1
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Li H, Lin Z, Guo X, Pan Z, Pan H, Wang D. Primer extension refractory PCR: an efficient and reliable genome walking method. Mol Genet Genomics 2024; 299:27. [PMID: 38466442 DOI: 10.1007/s00438-024-02126-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Accepted: 02/10/2024] [Indexed: 03/13/2024]
Abstract
Genome walking, a molecular technique for obtaining unknown flanking genomic sequences from a known genomic sequence, has been broadly applied to determine transgenic sites, mine new genetic resources, and fill in chromosomal gaps. This technique has advanced genomics, genetics, and related disciplines. Here, an efficient and reliable genome walking technique, called primer extension refractory PCR (PER-PCR), is presented. PER-PCR uses a set of primary, secondary, and tertiary walking primers. The middle 15 nt of the primary walking primer overlaps with the 3' parts of the secondary and tertiary primers. The 5' parts of the three primers are heterologous to each other. The short overlap allows the walking primer to anneal to its predecessor only in a relaxed-stringency PCR cycle, resulting in a series of single-stranded DNAs; however, the heterologous 5' part prevents the creation of a perfect binding site for the walking primer. In the next stringent cycle, the target single strand can be extended into a double-stranded DNA molecule by the sequence-specific primer and thus can be exponentially amplified by the remaining stringent cycles. The nontarget single strand fails to be enriched due to the lack of a perfect binding site for any primer. PER-PCR was validated by extension into unknown flanking regions of the hyg gene in rice and the gadR gene in Levilactobacillus brevis CD0817. In summary, in this study, a new practical PER-PCR method was constructed as a potential alternative to existing genome walking methods.
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Affiliation(s)
- Haixing Li
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, People's Republic of China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, 330047, People's Republic of China
| | - Zhiyu Lin
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, People's Republic of China
- Boya Bio-Pharmaceutical Group Co., Ltd, High-Tech Industrial Development Zone, Fuzhou, 344100, People's Republic of China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, 330047, People's Republic of China
- School of Chemistry and Chemical Engineering, Nanchang University, Nanchang, 330047, People's Republic of China
| | - Xinyue Guo
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, People's Republic of China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, 330047, People's Republic of China
| | - Zhenkang Pan
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, People's Republic of China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, 330047, People's Republic of China
| | - Hao Pan
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, 330047, People's Republic of China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, 330047, People's Republic of China
- School of Chemistry and Chemical Engineering, Nanchang University, Nanchang, 330047, People's Republic of China
| | - Dongying Wang
- Physical Education Department, Shanghai University of Traditional Chinese Medicine, Shanghai, 201203, People's Republic of China.
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Bridging PCR: An Efficient and Reliable Scheme Implemented for Genome-Walking. Curr Issues Mol Biol 2023; 45:501-511. [PMID: 36661519 PMCID: PMC9857710 DOI: 10.3390/cimb45010033] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 01/01/2023] [Accepted: 01/04/2023] [Indexed: 01/09/2023] Open
Abstract
The efficacy of the available genome-walking methods is restricted by low specificity, high background, or composite operations. We herein conceived bridging PCR, an efficient genome-walking approach. Three primers with random sequences, inner walker primer (IWP), bridging primer (BP), and outer walker primer (OWP), are involved in bridging PCR. The BP is fabricated by splicing OWP to the 5'-end of IWP's 5'-part. A bridging PCR set is constituted by three rounds of amplification reactions, sequentially performed by IWP, BP plus OWP, and OWP, respectively pairing with three nested sequence-specific primers (SSP). A non-target product arising from IWP alone undergoes end-lengthening mediated by BP. This modified non-target product is a preferentially formed hairpin between the lengthened ends, instead of binding with shorter OWP. Meanwhile, a non-target product, triggered by SSP alone or SSP plus IWP, is removed by nested SSP. As a result, only the target DNA is accumulated. The efficacy of bridging PCR was validated by walking the gadA/R genes of Levilactobacillus brevis CD0817 and the hyg gene of rice.
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3
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Wei C, Lin Z, Pei J, Pan H, Li H. Semi-Site-Specific Primer PCR: A Simple but Reliable Genome-Walking Tool. Curr Issues Mol Biol 2023; 45:512-523. [PMID: 36661520 PMCID: PMC9857434 DOI: 10.3390/cimb45010034] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 01/02/2023] [Accepted: 01/04/2023] [Indexed: 01/09/2023] Open
Abstract
Genome-walking has been frequently applied to molecular biology and related areas. Herein, a simple but reliable genome-walking technique, termed semi-site-specific primer PCR (3SP-PCR), is presented. The key to 3SP-PCR is the use of a semi-site-specific primer in secondary PCR that partially overlaps its corresponding primary site-specific primer. A 3SP-PCR set comprises two rounds of nested amplification reactions. In each round of reaction, any primer is allowed to partially anneal to the DNA template once only in the single relaxed-stringency cycle, creating a pool of single-stranded DNAs. The target single-stranded DNA can be converted into a double-stranded molecule directed by the site-specific primer, and thus can be exponentially amplified by the subsequent high-stringency cycles. The non-target one cannot be converted into a double-strand due to the lack of a perfect binding site to any primer, and thus fails to be amplified. We validated the 3SP-PCR method by using it to probe the unknown DNA regions of rice hygromycin genes and Levilactobacillus brevis CD0817 glutamic acid decarboxylase genes.
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Affiliation(s)
- Cheng Wei
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang 330047, China
| | - Zhiyu Lin
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang 330047, China
- School of Chemistry and Chemical Engineering, Nanchang University, Nanchang 330031, China
| | - Jinfeng Pei
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang 330047, China
| | - Hao Pan
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang 330047, China
- School of Chemistry and Chemical Engineering, Nanchang University, Nanchang 330031, China
| | - Haixing Li
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang 330047, China
- Correspondence:
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Kalendar R, Hunter C, Orbovic V. Editorial: Innovative applications of sequencing technologies in plant science. FRONTIERS IN PLANT SCIENCE 2022; 13:1058347. [PMID: 36388574 PMCID: PMC9644194 DOI: 10.3389/fpls.2022.1058347] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 10/11/2022] [Indexed: 05/28/2023]
Affiliation(s)
- Ruslan Kalendar
- Helsinki Institute of Life Science HiLIFE, Biocenter 3, University of Helsinki, Helsinki, Finland
- National Laboratory Astana, Nazarbayev University, Astana, Kazakhstan
| | - Charles Hunter
- Chemistry Research Unit, United States Department of Agriculture (USDA) Agricultural Research Service, Gainesville, FL, United States
| | - Vladimir Orbovic
- Citrus Research and Education Center, University of Florida/Institute of Food and Agricultural Sciences (IFAS), Lake Alfred, FL, United States
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Wang L, Jia M, Li Z, Liu X, Sun T, Pei J, Wei C, Lin Z, Li H. Wristwatch PCR: A Versatile and Efficient Genome Walking Strategy. Front Bioeng Biotechnol 2022; 10:792848. [PMID: 35497369 PMCID: PMC9039356 DOI: 10.3389/fbioe.2022.792848] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Accepted: 03/08/2022] [Indexed: 11/16/2022] Open
Abstract
Genome walking is a method used to retrieve unknown flanking DNA. Here, we reported wristwatch (WW) PCR, an efficient genome walking technique mediated by WW primers (WWPs). WWPs feature 5′- and 3′-overlap and a heterologous interval. Therefore, a wristwatch-like structure can be formed between WWPs under relatively low temperatures. Each WW-PCR set is composed of three nested (primary, secondary, and tertiary) PCRs individually performed by three WWPs. The WWP is arbitrarily annealed somewhere on the genome in the one low-stringency cycle of the primary PCR, or directionally to the previous WWP site in one reduced-stringency cycle of the secondary/tertiary PCR, producing a pool of single-stranded DNAs (ssDNAs). A target ssDNA incorporates a gene-specific primer (GSP) complementary at the 3′-end and the WWP at the 5′-end and thus can be exponentially amplified in the next high-stringency cycles. Nevertheless, a non-target ssDNA cannot be amplified as it lacks a perfect binding site for any primers. The practicability of the WW-PCR was validated by successfully accessing unknown regions flanking Lactobacillus brevis CD0817 glutamate decarboxylase gene and the hygromycin gene of rice. The WW-PCR is an attractive alternative to the existing genome walking techniques.
