Cloning of GS1 gene encodes glutamine synthetase 1 and construction of transformation vector

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Glutamine synthetase (EC 6.3.1.2) is an enzyme which assimilates ammonium into amino acids. Therefore, GS plays an essential role in the metabolism of nitrogen. In vascular plants, GS is devided into two groups: cytosol - located isoform (GS1) and plastid – located isoform (GS2). Surveys have shown that GS1 gene was used widely to generate transgenic plants. Effects on the growth characteristics of GS1 transgenic plants have been reported in many researches.

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Nội dung Text: Cloning of GS1 gene encodes glutamine synthetase 1 and construction of transformation vector

Biotechnology and Seedling CLONING OF GS1 GENE ENCODES GLUTAMINE SYNTHETASE 1 AND CONSTRUCTION OF TRANSFORMATION VECTOR Bui Van Thang1, Ngo Van Thanh2, Nguyen Thi Hong Gam3, Chu Hoang Ha4 1,2,3 Vietnam National University of Forestry 4 Institute of Biotechnology, VAST SUMMARY Glutamine synthetase (EC 6.3.1.2) is an enzyme which assimilates ammonium into amino acids. Therefore, GS plays an essential role in the metabolism of nitrogen. In vascular plants, GS is devided into two groups: cytosol - located isoform (GS1) and plastid – located isoform (GS2). Surveys have shown that GS1 gene was used widely to generate transgenic plants. Effects on the growth characteristics of GS1 transgenic plants have been reported in many researches. In this research, in order to prepare for generating GS1 transgenic plants, the 1074 bp – length cDNA of GS1 gene is successfully cloned from Pinus sylvestris. Compared the sequence of the isolated cDNA of GS1 with other sequences on Genbank (Accession number X69822.1 and X74429.1), the similarities are both higher than 99%. This result indicates a high sequence conservation of GS1 gene. The gene was then ligated into vector pBI121 to construct transformation vector pBI121 – GS1 which can be used in next steps to generate transgenic plants which have high - growth rate. Keywords: Glutamine synthetase 1, GS1 gene, Pinus sylvestris, transformation, vector construction. I. INTRODUCTION GS1 are derived from primary nitrogen uptake Glutamine synthetase (GS, E.C. 6.3.1.2) and from various internal nitrogen recycling assimilates ammonium into amino acids, thus pathways. In this way, cytosolic glutamine it is a key enzyme in efficient use of nitrogen synthetase is crucial for the remobilization of sources and nitrogen metabolism in organisms. protein – derived nitrogen (Stéphanie and In vascular plants, GS is an octameric enzyme Habash, 2009). of 320 to 380 kb (Stewart et al., 1980) that The GS1 genes in all plants studied are occurs as a number of isoenzymes, the subunits members of small gene families, and the of which are encoded by members of a small different members are differentially regulated multigene family (Bennett et al., 1989; (Bennett et al., 1989; Peterman and Goodman, Peterman and Goodman, 1991; Roche et al., 1991; Roche et al., 1993; Temple et al., 1995; 1993; Temple et al., 1995; Dubois et al., 1996). Dubois et al., 1996). Analysis of Arabidopsis In the photosynthetic tissues of many thaliana genome has identified five GS1 genes, angiosperms, GS2, a plastid - located isoform but only four of which appear to be expressed of GS, is responsible for the assimilation of (Ishiyama et al., 2004). Each of the GS genes ammonium derived from nitrate reduction and appears to participate in different metabolic photorespiration (Ireland and Lear, 1999). processes, based on where and how they are Whereas GS1, a cytosolic isoform, is the expressed. According to Martin et al. (2006), predominant enzyme in roots and non – in Zea mays, GS1-1 is expressed in root cortex, photosynthetic tissues and much less abundant GS1-2 in phloem, GS1-3, GS1-4, GS1-5 in in green tissues (Ireland and Lea, 1999). GS1 leaf. is particularly important for assimilating Surveys have shown that GS1 gene was ammonium from different sources for both used widely to generate transgenic plants. primary nitrogen assimilation and recycling. Ribarits et al. (2007) has generated transgenic JOURNAL OF FOREST SCIENCE AND TECHNOLOGY NO. 3 - 2016 3
