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Bose S, Suescún AV, Song J, Castillo-González C, Aklilu BB, Branham E, Lynch R, Shippen DE. tRNA ADENOSINE DEAMINASE 3 is required for telomere maintenance in Arabidopsis thaliana. PLANT CELL REPORTS 2020; 39:1669-1685. [PMID: 32959123 PMCID: PMC7655638 DOI: 10.1007/s00299-020-02594-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Accepted: 09/04/2020] [Indexed: 05/05/2023]
Abstract
KEY MESSAGE: tRNA Adenosine Deaminase 3 helps to sustain telomere tracts in a telomerase-independent fashion, likely through regulating cellular metabolism. Telomere length maintenance is influenced by a complex web of chromatin and metabolism-related factors. We previously reported that a lncRNA termed AtTER2 regulates telomerase activity in Arabidopsis thaliana in response to DNA damage. AtTER2 was initially shown to partially overlap with the 5' UTR of the tRNA ADENOSINE DEAMINASE 3 (TAD3) gene. However, updated genome annotation showed that AtTER2 was completely embedded in TAD3, raising the possibility that phenotypes ascribed to AtTER2 could be derived from TAD3. Here we show through strand-specific RNA-Seq, strand-specific qRT-PCR and bioinformatic analyses that AtTER2 does not encode a stable lncRNA. Further examination of the original tad3 (ter2-1/tad3-1) mutant revealed expression of an antisense transcript driven by a cryptic promoter in the T-DNA. Hence, a new hypomorphic allele of TAD3 (tad3-2) was examined. tad3-2 mutants showed hypersensitivity to DNA damage, but no deregulation of telomerase, suggesting that the telomerase phenotype of tad3-1 mutants reflects an off-target effect. Unexpectedly, however, tad3-2 plants displayed progressive loss of telomeric DNA over successive generations that was not accompanied by alteration of terminal architecture or end protection. The phenotype was exacerbated in plants lacking the telomerase processivity factor POT1a, indicating that TAD3 promotes telomere maintenance through a non-canonical, telomerase-independent pathway. The transcriptome of tad3-2 mutants revealed significant dysregulation of genes involved in auxin signaling and glucosinolate biosynthesis, pathways that intersect the stress response, cell cycle regulation and DNA metabolism. These findings indicate that the TAD3 locus indirectly contributes to telomere length homeostasis by altering the metabolic profile in Arabidopsis.
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Affiliation(s)
- Sreyashree Bose
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA
| | - Ana Victoria Suescún
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA
- Facultad de Ciencias, Instituto de Ciencias Ambientales Y Evolutivas, Universidad Austral de Chile, Valdivia, Chile
| | - Jiarui Song
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA
| | | | - Behailu Birhanu Aklilu
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA
- KWS Gateway Research Center, LLC, 1005 N Warson Rd, BRDG Park, St. Louis, MO, 63132, USA
| | - Erica Branham
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA
| | - Ryan Lynch
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA
| | - Dorothy E Shippen
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA.
- Department of Biochemistry and Biophysics, 300 Olsen Blvd, Room 413, College Station, TX, 77843-2128, USA.
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Schrumpfová PP, Fajkus J. Composition and Function of Telomerase-A Polymerase Associated with the Origin of Eukaryotes. Biomolecules 2020; 10:biom10101425. [PMID: 33050064 PMCID: PMC7658794 DOI: 10.3390/biom10101425] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 09/29/2020] [Accepted: 10/01/2020] [Indexed: 12/19/2022] Open
Abstract
The canonical DNA polymerases involved in the replication of the genome are unable to fully replicate the physical ends of linear chromosomes, called telomeres. Chromosomal termini thus become shortened in each cell cycle. The maintenance of telomeres requires telomerase—a specific RNA-dependent DNA polymerase enzyme complex that carries its own RNA template and adds telomeric repeats to the ends of chromosomes using a reverse transcription mechanism. Both core subunits of telomerase—its catalytic telomerase reverse transcriptase (TERT) subunit and telomerase RNA (TR) component—were identified in quick succession in Tetrahymena more than 30 years ago. Since then, both telomerase subunits have been described in various organisms including yeasts, mammals, birds, reptiles and fish. Despite the fact that telomerase activity in plants was described 25 years ago and the TERT subunit four years later, a genuine plant TR has only recently been identified by our group. In this review, we focus on the structure, composition and function of telomerases. In addition, we discuss the origin and phylogenetic divergence of this unique RNA-dependent DNA polymerase as a witness of early eukaryotic evolution. Specifically, we discuss the latest information regarding the recently discovered TR component in plants, its conservation and its structural features.