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Affiliation(s)
- Lingqin Wang
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
| | - Mengya Jia
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
| | - Zhaoqin Li
- Charles W. Davidson College of Engineering, San Jose State University, San Jose, CA, United States
| | - Xiaohua Liu
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
| | - Tianyi Sun
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
- Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, School of Environmental and Chemical Engineering, Nanchang University, Nanchang, China
| | - Jinfeng Pei
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
| | - Cheng Wei
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
| | - Zhiyu Lin
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
- Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, School of Environmental and Chemical Engineering, Nanchang University, Nanchang, China
| | - Haixing Li
- State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, China
- Sino-German Joint Research Institute, Nanchang University, Nanchang, China
- *Correspondence: Haixing Li,
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6
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Identification of the insertion site of transgenic DNA based on cyclization of the target gene with the flanking sequence and nested inverse PCR. TALANTA OPEN 2021. [DOI: 10.1016/j.talo.2021.100033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Asif M, Siddiqui HA, Naqvi RZ, Amin I, Asad S, Mukhtar Z, Bashir A, Mansoor S. Development of event-specific detection method for identification of insect resistant NIBGE-1601 cotton harboring double gene Cry1Ac-Cry2Ab construct. Sci Rep 2021; 11:3479. [PMID: 33568702 PMCID: PMC7876094 DOI: 10.1038/s41598-021-82798-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Accepted: 01/07/2021] [Indexed: 11/09/2022] Open
Abstract
Bt cotton expressing Cry1Ac is being cultivated in Pakistan. It has been observed that pink bollworm may have developed resistance against single Bt gene (Cry1Ac). For durable resistance, insect resistant NIBGE-1601 cotton harboring double gene Cry1Ac-Cry2Ab construct was developed. There was a need to characterize NIBGE-1601 event for intellectual property rights protection. The Presence of NIBGE Cry1Ac and NIBGE Cry2Ab genes was checked in NIBGE-1601 cotton plants through PCR, while there was no amplification using primers specific for Monsanto events (MON531, MON15985, MON1445). Using genome walking technology, NIBGE-601 event has been characterized. Event-specific primers of NIBGE-1601 were designed and evaluated to differentiate it from other cotton events mentioned above. NIBGE-1601 event detection primers are highly specific, therefore, can detect NIBGE 1601 event at different conditions using single or multiplex PCR. In the qualitative PCR, using NIBGE-1601 event specific primers, 0.05 ng was the limit of detection for NIBGE-1601double gene cotton genomic DNA. Thus event characterization and development of event-specific diagnostics will help in breeding new cotton varieties resistant to cotton bollworms.
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Affiliation(s)
- Muhammad Asif
- Agricultural Biotechnology Division, National Institute for Biotechnology and Genetic, Engineering, Faisalabad, Pakistan
| | - Hamid Anees Siddiqui
- Agricultural Biotechnology Division, National Institute for Biotechnology and Genetic, Engineering, Faisalabad, Pakistan.,Pakistan Institute of Engineering and Applied Sciences, Nilore, Pakistan
| | - Rubab Zahra Naqvi
- Agricultural Biotechnology Division, National Institute for Biotechnology and Genetic, Engineering, Faisalabad, Pakistan
| | - Imran Amin
- Agricultural Biotechnology Division, National Institute for Biotechnology and Genetic, Engineering, Faisalabad, Pakistan
| | - Shaheen Asad
- Agricultural Biotechnology Division, National Institute for Biotechnology and Genetic, Engineering, Faisalabad, Pakistan
| | - Zahid Mukhtar
- Agricultural Biotechnology Division, National Institute for Biotechnology and Genetic, Engineering, Faisalabad, Pakistan
| | - Aftab Bashir
- Department of Biological Sciences, Forman Christian College, Lahore, Pakistan
| | - Shahid Mansoor
- Agricultural Biotechnology Division, National Institute for Biotechnology and Genetic, Engineering, Faisalabad, Pakistan.
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Kim MS, Jo H, Kim JH, Bae DN, Pack IS, Kim CG, Kwon T, Nam J, Chung YS, Jeong SC. Elucidation of genomic organizations of transgenic soybean plants through de novo genome assembly with short paired-end reads. MOLECULAR BREEDING : NEW STRATEGIES IN PLANT IMPROVEMENT 2021; 41:1. [PMID: 37309526 PMCID: PMC10231564 DOI: 10.1007/s11032-020-01191-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 11/26/2020] [Indexed: 06/14/2023]
Abstract
Elucidation of the genomic organizations of transgene insertion sites is essential for the genetic studies of transgenic plants. Herein, we establish an analysis pipeline that identifies the transgene insertion sites as well as the presence of vector backbones, through de novo genome assembly with high-throughput sequencing data in two transgenic soybean lines, AtYUCCA6-#5 and 35S-UGT72E3/2-#7. Sequencing data of approximately 28× and 29× genome coverages for each line generated by high-throughput sequencing were de novo assembled. The databases generated from the de novo assembled sequences were used to search contigs that contained putative insertion sites and their flanking sequences (integration sites) of transgene fragments using transgenic vector sequences as queries. The predicted integration site sequences, which are located at three annotated genes that might regulate plant development or confer disease resistance, were then confirmed by local alignment against the soybean reference genome and PCR amplification. As results, we revealed the precise transgene-flanking sequences and sequence rearrangements at insertion sites in both the transgenic lines, as well as the aberrant insertion of a transgene fragment. Consequently, relative to experimental or enrichment technologies, our approach is straightforward and time-effective, providing an alternative method for the identification of insertion sites in transgenic plants.
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Affiliation(s)
- Myung-Shin Kim
- Bio-Evaluation Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju, Chungbuk 28116 Republic of Korea
| | - Hojin Jo
- Bio-Evaluation Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju, Chungbuk 28116 Republic of Korea
| | - Ji Hong Kim
- Bio-Evaluation Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju, Chungbuk 28116 Republic of Korea
| | - Dong Nyuk Bae
- Bio-Evaluation Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju, Chungbuk 28116 Republic of Korea
| | - In-Soon Pack
- Bio-Evaluation Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju, Chungbuk 28116 Republic of Korea
| | - Chang-Gi Kim
- Bio-Evaluation Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju, Chungbuk 28116 Republic of Korea
| | - Tackmin Kwon
- Department of Molecular Genetics, College of Natural Resources and Life Science, Dong-A University, Busan, 49315 Republic of Korea
| | - Jaesung Nam
- Department of Molecular Genetics, College of Natural Resources and Life Science, Dong-A University, Busan, 49315 Republic of Korea
| | - Young-Soo Chung
- Department of Molecular Genetics, College of Natural Resources and Life Science, Dong-A University, Busan, 49315 Republic of Korea
| | - Soon-Chun Jeong
- Bio-Evaluation Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju, Chungbuk 28116 Republic of Korea
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Fraiture MA, Papazova N, Roosens NHC. DNA walking strategy to identify unauthorized genetically modified bacteria in microbial fermentation products. Int J Food Microbiol 2020; 337:108913. [PMID: 33126077 DOI: 10.1016/j.ijfoodmicro.2020.108913] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 10/06/2020] [Accepted: 10/07/2020] [Indexed: 01/07/2023]
Abstract
Recently, unexpected contaminations of unauthorized genetically modified microorganisms (GMM) carrying antimicrobial resistance (AMR) genes were reported in microbial fermentation products commercialized on the food and feed chain. To guarantee the traceability and safety of the food and feed chain, whole-genome sequencing (WGS) has played a key role to prove GMM contaminations via the characterization of unnatural associations of sequences. However, WGS requires a prior microbial isolation of the GMM strain, which can be difficult to successfully achieve. Therefore, in order to avoid such bottleneck, a culture-independent approach was proposed in this study. First, the screening for the aadD gene, an AMR gene conferring a resistance to kanamycin, and for the pUB110 shuttle vector, carrying the aadD gene and commonly used to produce GMM, is performed. In case of a positive signal, DNA walking methods anchored on the two borders of the detected pUB110 shuttle vector are applied to characterize unknown flanking regions. Following to the sequencing of the generated amplicons, unnatural associations of sequences can be identified, allowing to demonstrate the presence of unauthorized GMM. The developed culture-independent strategy was successfully applied on commercialized microbial fermentation products, allowing to prove the presence of GMM contaminations in the food and feed chain.
