Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris

Cock, J. Mark; Iw, Brock; Watson, Adam T.; Swarup, Ranjan; Ap, Morby; Cullimore, Julie V.

doi:10.1007/bf00037059

Cited by 59 publications

(42 citation statements)

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“…These observations have recently been confirmed by reporter gene studies that show that the expression from the soybean GS gene promoter is induced by ammonium only in transgenic Lotus corniculatus, a legume, and not in transgenic tobacco (Miao et al, 1991). In contrast, Cock et al (1990) failed to find an effect of ammonium on specifically inducing the expression of GS genes in either the roots or nodules of bean. Thus, whether GS gene expression is substrate inducible or not may depend on the species in question.…”

Section: Discussionmentioning

confidence: 80%

“…Hirel et al (1987) concluded that GS gene expression in soybean is directly regulated by ammonium, when either supplied externally to roots or made available as a result of nitrogen fixation in nodules. However, a similar study in bean (Cock et al, 1990) failed to find a major role for ammonium in specifically inducing GS gene expression in either roots or nodules.…”

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confidence: 93%

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Differential Expression within the Glutamine Synthetase Gene Family of the Model Legume Medicago truncatula

et al. 1993

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The glutamine synthetase (CS) gene family of Medicago truncatula Caertn. contains three genes related to cytosolic GS (MtCSa, MtCSb, and MtCSc), although one of these (MtGSc) appears not to be expressed. Sequence analysis suggests that the genes are more highly conserved interspecifically rather than intraspecifically: MtCSa and MtCSb are more similar to their homologs in Medicago sativa and Pisum sativum than to each other. Studies in which gene-specific probes are used show that both MtCSa and MtCSb are induced during symbiotic root nodule development, although not coordinately. MtCSa is the most highly expressed CS gene in nodules but is also expressed to lower extents in a variety of other organs. MtCSb shows higher levels of expression in roots and the photosynthetic cotyledons of seedlings than in nodules or other organs. In roots, both genes are expressed in the absence of an exogenous nitrogen source. However the addition of nitrate leads to a short-term, 2-to 3-fold increase in the abundance of both mRNAs, and the addition of ammonium leads to a 2-fold increase in MtCSb mRNA. The nitrogen supply, therefore, influentes the expression of the two genes in roots, but it is clearly not the major effector of their expression. In the discussion section, the expression of the CS gene family of the model legume M. truncatula is compared to those of other leguminous plants.GS (EC 6.3.1.2) is a key enzyme in the nitrogen metabolism of higher plants, catalyzing the assimilation of ammonium to form Gln. This ammonium is derived from the primary nitrogen sources of the plant (through the reduction of soil nitrate and, in the case of legumes, by the symbiotic fixation of atmospheric nitrogen), as well as from other metabolic pathways such as photorespiration, phenylpropanoid metabolism, and the catabolism of amino acids (Lea et al., 1990). These pathways occur to varying extents in different tissues and subcellular locations, which is reflected by the fact that in higher plants GS exists as a number of distinct isoenzymes located in both the cytosol and the chloroplast, which have different activities in different organs (McNally and Hirel, 1983). These multiple isoenzymes are encoded by a small family of genes that, in tum, have been shown to be differentially expressed in both a developmental-and organ-'This work was supported by a fellowship to A.C.S. from the

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Section: Discussionmentioning

confidence: 80%

mentioning

confidence: 93%

Differential Expression within the Glutamine Synthetase Gene Family of the Model Legume Medicago truncatula

et al. 1993

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“…To investigate the possible involvement of AtAMT2 in ammonium recycling after photorespiration, plants were exposed to double the normal concentration of CO 2 in the atmosphere to repress photorespiration. Alterations in the CO 2 to O 2 ratio have been found to alter the expression of GS2 in Phaseolus vulgaris, a gene that is involved in ammonium recycling after photorespiration (Wallsgrove et al, 1987;Cock et al, 1991). In contrast, no such regulation was found for GS2 in Arabidopsis (Beckmann et al, 1997).…”

Section: Discussionmentioning

confidence: 99%

Characterization of Arabidopsis AtAMT2, a High-Affinity Ammonium Transporter of the Plasma Membrane