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Affiliation(s)
- Petra Procházková Schrumpfová
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic;
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-62500 Brno, Czech Republic
- Correspondence:
| | - Jiří Fajkus
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic;
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-62500 Brno, Czech Republic
- The Czech Academy of Sciences, Institute of Biophysics, Královopolská 135, 612 65 Brno, Czech Republic
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De la Torre-Espinosa ZY, Barredo-Pool F, Castaño de la Serna E, Sánchez-Teyer LF. Active telomerase during leaf growth and increase of age in plants from Agave tequilana var. Azul. PHYSIOLOGY AND MOLECULAR BIOLOGY OF PLANTS : AN INTERNATIONAL JOURNAL OF FUNCTIONAL PLANT BIOLOGY 2020; 26:639-647. [PMID: 32255928 PMCID: PMC7113356 DOI: 10.1007/s12298-020-00781-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Revised: 01/28/2020] [Accepted: 02/19/2020] [Indexed: 06/11/2023]
Abstract
In plants, previous studies show that telomerase activity contributes to the maintenance of telomeric length for the proper development of organs and tissues. In this work, we investigated telomerase activity in A. tequilana during several years of cultivation. We found that during growth of the leaf there are two crucial phases: (1) the onset of cell elongation in 3 years and (2) differentiation of vascular bundles in 6 years. This coincides with the ages where the highest telomerase activity is seen. Therefore indicates that telomerase is associated with cellular activities such as; elongation, division, and cell differentiation. Likewise, we detected high activity during the period of vegetative growth, indicating that telomerase also contributes to telomeric maintenance on the leaf in A. tequilana.
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Affiliation(s)
- Zamaria Yoselin De la Torre-Espinosa
- Unidad de Bioquímica y Biología Molecular de Plantas, Centro de Investigación Científica de Yucatán, A.C. Calle 43 No. 130, Colonia Chuburná de Hidalgo, Mérida, Yucatan Mexico
- Unidad de Biotecnología, Centro de Investigación Científica de Yucatán, A.C. Calle 43 No. 130, Colonia Chuburná de Hidalgo, Mérida, Yucatan Mexico
| | - Felipe Barredo-Pool
- Unidad de Biotecnología, Centro de Investigación Científica de Yucatán, A.C. Calle 43 No. 130, Colonia Chuburná de Hidalgo, Mérida, Yucatan Mexico
| | - Enrique Castaño de la Serna
- Unidad de Bioquímica y Biología Molecular de Plantas, Centro de Investigación Científica de Yucatán, A.C. Calle 43 No. 130, Colonia Chuburná de Hidalgo, Mérida, Yucatan Mexico
| | - Lorenzo Felipe Sánchez-Teyer
- Unidad de Biotecnología, Centro de Investigación Científica de Yucatán, A.C. Calle 43 No. 130, Colonia Chuburná de Hidalgo, Mérida, Yucatan Mexico
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Jurečková JF, Sýkorová E, Hafidh S, Honys D, Fajkus J, Fojtová M. Tissue-specific expression of telomerase reverse transcriptase gene variants in Nicotiana tabacum. PLANTA 2017; 245:549-561. [PMID: 27900472 DOI: 10.1007/s00425-016-2624-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Accepted: 11/23/2016] [Indexed: 06/06/2023]
Abstract
MAIN CONCLUSION In tobacco, three sequence variants of the TERT gene have been described. We revealed unbalanced levels of TERT variant transcripts in vegetative tobacco tissues and enhanced TERT transcription and telomerase activity in reproductive tissues. Telomerase is a ribonucleoprotein complex responsible for the maintenance of telomeres, structures delimiting ends of linear eukaryotic chromosomes. In the Nicotiana tabacum (tobacco) allotetraploid plant, three sequence variants (paralogs) of the gene coding for the telomerase reverse transcriptase subunit (TERT) have been described, two of them derived from the maternal N. sylvestris genome (TERT_Cs, TERT_D) and one originated from the N. tomentosiformis paternal genome (TERT_Ct). In this work, we analyzed the transcription of TERT variants in correlation with telomerase activity in tobacco tissues. High and approximately comparable levels of TERT_Ct and TERT_Cs transcripts were detected in seedlings, roots, flower buds and leaves, while the transcript of the TERT_D variant was markedly underrepresented. Similarly, in N. sylvestris tissues, TERT_Cs transcript significantly predominated. A specific pattern of TERT transcripts was found in samples of tobacco pollen with the TERT_Cs variant clearly dominating particularly at the early stage of pollen development. Detailed analysis of TERT_C variants representation in functionally distinct fractions of pollen transcriptome revealed their prevalence in large ribonucleoprotein particles encompassing translationally silent mRNA; only a minority of TERT_Ct and TERT_Cs transcripts were localized in actively translated polysomes. Histones of the TERT_C chromatin were decorated predominantly with the euchromatin-specific epigenetic modification in both telomerase-positive and telomerase-negative tobacco tissues. We conclude that the existence and transcription pattern of tobacco TERT paralogs represents an interesting phenomenon and our results indicate its functional significance. Nicotiana species have again proved to be appropriate and useful model plants in telomere biology studies.