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Affiliation(s)
- Marie-Alice Fraiture
- Sciensano, Transversal activities in Applied Genomics (TAG), J. Wytsmanstraat 14, 1050 Brussels, Belgium.
| | - Nina Papazova
- Sciensano, Transversal activities in Applied Genomics (TAG), J. Wytsmanstraat 14, 1050 Brussels, Belgium.
| | - Nancy H C Roosens
- Sciensano, Transversal activities in Applied Genomics (TAG), J. Wytsmanstraat 14, 1050 Brussels, Belgium.
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10
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Simple innovative adaptor to improve genome walking with convenient PCR. J Genet Eng Biotechnol 2020; 18:64. [PMID: 33083895 PMCID: PMC7575660 DOI: 10.1186/s43141-020-00082-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Accepted: 09/30/2020] [Indexed: 11/10/2022]
Abstract
BACKGROUND Various polymerase chain reaction (PCR)-based methods have been applied for the development of genome walking (GW) technique. These methods which could be based on the application of restriction enzymes or primers have various efficiencies to identify the unknown nucleotide sequences. The present study was conducted to design a new innovative double-strand adaptor using MAP30 gene sequence of Momordica charantia plant as a model to improve genome walking with convenient PCR. RESULTS The adaptor was designed using multiple restriction sites of Hind III, BamH I, EcoR I, and Bgl II enzymes with no restriction site in a known sequence of the MAP30 gene. In addition, no modification was required to add phosphate, amine, or other groups to the adaptor, since restriction enzyme digestion of double-strand adaptor provided the 5' phosphate group. Here, preparation of the phosphate group in the genomic DNA of the plant digestion with restriction enzymes was performed followed by ligation with digested adaptor containing 5' phosphate group. CONCLUSION PCR was done to amplify the unknown sequence using MAP30 gene-specific primer and adaptor primer. Results confirmed the ability of the technique for successful identification of the sequence. Consequently, a newly designed adaptor in the developed technique reduced the time and cost of the method compared to the conventional genome walking; also, cloning and culturing of bacterial steps could be eliminated.
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11
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Palindromic sequence-targeted (PST) PCR: a rapid and efficient method for high-throughput gene characterization and genome walking. Sci Rep 2019; 9:17707. [PMID: 31776407 PMCID: PMC6881309 DOI: 10.1038/s41598-019-54168-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 11/07/2019] [Indexed: 11/23/2022] Open
Abstract
Genome walking (GW) refers to the capture and sequencing of unknown regions in a long DNA molecule that are adjacent to a region with a known sequence. A novel PCR-based method, palindromic sequence-targeted PCR (PST-PCR), was developed. PST-PCR is based on a distinctive design of walking primers and special thermal cycling conditions. The walking primers (PST primers) match palindromic sequences (PST sites) that are randomly distributed in natural DNA. The PST primers have palindromic sequences at their 3′-ends. Upstream of the palindromes there is a degenerate sequence (8–12 nucleotides long); defined adapters are present at the 5′-termini. The thermal cycling profile has a linear amplification phase and an exponential amplification phase differing in annealing temperature. Changing the annealing temperature to switch the amplification phases at a defined cycle controls the balance between sensitivity and specificity. In contrast to traditional genome walking methods, PST-PCR is rapid (two to three hours to produce GW fragments) as it uses only one or two PCR rounds. Using PST-PCR, previously unknown regions (the promoter and intron 1) of the VRN1 gene of Timothy-grass (Phleum pratense L.) were captured for sequencing. In our experience, PST-PCR had higher throughput and greater convenience in comparison to other GW methods.
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12
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Chen W, Wang P. Molecular Analysis for Characterizing Transgenic Events. Methods Mol Biol 2019; 1864:397-410. [PMID: 30415348 DOI: 10.1007/978-1-4939-8778-8_24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
To develop a commercial trait product, a large number of transgenic events are often produced to obtain the event with desired level of expression. It is crucial to develop efficient and sensitive molecular characterization methods to advance events with stable transgene expression, free of vector backbone sequences and without major changes to the native genome caused by transgene insertion. Here, we discuss a variety of analytical tools, including quantitative PCR (qPCR), Southern blot analysis, and various sequencing technologies, which have been widely used to determine the insert copy number, presence/absence of vector backbone sequences, integrity of the T-DNA, and genomic location of the T-DNA insertion. Moreover, since the discovery of RNA interference in 1998 (Fire et al., Nature 391:806-811, 1998), RNAi has emerged as another powerful tool in in the development of a new transgenic trait for insect control. RNAi creates a double-stranded RNA duplex as the active molecule which forms a strong secondary structure, resulting in challenges for detection. In addition to molecular analysis at the DNA level, this chapter describes detection methods of the active molecules (i.e., double-stranded RNA) for RNAi-based traits.
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MESH Headings
- Biotechnology/instrumentation
- Biotechnology/methods
- Blotting, Southern
- Commerce
- Crops, Agricultural/genetics
- DNA, Bacterial/genetics
- DNA, Plant/analysis
- DNA, Plant/genetics
- Genome, Plant/genetics
- Plants, Genetically Modified/genetics
- Polymerase Chain Reaction
- Quantitative Trait Loci/genetics
- RNA Interference
- RNA, Double-Stranded/analysis
- RNA, Double-Stranded/genetics
- RNA, Plant/analysis
- RNA, Plant/genetics
- Transformation, Genetic
- Transgenes/genetics
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Affiliation(s)
- Wei Chen
- Corteva Agriscience™, Agriculture Division of DowDuPont™, Johnston, IA, USA.
| | - PoHao Wang
- Corteva Agriscience™, Agriculture Division of DowDuPont™, Johnston, IA, USA
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Chen J, Wu C, Zhang B, Cai Z, Wei L, Li Z, Li G, Guo T, Li Y, Guo W, Wang X. PiggyBac Transposon-Mediated Transgenesis in the Pacific Oyster ( Crassostrea gigas) - First Time in Mollusks. Front Physiol 2018; 9:811. [PMID: 30061837 PMCID: PMC6054966 DOI: 10.3389/fphys.2018.00811] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 06/08/2018] [Indexed: 11/25/2022] Open
Abstract
As an effective method of transgenesis, the plasmid of PiggyBac transposon containing GFP (PiggyBac) transposon system has been widely used in various organisms but not yet in mollusks. In this work, piggyBac containing green fluorescent protein (GFP) was transferred into the Pacific oyster (Crassostrea gigas) by sperm-mediated gene transfer with or without electroporation. Fluorescent larvae were then observed and isolated under an inverted fluorescence microscope, and insertion of piggyBac was tested by polymerase chain reaction (PCR) using genomic DNA as template. Oyster larvae with green fluorescence were observed after transgenesis with or without electroporation, but electroporation increased the efficiency of sperm-mediated transgenesis. Subsequently, the recombinant piggyBac plasmid containing gGH (piggyBac-gGH) containing GFP and a growth hormone gene from orange-spotted grouper (gGH) was transferred into oysters using sperm mediation with electroporation, and fluorescent larvae were observed and isolated. The insertion of piggyBac-gGH was tested by PCR and genome walking analysis. PCR analysis indicated that piggyBac-gGH was transferred into oyster larvae; genome walking analysis further showed the detailed location where piggyBac-gGH was inserted in the oyster genome. This is the first time that piggyBac transposon-mediated transgenesis has been applied in mollusks.