Biotechnology and Seedling tobacco with mutated GS genes driven by reported. More consistent results have been tapetum and microspore – specific promoters. obtained with transgenic clones of hybrid Consequently, the plants were male sterile, but poplar. Clones expressing a GS1a gene from this could be reversed by spraying with the conifer Populus sylvestris, under the glutamine. This result demonstrated the control of the CaMV 35S promoter, have been importance of GS1 in anthers and pollen. shown to have higher vegetative growth with There is also evidence of compensation enhanced nitrogen assimilation efficiency, between GS1 and GS2 enzyme levels in higher net photosynthetic rates, higher rates of transgenic plants. For example, wheat lines photorespiration and enhanced resistance to transformed with the GS1 gene PvGln-α under water stress (Kirby et al., 2006). Many of these the control of the Rubisco small subunit benefits have been sustained in a 3 – year field promoter had more GS1 and less GS2 enzyme test (Jing et al., 2004). activity in the flag leaves during grain filling In this research, we isolated GS1 gene and (Habash et al., 2001). then constructed transformation vector pBI121 Effects on the growth characteristics of the – GS1 which can be used in next steps to transgenic plants have been reported. Fuentes generate transgenic plants which have high- et al. (2001) found that T1 generation tobacco growth rate. plants, transformed with CaMV 35S: GS1 II. MATERIALS AND METHODS constructs, were similar to the wild type under 2.1. Materials high N nutrition but were greener and had Pinus sylvestris (leaf, stem and root); pBT higher shoot and root dry weight than the T/A cloning vector (Institue of controls in low N. In contrast, Oliveira et al. Biotechnology); pBI121-GUS with nptII (2002) found that similar tobacco selection gene (which resists kanamycin) transformants grew better under both N – transformation vector; E. coli strain DH5α sufficient and N – limitting conditions. In part, from Invitrogen. this might be because transformed plants Two specific DNA primers for amplifying appeared to mature earlier (Vincent et al., GS1 were designed based on the GS1 gene 1997). Martin et al. (2006) transformed maize sequence of Pinus sylvestris (Accession with GS1 GLN1-3 gene, driven by a number X69822.1). Forward primer (GS1F): constitutive CsVMV promoter, and the 5’-ATG TCG AGC GTA TTA ACA GAC C- resulting plants had higher activities of GS1 3’; Reverse primer (GS1R): 5’-TTA AGG TTT and an increase in grain yield and number. CCA TAG AAT GGT CG-3’ (the two primers Some wheat lines transformed with the GS1 were conjugated with restriction sites of XbaI gene PvGln-α, under the control of the Rubisco and SacI). small subunit promoter, also showed increased Chemicals: restriction enzyme (XbaI, SacI), grain yield, although this was due to increased T4 DNA ligase, Taq polymerase, Gel grain weight (Habash et al., 2001). In many of purification Kit from Fermentas, QIAquick Gel the studies, the effects varied between different Extraction Kit, QIAprep Spin Miniprep Kit transformed lines in the same experiment (Fei (QIAGEN), PureLink TM Plant RNA Reagent et al., 2003, 2006). Kit, FastTrack® MAG mRNA Isolation Kit Some researches of generating of GS1- (Invitrogen), ReverAidTM H Minus First Strand transformation in forest plants were also Synthesis Kit. 4 JOURNAL OF FOREST SCIENCE AND TECHNOLOGY NO. 3 - 2016
