Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.31 (beta-glucuronidase)
 7,680 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chloroplast and cytosolic isoforms of glutamine synthetase (GS; EC 6.3.1.2) are encoded by separate nuclear genes in plants. Here we report that the promoters for chloroplast GS2 and cytosolic GS3A of Pisum sativum confer nonoverlapping, cell-specific expression patterns on the beta-glucuronidase (GUS) reporter gene in transgenic tobacco. The promoter for chloroplast GS2 directs GUS expression within photosynthetic cell types (e.g., palisade parenchymal cells of the leaf blade, chlorenchymal cells of the midrib and stem, and photosynthetic cells of tobacco cotyledons). The promoter for chloroplast GS2 retains the ability to confer light-regulated gene expression in the heterologous transgenic tobacco system in a manner analogous to the light-regulated expression of the cognate gene for chloroplast GS2 in pea. These expression patterns reflect the physiological role of the chloroplast GS2 isoform in the assimilation of ammonia generated by nitrite reduction and photorespiration. In contrast, the promoter for cytosolic GS3A directs expression of GUS specifically within the phloem elements in all organs of mature plants. This phloem-specific expression pattern suggests that the cytosolic GS3A isoenzyme functions to generate glutamine for intercellular nitrogen transport. In germinating seedlings, the intense expression of the cytosolic GS3A-GUS transgene in the vasculature of cotyledons reveals a role for cytosolic GS in the mobilization of seed storage reserves. The distinct, cell-specific patterns of expression conferred by the promoters for chloroplast GS2 and cytosolic GS3A indicate that the corresponding GS isoforms perform separate metabolic functions.
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PMID:Cell-specific expression in transgenic plants reveals nonoverlapping roles for chloroplast and cytosolic glutamine synthetase. 197 Jun 38

The glutamine synthetase (GS) gene family in pea (Pisum sativum) consists of four nuclear genes encoding distinct isoenzymes. Molecular studies have show that the GS2 gene encoding chloroplast-localized GS is expected in specific cell types and is regulated by diverse factors such as light and photorespiration. Here, we present the nucleotide sequence of the pea GS2 gene promoter. To identify the elements involved in regulation of GS2 expression, GS2 promoter-deletion analyses were performed using GS2-GUS fusions in tobacco (Nicotiana tabacum). This analysis revealed that the GS2 transit peptide is not required for mesophyll cell-specific expression of beta-glucuronidase (GUS). GUS activity was induced 2- to 4-fold in light-grown versus etiolated T1 seedlings. However, high levels of GUS activity were observed in etiolated seedlings. This observation demonstrated that regulation of expression of GS2, a nonphotosynthetic light-regulated gene, involves additional factors. A 323-bp GS2 promoter sequence is sufficient to confer light regulation to the GUS reporter gene in leaves of mature transgenic tobacco. Light-regulated expression of this pea gene promoter is observed in both tobacco and Arabidopsis, suggesting that the regulatory elements are conserved. Gel-shift analysis detected DNA-protein complexes formed with potential transcription elements within this short, light-responsive GS2 promoter fragment.
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PMID:Cis elements and trans-acting factors affecting regulation of a nonphotosynthetic light-regulated gene for chloroplast glutamine synthetase. 763 Sep 38

There is growing evidence that AT-rich promoter elements play a role in transcription of plant genes. For the promoter of the nuclear gene for chloroplast glutamine synthetase from pea (GS2), the deletion of a 33-bp AT-rich sequence (box 1 native) from the 5' end of a GS2 promoter-beta-glucuronidase (GUS) fusion resulted in a 10-fold reduction in GUS activity. The box 1 native element was used in gel shift analysis and two distinct complexes were detected. One complex is related to the low-mobility complex reported previously for AT-rich elements from several other plant promoters. A multimer of the box 1 sequence was used to isolate a cDNA encoding an AT-rich DNA binding protein (ATBP-1). ATBP-1 is not a high-mobility group protein, but it is a novel protein that combines a high-mobility group I/Y-like DNA binding domain with a glutamine-rich putative transcriptional domain.
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PMID:A novel AT-rich DNA binding protein that combines an HMG I-like DNA binding domain with a putative transcription domain. 790 5

In bacteria and yeast, glutamine synthetase (GS) expression is tightly regulated by the metabolic status of the cell, both at the transcriptional and posttranscriptional levels. We discuss the relative contributions of light and metabolic cues on the regulation of members of the GS gene family (chloroplastic GS2 and cytosolic GS1) in Arabidopsis. These studies reveal that the dramatic induction of mRNA for chloroplastic GS2 by light is mediated in part by phytochrome and in part by light-induced changes in sucrose (Suc) levels. In contrast, the modest induction of mRNA for cytosolic GS1 by light is primarily mediated by changes in the levels of carbon metabolites. Suc induction of mRNA for GS2 and GS1 occurs in a time- and dose-dependent manner. Suc-induced changes in GS mRNA levels were also observed at the level of GS enzyme activity. In contrast, amino acids were shown to antagonize the Suc induction of GS, both at the level of mRNA accumulation and that of enzyme activity. For GS2, the gene whose expression was the most dramatically regulated by metabolites, we used a GS2 promoter-beta-glucuronidase fusion to demonstrate that transcriptional control is involved in this metabolic regulation. Our results suggest that the metabolic regulation of GS expression in plants is controlled by the relative abundance of carbon skeletons versus amino acids. This would allow nitrogen assimilation into glutamine to proceed (or not) according to the metabolic status and biosynthetic needs of the plant. This type of GS gene regulation is reminiscent of the nitrogen regulatory system in bacteria, and suggests an evolutionary link between metabolic sensing and signaling in bacteria and plants.
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PMID:Carbon and amino acids reciprocally modulate the expression of glutamine synthetase in Arabidopsis. 1048 86