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Affiliation(s)
- Jun Chen
- School of Agriculture, Ludong University, Yantai, China
| | - Changlu Wu
- School of Agriculture, Ludong University, Yantai, China
| | - Baolu Zhang
- Consultation Center, State Oceanic Administration, Beijing, China
| | - Zhongqiang Cai
- Changdao Enhancement and Experiment Station, Chinese Academy of Fishery Sciences, Yantai, China
| | - Lei Wei
- School of Agriculture, Ludong University, Yantai, China
| | - Zhuang Li
- School of Agriculture, Ludong University, Yantai, China
| | - Guangbin Li
- School of Agriculture, Ludong University, Yantai, China
| | - Ting Guo
- School of Agriculture, Ludong University, Yantai, China
| | - Yongchuan Li
- School of Agriculture, Ludong University, Yantai, China
| | - Wen Guo
- Center for Mollusc Study and Development, Marine Biology Institute of Shandong Province, Qingdao, China
| | - Xiaotong Wang
- School of Agriculture, Ludong University, Yantai, China
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Chang K, Wang Q, Shi X, Wang S, Wu H, Nie L, Li H. Stepwise partially overlapping primer-based PCR for genome walking. AMB Express 2018; 8:77. [PMID: 29744607 PMCID: PMC5943200 DOI: 10.1186/s13568-018-0610-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Accepted: 05/04/2018] [Indexed: 11/10/2022] Open
Abstract
A stepwise partially overlapping primer-based PCR (SWPOP-PCR) method for isolating flanking unknown DNA regions was developed, which comprises three rounds of nested PCRs sequentially driven by SWPOP primer-nested specific primer pairs. SWPOP primer set is characterized by a partial overlap of 10 bp with 3′-part of the latter primer is identical to 5′-part of the former one, which makes the SWPOP primer in use anneal to SWPOP site of the prior PCR product only at relatively low temperature. For each PCR, target single-stranded DNA primed by the SWPOP primer in the exclusive one low-stringency cycle is converted into double-stranded form in the following high-stringency cycle due to the presence of a perfect annealing site for the specific primer. This double-stranded DNA bounded by the specific primer and the SWPOP primer is exponentially amplified in the remaining high-stringency cycles. Non-target single-stranded DNA, however, cannot be amplified given the lack of perfect complementary sequences for any primers. Therefore, the partial overlap of a SWPOP primer set preferentially synthesizes target products but inhibits nonspecific amplification. We successfully exploited SWPOP-PCR to obtain the DNA sequences flanking glutamate decarboxylase gene (gadA) locus in Lactobacillus brevis NCL912 and hygromycin gene (hyg) integrated in rice.
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15
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Bhat A, Mishra S, Kaul S, Dhar MK. Elucidation and functional characterization of CsPSY and CsUGT promoters in Crocus sativus L. PLoS One 2018; 13:e0195348. [PMID: 29634744 PMCID: PMC5892871 DOI: 10.1371/journal.pone.0195348] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 03/20/2018] [Indexed: 11/18/2022] Open
Abstract
The dried stigmas of Crocus sativus constitute the saffron, which is considered to be the costliest spice of the world. Saffron is valuable for its constituents, which are mainly apocarotenoids. In order to enhance the production of apocarotenoids, it is imperative to understand the regulation of apocarotenoid biosynthetic pathway. In C. sativus, although the pathway has been elucidated, the information regarding the regulation of the pathwaygenes is scanty. During the present investigation, the characterization of promoters regulating the expression of two important genes i.e. CsPSY and CsUGT was performed. We successfully cloned the promoters of both the genes, which were functionally characterized in Crocus sativus and Nicotiana tabaccum. In silico analysis of the promoters demonstrated the presence of several important cis regulatory elements responding tolight, hormonesand interaction with transcription factors (TFs). Further analysis suggested the regulation of CsPSY promoter by Abscisic acid (ABA) and that of CsUGT by Gibberellic acid (GA). In addition, we also observed ABA and GA mediated modulation in the expression of significant TFs and CsPSY and CsUGT transcripts. Overall, the study addresses issues related to regulation of key genes of apocarotenoid pathway in C.sativus.
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Affiliation(s)
- Archana Bhat
- Genome Research Laboratory, School of Biotechnology, University of Jammu, Jammu, India
| | - Sonal Mishra
- Genome Research Laboratory, School of Biotechnology, University of Jammu, Jammu, India
| | - Sanjana Kaul
- Genome Research Laboratory, School of Biotechnology, University of Jammu, Jammu, India
| | - Manoj K. Dhar
- Genome Research Laboratory, School of Biotechnology, University of Jammu, Jammu, India
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16
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Evans T, Johnson AD, Loose M. Virtual Genome Walking across the 32 Gb Ambystoma mexicanum genome; assembling gene models and intronic sequence. Sci Rep 2018; 8:618. [PMID: 29330416 PMCID: PMC5766544 DOI: 10.1038/s41598-017-19128-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Accepted: 12/19/2017] [Indexed: 11/09/2022] Open
Abstract
Large repeat rich genomes present challenges for assembly using short read technologies. The 32 Gb axolotl genome is estimated to contain ~19 Gb of repetitive DNA making an assembly from short reads alone effectively impossible. Indeed, this model species has been sequenced to 20× coverage but the reads could not be conventionally assembled. Using an alternative strategy, we have assembled subsets of these reads into scaffolds describing over 19,000 gene models. We call this method Virtual Genome Walking as it locally assembles whole genome reads based on a reference transcriptome, identifying exons and iteratively extending them into surrounding genomic sequence. These assemblies are then linked and refined to generate gene models including upstream and downstream genomic, and intronic, sequence. Our assemblies are validated by comparison with previously published axolotl bacterial artificial chromosome (BAC) sequences. Our analyses of axolotl intron length, intron-exon structure, repeat content and synteny provide novel insights into the genic structure of this model species. This resource will enable new experimental approaches in axolotl, such as ChIP-Seq and CRISPR and aid in future whole genome sequencing efforts. The assembled sequences and annotations presented here are freely available for download from https://tinyurl.com/y8gydc6n . The software pipeline is available from https://github.com/LooseLab/iterassemble .
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Affiliation(s)
- Teri Evans
- School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Andrew D Johnson
- School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Matthew Loose
- School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK.
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Kamle M, Kumar P, Patra JK, Bajpai VK. Current perspectives on genetically modified crops and detection methods. 3 Biotech 2017; 7:219. [PMID: 28674844 PMCID: PMC5495694 DOI: 10.1007/s13205-017-0809-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Accepted: 05/02/2017] [Indexed: 01/31/2023] Open
Abstract
Genetically modified (GM) crops are the fastest adopted commodities in the agribiotech industry. This market penetration should provide a sustainable basis for ensuring food supply for growing global populations. The successful completion of two decades of commercial GM crop production (1996-2015) is underscored by the increasing rate of adoption of genetic engineering technology by farmers worldwide. With the advent of introduction of multiple traits stacked together in GM crops for combined herbicide tolerance, insect resistance, drought tolerance or disease resistance, the requirement of reliable and sensitive detection methods for tracing and labeling genetically modified organisms in the food/feed chain has become increasingly important. In addition, several countries have established threshold levels for GM content which trigger legally binding labeling schemes. The labeling of GM crops is mandatory in many countries (such as China, EU, Russia, Australia, New Zealand, Brazil, Israel, Saudi Arabia, Korea, Chile, Philippines, Indonesia, Thailand), whereas in Canada, Hong Kong, USA, South Africa, and Argentina voluntary labeling schemes operate. The rapid adoption of GM crops has increased controversies, and mitigating these issues pertaining to the implementation of effective regulatory measures for the detection of GM crops is essential. DNA-based detection methods have been successfully employed, while the whole genome sequencing using next-generation sequencing (NGS) technologies provides an advanced means for detecting genetically modified organisms and foods/feeds in GM crops. This review article describes the current status of GM crop commercialization and discusses the benefits and shortcomings of common and advanced detection systems for GMs in foods and animal feeds.
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Affiliation(s)
- Madhu Kamle
- Department of Forestry, North Eastern Regional Institute of Science and Technology (Deemed University), Nirjuli, Arunachal Pradesh, 791109, India
| | - Pradeep Kumar
- Department of Forestry, North Eastern Regional Institute of Science and Technology (Deemed University), Nirjuli, Arunachal Pradesh, 791109, India.
| | - Jayanta Kumar Patra
- Research Institute of Biotechnology and Medical Converged Science, Dongguk University-Seoul, Ilsandong-gu, Gyeonggido, 10326, Korea
| | - Vivek K Bajpai
- Department of Applied Microbiology and Biotechnology, Microbiome Laboratory, Yeungnam University, Gyeongsan, Gyeongbuk, 38541, Korea.