Biotechnology and Seedling 2.2. Methods transforming the recombinant vector pBT – 2.2.1. Gene cloning of GS1 gene GS1 into E.coli strain DH5α using heat – shock Firstly, total RNA was isolated from the (42oC for 90 seconds). The recombinant E.coli mixture of leaf, stem and root of Pinus was screened on LB medium (added 100 mg/l sylvestris: using the protocol of PureLink TM Ampicillin, 0.004% X-gal, 100µM IPTG) and Plant RNA Reagent Kit from Invitrogen then extracted plasmid, tested using PCR (USA). In the next step, mRNA was purified method and XbaI/SacI double digestion. from total RNA by using FastTrack® MAG GS1 gene which was cloned successfully is mRNA Isolation Kit (Invitrogen), according to sequenced by automatic DNA sequencer (ABI the manufacturer’s instruction. mRNA was PRISM 377, Applied Biosystems, USA) and then used as the template for cDNA synthesis, compared with those of the GS1 genes on and first – strand cDNA was reverse – Genebank. transcribed using reverse transcriptase which 2.2.2. Construction of transformation vector was supplied with ReverAidTM H Minus First pBI121–GS1 Strand Synthesis Kit, according to the Firstly, pBI121 – GUS and pBT – GS1 were manufacturer’s instruction. double digested by the same restriction Subsequently, the first strand of cDNA was enzymes (XbaI/SacI). The mixture of double used as template for polymerase chain reaction digestion reaction included 18.0 µl deionized amplification of the GS1 gene using two H2O, 4.0 µl Tango buffer (10X), 10.0 µl vector primers GS1F and GS1R. The mixture of PCR (pBI121 – GUS or pBT – GS1), 4.0 µl XbaI (1 reaction included 15.7 µl deionized H2O, 2.5 U/µl), 4.0 µl SacI (1 U/µl). The mixture was µl PCR buffer (10X), 2.5 µl MgCl2 (50mM), 1 incubated at 37oC for 3h. µl dNTP (10mM), 1 µl each of primers Next, vector pBI121 and GS1 gene which (GS1F/GS1R, 10 µM), 1 µl DNA template (50 were double digested were purified using gel ng/µl) and 0.3 µl Taq DNA polymerase (5 purification kit (Bioneer, Korea) and then U/µl). ligated together with the catalysation of T4 The PCR reaction was performed at 94oC at 5 DNA ligase. The mixture of ligation reaction min, then 35 cycles of PCR as follows: included 6.0 µl deionized H2O, 2.0 µl T4 DNA [denaturation at 94oC for 1 min, annealing at ligase buffer (10X), 5.0 µl pBI121 vector, 5.0 55oC for 45 second, extension at 72oC for 1.5 µl GS1, 2.0 µl T4 DNA ligase (1 U/µl). The min], 72oC for 8 min, store at 4oC. PCR products mixture was incubated at 22oC for 2h. were separated on a 1% (w/v) of agarose gel Subsequently, the recombinant vector using electrophoresis, stained with ethidium pBI121 – GS1 is transformed into E.coli strain bromide and photographed under UV light. DH5α using heat - shock (42oC for 90 second). GS1 gene was then cloned into pBT T/A The recombinant E.coli was screened on LB cloning vector. The mixture of ligation medium (added 50 mg/l kanamycin) and then reaction included 9.0 µl deionized H2O, 2.0 µl extracted plasmid, tested using PCR method T4 DNA ligase buffer (10X), 1.0 µl pBT and XbaI/SacI double digestion. cloning vector, 7.0 µl GS1, 1.0 µl T4 DNA III. RESULTS AND DISCUSSION ligase (1 U/µl). The mixture was incubated at 3.1. Cloning of GS1 gene 22oC for 2h. The mRNA which was isolated from The ligation mixture was then used for mixture of leaf, stem and root of Pinus JOURNAL OF FOREST SCIENCE AND TECHNOLOGY NO. 3 - 2016 5
Biotechnology and Seedling sylvestris was used for first – strand cDNA (w/v) agarose gel electrophoresis. The result in synthesis. The first – strand cDNA was then figure 1 shows that, only one clear band of amplified by using PCR reaction with the approximately 1.1 kb was amplified, which specific primers GS1F/GS1R. The PCR was consistent with predictions. product of GS1 gene was separated by 1% Figure 1. Amplifying of GS1 from mRNA of P. sylvestris M: Marker 1kb; lane 1: PCR product amplifed of GS1 GS1 gene was ligated into pBT T/A cloning were selected for plasmid extraction (the blue vector to create recombination vector pBT – one was for negative control). The plasmids GS1 which was transformed into E.coli strain were also used for PCR reaction to amplify DH5α using heat – shock. E. coli was then GS1 gene using specific primers GS1F/GS1R. cultured on selection medium (LB + 100 mg/l The result in figure 2A and 2B shows that GS1 ampicillin, 0.004% X-gal + 100 µM IPTG) for gene was successfully cloned to vector pBT 12 hours. 