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Affiliation(s)
- Jana Fišerová Jurečková
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology (CEITEC) and Faculty of Science, Masaryk University, Kamenice 5, 625 00, Brno, Czech Republic
| | - Eva Sýkorová
- Institute of Biophysics, Academy of Sciences of the Czech Republic v.v.i., Královopolská 135, 612 65, Brno, Czech Republic
| | - Said Hafidh
- Institute of Experimental Botany, Academy of Sciences of the Czech Republic v.v.i., Rozvojová 263, 165 02, Prague, Czech Republic
| | - David Honys
- Institute of Experimental Botany, Academy of Sciences of the Czech Republic v.v.i., Rozvojová 263, 165 02, Prague, Czech Republic
| | - Jiří Fajkus
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology (CEITEC) and Faculty of Science, Masaryk University, Kamenice 5, 625 00, Brno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic v.v.i., Královopolská 135, 612 65, Brno, Czech Republic
| | - Miloslava Fojtová
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology (CEITEC) and Faculty of Science, Masaryk University, Kamenice 5, 625 00, Brno, Czech Republic.
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Procházková Schrumpfová P, Schořová Š, Fajkus J. Telomere- and Telomerase-Associated Proteins and Their Functions in the Plant Cell. FRONTIERS IN PLANT SCIENCE 2016; 7:851. [PMID: 27446102 PMCID: PMC4924339 DOI: 10.3389/fpls.2016.00851] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 05/31/2016] [Indexed: 05/20/2023]
Abstract
Telomeres, as physical ends of linear chromosomes, are targets of a number of specific proteins, including primarily telomerase reverse transcriptase. Access of proteins to the telomere may be affected by a number of diverse factors, e.g., protein interaction partners, local DNA or chromatin structures, subcellular localization/trafficking, or simply protein modification. Knowledge of composition of the functional nucleoprotein complex of plant telomeres is only fragmentary. Moreover, the plant telomeric repeat binding proteins that were characterized recently appear to also be involved in non-telomeric processes, e.g., ribosome biogenesis. This interesting finding was not totally unexpected since non-telomeric functions of yeast or animal telomeric proteins, as well as of telomerase subunits, have been reported for almost a decade. Here we summarize known facts about the architecture of plant telomeres and compare them with the well-described composition of telomeres in other organisms.
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Affiliation(s)
- Petra Procházková Schrumpfová
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk UniversityBrno, Czech Republic
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk UniversityBrno, Czech Republic
- *Correspondence: Petra Procházková Schrumpfová,
| | - Šárka Schořová
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk UniversityBrno, Czech Republic
| | - Jiří Fajkus
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk UniversityBrno, Czech Republic
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk UniversityBrno, Czech Republic
- Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i.Brno, Czech Republic
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6
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Dehghan Nayeri F. Identification of transcription factors linked to cell cycle regulation in Arabidopsis. PLANT SIGNALING & BEHAVIOR 2014; 9:e972864. [PMID: 25482767 PMCID: PMC4622563 DOI: 10.4161/15592316.2014.972864] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 07/24/2014] [Accepted: 07/25/2014] [Indexed: 06/04/2023]
Abstract
Cell cycle is an essential process in growth and development of living organisms consists of the replication and mitotic phases separated by 2 gap phases; G1 and G2. It is tightly controlled at the molecular level and especially at the level of transcription. Precise regulation of the cell cycle is of central significance for plant growth and development and transcription factors are global regulators of gene expression playing essential roles in cell cycle regulation. This study has uncovered TFs that are involved in the control of cell cycle progression. With the aid of multi-parallel quantitative RT-PCR, the expression changes of 1880 TFs represented in the Arabidopsis TF platform was monitored in Arabidopsis synchronous MM2d cells during a 19 h period representing different time points corresponding to the 4 cell cycle phases after treatment of MM2d cells with Aphidicolin. Comparative TF expression analyses performed on synchronous cells resulted in the identification of 239 TFs differentially expressed during the cell cycle, while about one third of TFs were constitutively expressed through all time points. Phase-specific TFs were also identified.
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Affiliation(s)
- Fatemeh Dehghan Nayeri
- Max-Planck Institute of Molecular Plant Physiology; Am Mühlenberg 1; Potsdam-Golm, Germany
- Department of Agricultural Biotechnology; Faculty of Engineering and Technology; Imam Khomeini International University; Qazvin, Iran
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7
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Zachová D, Fojtová M, Dvořáčková M, Mozgová I, Lermontova I, Peška V, Schubert I, Fajkus J, Sýkorová E. Structure-function relationships during transgenic telomerase expression in Arabidopsis. PHYSIOLOGIA PLANTARUM 2013; 149:114-26. [PMID: 23278240 DOI: 10.1111/ppl.12021] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Revised: 12/13/2012] [Accepted: 12/14/2012] [Indexed: 05/11/2023]
Abstract
Although telomerase (EC 2.7.7.49) is important for genome stability and totipotency of plant cells, the principles of its regulation are not well understood. Therefore, we studied subcellular localization and function of the full-length and truncated variants of the catalytic subunit of Arabidopsis thaliana telomerase, AtTERT, in planta. Our results show that multiple sites in AtTERT may serve as nuclear localization signals, as all the studied individual domains of the AtTERT were targeted to the nucleus and/or the nucleolus. Although the introduced genomic or cDNA AtTERT transgenes display expression at transcript and protein levels, they are not able to fully complement the lack of telomerase functions in tert -/- mutants. The failure to reconstitute telomerase function in planta suggests a more complex telomerase regulation in plant cells than would be expected based on results of similar experiments in mammalian model systems.