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Schandry N, de Lange O, Prior P, Lahaye T. TALE-Like Effectors Are an Ancestral Feature of the Ralstonia solanacearum Species Complex and Converge in DNA Targeting Specificity. FRONTIERS IN PLANT SCIENCE 2016; 7:1225. [PMID: 27582755 PMCID: PMC4987410 DOI: 10.3389/fpls.2016.01225] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 08/02/2016] [Indexed: 05/19/2023]
Abstract
Ralstonia solanacearum, a species complex of bacterial plant pathogens divided into four monophyletic phylotypes, causes plant diseases in tropical climates around the world. Some strains exhibit a broad host range on solanaceous hosts, while others are highly host-specific as for example some banana-pathogenic strains. Previous studies showed that transcription activator-like (TAL) effectors from Ralstonia, termed RipTALs, are capable of activating reporter genes in planta, if these are preceded by a matching effector binding element (EBE). RipTALs target DNA via their central repeat domain (CRD), where one repeat pairs with one DNA-base of the given EBE. The repeat variable diresidue dictates base repeat specificity in a predictable fashion, known as the TALE code. In this work, we analyze RipTALs across all phylotypes of the Ralstonia solanacearum species complex. We find that RipTALs are prevalent in phylotypes I and IV but absent from most phylotype III and II strains (10/12, 8/14, 1/24, and 1/5 strains contained a RipTAL, respectively). RipTALs originating from strains of the same phylotype show high levels of sequence similarity (>98%) in the N-terminal and C-terminal regions, while RipTALs isolated from different phylotypes show 47-91% sequence similarity in those regions, giving rise to four RipTAL classes. We show that, despite sequence divergence, the base preference for guanine, mediated by the N-terminal region, is conserved across RipTALs of all classes. Using the number and order of repeats found in the CRD, we functionally sub-classify RipTALs, introduce a new simple nomenclature, and predict matching EBEs for all seven distinct RipTALs identified. We experimentally study RipTAL EBEs and uncover that some RipTALs are able to target the EBEs of other RipTALs, referred to as cross-reactivity. In particular, RipTALs from strains with a broad host range on solanaceous hosts cross-react on each other's EBEs. Investigation of sequence divergence between RipTAL repeats allows for a reconstruction of repeat array biogenesis, for example through slipped strand mispairing or gene conversion. Using these studies we show how RipTALs of broad host range strains evolved convergently toward a shared target sequence. Finally, we discuss the differences between TALE-likes of plant pathogens in the context of disease ecology.
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Affiliation(s)
- Niklas Schandry
- Center for Plant Molecular Biology, University of TübingenTübingen, Germany
| | - Orlando de Lange
- Center for Plant Molecular Biology, University of TübingenTübingen, Germany
| | - Philippe Prior
- UMR Peuplements Végétaux et Bioagresseurs en Milieu Tropical, Centre de Coopération Internationale en Recherche Agronomique pour le Développement – Institut National de la Recherche AgronomiqueSaint-Pierre, France
| | - Thomas Lahaye
- Center for Plant Molecular Biology, University of TübingenTübingen, Germany
- *Correspondence: Thomas Lahaye,
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Fraiture MA, Herman P, Taverniers I, De Loose M, Deforce D, Roosens NH. Current and new approaches in GMO detection: challenges and solutions. BIOMED RESEARCH INTERNATIONAL 2015; 2015:392872. [PMID: 26550567 PMCID: PMC4624882 DOI: 10.1155/2015/392872] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Accepted: 09/07/2015] [Indexed: 11/17/2022]
Abstract
In many countries, genetically modified organisms (GMO) legislations have been established in order to guarantee the traceability of food/feed products on the market and to protect the consumer freedom of choice. Therefore, several GMO detection strategies, mainly based on DNA, have been developed to implement these legislations. Due to its numerous advantages, the quantitative PCR (qPCR) is the method of choice for the enforcement laboratories in GMO routine analysis. However, given the increasing number and diversity of GMO developed and put on the market around the world, some technical hurdles could be encountered with the qPCR technology, mainly owing to its inherent properties. To address these challenges, alternative GMO detection methods have been developed, allowing faster detections of single GM target (e.g., loop-mediated isothermal amplification), simultaneous detections of multiple GM targets (e.g., PCR capillary gel electrophoresis, microarray, and Luminex), more accurate quantification of GM targets (e.g., digital PCR), or characterization of partially known (e.g., DNA walking and Next Generation Sequencing (NGS)) or unknown (e.g., NGS) GMO. The benefits and drawbacks of these methods are discussed in this review.
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Affiliation(s)
- Marie-Alice Fraiture
- Platform of Biotechnology and Molecular Biology (PBB) and Biosafety and Biotechnology Unit (SBB), Scientific Institute of Public Health (WIV-ISP), J. Wytsmanstraat 14, 1050 Brussels, Belgium
- Technology and Food Sciences Unit, Institute for Agricultural and Fisheries Research (ILVO), Burg. Van Gansberghelaan 115, Bus 1, 9820 Merelbeke, Belgium
- Laboratory of Pharmaceutical Biotechnology, Faculty of Pharmaceutical Sciences, Ghent University, Ottergemsesteenweg 460, 9000 Ghent, Belgium
| | - Philippe Herman
- Platform of Biotechnology and Molecular Biology (PBB) and Biosafety and Biotechnology Unit (SBB), Scientific Institute of Public Health (WIV-ISP), J. Wytsmanstraat 14, 1050 Brussels, Belgium
| | - Isabel Taverniers
- Technology and Food Sciences Unit, Institute for Agricultural and Fisheries Research (ILVO), Burg. Van Gansberghelaan 115, Bus 1, 9820 Merelbeke, Belgium
| | - Marc De Loose
- Technology and Food Sciences Unit, Institute for Agricultural and Fisheries Research (ILVO), Burg. Van Gansberghelaan 115, Bus 1, 9820 Merelbeke, Belgium
- Department of Plant Biotechnology and Bioinformatics, Faculty of Sciences, Ghent University, Technologiepark 927, 9052 Ghent, Belgium
| | - Dieter Deforce
- Laboratory of Pharmaceutical Biotechnology, Faculty of Pharmaceutical Sciences, Ghent University, Ottergemsesteenweg 460, 9000 Ghent, Belgium
| | - Nancy H. Roosens
- Platform of Biotechnology and Molecular Biology (PBB) and Biosafety and Biotechnology Unit (SBB), Scientific Institute of Public Health (WIV-ISP), J. Wytsmanstraat 14, 1050 Brussels, Belgium
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Chen J, Dai L, Wang B, Liu L, Peng D. Cloning of expansin genes in ramie (Boehmeria nivea L.) based on universal fast walking. Gene 2015; 569:27-33. [PMID: 25481635 DOI: 10.1016/j.gene.2014.11.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 11/11/2014] [Accepted: 11/13/2014] [Indexed: 10/24/2022]
Abstract
Gene cloning is the first step to study the expression profiles and functions of a particular gene; considerable cloning methods have been developed. Expansin, thought to involve in the cell-wall modification events, was not cloned in ramie (Boehmeria nivea L.), which is one of the most important bast fiber crops with little conducted molecular research, especially on its fiber development. Studying the expansin gene family will uncover its possible relationship with ramie fiber development and other growth events. As a result, five expansin genes were cloned with full-length and their sequence information was investigated. Additionally, the phylogenetic analysis was conducted, which suggested that the cloned genes belong to the α-subfamily, and these genes expressed differently during ramie fiber developmental process. In this study, we aimed to apply a strategy for cloning novel full-length genes from genomic DNA of ramie, based on using degenerate primers, touchdown polymerase chain reaction and universal fast walking protocols. By cloning five full-length expansin genes, we believe the polymerase chain reaction-based gene cloning strategy could be applied to general gene studies in ramie and other crops.
