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Topoisomerase VI participates in an insulator-like function that prevents H3K9me2 spreading. Proc Natl Acad Sci U S A 2022; 119:e2001290119. [PMID: 35759655 PMCID: PMC9271158 DOI: 10.1073/pnas.2001290119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The organization of the genome into transcriptionally active and inactive chromatin domains requires well-delineated chromatin boundaries and insulator functions in order to maintain the identity of adjacent genomic loci with antagonistic chromatin marks and functionality. In plants that lack known chromatin insulators, the mechanisms that prevent heterochromatin spreading into euchromatin remain to be identified. Here, we show that DNA Topoisomerase VI participates in a chromatin boundary function that safeguards the expression of genes in euchromatin islands within silenced heterochromatin regions. While some transposable elements are reactivated in mutants of the Topoisomerase VI complex, genes insulated in euchromatin islands within heterochromatic regions of the Arabidopsis thaliana genome are specifically down-regulated. H3K9me2 levels consistently increase at euchromatin island loci and decrease at some transposable element loci. We further show that Topoisomerase VI physically interacts with S-adenosylmethionine synthase methionine adenosyl transferase 3 (MAT3), which is required for H3K9me2. A Topoisomerase VI defect affects MAT3 occupancy on heterochromatic elements and its exclusion from euchromatic islands, thereby providing a possible mechanistic explanation to the essential role of Topoisomerase VI in the delimitation of chromatin domains.
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Zhang Z, Guo Y, Marasigan KM, Conner JA, Ozias-Akins P. Gene activation via Cre/lox-mediated excision in cowpea (Vigna unguiculata). PLANT CELL REPORTS 2022; 41:119-138. [PMID: 34591155 PMCID: PMC8803690 DOI: 10.1007/s00299-021-02789-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 09/15/2021] [Indexed: 05/11/2023]
Abstract
Expression of Cre recombinase by AtRps5apro or AtDD45pro enabled Cre/lox-mediated recombination at an early embryonic developmental stage upon crossing, activating transgenes in the hybrid cowpea and tobacco. Genetic engineering ideally results in precise spatiotemporal control of transgene expression. To activate transgenes exclusively in a hybrid upon fertilization, we evaluated a Cre/lox-mediated gene activation system with the Cre recombinase expressed by either AtRps5a or AtDD45 promoters that showed activity in egg cells and young embryos. In crosses between Cre recombinase lines and transgenic lines harboring a lox-excision reporter cassette with ZsGreen driven by the AtUbq3 promoter after Cre/lox-mediated recombination, we observed complete excision of the lox-flanked intervening DNA sequence between the AtUbq3pro and the ZsGreen coding sequence in F1 progeny upon genotyping but no ZsGreen expression in F1 seeds or seedlings. The incapability to observe ZsGreen fluorescence was attributed to the activity of the AtUbq3pro. Strong ZsGreen expression in F1 seeds was observed after recombination when ZsGreen was driven by the AtUbq10 promoter. Using the AtDD45pro to express Cre resulted in more variation in recombination frequencies between transgenic lines and crosses. Regardless of the promoter used to regulate Cre, mosaic F1 progeny were rare, suggesting gene activation at an early embryo-developmental stage. Observation of ZsGreen-expressing tobacco embryos at the globular stage from crosses with the AtRps5aproCre lines pollinated by the AtUbq3prolox line supported the early activation mode.
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Affiliation(s)
- Zhifen Zhang
- Department of Horticulture and Institute of Plant Breeding, Genetics and Genomics, University of Georgia, 2356 Rainwater Rd, Tifton, GA, 31793, USA
| | - Yinping Guo
- Department of Horticulture and Institute of Plant Breeding, Genetics and Genomics, University of Georgia, 2356 Rainwater Rd, Tifton, GA, 31793, USA
| | - Kathleen Monfero Marasigan
- Department of Horticulture and Institute of Plant Breeding, Genetics and Genomics, University of Georgia, 2356 Rainwater Rd, Tifton, GA, 31793, USA
| | - Joann A Conner
- Department of Horticulture and Institute of Plant Breeding, Genetics and Genomics, University of Georgia, 2356 Rainwater Rd, Tifton, GA, 31793, USA
| | - Peggy Ozias-Akins
- Department of Horticulture and Institute of Plant Breeding, Genetics and Genomics, University of Georgia, 2356 Rainwater Rd, Tifton, GA, 31793, USA.