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Affiliation(s)
- Dagmar Zachová
- Faculty of Science and Central European Institute of Technology, Masaryk University, CZ-61137, Brno, Czech Republic
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Ševčíková T, Bišová K, Fojtová M, Lukešová A, Hrčková K, Sýkorová E. Completion of cell division is associated with maximum telomerase activity in naturally synchronized cultures of the green alga Desmodesmus quadricauda. FEBS Lett 2013; 587:743-8. [PMID: 23395610 DOI: 10.1016/j.febslet.2013.01.058] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 01/17/2013] [Accepted: 01/23/2013] [Indexed: 10/27/2022]
Abstract
Telomerase maintains the ends of eukaryotic chromosomes, and its activity is an important parameter correlating with the proliferative capacity of cells. We have investigated cell cycle-specific changes in telomerase activity using cultures of Desmodesmus quadricauda, a model alga naturally synchronized by light/dark entrainment. A quantitative telomerase assay revealed high activity in algal cultures, with slight changes during the light period. Significantly increased telomerase activity was observed at the end of the dark phase, when cell division was complete. In contrast to other models, a natural separation between nuclear and cellular division typical for the cell cycle in D. quadricauda made this observation possible.
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Affiliation(s)
- Tereza Ševčíková
- Institute of Biophysics, Academy of Sciences of the Czech Republic, vvi, 612 65 Brno, Czech Republic
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9
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Sýkorová E, Fulnečková J, Mokroš P, Fajkus J, Fojtová M, Peška V. Three TERT genes in Nicotiana tabacum. Chromosome Res 2012; 20:381-94. [PMID: 22543812 DOI: 10.1007/s10577-012-9282-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 03/15/2012] [Accepted: 03/29/2012] [Indexed: 01/15/2023]
Abstract
Telomerase is essential for proper functioning of telomeres in eukaryotes. We cloned and characterised genes for the protein subunit of telomerase (TERT) in the allotetraploid Nicotiana tabacum (tobacco) and its diploid progenitor species Nicotiana sylvestris and Nicotiana tomentosiformis with the aim of determining if allopolyploidy (hybridisation and genome duplication) influences TERT activity and divergence. Two of the three sequence variants present in the tobacco genome (NtTERT-C/s and NtTERT-D) revealed similarity to two sequence variants found in N. sylvestris and another variant (NtTERT-C/t) was similar to TERT of N. tomentosiformis. Variants of N. sylvestris origin showed less similarity to each other (80.5 % in the genomic region; 90.1 % in the coding sequence) than that between the NtTERT-C/s and NtTERT-C/t variants (93.6 and 97.2 %, respectively). The NtTERT-D variant was truncated at the 5' end, and indels indicated that it was a pseudogene. All tobacco variants were transcribed and alternatively spliced sequences were detected. Analysis of gene arrangements uncovered a novel exon in the N-terminal domain of TERT variants, a feature that is likely to be commonly found in Solanaceae species. In addition, species-specific duplications were observed within exon 5. The putative function, copy number and evolutionary origin of these NtTERT sequence variants are discussed.
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Affiliation(s)
- Eva Sýkorová
- Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno, Czech Republic.
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Fojtová M, Peška V, Dobšáková Z, Mozgová I, Fajkus J, Sýkorová E. Molecular analysis of T-DNA insertion mutants identified putative regulatory elements in the AtTERT gene. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:5531-45. [PMID: 21865176 PMCID: PMC3223050 DOI: 10.1093/jxb/err235] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Analysis of plants bearing a T-DNA insertion is a potent tool of modern molecular biology, providing valuable information about the function and involvement of genes in metabolic pathways. A collection of 12 Arabidopsis thaliana lines with T-DNA insertions in the gene coding for the catalytic subunit of telomerase (AtTERT) and in adjacent regions was screened for telomerase activity [telomere repeat amplification protocol (TRAP) assay], telomere length (terminal restriction fragments), and AtTERT transcription (quantitative reverse transcription-PCR). Lines with the insertion located upstream of the start codon displayed unchanged telomere stability and telomerase activity, defining a putative minimal AtTERT promoter and the presence of a regulatory element linked to increased transcription in the line SALK_048471. Lines bearing a T-DNA insertion inside the protein-coding region showed telomere shortening and lack of telomerase activity. Transcription in most of these lines was unchanged upstream of the T-DNA insertion, while it was notably decreased downstream. The expression profile varied markedly in mutant lines harbouring insertions at the 5' end of AtTERT which showed increased transcription and abolished tissue specificity. Moreover, the line FLAG_385G01 (T-DNA insertion inside intron 1) revealed the presence of a highly abundant downstream transcript with normal splicing but without active telomerase. The role of regulatory elements found along the AtTERT gene is discussed in respect to natural telomerase expression and putative intron-mediated enhancement.