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Affiliation(s)
- Jie Chen
- MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, #1 Shizishan Street, Hongshan District, Wuhan 430070, Hubei Province, China.
| | - Lunjin Dai
- MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, #1 Shizishan Street, Hongshan District, Wuhan 430070, Hubei Province, China.
| | - Bo Wang
- MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, #1 Shizishan Street, Hongshan District, Wuhan 430070, Hubei Province, China.
| | - Lijun Liu
- MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, #1 Shizishan Street, Hongshan District, Wuhan 430070, Hubei Province, China.
| | - Dingxiang Peng
- MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, #1 Shizishan Street, Hongshan District, Wuhan 430070, Hubei Province, China.
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21
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Fraiture MA, Herman P, Lefèvre L, Taverniers I, De Loose M, Deforce D, Roosens NH. Integrated DNA walking system to characterize a broad spectrum of GMOs in food/feed matrices. BMC Biotechnol 2015; 15:76. [PMID: 26272331 PMCID: PMC4535744 DOI: 10.1186/s12896-015-0191-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 07/29/2015] [Indexed: 01/28/2023] Open
Abstract
Background In order to provide a system fully integrated with qPCR screening, usually used in GMO routine analysis, as well as being able to detect, characterize and identify a broad spectrum of GMOs in food/feed matrices, two bidirectional DNA walking methods targeting p35S or tNOS, the most common transgenic elements found in GM crops, were developed. These newly developed DNA walking methods are completing the previously implemented DNA walking method targeting the t35S pCAMBIA element. Methods Food/feed matrices containing transgenic crops (Bt rice or MON863 maize) were analysed using the integrated DNA walking system. Results First, the newly developed DNA walking methods, anchored on the sequences used for the p35S or tNOS qPCR screening, were tested on Bt rice that contains these two transgenic elements. Second, the methods were assessed on a maize sample containing a low amount of the GM MON863 event, representing a more complex matrix in terms of genome size and sensitivity. Finally, to illustrate its applicability in GMO routine analysis by enforcement laboratories, the entire workflow of the integrated strategy, including qPCR screening to detect the potential presence of GMOs and the subsequent DNA walking methods to characterize and identify the detected GMOs, was applied on a GeMMA Scheme Proficiency Test matrix. Via the characterization of the transgene flanking region between the transgenic cassette and the plant genome as well as of a part of the transgenic cassette, the presence of GMOs was properly confirmed or infirmed in all tested samples. Conclusion Due to their simple procedure and their short time-frame to get results, the developed DNA walking methods proposed here can be easily implemented in GMO routine analysis by the enforcement laboratories. In providing crucial information about the transgene flanking regions and/or the transgenic cassettes, this DNA walking strategy is a key molecular tool to prove the presence of GMOs in any given food/feed matrix. Electronic supplementary material The online version of this article (doi:10.1186/s12896-015-0191-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Marie-Alice Fraiture
- Scientific Institute of Public Health (WIV-ISP), Platform of Biotechnology and Molecular Biology (PBB) and Biosafety and Biotechnology Unit (SBB), J. Wytsmanstraat 14, 1050, Brussels, Belgium. .,Institute for Agricultural and Fisheries Research (ILVO), Technology and Food Sciences Unit, Burg. Van Gansberghelaan 115 bus 1, 9820, Merelbeke, Belgium. .,Ghent University, Faculty of Pharmaceutical Sciences, Laboratory of Pharmaceutical Biotechnology, Ottergemsesteenweg 460, 9000, Ghent, Belgium.
| | - Philippe Herman
- Scientific Institute of Public Health (WIV-ISP), Platform of Biotechnology and Molecular Biology (PBB) and Biosafety and Biotechnology Unit (SBB), J. Wytsmanstraat 14, 1050, Brussels, Belgium.
| | - Loic Lefèvre
- Scientific Institute of Public Health (WIV-ISP), Platform of Biotechnology and Molecular Biology (PBB) and Biosafety and Biotechnology Unit (SBB), J. Wytsmanstraat 14, 1050, Brussels, Belgium.
| | - Isabel Taverniers
- Institute for Agricultural and Fisheries Research (ILVO), Technology and Food Sciences Unit, Burg. Van Gansberghelaan 115 bus 1, 9820, Merelbeke, Belgium.
| | - Marc De Loose
- Institute for Agricultural and Fisheries Research (ILVO), Technology and Food Sciences Unit, Burg. Van Gansberghelaan 115 bus 1, 9820, Merelbeke, Belgium. .,Ghent University, Faculty of Sciences, Department of Plant Biotechnology and Bioinformatics, Technologiepark 927, 9052, Ghent, Belgium.
| | - Dieter Deforce
- Ghent University, Faculty of Pharmaceutical Sciences, Laboratory of Pharmaceutical Biotechnology, Ottergemsesteenweg 460, 9000, Ghent, Belgium.
| | - Nancy H Roosens
- Scientific Institute of Public Health (WIV-ISP), Platform of Biotechnology and Molecular Biology (PBB) and Biosafety and Biotechnology Unit (SBB), J. Wytsmanstraat 14, 1050, Brussels, Belgium.
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22
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Esher SK, Granek JA, Alspaugh JA. Rapid mapping of insertional mutations to probe cell wall regulation in Cryptococcus neoformans. Fungal Genet Biol 2015; 82:9-21. [PMID: 26112692 DOI: 10.1016/j.fgb.2015.06.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Revised: 06/13/2015] [Accepted: 06/16/2015] [Indexed: 11/16/2022]
Abstract
Random insertional mutagenesis screens are important tools in microbial genetics studies. Investigators in fungal systems have used the plant pathogen Agrobacterium tumefaciens to create tagged, random mutations for genetic screens in their fungal species of interest through a unique process of trans-kingdom cellular transconjugation. However, identifying the locations of insertion has traditionally required tedious PCR-based methods, limiting the effective throughput of this system. We have developed an efficient genomic sequencing and analysis method (AIM-Seq) to facilitate identification of randomly generated genomic insertions in microorganisms. AIM-Seq combines batch sampling, whole genome sequencing, and a novel bioinformatics pipeline, AIM-HII, to rapidly identify sites of genomic insertion. We have specifically applied this technique to Agrobacterium-mediated transconjugation in the human fungal pathogen Cryptococcus neoformans. With this approach, we have screened a library of C. neoformans cell wall mutants, selecting twenty-seven mutants of interest for analysis by AIM-Seq. We identified thirty-five putative genomic insertions in known and previously unknown regulators of cell wall processes in this pathogenic fungus. We confirmed the relevance of a subset of these by creating independent mutant strains and analyzing resulting cell wall phenotypes. Through our sequence-based analysis of these mutations, we observed "typical" insertions of the Agrobacterium transfer DNA as well as atypical insertion events, including large deletions and chromosomal rearrangements. Initially applied to C. neoformans, this mutant analysis tool can be applied to a wide range of experimental systems and methods of mutagenesis, facilitating future microbial genetic screens.
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Affiliation(s)
- Shannon K Esher
- Department of Molecular Genetics & Microbiology, Duke University School of Medicine, Durham, NC 27710, USA.
| | - Joshua A Granek
- Department of Molecular Genetics & Microbiology, Duke University School of Medicine, Durham, NC 27710, USA; Department of Bioinformatics and Biostatistics, Duke University School of Medicine, Durham, NC 27710, USA; Duke Center for the Genomics of Microbial Systems, Duke University School of Medicine, Durham, NC 27710, USA.
| | - J Andrew Alspaugh
- Department of Molecular Genetics & Microbiology, Duke University School of Medicine, Durham, NC 27710, USA; Department of Medicine, Duke University School of Medicine, Durham, NC 27710, USA.