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Kurbidaeva A, Purugganan M. Insulators in Plants: Progress and Open Questions. Genes (Basel) 2021; 12:genes12091422. [PMID: 34573404 PMCID: PMC8470105 DOI: 10.3390/genes12091422] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Revised: 09/08/2021] [Accepted: 09/14/2021] [Indexed: 11/16/2022] Open
Abstract
The genomes of higher eukaryotes are partitioned into topologically associated domains or TADs, and insulators (also known as boundary elements) are the key elements responsible for their formation and maintenance. Insulators were first identified and extensively studied in Drosophila as well as mammalian genomes, and have also been described in yeast and plants. In addition, many insulator proteins are known in Drosophila, and some have been investigated in mammals. However, much less is known about this important class of non-coding DNA elements in plant genomes. In this review, we take a detailed look at known plant insulators across different species and provide an overview of potential determinants of plant insulator functions, including cis-elements and boundary proteins. We also discuss methods previously used in attempts to identify plant insulators, provide a perspective on their importance for research and biotechnology, and discuss areas of potential future research.
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Zhou J, Li D, Zheng C, Xu R, Zheng E, Yang Y, Chen Y, Yu C, Yan C, Chen J, Wang X. Targeted Transgene Expression in Rice Using a Callus Strong Promoter for Selectable Marker Gene Control. FRONTIERS IN PLANT SCIENCE 2020; 11:602680. [PMID: 33362834 PMCID: PMC7759479 DOI: 10.3389/fpls.2020.602680] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Accepted: 11/06/2020] [Indexed: 06/12/2023]
Abstract
Precise expression of a transgene in the desired manner is important for plant genetic engineering and gene function deciphering, but it is a challenge to obtain specific transgene expression free from the interference of the constitutive promoters used to express the selectable marker gene, such as the Cauliflower mosaic virus (CaMV) 35S promoter. So, the solutions to avoid these inappropriate regulations are largely demanded. In this study, we report the characterization of a callus strong promoter (CSP1) in rice and its application for accurate transgene expression. Our results indicate that the high expression of the CSP1 promoter in the callus enables efficient selection of hygromycin equivalent to that provided by the CaMV 35S promoter, whereas its expression in other tissues is low. To evaluate possible leaky effects, the expression of a β-glucuronidase reporter driven by six specific promoters involving hormone signaling, pathogen response, cell fate determination, and proliferation was observed in transgenic rice plants generated by CSP1-mediated selection. Distinct β-glucuronidase expression was found consistently in most of the transgenic lines obtained for each promoter. In addition, we applied these specific marker lines to investigate the root cellular responses to exogenous cytokinin and auxin treatment. The results reveal that the root growth inhibition by cytokinin was differently regulated at high and low concentrations. In summary, we have established the feasibility of using callus-specific promoter-dependent selection to mitigate the transgene misexpression in rice. By enabling efficient transformation, rice plants with reliable transgene expression will be easily acquired for broad applications.
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Affiliation(s)
- Jie Zhou
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products, Ministry of Agriculture Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Dongyue Li
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products, Ministry of Agriculture Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Chao Zheng
- College of Plant Protection, Northwest A&F University, Yangling, China
| | - Rumeng Xu
- College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua, China
| | - Ersong Zheng
- College of Plant Protection, Northwest A&F University, Yangling, China
| | - Yong Yang
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products, Ministry of Agriculture Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Yang Chen
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products, Ministry of Agriculture Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Chulang Yu
- Institute of Plant Virology, Ningbo University, Ningbo, China
| | - Chengqi Yan
- Institute of Biotechnology, Ningbo Academy of Agricultural Sciences, Ningbo, China
| | - Jianping Chen
- Institute of Plant Virology, Ningbo University, Ningbo, China
| | - Xuming Wang
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products, Ministry of Agriculture Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
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Tran A, Johnson DA. Mutational analysis identifies functional Rap1, Su(Hw), and CTCF insulator sites in Arabidopsis thaliana. PLANT CELL REPORTS 2020; 39:1743-1753. [PMID: 32959125 DOI: 10.1007/s00299-020-02601-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 09/10/2020] [Indexed: 06/11/2023]
Abstract
Genetic analysis identifies multiple, potential protein binding sites important for insulator function in Arabidopsis thaliana: Rap1 site in UASrpg, Su(Hw) site in UASrpg, and CTCF site in BEAD1c. Three non-plant insulators UASrpg, BEAD1c, and gypsy isolated from Ashbya gossypii, Homo sapiens and Drosophila melanogaster gypsy retrotransposon, respectively, demonstrate insulator function in transgenic Arabidopsis thaliana. Here, the hypothesis that DNA sequences functional in A. thaliana are the same as those in the original host as previously assumed, was tested. Genetic analyses of the cloned fragments in an enhancer blocking assay system was performed through deletions and mutations to identify more precisely which sequences within the cloned fragments function as insulators. Significant loss of insulator activity was observed when the UASrpg Rap1 binding site R2 was mutated but not R1. Cloned fragments containing BEAD1c are effective insulators in our assay system and the previously investigated gypsy insulator is non-functional. Further analyses identified potential Su(Hw) and CTCF sites within UASrpg, of which only the Su(Hw) site was functional. Thus, the activity of non-plant insulators in A. thaliana is context dependent. These results support the hypothesis that insulator function is conserved across kingdoms.