et al. 2002

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AtAMT2 is an ammonium transporter that is only distantly related to the five members of the AtAMT1 family of high-affinity ammonium transporters in Arabidopsis. The short-lived radioactive ion 13 NH 4 ϩ was used to show that AtAMT2, expressed in yeast (Saccharomyces cerevisiae), is a high-affinity transporter with a K m for ammonium of about 20 m. Changes in external pH between 5.0 and 7.5 had little effect on the K m for ammonium, indicating that NH 4 ϩ , not NH 3 , is the substrate for AtAMT2. The AtAMT2 gene was expressed in all organs of Arabidopsis and was subject to nitrogen (N) regulation, at least in roots where expression was partially repressed by high concentrations of ammonium nitrate and derepressed in the absence of external N. Although expression of AtAMT2 in shoots responded little to changes in root N status, transcript levels in leaves declined under high CO 2 conditions. Transient expression of an AtAMT2-green fluorescent protein fusion protein in Arabidopsis leaf epidermal cells indicated a plasma membrane location for the AtAMT2 protein.Thus, AtAMT2 is likely to play a significant role in moving ammonium between the apoplast and symplast of cells throughout the plant. However, a dramatic reduction in the level of AtAMT2 transcript brought about by dsRNA interference with gene expression had no obvious effect on plant growth or development, under the conditions tested.Ammonium and nitrate are thought to be the primary sources of nitrogen (N) for most plants growing in agricultural soils. Acquisition of these inorganic nutrients from the soil solution involves a variety of different transporters, which transport the ions from the apoplast of root epidermal and cortical cells into the symplast. Although ammonium concentrations are often 10 to 1,000 times lower than those of nitrate in well-aerated soil, ammonium nutrition plays an essential role in waterlogged and acid soils (Marschner, 1995). Furthermore, ammonium seems to be a preferred source of N and is taken up more rapidly than nitrate when both ions are presented simultaneously to plants (Gazzarrini et al., 1999).Physiological studies of ammonium transport into roots have revealed biphasic kinetics in several species (Fried et al., 1965;Vale et al., 1988;Wang et al., 1993). The so-called high-affinity ammonium transport system is predominant at low (submillimolar) concentrations of substrate (NH 4 ϩ ) and exhibits saturation kinetics. A second component of ammonium uptake is the low-affinity transport system, which becomes significant at higher external ammonium concentrations (above 1 mm) and exhibits nonsaturation kinetics (Wang et al., 1993;Kronzucker et al., 1996). Although the molecular basis of low-affinity transport system activity remains unknown, there is growing evidence that members of the AMT1 family of transporters are responsible for high-affinity ammonium transport system activity in plants. The first AMT1 gene to be discovered in plants was AtAMT1;1 from Arabidopsis, which was cloned by complementation of a yeast (Sacchar...

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“…It has been shown that the light-induced increase of steady-state level of GS2 mRNA was correlated with that of GS2 polypeptide in pea leaves, suggesting that the transcriptional activation was likely to be one mechanism regulating GS2 expression (28). A recent study by Cock et al (5) showed that the GS2 polypeptide remained at a high abundance in older leaves of Phaseolus vulgaris seedlings despite a decrease in abundance of GS2 mRNA. The most likely explanation for this observation could be that (a) GS2 polypeptide was more stable than the mRNA, or (b) a lower abundance of GS2 mRNA supported a greater translational activity, as they suggested (5).…”

Section: Changes In Polypeptide Levels Of Gs1 and Gs2 In 2-cm Segmentmentioning

confidence: 98%

Changes in Cytosolic Glutamine Synthetase Polypeptide and its mRNA in a Leaf Blade of Rice Plants during Natural Senescence

Kamachi

Yamaya²,

Hayakawa³

et al. 1992

Plant Physiol.

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Changes in the levels of cytosolic glutamine synthetase (GSI) and chloroplastic glutamine synthetase (GS2) polypeptides and of their corresponding mRNAs have been investigated in segments of the 13th leaf of hydroponically grown rice (Oryza satlva L.) plants during natural senescence. The leaf blade on the main stem at early (0 day), middle (15 days), and late (25 days) stages of senescence was harvested and cut into 18 or 19 segments, 2 centimeters in length from the base to the tip. The amount of GS1 polypeptide, detected with specific antibody for the GS1, was greatest near the middle of the leaf blade (segments 11-13).There was little difference in the GS1 content between corresponding leaf segments obtained at the early and middle stages of senescence. At the late senescence stage, all segments had lost some GS1 polypeptide, but more than 50% of GS1 detected at both the early and middle stages was still detectable in segments. The relative content of mRNA for GS1 in the total RNA in all segments was very low during eariy senescence but increased in all leaf segments during later senescence. At the late stage of senescence, GSI mRNA in the total RNA increased about 4.2-to 4.6-fold in segments 12 to 16 in the day-25 samples compared with those in the early stage. The content of the GS2 polypeptide, as well as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein, was highest in segment 17 in the 0-day samples. During senescence, this peak became lower and broader, and finally disappeared, I.e. Evidence has accumulated to assess the relative functions of GS12 and GS2 in leaves, although similarities in their physical properties, their immunological cross-reactivities, and their nucleotide and amino acid sequence homologies have made it difficult to understand their distinct functions. Studies with barley mutants lacking GS2 clearly show that a major role of GS2 is the reassimilation of NH4' released during photorespiration (30). Because these mutants are able to grow normally under nonphotorespiratory conditions, it appears that the GS 1 in leaves and the root GS are important enzymes for plant growth and development. Therefore, GS 1 and root GS should have major roles in assimilation of NH4' generated by processes other than photorespiration, such as NH4' produced by nitrate reduction or protein degradation and absorption of NH4+ from the soil (15,22,23). Nitrogen released from older senescing leaves is a major source of nitrogen for developing leaves and ears in mature rice plants (16,17). The remobilization of this nitrogen involves (a) degradation of leaf proteins, such as Rubisco (10,16,17), and (b) conversion of the hydrolyzed amino acids to glutamine, which is a major form of transportable nitrogen in phloem sap of rice plants (9). GS 1 is a candidate for the synthesis of glutamine in senescing rice leaves.Using an attached whole leaf blade of naturally senescing rice plants, we recently showed that the content of GS1 polypeptide, located in the cytosol, remained constant and t...

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Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris

Cited by 59 publications

References 42 publications

Differential Expression within the Glutamine Synthetase Gene Family of the Model Legume Medicago truncatula

Differential Expression within the Glutamine Synthetase Gene Family of the Model Legume Medicago truncatula

Characterization of Arabidopsis AtAMT2, a High-Affinity Ammonium Transporter of the Plasma Membrane

Changes in Cytosolic Glutamine Synthetase Polypeptide and its mRNA in a Leaf Blade of Rice Plants during Natural Senescence

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