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Affiliation(s)
- Miloslava Fojtová
- Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic
- Department of Functional Genomics and Proteomics, Faculty of Science and CEITEC - Central European Institute of Technology, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic
| | - Vratislav Peška
- Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic
- Department of Functional Genomics and Proteomics, Faculty of Science and CEITEC - Central European Institute of Technology, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic
| | - Zuzana Dobšáková
- Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic
- To whom correspondence should be addressed. E-mail:
| | - Iva Mozgová
- Department of Functional Genomics and Proteomics, Faculty of Science and CEITEC - Central European Institute of Technology, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic
| | - Jiří Fajkus
- Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic
- Department of Functional Genomics and Proteomics, Faculty of Science and CEITEC - Central European Institute of Technology, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic
| | - Eva Sýkorová
- Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265 Brno, Czech Republic
- Department of Functional Genomics and Proteomics, Faculty of Science and CEITEC - Central European Institute of Technology, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic
- To whom correspondence should be addressed. E-mail:
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Watson JM, Riha K. Telomeres, Aging, and Plants: From Weeds to Methuselah – A Mini-Review. Gerontology 2011; 57:129-36. [DOI: 10.1159/000310174] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 01/15/2010] [Indexed: 01/01/2023] Open
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12
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Watson JM, Riha K. Comparative biology of telomeres: where plants stand. FEBS Lett 2010; 584:3752-9. [PMID: 20580356 PMCID: PMC3767043 DOI: 10.1016/j.febslet.2010.06.017] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 06/11/2010] [Accepted: 06/14/2010] [Indexed: 01/02/2023]
Abstract
Telomeres are essential structures at the ends of eukaryotic chromosomes. Work on their structure and function began almost 70 years ago in plants and flies, continued through the Nobel Prize winning work on yeast and ciliates, and goes on today in many model and non-model organisms. The basic molecular mechanisms of telomeres are highly conserved throughout evolution, and our current understanding of how telomeres function is a conglomeration of insights gained from many different species. This review will compare the current knowledge of telomeres in plants with other organisms, with special focus on the functional length of telomeric DNA, the search for TRF homologs, the family of POT1 proteins, and the recent discovery of members of the CST complex.
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Affiliation(s)
- J Matthew Watson
- Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, Vienna, Austria
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Abstract
The phytohormone auxin is a major regulator of plant growth and development. Many aspects of these processes depend on the multiple controls exerted by auxin on cell division and cell expansion. The detailed mechanisms by which auxin controls these essential cellular responses are still poorly understood, despite recent progress in the identification of auxin receptors and components of auxin signaling pathways. The purpose of this review is to provide an overview of the present knowledge of the molecular mechanisms involved in the auxin control of cell division and cell expansion. In both cases, the involvement of at least two signaling pathways and of multiple targets of auxin action reflects the complexity of the subtle regulation of auxin-mediated cellular responses. In addition, it offers the necessary flexibility for generating differential responses within a given cell depending on its developmental context.
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Affiliation(s)
- Catherine Perrot-Rechenmann
- Institut des Sciences du Végétal, UPR2355 CNRS, 1 Avenue de la Terrasse, 91198 Gif sur Yvette, Cedex, France.
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Liu PF, Chang WC, Wang YK, Munisamy SB, Hsu SH, Chang HY, Wu SH, Pan RL. Differential regulation of Ku gene expression in etiolated mung bean hypocotyls by auxins. ACTA ACUST UNITED AC 2007; 1769:443-54. [PMID: 17507104 DOI: 10.1016/j.bbaexp.2007.04.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Revised: 03/15/2007] [Accepted: 04/03/2007] [Indexed: 10/23/2022]
Abstract
Plant Ku genes were identified very recently in Arabidopsis thaliana, and their roles in repair of double-stranded break DNA and maintenance of telomere integrity were scrutinized. In this study, the cDNAs encoding Ku70 (VrKu70) and Ku80 (VrKu80) were isolated from mung bean (Vigna radiata L.) hypocotyls. Both genes were expressed widely among different tissues of mung bean with the highest levels in hypocotyls and leaves. The VrKu gene expression was stimulated by exogenous auxins in a concentration- and time-dependent manner. The stimulation could be abolished by auxin transport inhibitors, N-(1-naphthyl) phthalamic acid and 2,3,5-triiodobenzoic acid implicating that exogenous auxins triggered the effects following their uptake by the cells. Further analysis using specific inhibitors of auxin signaling showed that the stimulation of VrKu expression by 2,4-dichlorophenoxyacetic acid (2,4-D) was suppressed by intracellular Ca(2+) chelators, calmodulin antagonists, and calcium/calmodulin dependent protein kinase inhibitors, suggesting the involvement of calmodulin in the signaling pathway. On the other hand, exogenous indole-3-acetic acid (IAA) and alpha-naphthalene acetic acid (NAA) stimulated VrKu expression through the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Altogether, it is thus proposed that 2,4-D and IAA (or NAA) regulate the expression of VrKu through two distinct pathways.