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Affiliation(s)
- Anh Tran
- Biology Department, University of Ottawa, Ottawa, Ontario, Canada.
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Pérez-González A, Caro E. Benefits of using genomic insulators flanking transgenes to increase expression and avoid positional effects. Sci Rep 2019; 9:8474. [PMID: 31186481 PMCID: PMC6560062 DOI: 10.1038/s41598-019-44836-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Accepted: 05/23/2019] [Indexed: 01/03/2023] Open
Abstract
For more than 20 years, plant biologists have tried to achieve complete control of transgene expression. Until the techniques to target transgenes to safe harbor sites in the genome become routine, flanking transgenes with genetic insulators, DNA sequences that create independent domains of gene expression, can help avoid positional effects and stabilize their expression. We have, for the first time, compared the effect of three insulator sequences previously described in the literature and one never tested before. Our results indicate that their use increases transgene expression, but only the last one reduces variability between lines and between individuals. We have analyzed the integration of insulator-flanked T-DNAs using whole genome re-sequencing (to our knowledge, also for the first time) and found data suggesting that chiMARs can shelter transgene insertions from neighboring repressive epigenetic states. Finally, we could also observe a loss of accuracy of the RB insertion in the lines harboring insulators, evidenced by a high frequency of truncation of T-DNAs and of insertion of vector backbone that, however, did not affect transgene expression. Our data supports that the effect of each genetic insulator is different and their use in transgenic constructs should depend on the needs of each specific experiment.
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Affiliation(s)
- Ana Pérez-González
- Centre for Plant Biotechnology and Genomics Universidad Politécnica de Madrid (UPM) - Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) Campus Montegancedo UPM Pozuelo de Alarcón (Madrid), Madrid, Spain
| | - Elena Caro
- Centre for Plant Biotechnology and Genomics Universidad Politécnica de Madrid (UPM) - Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) Campus Montegancedo UPM Pozuelo de Alarcón (Madrid), Madrid, Spain.
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Zhou J, Yu F, Wang X, Yang Y, Yu C, Liu H, Cheng Y, Yan C, Chen J. Specific expression of DR5 promoter in rice roots using a tCUP derived promoter-reporter system. PLoS One 2014; 9:e87008. [PMID: 24466314 PMCID: PMC3899362 DOI: 10.1371/journal.pone.0087008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Accepted: 12/15/2013] [Indexed: 11/19/2022] Open
Abstract
Variation of transgene expression caused by either position effect at the insertion site or the promoter/enhancer elements employed for the expression of selectable marker genes has complicated phenotype characterization and caused misinterpretation. We have developed a reporter system in rice to analyze the influence of vector configuration, spacer and selectable marker gene promoter on the expression of the promoterless GUS reporter and DR5 promoter. Our results indicate that a spacer inserted between the reversed 35S promoter and the GUS reporter could reduce leaky expression of the reporter but was unable to block the nonspecific expression of DR5::GUS. Stacking the selectable marker unit in head to tail with the GUS reporter aided the gene specific expression of the GUS reporter under the DR5 promoter even when the 35S promoter is used for expression of the selectable marker. Compared to 35S under this configuration, a quick and distinctive expression of DR5::GUS was observed in the root cap, quiescent center and xylem cells in the root apical meristem by using the tCUP derived promoter (tCUP1) for selection, that is similar to the pattern obtained by a sensitive DR5 variant (DR5rev) in Arabidopsis. These data suggest a conserved property of the tCUP promoter in preventing enhancer-promoter interactions in rice as it does in Arabidopsis, and also demonstrate that an analogous distal auxin maximum exists in roots of rice. Therefore, the tCUP promoter based selection system provides a new strategy for specific expression of transgenes in rice.