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23
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Partially overlapping primer-based PCR for genome walking. PLoS One 2015; 10:e0120139. [PMID: 25811779 PMCID: PMC4374871 DOI: 10.1371/journal.pone.0120139] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Accepted: 02/04/2015] [Indexed: 11/25/2022] Open
Abstract
Current genome walking methods are cumbersome to perform and can result in non-specific products. Here, we demonstrate the use of partially overlapping primer-based PCR (POP-PCR), a direct genome walking technique for the isolation of unknown flanking regions. This method exploits the partially overlapping characteristic at the 3’ ends of a set of POP primers (walking primers), which guarantees that the POP primer only anneals to the POP site of the preceding PCR product at relatively low temperatures. POP primer adaptation priming at the genomic DNA/POP site occurs only once due to one low-/reduced-stringency cycle in each nested PCR, resulting in the synthesis of a pool of single-stranded DNA molecules. Of this pool, the target single-stranded DNA is replicated to the double-stranded form bound by the specific primer and the POP primer in the subsequent high-stringency cycle due to the presence of the specific primer-binding site. The non-target single stranded DNA does not become double stranded due to the absence of a binding site for any of the primers. Therefore, the POP-PCR enriches target DNA while suppressing non-target products. We successfully used POP-PCR to retrieve flanking regions bordering the gadA locus in Lactobacillus brevis NCL912, malQ in Pichia pastoris GS115, the human aldolase A gene, and hyg in rice.
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24
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Malé PJG, Bardon L, Besnard G, Coissac E, Delsuc F, Engel J, Lhuillier E, Scotti-Saintagne C, Tinaut A, Chave J. Genome skimming by shotgun sequencing helps resolve the phylogeny of a pantropical tree family. Mol Ecol Resour 2014; 14:966-75. [DOI: 10.1111/1755-0998.12246] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 02/09/2014] [Accepted: 02/22/2014] [Indexed: 12/13/2022]
Affiliation(s)
- Pierre-Jean G. Malé
- UMR 5174 Laboratoire Évolution & Diversité Biologique; CNRS; Université Paul Sabatier; ENFA; 118 route de Narbonne F-31062 Toulouse France
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto ON M5S 3G5 Canada
| | - Léa Bardon
- UMR 5174 Laboratoire Évolution & Diversité Biologique; CNRS; Université Paul Sabatier; ENFA; 118 route de Narbonne F-31062 Toulouse France
| | - Guillaume Besnard
- UMR 5174 Laboratoire Évolution & Diversité Biologique; CNRS; Université Paul Sabatier; ENFA; 118 route de Narbonne F-31062 Toulouse France
| | - Eric Coissac
- Laboratoire d'Ecologie Alpine CNRS; UMR5553; Université Joseph Fourier; BP 53 F-38041 Grenoble Cedex 9 France
| | - Frédéric Delsuc
- Institut des Sciences de l'Evolution; UMR 5554-CNRS; Université Montpellier 2; Place Eugène Bataillon Montpellier France
| | - Julien Engel
- UMR ECOFOG; INRA; Université Antilles-Guyane; CNRS; CIRAD; AgroParisTech; Campus agronomique BP 709 F-97387 Kourou Cedex France
| | - Emeline Lhuillier
- INRA; UAR 1209 Département de Génétique Animale; INRA Auzeville; F-31326 Castanet-Tolosan France
- GeT-PlaGe; Genotoul; INRA Auzeville; F-31326 Castanet-Tolosan France
| | - Caroline Scotti-Saintagne
- UMR ECOFOG; INRA; Université Antilles-Guyane; CNRS; CIRAD; AgroParisTech; Campus agronomique BP 709 F-97387 Kourou Cedex France
| | - Alexandra Tinaut
- UMR ECOFOG; INRA; Université Antilles-Guyane; CNRS; CIRAD; AgroParisTech; Campus agronomique BP 709 F-97387 Kourou Cedex France
| | - Jérôme Chave
- UMR 5174 Laboratoire Évolution & Diversité Biologique; CNRS; Université Paul Sabatier; ENFA; 118 route de Narbonne F-31062 Toulouse France
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Xu W, Shang Y, Zhu P, Zhai Z, He J, Huang K, Luo Y. Randomly broken fragment PCR with 5' end-directed adaptor for genome walking. Sci Rep 2013; 3:3465. [PMID: 24322619 PMCID: PMC3857568 DOI: 10.1038/srep03465] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Accepted: 11/25/2013] [Indexed: 11/09/2022] Open
Abstract
Many genome walking methods based on polymerase chain reaction (PCR) are available, including those with and without restriction enzyme modification. Nevertheless, these methods suffer from low reproducibility, inefficiency, and non-specificity. Here, we present a traceable and efficient PCR strategy: randomly broken fragment PCR with 5' end-directed adaptor for genome walking. The genome is first fragmented randomly. After blunting ends, the fragments are ligated to the 5' end-directed adaptors. Semi-nested PCR is then performed. Thus, we can obtain an unknown sequence by cloning the fragments of interest, followed by sequencing. This method effectively bypasses the above-mentioned obstacles and offers the advances: 1) genome fragmentation without using restriction enzymes; 2) enhancement of primer specificity and the prevention of self-ligation between the adaptors by employing a 5' end-directed adaptor. All of the steps in this new method are straightforward, and the unknown sequence can be definitively obtained by merely applying the method once.
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Affiliation(s)
- Wentao Xu
- 1] Laboratory of Food Safety, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China [2] The Supervision, Inspection & Testing Center of Genetically Modified Food Safety, Ministry of Agriculture, Beijing 100083, China [3]
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26
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Fraiture MA, Herman P, Taverniers I, De Loose M, Deforce D, Roosens NH. An innovative and integrated approach based on DNA walking to identify unauthorised GMOs. Food Chem 2013; 147:60-9. [PMID: 24206686 DOI: 10.1016/j.foodchem.2013.09.112] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 07/12/2013] [Accepted: 09/19/2013] [Indexed: 01/23/2023]
Abstract
In the coming years, the frequency of unauthorised genetically modified organisms (GMOs) being present in the European food and feed chain will increase significantly. Therefore, we have developed a strategy to identify unauthorised GMOs containing a pCAMBIA family vector, frequently present in transgenic plants. This integrated approach is performed in two successive steps on Bt rice grains. First, the potential presence of unauthorised GMOs is assessed by the qPCR SYBR®Green technology targeting the terminator 35S pCAMBIA element. Second, its presence is confirmed via the characterisation of the junction between the transgenic cassette and the rice genome. To this end, a DNA walking strategy is applied using a first reverse primer followed by two semi-nested PCR rounds using primers that are each time nested to the previous reverse primer. This approach allows to rapidly identify the transgene flanking region and can easily be implemented by the enforcement laboratories.
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Affiliation(s)
- Marie-Alice Fraiture
- Scientific Institute of Public Health (WIV-ISP), Platform of Biotechnology and Molecular Biology (PBB), J. Wytsmanstraat 14, 1050 Brussels, Belgium; Scientific Institute of Public Health (WIV-ISP), Biosafety and Biotechnology Unit (SBB), J. Wytsmanstraat 14, 1050 Brussels, Belgium; Institute for Agricultural and Fisheries Research (ILVO), Technology and Food Sciences Unit, Burg. Van Gansberghelaan 115, bus 1, 9820 Merelbeke, Belgium; University of Gent (UGent), Faculty of Pharmaceutical Sciences, Laboratory of Pharmaceutical Biotechnology, Harelbekestraat 72, 9000 Ghent, Belgium
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27
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Liu T, Fang Y, Yao W, Guan Q, Bai G, Jing Z. A tailing genome walking method suitable for genomes with high local GC content. Anal Biochem 2013; 441:101-3. [PMID: 23831478 DOI: 10.1016/j.ab.2013.06.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Revised: 06/13/2013] [Accepted: 06/25/2013] [Indexed: 11/30/2022]
Abstract
The tailing genome walking strategies are simple and efficient. However, they sometimes can be restricted due to the low stringency of homo-oligomeric primers. Here we modified their conventional tailing step by adding polythymidine and polyguanine to the target single-stranded DNA (ssDNA). The tailed ssDNA was then amplified exponentially with a specific primer in the known region and a primer comprising 5' polycytosine and 3' polyadenosine. The successful application of this novel method for identifying integration sites mediated by φC31 integrase in goat genome indicates that the method is more suitable for genomes with high complexity and local GC content.
