Control of the Synthesis and Subcellular Targeting of the Two GDH Genes Products in Leaves and Stems of Nicotiana plumbaginifolia and Arabidopsis thaliana

Fontaine, Jean-Xavier; Saladino, Francesca; Agrimonti, Caterina; Bedu, Magali; Tercé‐Laforgue, Thérèse; Tétu, Thierry; Hirel, Bertrand; Restivo, Francesco Maria; Dubois, Frédéric

doi:10.1093/pcp/pcj008

Cited by 45 publications

(55 citation statements)

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“…Fontaine et al (2006) recently generated transgenic tobacco lines with decreased levels of the a-subunit and identified an Arabidopsis mutant similarly affected. Further work with these lines, as well as lines with perturbed levels of the b-subunit (Purnell et al, 2005;Fontaine et al, 2006), is required to determine the in vivo reaction directions of isoenzymes 7 and 1, respectively, in different tissues at different developmental stages and in response to various environmental signals.…”

Section: Resultsmentioning

confidence: 99%

“…In leaves with elevated NH 4 1 levels (e.g. senescing leaves), GDH protein is also detected in the cytosol of phloem companion cells (Paczek et al, 2002;Dubois et al, 2003;Tercé-Laforgue et al, 2004a;Kichey et al, 2005;Fontaine et al, 2006).…”

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confidence: 99%

“…Transgenic plants with modulated GDH a-or b-subunit levels have recently been reported (Purnell et al, 2005;Fontaine et al, 2006). Purnell et al (2005) generated transgenic tobacco (Nicotiana tabacum) lines with increased b-subunit and isoenzyme 1 levels.…”

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confidence: 99%

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Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in Vivo

Purnell

Botella

2006

Plant Physiol.

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Glutamate (Glu) dehydrogenase (GDH, EC 1.4.1.2-1.4.1.4) catalyzes in vitro the reversible amination of 2-oxoglutarate to Glu. The in vivo direction(s) of the GDH reaction in higher plants and hence the role(s) of this enzyme is unclear, a situation confounded by the existence of isoenzymes comprised totally of either GDH b-(isoenzyme 1) or a-(isoenzyme 7) subunits, as well as another five a-b isoenzyme permutations. To clarify the in vivo direction of the reaction catalyzed by GDH isoenzyme 1, [ 15 N]Glu was supplied to roots of two independent transgenic tobacco (Nicotiana tabacum) lines with increased isoenzyme 1 levels (S4-H and S49-H). The [ 15 N]ammonium (NH 4 1 ) accumulation rate in these lines was elevated approximately 65% compared with a null segregant control line, indicating that isoenzyme 1 catabolizes Glu in roots. Leaf glutamine synthetase (GS) was inhibited with a GS-specific herbicide to quantify any contribution by GDH toward photorespiratory NH 4 1 reassimilation. Transgenic line S49-H did not show enhanced resistance to the herbicide, indicating that the large pool of isoenzyme 1 in S49-H leaves was unable to compensate for GS and suggesting that isoenzyme 1 does not assimilate NH 4 1 in vivo.The intricate linkage of plant C and N metabolism requires constant balancing at the cellular level. Fundamentally, this involves orchestrating cellular levels of three metabolites: ammonium (NH 4

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Section: Resultsmentioning

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Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in Vivo

Purnell

Botella

2006

Plant Physiol.

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“…2,8 However, this hypothesis has not been demonstrated until recently, since the previously characterized gdh mutants as well as the transgenic plants overexpressing GDH did not exhibit a visible phenotype that supports the proposed role of GDH. 5,6,[8][9][10] In particular, all previous gdh mutants contained mutations only in one of the two GDH genes. [8][9][10] It was possible that the effects of the loss of one functional GDH were masked by the redundant function of the other GDH in previous studies.…”

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“…5,6,[8][9][10] In particular, all previous gdh mutants contained mutations only in one of the two GDH genes. [8][9][10] It was possible that the effects of the loss of one functional GDH were masked by the redundant function of the other GDH in previous studies. Recently, we have isolated mutants for both of the two known Arabidopsis GDH genes and obtained a gdh double mutant (gdh1-2/gdh2-1) from crossing gdh1 and gdh2 mutants.…”

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Glutamate deamination by glutamate dehydrogenase plays a central role in amino acid catabolism in plants

