Cell-specific gene expression in plants.
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Gene Expression↗
Biomedical subjects
G M Coruzzi
Publications and source records attributed to G M Coruzzi.
Developmentally Regulated Expression of the Gene Family for Cytosolic Glutamine Synthetase in Pisum sativum.
In Pisum sativum, two classes of genes encode distinct isoforms of cytosolic glutamine synthetase (GS). The first class comprises two nearly identical or "twin" GS genes (GS341 and GS132), while the second comprises a single GS gene (GS299) distinct in both coding and noncoding regions from the "twin" GS genes. Gene-specific analyses were used to monitor the individual contribution of each gene for cytosolic GS during root nodule development and in cotyledons during germination, two contexts where large amounts of ammonia must be assimilated by GS for nitrogen transport. mRNAs corresponding to all three genes for cytosolic GS were shown to accumulate coordinately during a time course of nodule development. All the GS mRNAs also accumulate to wild-type levels in mutant nodules formed by a nifD(-) strain of Rhizobium leguminosarum indicating that induced GS expression in pea root nodules does not depend on the production of ammonia. Distinct patterns of expression for the two classes of GS genes were observed in certain mutant root nodules and most dramatically in cotyledons of germinating seedlings. The different patterns of expression between the two classes of genes for cytosolic GS suggests that their distinct gene products may serve nonoverlapping functions during pea development.
Journal Article↗
Photorespiration and light act in concert to regulate the expression of the nuclear gene for chloroplast glutamine synthetase.
In Pisum sativum, distinct chloroplast and cytosolic forms of glutamine synthetase (GS) are encoded by homologous nuclear genes that are differentially expressed in vivo (Tingey, S. V., Tsai, F.-Y., Edwards, J. W., Walker, E. L., and Coruzzi, G. M. [1988]. J. Biol. Chem. 263, 9651-9657). In leaves, light selectively affects the expression of the nuclear gene for chloroplast GS2. Differences in the maximal levels of GS2 mRNA in etiolated plants treated with red or white light indicate that only part of the white-light-induced accumulation of GS2 mRNA is due to a phytochrome-mediated response. The kinetics of GS2 mRNA accumulation in response to white-light illumination of etiolated or dark-adapted green plants indicates that GS2 mRNA accumulates more rapidly in plants containing mature, photosynthetically competent chloroplasts. Other evidence that GS2 mRNA levels are affected by the metabolic status of chloroplasts concerns the selective induction of GS2 mRNA in plants grown under conditions that result in the production of photorespiratory ammonia. These results indicate that the light-induced accumulation of GS2 mRNA in leaves results from the action of phytochrome as well as light-induced changes in chloroplast metabolism.
Base Sequence↗
Chloroplast and cytosolic glutamine synthetase are encoded by homologous nuclear genes which are differentially expressed in vivo.
We have shown that the individual members of the plant gene family for glutamine synthetase (GS) are differentially expressed in vivo, and each encode distinct GS polypeptides which are targeted to different subcellular compartments (chloroplast or cytosol). At the polypeptide level, chloroplast GS (GS2) and cytosolic GS (GS1 and GSn) are distinct and show an organ-specific distribution. We have characterized full length cDNA clones encoding chloroplast or cytosolic GS of pea. In vitro translation products encoded by three different GS cDNA clones, correspond to the mature GS2, GS1, and GSn polypeptides present in vivo. pGS185 encodes a precursor to the chloroplast GS2 polypeptide as shown by in vitro chloroplast uptake experiments. The pGS185 translation product is imported into the chloroplast stroma and processed to a polypeptide which corresponds in size and charge to that of mature chloroplast stromal GS2 (44 kDa). The 49 amino terminal amino acids encoded by pGS185 are designated as a chloroplast transit peptide by functionality in vitro, and amino acid homology to other transit peptides. The cytosolic forms of GS (GS1 and GSn) are encoded by highly homologous but distinct mRNAs. pGS299 encodes the cytosolic GS1 polypeptide (38 kDa), while pGS341 (Tingey, S. V., Walker, E. L., and Coruzzi, G. M. (1987) EMBO. J. 6, 1-9) encodes a cytosolic GSn polypeptide (37 kDa). The homologous nuclear genes for chloroplast and cytosolic GS show different patterns of expression in vivo. GS2 expression in leaves is modulated by light, at the level of steady state mRNA and protein, while the expression of cytosolic GS is unaffected by light. The light-induced expression of GS2 is due at least in part to a phytochrome mediated response. Nucleotide sequence analysis indicates that chloroplast and cytosolic GS have evolved from a common ancestor and suggest a molecular mechanism for chloroplast evolution.
Amino Acid Sequence↗
Glutamine synthetase genes of pea encode distinct polypeptides which are differentially expressed in leaves, roots and nodules.
We have characterized the distinct polypeptides, primary translation products and mRNAs encoding glutamine synthetase (GS) in the various organs of pea. Western blot analysis of soluble protein has identified five distinct GS polypeptides which are expressed at different relative levels in leaves, roots and nodules of pea. Of the two GS polypeptides in leaves (44 and 38 kd), the 44-kd GS polypeptide is predominant and is localized to the chloroplast stroma. In roots, the predominant GS polypeptide is 38 kd. Upon Rhizobium infection of roots, three 37-kd GS polypeptides increase in abundance in the nodules relative to uninfected roots. cDNA clones encoding three different GS mRNAs have been characterized. Hybrid-select translation has identified three different GS primary translation products (49, 38 and 37 kd). Two cDNA clones (pGS134 and pGS341) are homologous to GS mRNAs most abundant in nodules which encode the 38- and 37-kd GS primary translation products. A third cDNA (pGS197) corresponds to a larger GS mRNA species specific to leaf poly(A) RNA, which encodes a 49-kd putative precursor to the mature chloroplast GS polypeptide. cDNA sequence analysis and Southern blot analysis of pea nuclear DNA identifies at least three genes encoding GS in pea which are related but distinct in structure and in vivo pattern of expression.
Amino Acid Sequence↗
Glutamine Synthetase of Nicotiana plumbaginifolia: Cloning and in Vivo Expression.
We have characterized the distinct forms of glutamine synthetase (GS) which are present in leaves and roots of Nicotiana plumbaginifolia. Mature leaves contain a single GS polypeptide (44 kilodaltons in size) which is localized to the stroma of intact chloroplasts. In contrast, the GS polypeptide in roots is distinct in size (38 kilodaltons) and charge. A lectin stain of leaf soluble protein indicates that the size difference of these mature GS polypeptides is not the result of posttranslational glycosylation. cDNA clones encoding a GS mRNA of N. plumbaginifolia were characterized and used as molecular probes to examine GS transcripts in leaves and roots. GS mRNA hybrid-selected from leaves or roots translated in vitro into distinct GS primary translation products (49 or 38 kilodaltons). The 49 kilodalton GS primary translation product, specific to leaf poly(A)RNA is proposed to be a precursor to the mature 44 kilodalton chloroplast stromal GS polypeptide. The 38 kilodalton GS primary translation product encoded by root GS mRNA, corresponds in size to the polypeptide encoded by the GS cDNA clones characterized. Southern blot analysis of nuclear DNA indicates that there are several different genomic fragments encoding GS in N. plumbaginifolia.
Journal Article↗