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Affiliation(s)
- Jie Zhou
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
| | - Feibo Yu
- College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua, P. R. China
| | - Xuming Wang
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
| | - Yong Yang
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
| | - Chulang Yu
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
| | - Hongjia Liu
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
| | - Ye Cheng
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
| | - Chengqi Yan
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
- * E-mail: (JC); (CY)
| | - Jianping Chen
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, MOA Key Laboratory for Plant Protection and Biotechnology, Zhejiang Provincial Key Laboratory of Plant Virology, Zhejiang Academy of Agricultural Sciences, Hangzhou, P. R. China
- * E-mail: (JC); (CY)
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Thilmony R, Guttman ME, Lin JW, Blechl AE. The wheat HMW-glutenin 1Dy10 gene promoter controls endosperm expression in Brachypodium distachyon. GM CROPS & FOOD 2014; 5:36-43. [PMID: 24322586 PMCID: PMC5033164 DOI: 10.4161/gmcr.27371] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 11/26/2013] [Accepted: 11/27/2013] [Indexed: 12/18/2022]
Abstract
The grass species Brachypodium distachyon has emerged as a model system for the study of gene structure and function in temperate cereals. As a first demonstration of the utility of Brachypodium to study wheat gene promoter function, we transformed it with a T-DNA that included the uidA reporter gene under control of a wheat High-Molecular-Weight Glutenin Subunit (HMW-GS) gene promoter and transcription terminator. For comparison, the same expression cassette was introduced into wheat by biolistics. Histochemical staining for β-glucuronidase (GUS) activity showed that the wheat promoter was highly expressed in the endosperms of all the seeds of Brachypodium and wheat homozygous plants. It was not active in any other tissue of transgenic wheat, but showed variable and sporadic activity in a minority of styles of the pistils of four homozygous transgenic Brachypodium lines. The ease of obtaining transgenic Brachypodium plants and the overall faithfulness of expression of the wheat HMW-GS promoter in those plants make it likely that this model system can be used for studies of other promoters from cereal crop species that are difficult to transform.
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Affiliation(s)
- Roger Thilmony
- USDA-ARS; Western Regional Research Center; Crop Improvement and Utilization Research Unit; Albany, CA USA
| | - Mara E Guttman
- USDA-ARS; Western Regional Research Center; Crop Improvement and Utilization Research Unit; Albany, CA USA
| | - Jeanie W Lin
- USDA-ARS; Western Regional Research Center; Crop Improvement and Utilization Research Unit; Albany, CA USA
| | - Ann E Blechl
- USDA-ARS; Western Regional Research Center; Crop Improvement and Utilization Research Unit; Albany, CA USA
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Singer SD, Liu Z, Cox KD. Minimizing the unpredictability of transgene expression in plants: the role of genetic insulators. PLANT CELL REPORTS 2012; 31:13-25. [PMID: 21987122 DOI: 10.1007/s00299-011-1167-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2011] [Accepted: 09/27/2011] [Indexed: 05/20/2023]
Abstract
The genetic transformation of plants has become a necessary tool for fundamental plant biology research, as well as the generation of engineered plants exhibiting improved agronomic and industrial traits. However, this technology is significantly hindered by the fact that transgene expression is often highly variable amongst independent transgenic lines. Two of the major contributing factors to this type of inconsistency are inappropriate enhancer-promoter interactions and chromosomal position effects, which frequently result in mis-expression or silencing of the transgene, respectively. Since the precise, often tissue-specific, expression of the transgene(s) of interest is often a necessity for the successful generation of transgenic plants, these undesirable side effects have the potential to pose a major challenge for the genetic engineering of these organisms. In this review, we discuss strategies for improving foreign gene expression in plants via the inclusion of enhancer-blocking insulators, which function to impede enhancer-promoter communication, and barrier insulators, which block the spread of heterochromatin, in transgenic constructs. While a complete understanding of these elements remains elusive, recent studies regarding their use in genetically engineered plants indicate that they hold great promise for the improvement of transgene expression, and thus the future of plant biotechnology.
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Affiliation(s)
- Stacy D Singer
- Department of Plant Pathology and Plant-Microbe Biology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456, USA
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