Miyashita

Good

2008

Plant Signaling & Behavior

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Glutamate is of central importance in plant N metabolism since the biosynthesis of all other amino acids requires this compound. Glutamate dehydrogenase (GDH; EC 1.4.1.2), which catalyzes in vitro reversible reductive amination of 2-oxoglutatre to form glutamate, is a key player in the metabolism of glutamate. While most previous studies have indicated that the oxidative deamination is the in vivo direction of the GDH reaction, its physiological role has remained ambiguous for decades. We have recently isolated mutants for the two known Arabidopsis GDH genes and created a gdh double mutant. Our recent work revealed an increased susceptibility of the gdh double mutant to dark-induced C starvation, the first phenotype associated with the loss of GDH activity in plants. Monitoring the amino acid breakdown during the dark treatment also suggested that the deamination of glutamate catalyzed by GDH is central to the catabolism of many other amino acids.Nitrogen is a major limiting factor for plant growth and development and therefore the incorporation of inorganic N into amino acids is of central importance in agriculture. GDH had been viewed as the major ammonium assimilatory enzyme in the past. However, the discovery of glutamine synthetase (GS)/glutamate synthase (GOGAT) pathway as the sole port of ammonium assimilation raised the long-lasting question regarding the role played by GDH. 1,2 This was confounded by the uncertainty about the in vivo direction of the GDH reaction, which reversibly aminates 2-oxoglutatrate or deaminates glutamate in vitro. Plants contain at least two GDH genes encoding either the α or β subunit of GDH. 3 Random assembling of the two subunits in the hexameric holoenzyme results in the seven isoenzymes which can be visualized on a non-denaturing gel [β 6 (isoenzyme 1), α 1 β 5 … α 5 β 1, α 6 (isoenzyme 7)]. 4 For the in vivo direction that GDH catalyzes, oxidative deamination has been supported by many labeling experiments. 2 In two recent studies, the overexpression of either α or β subunit of GDH resulted in the increased release of 15 NH 4 + after [ 15 N]glutamate feeding, demonstrating the deaminating role of the distinct GDH isoenzymes. 5,6 In contrast, 15 NH 4 + incorporation into glutamate through GDH was demonstrated under salt stress in which continued 15 NH 4 + assimilation occurred in the presence of the GS inhibitor, methionine sulfoximine. 7 Nevertheless, most previous results supported the current consensus that GDH deaminates glutamate in vivo under normal growth conditions.Although previous labeling experiments were useful to define the in vivo direction of the GDH reaction, the physiological role of GDH remained speculative. For this reason, GDH expression has been extensively studied at the transcript, protein and enzyme activity levels. In these previous studies, the regulation of GDH by light/dark cycle, sugar levels and ammonia addition was documented. 2 In brief, expression of GDH appears to be controlled by the cellular energy state or sugar levels since the dark-ind...

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Nitrogen Assimilation and its Relevance to Crop Improvement

Lea

Miflin

2018

Annual Plant Reviews Online

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The majority if not all of the organic nitrogen in plants is derived from the assimilation of ammonia into the amide position of glutamine by the enzyme glutamine synthetase (GS). A second enzyme, glutamate synthase, also known as glutamine:2‐oxoglutarate amidotransferase (GOGAT), carries out the transfer of the amide group of glutamine to 2‐oxoglutarate to yield two molecules of glutamate and thus completes the assimilation of ammonia into amino acids. This GS/GOGAT pathway of ammonia assimilation is of crucial importance for crop growth and productivity and ultimately animal and human nutrition. Glutamate dehydrogenase (GDH) is now considered to be only involved in glutamate catabolism to form ammonia, an important role in N recycling within the plant. Nitrogen is also often diverted from glutamine to asparagine as a temporary measure during periods of carbohydrate shortage and excess of reduced nitrogen. This diversion requires the action of asparagine synthetase in the anabolic reaction and asparaginase in the catabolic reaction. This chapter describes the properties of these enzymes in the assimilation and reassimilation of nitrogen and in particular the genes that encode them, their complexity and the time and place they are expressed. Plant transformation has allowed the construction of a range of plants with enhanced and decreased activity of several of these enzymes, some of which have shown improved agronomic performance.

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Control of the Synthesis and Subcellular Targeting of the Two GDH Genes Products in Leaves and Stems of Nicotiana plumbaginifolia and Arabidopsis thaliana

Cited by 45 publications

References 26 publications

Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in Vivo

Tobacco Isoenzyme 1 of NAD(H)-Dependent Glutamate Dehydrogenase Catabolizes Glutamate in Vivo

Glutamate deamination by glutamate dehydrogenase plays a central role in amino acid catabolism in plants

Nitrogen Assimilation and its Relevance to Crop Improvement

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