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Affiliation(s)
- Pei-Feng Liu
- Department of Life Sciences and Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsin Chu, Taiwan 30043, Republic of China
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15
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Zellinger B, Riha K. Composition of plant telomeres. ACTA ACUST UNITED AC 2007; 1769:399-409. [PMID: 17383025 DOI: 10.1016/j.bbaexp.2007.02.001] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2006] [Revised: 02/01/2007] [Accepted: 02/09/2007] [Indexed: 12/15/2022]
Abstract
Telomeres are essential elements of eukaryotic chromosomes that differentiate native chromosome ends from deleterious DNA double-strand breaks (DSBs). This is achieved by assembling chromosome termini in elaborate high-order nucleoprotein structures that in most organisms encompass telomeric DNA, specific telomere-associated proteins as well as general chromatin and DNA repair factors. Although the individual components of telomeric chromatin are evolutionary highly conserved, cross species comparisons have revealed a remarkable flexibility in their utilization at telomeres. This review outlines the strategies used for chromosome end protection and maintenance in mammals, yeast and flies and discusses current progress in deciphering telomere structure in plants.
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Affiliation(s)
- Barbara Zellinger
- Gregor Mendel Institute of Plant Molecular Biology, Austrian Academy of Sciences, Dr. Bohrgasse 3, A-1030 Vienna, Austria
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16
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Zhang L, Tamura K, Shin-ya K, Takahashi H. The telomerase inhibitor telomestatin induces telomere shortening and cell death in Arabidopsis. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:39-44. [PMID: 16473138 DOI: 10.1016/j.bbamcr.2005.12.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2005] [Revised: 10/27/2005] [Accepted: 12/05/2005] [Indexed: 01/06/2023]
Abstract
The cellular response to telomere dysfunction in plants was investigated with the use of telomestatin, an inhibitor of human telomerase activity. Telomestatin bound to plant telomeric repeat sequence, and inhibited telomerase activity in suspension-cultured cells of Arabidopsis thaliana and Oryza sativa (rice) in a dose-dependent manner. The inhibitor did not affect transcript level of the TERT gene, which encodes the catalytic subunit of telomerase, in the plant cells. Inhibition of telomerase activity by telomestatin resulted in rapid shortening of telomeres and the induction of cell death by an apoptosis-like mechanism in Arabidopsis cells. These results suggest that telomerase contributes to the survival of proliferating plant cells by maintaining telomere length, and that telomere erosion triggers cell death.
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Affiliation(s)
- Lili Zhang
- Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan
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17
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Abstract
The role model systems have played in understanding telomere biology has been enormous, and understanding has rapidly transferred to human telomere research. Most work using model organisms to study telomerase and nontelomerase-based telomere-maintenance systems has centered on yeasts, ciliates, and insects. But it is now timely to put considerably more effort into plant models for a number of reasons: (i) the rice and Arabidopsis genome sequencing projects make data mining possible; (ii) extensive collections of insertion mutants of Arabidopsis thaliana enable phenotypic effects of protein gene knockouts to be analyzed, including for those genes involved in telomere structure, function (including, for example, in meiosis), and maintenance; and (iii) the variability of plant telomeres is considerable and ranges from the telomerase-mediated synthesis of the Arabidopsis-type (TTTAGGG) and vertebrate-type (TTAGGG) repeats to sequences synthesized by telomerase-independent mechanism(s) that are still to be discovered. Here we describe how the understanding of telomere biology has been advanced by methods used to isolate telomeric sequences and prove that the putative sequences isolated are indeed telomeric. We show how assays designed to prove the activity of telomerase [e.g., telomeric repeat amplification protocol (TRAP)] lead not only to an understanding of telomere structure and function, but also to the understanding of cell activity in development and in the cell cycle. We review how assays designed to reveal protein/protein and protein/nucleic acid interactions promote understanding of the structure and activities of plant telomeres. Together, the data are making significant contributions to telomere biology in general and could have medical implications.
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Affiliation(s)
- Jirí Fajkus
- Academy of Sciences of the Czech Republic, Brno, Czech Republic.
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18
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Oguchi K, Tamura K, Takahashi H. Characterization of Oryza sativa telomerase reverse transcriptase and possible role of its phosphorylation in the control of telomerase activity. Gene 2005; 342:57-66. [PMID: 15527966 DOI: 10.1016/j.gene.2004.07.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2004] [Revised: 07/05/2004] [Accepted: 07/19/2004] [Indexed: 01/01/2023]
Abstract
Telomerase reverse transcriptase (TERT) has been characterized in the dicotyledon Arabidopsis thaliana. A TERT homolog has now been identified in the monocotyledon rice (Oryza sativa L.) on the basis of its predicted homology to the A. thaliana enzyme (AtTERT). At least five alternatively spliced transcripts of the rice TERT (OsTERT) gene were detected. The full-length OsTERT protein shares structural features with TERTs of other species, including a calculated molecular size of 144 kDa, an isoelectric point of 9.6, and conserved sequence motifs. Phylogenetic analysis showed that OsTERT clusters with AtTERT and is more related to the human and mouse enzymes than to those of yeast and ciliated protozoa, consistent with the evolutionary relations among these eukaryotes. Telomerase activity was abundant in shoot apices and cultured cells but was low or absent in leaves or roots of rice plants, whereas similarly spliced OsTERT transcripts were detected in all tissues examined and cultured cells. Similar to mouse and human TERT proteins, OsTERT contains two putative phosphorylation sites for Akt kinase. Incubation of a rice cell extract with Akt or with protein phosphatase 2A potentiated or inhibited telomerase activity, respectively, whereas Akt did not affect the activity in Arabidopsis cell extract. In addition, the kinase activated the telomerase in a leaf extract. The mechanism of telomerase regulation in rice thus appears to differ from that in Arabidopsis (which is mediated predominantly at the level of AtTERT transcription), possibly reflecting the taxonomic distance between monocotyledons and dicotyledons.
