Heins L. The chloroplastic protein import machinery contains a Rieske-type iron-sulfur cluster and a mononuclear iron-binding protein. EMBO J 1997; 16:7342-50. [PMID: 9405363 PMCID: PMC1170334 DOI: 10.1093/emboj/16.24.7342] [Citation(s) in RCA: 143] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Transport of precursor proteins across the chloroplastic envelope membranes requires the interaction of protein translocons localized in both the outer and inner envelope membranes. Analysis by blue native gel electrophoresis revealed that the translocon of the inner envelope membranes consisted of at least six proteins with molecular weights of 36, 45, 52, 60, 100 and 110 kDa, respectively. Tic110 and ClpC, identified as components of the protein import apparatus of the inner envelope membrane, were prominent constituents of this complex. The amino acid sequence of the 52 kDa protein, deduced from the cDNA, contains a predicted Rieske-type iron-sulfur cluster and a mononuclear iron-binding site. Diethylpyrocarbonate, a Rieske-type protein-modifying reagent, inhibits the translocation of precursor protein across the inner envelope membrane, whereas binding of the precursor to the outer envelope membrane is still possible. In another independent experimental approach, the 52 kDa protein could be co-purified with a trapped precursor protein in association with the chloroplast protein translocon subunits Toc86, Toc75, Toc34 and Tic110. Together, these results strongly suggest that the 52 kDa protein, named Tic55 due to its calculated molecular weight, is a member of the chloroplastic inner envelope protein translocon.
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Affiliation(s)
- A Caliebe
- Botanisches Institut, Christian-Albrechts-Universität, Am Botanischen Garten 1-9, D-24118 Kiel, Germany
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