5 white and 1 blue colonies of E. coli and transformed into E.coli DH5α. Figure 2. Plasmid pBT – GS1 extracted from E.coli (A) and PCR reaction of GS1 (B) (A: M: Marker 1kb; lane 1 - 5: white clones of E.coli; lane 6: blue clone; B: M: Marker 1kb; lane 1 – 5: PCR product amplifed of GS1 from plasmid pBT – GS1) The plasmids were then used for next step sequences on Genebank (Accession number of sequencing. Sequencing results indicated X69822.1 and X74429.1), the similarities are that the sequence of full – length cDNA of both higher than 99%. This result indicates a GS1 contained an entire open reading frame high sequence conservation of GS1 gene. (ORF) of 1074 bp, from start codon ATG to stop codon TAA. Compared the sequence of 3.2. Construction of transformation vector the isolated cDNA of GS1 with other pBI121–GS1 6 JOURNAL OF FOREST SCIENCE AND TECHNOLOGY NO. 3 - 2016
Biotechnology and Seedling The binary vector pBI121 was used for digestion of pBT – GS1 and pBI121 using vector construction. The T–DNA region of XbaI/SacI, the result is showed in Figure 3A. standard binary vector pBI121 contains the Vector pBT – GS1 was digested into 2 bands, cauliflower mosaic virus 35S promoter (CaMV the first band (about 2.7 kb) is the linear 35S promoter) and NOS terminator which backbone of vector pBT, and the another band regulate the expression of beta – glucuronidase (about 1.1 kb) is GS1 gene. Similarly, vector reporter gene (gus gene). After ligating into pBI121- Gus was also digested into 2 bands, vector pBI121, the target gene (GS1) replaces the first one (about 12 kb) is the linear gus gene. Besides, the vector also contains backbone of vector pBI121, and the another kanamycin - resistant gene (nptII gene) which one (about 1.8 kb) is Gus gene. can be used for selection. We used Gel purification Kit (Fermentas, The two primers which is used for Korea) to purify the linear vector pBI121 amplifying GS1 is conjugated with XbaI (in (without Gus gene) and the target gene (GS1). GS1F) and SacI (in GS1R) restriction enzyme The result in figure 3B shows that the bands of sites. Therefore, the recombinant vector pBT – linear vector pBI121 and target gene GS1 are GS1 contains XbaI and SacI sites in the two very clear, which means that we are successful ends of GS1 gene. As the same, vector pBI121 in purification of vector pBI121 (without Gus contains XbaI and SacI sites in the two ends of gene) and GS1 gene for next steps. gus gene. As the consequence, after double Figure 3. pBI121-Gus and pBT – GS1 after XbaI/SacI double digestion (A) and gel purification (B) (A: M: Marker 1kb; lane 1: pBT - GS1; lane 2: pBI121-Gus; B: M: Marker 1kb; lane 1: GS1 gene; lane 2: pBI121- without Gus gene) In the next step, GS1 gene is ligated into E.coli were used for GS1- amplified PCR vector pBI121 with the catalysis of T4 DNA reaction and XbaI/SacI double digestion. ligase. The recombinant vector (pBI121 – The result of PCR reaction in figure 4A GS1) was transformed into E.coli strain DH5α shows that we amplified successfully GS1 gene by heat-shock (42oC for 90 seconds). E.coli from plasmid of 11 E.coli clones. The was then cultured on LB medium which XbaI/SacI double digestion of plasmid from contained 50 mg/l kanamycin. The plasmids clone 1 also confirmed the existence of GS1 which were extracted from survival clones of gene (figure 4B). FORESTRY SCIENCE AND TECHNOLOGY JOURNAL NO. 3 - 2016 7