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Affiliation(s)
- Keiko Oguchi
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
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19
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Abstract
The stability of eukaryotic genomes is provided in part by the integrity of telomeres, the nucleoprotein caps on the ends of chromosome. Recent studies reveal that proper telomere architecture is required for long-term proliferation capacity. Here we describe molecular mechanisms that protect and maintain chromosome ends and discuss why Arabidopsis is emerging as a powerful new model for elucidating fundamental aspects of telomere biology.
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Affiliation(s)
- Karel Riha
- Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, Texas 77843-2128, USA
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20
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21
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Yang SW, Kim DH, Lee JJ, Chun YJ, Lee JH, Kim YJ, Chung IK, Kim WT. Expression of the telomeric repeat binding factor gene NgTRF1 is closely coordinated with the cell division program in tobacco BY-2 suspension culture cells. J Biol Chem 2003; 278:21395-407. [PMID: 12646586 DOI: 10.1074/jbc.m209973200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Telomeres are vital for preserving chromosome integrity during cell division. Several genes encoding potential telomere-binding proteins have recently been identified in higher plants, but nothing is known about their function or regulation during cell division. In this study, we have isolated and characterized a cDNA clone, pNgTRF1, encoding a putative double-stranded telomeric repeat binding factor of Nicotiana glutinosa, a diploid tobacco plant. The predicted protein sequence of NgTRF1 (Mr = 75,000) contains a single Myb-like domain with significant homology to a corresponding motif in human TRF1/Pin2 and TRF2. Gel retardation assays revealed that bacterially expressed full-length NgTRF1 was able to form a specific complex only with probes containing three or more contiguous telomeric TTTAGGG repeats. The Myb-like domain of NgTRF1 is essential, but not sufficient, to bind the telomeric repeat sequence. The glutamine-rich extreme C-terminal region, which does not exist in animal proteins, was additionally required to form a specific telomere-protein complex. The dissociation constant (Kd) of the Myb motif plus the glutamine-rich domain of NgTRF1 to the two-telomeric repeat sequence was evaluated to be 4.5 +/- 0.2 x 10-9 m, which is comparable to that of the Myb domain of human TRF1. Expression analysis showed that NgTRF1 gene activity was inversely correlated with the cell division capacity of tobacco root cells and during the 9-day culture period of BY-2 suspension cells, while telomerase activity was positively correlated with cell division. In synchronized BY-2 cells, NgTRF1 was selectively expressed in G1 phase, whereas telomerase activity peaked in S phase. These findings suggest that telomerase activity and NgTRF1 expression are differentially regulated in an opposing fashion during growth and cell division in tobacco plants. The possible physiological functions of NgTRF1 in tobacco cells are also discussed.
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MESH Headings
- Amino Acid Motifs
- Amino Acid Sequence
- Arabidopsis/genetics
- Base Sequence
- Binding, Competitive
- Blotting, Northern
- Blotting, Southern
- Cell Division
- Cell Nucleus/metabolism
- Cloning, Molecular
- DNA/metabolism
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- G1 Phase
- Gene Deletion
- Gene Expression Regulation
- Gene Library
- Green Fluorescent Proteins
- Humans
- Indomethacin/pharmacology
- Kinetics
- Luminescent Proteins/metabolism
- Models, Genetic
- Molecular Sequence Data
- Mutation
- Nucleic Acid Hybridization
- Polymerase Chain Reaction
- Protein Binding
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- S Phase
- Sequence Homology, Amino Acid
- Species Specificity
- Subcellular Fractions
- Telomerase/metabolism
- Telomere/genetics
- Telomere/metabolism
- Telomeric Repeat Binding Protein 1/biosynthesis
- Telomeric Repeat Binding Protein 1/genetics
- Time Factors
- Nicotiana/genetics
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Affiliation(s)
- Seong Wook Yang
- Department of Biology, College of Science, Yonsei University, Seoul 120-749, Korea
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22
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Ramirez-Parra E, Fründt C, Gutierrez C. A genome-wide identification of E2F-regulated genes in Arabidopsis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2003; 33:801-11. [PMID: 12609051 DOI: 10.1046/j.1365-313x.2003.01662.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The completion of the Arabidopsis genomic sequence offers the possibility to extract global information about regulatory mechanisms. Here, we describe a data mining strategy in combination with gene expression analysis to identify bona fide genes regulated by the E2F transcription factor. Starting with a genome-wide search of chromosomal sites containing E2F-binding sites, we studied in depth two of the most abundant E2F-binding sites within the Arabidopsis genome and identified over 180 potential E2F target genes. Among them and in addition to cell cycle-related genes, we have also identified genes belonging to other functional categories, e.g. transcription, stress and defense or signaling. We have determined the expression levels of genes selected from different categories under two experimental situations. Using cultured cells partially synchronized with aphidicolin, we found that most potential E2F targets identified in silico show a cell cycle-regulated expression pattern with a peak in early/mid S-phase. In addition, we used Arabidopsis transgenic plants expressing a DP gene containing a truncated DNA-binding domain, which likely has a dominant-negative effect on AtE2Fa, b and c (also named AtE2F3, 1 and 2, respectively), which require DP for efficient DNA binding. Contrary to the up-regulation observed in early/mid S-phase-cultured cells, the expression of a large number of potential E2F targets was decreased in the transgenic plants. Our results strongly support that the RBR/E2F pathway plays a crucial role in regulating the expression of the genes identified in this study.