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Affiliation(s)
- Taian Liu
- State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Public Health of Agricultural Ministry, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou 730046, China
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28
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The development of APE-PCR for the cloning of genomic insertion sites of DNA elements. Biologia (Bratisl) 2013. [DOI: 10.2478/s11756-013-0214-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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29
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Identification of a genomic region containing a novel promoter resistant to glucose repression and over-expression of β-glucosidase gene in Hypocrea orientalis EU7-22. Int J Mol Sci 2013; 14:8479-90. [PMID: 23594998 PMCID: PMC3645756 DOI: 10.3390/ijms14048479] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2013] [Revised: 03/08/2013] [Accepted: 04/12/2013] [Indexed: 11/28/2022] Open
Abstract
A high concentration of glucose in the medium could greatly inhibit the expression of cellulase in filamentous fungi. The aspartic protease from fungus Hypocrea orientalis EU7-22 could efficiently express under both induction condition and glucose repression condition. Based on the sequence of structure gene of aspartic protease, the upstream sequence harboring the putative promoter proA for driving the expression of aspartic protease was obtained by genome walking. The upstream sequence contained the typical promoter motifs “TATA” and “CAAT”. The β-glucosidase gene (Bgl1) from H. orientalis was cloned and recombined with promoter proA and terminator trpC. The expression cassette was ligated to the binary vector to form pUR5750-Bgl1, and then transferred into the host strain EU7-22 via Agrobacterium tumefaciens mediated transformation (ATMT), using hygromycin B resistance gene as the screening marker. Four transformants Bgl-1, Bgl-2, Bgl-3 and Bgl-4 were screened. Compared with the host strain EU7-22, the enzyme activities of filter paper (FPA) and β-glucosidase (BG) of transformant Bgl-2 increased by 10.6% and 19.1% under induction condition, respectively. The FPA and BG activities were enhanced by 22.2% and 700% under 2% glucose repression condition, respectively, compared with the host strain. The results showed that the putative promoter proA has successfully driven the over-expression of Bgl1 gene in H. orientalis under glucose repression condition.
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RNA-seq pinpoints a Xanthomonas TAL-effector activated resistance gene in a large-crop genome. Proc Natl Acad Sci U S A 2012; 109:19480-5. [PMID: 23132937 DOI: 10.1073/pnas.1212415109] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transcription activator-like effector (TALE) proteins of the plant pathogenic bacterial genus Xanthomonas bind to and transcriptionally activate host susceptibility genes, promoting disease. Plant immune systems have taken advantage of this mechanism by evolving TALE binding sites upstream of resistance (R) genes. For example, the pepper Bs3 and rice Xa27 genes are hypersensitive reaction plant R genes that are transcriptionally activated by corresponding TALEs. Both R genes have a hallmark expression pattern in which their transcripts are detectable only in the presence and not the absence of the corresponding TALE. By transcriptome profiling using next-generation sequencing (RNA-seq), we tested whether we could avoid laborious positional cloning for the isolation of TALE-induced R genes. In a proof-of-principle experiment, RNA-seq was used to identify a candidate for Bs4C, an R gene from pepper that mediates recognition of the Xanthomonas TALE protein AvrBs4. We identified one major Bs4C candidate transcript by RNA-seq that was expressed exclusively in the presence of AvrBs4. Complementation studies confirmed that the candidate corresponds to the Bs4C gene and that an AvrBs4 binding site in the Bs4C promoter directs its transcriptional activation. Comparison of Bs4C with a nonfunctional allele that is unable to recognize AvrBs4 revealed a 2-bp polymorphism within the TALE binding site of the Bs4C promoter. Bs4C encodes a structurally unique R protein and Bs4C-like genes that are present in many solanaceous genomes seem to be as tightly regulated as pepper Bs4C. These findings demonstrate that TALE-specific R genes can be cloned from large-genome crops with a highly efficient RNA-seq approach.
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31
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Genome walking by next generation sequencing approaches. BIOLOGY 2012; 1:495-507. [PMID: 24832505 PMCID: PMC4009806 DOI: 10.3390/biology1030495] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/01/2012] [Revised: 08/31/2012] [Accepted: 09/25/2012] [Indexed: 01/07/2023]
Abstract
Genome Walking (GW) comprises a number of PCR-based methods for the identification of nucleotide sequences flanking known regions. The different methods have been used for several purposes: from de novo sequencing, useful for the identification of unknown regions, to the characterization of insertion sites for viruses and transposons. In the latter cases Genome Walking methods have been recently boosted by coupling to Next Generation Sequencing technologies. This review will focus on the development of several protocols for the application of Next Generation Sequencing (NGS) technologies to GW, which have been developed in the course of analysis of insertional libraries. These analyses find broad application in protocols for functional genomics and gene therapy. Thanks to the application of NGS technologies, the original vision of GW as a procedure for walking along an unknown genome is now changing into the possibility of observing the parallel marching of hundreds of thousands of primers across the borders of inserted DNA molecules in host genomes.
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Volpicella M, Leoni C, Fanizza I, Rius S, Gallerani R, Ceci LR. Genome walking by Klenow polymerase. Anal Biochem 2012; 430:200-2. [PMID: 22922302 DOI: 10.1016/j.ab.2012.08.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Revised: 08/10/2012] [Accepted: 08/11/2012] [Indexed: 11/26/2022]
Abstract
Genome walking procedures are all based on a final polymerase chain reaction amplification, regardless of the strategy employed for the synthesis of the substrate molecule. Here we report a modification of an already established genome walking strategy in which a single-strand DNA substrate is obtained by primer extension driven by Klenow polymerase and which results suitable for the direct sequencing of complex eukaryotic genomes. The efficacy of the method is demonstrated by the identification of nucleotide sequences in the case of two gene families (chiA and P1) in the genomes of several maize species.
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Affiliation(s)
- Mariateresa Volpicella
- Department of Biosciences, Biotechnologies, and Pharmacological Sciences, University of Bari, 70126 Bari, Italy
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Spalinskas R, Van den Bulcke M, Van den Eede G, Milcamps A. LT-RADE: An Efficient User-Friendly Genome Walking Method Applied to the Molecular Characterization of the Insertion Site of Genetically Modified Maize MON810 and Rice LLRICE62. FOOD ANAL METHOD 2012. [DOI: 10.1007/s12161-012-9438-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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34
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Olsen KM, Kooyers NJ, Small LL. Recurrent gene deletions and the evolution of adaptive cyanogenesis polymorphisms in white clover (Trifolium repens L.). Mol Ecol 2012; 22:724-38. [PMID: 22694056 DOI: 10.1111/j.1365-294x.2012.05667.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the molecular evolution of genes that underlie intraspecific polymorphisms can provide insights into the process of adaptive evolution. For adaptive polymorphisms characterized by gene presence/absence (P/A) variation, underlying loci commonly show signatures of long-term balancing selection, with gene-presence and gene-absence alleles maintained as two divergent lineages. We examined the molecular evolution of two unlinked P/A polymorphisms that underlie a well-documented adaptive polymorphism for cyanogenesis (hydrogen cyanide release with tissue damage) in white clover. Both cyanogenic and acyanogenic plants occur in this species, and the ecological forces that maintain this chemical defence polymorphism have been studied for several decades. Using a sample of 65 plants, we investigated the molecular evolution of sequences flanking the two underlying cyanogenesis genes: Ac/ac (controlling the presence/absence of cyanogenic glucosides) and Li/li (controlling the presence/absence of their hydrolysing enzyme, linamarase). A combination of genome walking, PCR assays, DNA sequence analysis and Southern blotting was used to test whether these adaptive P/A polymorphisms show evidence of long-term balancing selection, or whether gene-absence alleles have evolved repeatedly through independent deletion events. For both loci, we detect no signatures of balancing selection in the closest flanking genomic sequences. Instead, we find evidence for variation in the size of the deletions characterizing gene-absence alleles. These observations strongly suggest that both of these polymorphisms have been evolving through recurrent gene deletions over time. We discuss the genetic mechanisms that could account for this surprising pattern and the implications of these findings for mechanisms of rapid adaptive evolution in white clover.
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Affiliation(s)
- Kenneth M Olsen
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130-4899, USA.
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