Biotechnology and Seedling Figure 4. Confirmation of GS1 by PCR reaction (A) and pBI121-GS1 after XbaI/SacI double digestion (B) (A: M: Marker 1kb; lane 1 – 11: GS1 amplification from 11 E.coli clones; B: M: Marker 1kb; lane 1: pBI121-GS1 after XbaI/SacI double digestion) IV. CONCLUSION synthetase enzymes and the corresponding transcripts GS1 gene from mRNA of Pinus sylvestris is shows organand cell-specific patterns of protein synthesis and gene expression. Plant Mol Biol 31: 807–817. successfully cloned. The gene has 1074 bp in 3. Fei, H.M., Chaillou, S., Hirel, B., et al. (2003) length from start codon ATG to stop codon Overexpression of a soybean cytosolic glutamine TAA. Compared the sequence of the isolated synthetase gene linked to organ-specific promoters in GS1 with the other sequences on Genebank pea plants grown in different concentrations of nitrate. (Accession number X69822.1 and X74429.1), Planta 216: 467–474. the similarities are both higher than 99%. This 4. Fei, H., Chaillou, S., Hirel, B., et al. (2006) result indicates a high sequence conservation Effects of the overexpression of a soybean cytosolic glutamine synthetase gene (GS1-5) linked to organ- of GS1 gene. specific promoters on growth and nitrogen accumulation The transformation vector pBI121 – GS1 of pea plants supplied with ammonium. Plant used for next steps of generating of transgenic Physiology and Biochemistry 44: 543–550. plants via Agrobacterium – mediated 5. Fuentes, S.I., Allen, D.J., Ortiz-Lopez, A., et al. transformation is successfully constructed. (2001) Over-expression of cytosolic glutamine synthetase increases photosynthesis and growth at low Acknowledgements nitrogen concentrations. Journal of Experimental Botany This study was implemented by the 52: 1071–1081. financial support of research project “Creation 6. Habash, D.Z., Massiah, A.J., Rong, H.L., et al. of transgenic Eucalyptus urophylla to improve (2001) The role of cytoplasmic glutamine synthetase in growth rate” (Agriculture Biotechnology wheat. Annals of Applied Biology 138: 83–89. Program, Ministry of Agriculture and Rural 7. Ireland RJ, Lea PJ (1999) The enzymes of Development, Viet Nam). glutamine, glutamate, asparagine, and aspartate metabolism. In BK Singh, ed, Plant Amino Acids, REFERENCES Biochemistry and Biotechnology. Marcel Dekker, New 1. Bennett MJ, Lightfoot DA, Cullimore JV (1989) York, 49–109. cDNA sequences and differential expression of the gene 8. Ishiyama, K., Inoue, E., Watanabe-Takahashi, A., encoding the glutamine synthetase γ polypeptide of et al. (2004) Kinetic properties and ammonium- Phaseolus vulgaris L. Plant Mol Biol 12: 553–565. dependent regulation of cytosolic isoenzymes of 2. Dubois F, Brugiere N, Sangwan RS, Hirel B glutamine synthetase in Arabidopsis. Journal of (1996) Localization of tobacco cytosolic glutamine Biological Chemistry 279: 16598–16605. 8 FORESTRY SCIENCE AND TECHNOLOGY JOURNAL NO. 3 - 2016
Biotechnology and Seedling TÁCH DÒNG GEN GS1 MÃ HÓA GLUTAMINE SYNTHETASE 1 VÀ THIẾT KẾ CẤU TRÚC VECTOR CHUYỂN GEN THỰC VẬT Bùi Văn Thắng1, Ngô Văn Thanh2, Nguyễn Thị Hồng Gấm3, Chu Hoàng Hà4 1,2,3 Trường Đại học Lâm nghiệp 4 Viện Khoa học Công nghệ Việt Nam TÓM TẮT Glutamine synthetase (GS, EC 6.3.1.2) là enzyme xúc tác cho phản ứng đồng hóa ammonium thành các axit amin. Do đó, GS giữ vai trò thiết yếu trong cơ chế trao đổi nitơ ở thực vật. Ở thực vật bậc cao, GS được chia thành 2 nhóm: GS1 (tồn tại trong tế bào chất) và GS2 (tồn tại trong thể hạt). Gen GS1 đã được sử dụng trong tạo giống cây trồng biến đổi gen cải thiện khả năng sinh trưởng. Trong nghiên cứu này, để tạo tiền đề cho việc tạo giống cây trồng biến đổi gen có khả năng sinh trưởng nhanh, chúng tôi đã tách dòng thành công gen GS1 từ mRNA của cây Thông Pinus sylvestris. Gen GS1 đã được tách dòng có kích thước 1.074 bp, có trình tự giống với các trình tự gen GS1 đã công bố trên Ngân hàng gen quốc tế -NCBI (mức độ tương đồng cao hơn 99%). Gen GS1 sau đó được gắn vào vector chuyển gen thực vật pBI121 để tạo cấu trúc vector pBI121 - GS1 (trong đó, gen GS1 được điều khiển bởi promoter 35S). Cấu trúc vector này sẽ được sử dụng để chuyển gen vào cây trồng lâm nghiệp nhằm cải thiện khả năng sinh trưởng. Từ khóa: Gen GS1, glutamine synthetase 1, Pinus sylvestris, tách dòng gen, thiết kế vector chuyển gen. Reviewer : Dr. Nguyen Trung Nam Received : 07/4/2016 Revised : 15/4/2016 Accepted : 22/4/2016 FORESTRY SCIENCE AND TECHNOLOGY JOURNAL NO. 3 - 2016 9