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Affiliation(s)
- Elena Ramirez-Parra
- Centro de Biologia Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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23
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Yang SW, Jin E, Chung IK, Kim WT. Cell cycle-dependent regulation of telomerase activity by auxin, abscisic acid and protein phosphorylation in tobacco BY-2 suspension culture cells. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 29:617-26. [PMID: 11874574 DOI: 10.1046/j.0960-7412.2001.01244.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Telomerase is a specialized RNA-directed DNA polymerase that adds telomeric repeats onto the ends of linear eukaryotic chromosomes. It was recently reported that the low, basal level of telomerase activity markedly increased at early S-phase of the cell cycle, and auxin further increased the S-phase-specific telomerase activity in tobacco BY-2 cells. In this study we show that abscisic acid (ABA), a phytohormone known to induce the cyclin-dependent protein kinase inhibitor, effectively abolished both the auxin- and S-phase-specific activation of telomerase in a concentration- and time-dependent fashion in synchronized tobacco BY-2 cells. These results suggest that there exists a hormonal cross-talk between auxin and ABA for the regulation of telomerase activity during the cell cycle of tobacco cells. Treatment of synchronized BY-2 cells with the protein kinase inhibitor staurosporine or H-7 effectively prevented the S-phase-specific activation of telomerase activity. By contrast, when okadaic acid or cantharidin, potent inhibitors of protein phosphatase 2A (PP2A), was applied to the cells, the S-phase-specific high level of telomerase activity was continuously maintained in the cell cycle for at least 14 h after release from M-phase arrest. Incubation of tobacco cell extracts with exogenous PP2A rapidly abrogated in vitro telomerase activity, while okadaic acid and cantharidin blocked the action of PP2A, effectively restoring in vitro telomerase activity. Taken together, these findings are discussed in the light of the suggestion that antagonistic functions of auxin and ABA, and reciprocal phosphorylation and dephosphorylation of telomerase complex, are necessarily involved in the cell cycle-dependent modulation of telomerase activity in tobacco cells.
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Affiliation(s)
- Seong Wook Yang
- Department of Biology, College of Science, Yonsei University, Seoul 120-749, Korea
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24
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Skene KR. Cluster roots: model experimental tools for key biological problems. JOURNAL OF EXPERIMENTAL BOTANY 2001; 52:479-485. [PMID: 11326054 DOI: 10.1093/jexbot/52.suppl_1.479] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The cluster root is made up of a number of determinate rootlets tightly grouped along the parent root. Each rootlet grows for a limited time, and then the meristem stops dividing and differentiates. Following cessation of growth, an exudative burst occurs, wherein, over 2-3 d, large amounts of organic acids, as well as phosphatases and phenolics, are exuded from the rootlets. There is a concomitant acidification of the rhizosphere. It is suggested that the temporal and spatial predictability of developmental and functional events in these structures makes them valuable as experimental tools with which to investigate key issues in plant developmental biology, physiology, ecophysiology, evolutionary biology, and biotechnology.
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Affiliation(s)
- K R Skene
- Department of Biological Sciences, University of Dundee, Dundee DD1 4HN, Scotland, UK.
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25
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Raz V, Koornneef M. Cell division activity during apical hook development. PLANT PHYSIOLOGY 2001; 125:219-26. [PMID: 11154331 PMCID: PMC61004 DOI: 10.1104/pp.125.1.219] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2000] [Revised: 08/01/2000] [Accepted: 08/16/2000] [Indexed: 05/20/2023]
Abstract
Growth during plant development is predominantly governed by the combined activities of cell division and cell elongation. The relative contribution of both activities controls the growth of a tissue. A fast change in growth is exhibited at the apical hypocotyl of etiolated seedlings where cells grow at different rates to form a hook-like structure, which is traditionally assumed to result from differential cell elongation. Using new tools we show asymmetric distribution of cell division during early stages of hook development. Cell divisions in the apical hook were predominantly found in subepidermal layers during an early step of hook development, but were absent in mutants exhibiting a hookless phenotype. In addition, during exaggeration of hook curvature, which is mediated by ethylene, a rapid change in the combined activities of cell division and cell elongation was detected. Our results indicate a fast change in cell division activity during apical hook development. We suggest that cell division together with cell elongation contributes to apical hook growth. Our results emphasize the change in the relative contribution of cell division and cell elongation in a fast growing structure like the apical hook.
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Affiliation(s)
- V Raz
- Laboratory of Genetics, Wageningen University, Dreijenlaan 2, 6703 HA Wageningen, The Netherlands.
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26
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Riha K, McKnight TD, Fajkus J, Vyskot B, Shippen DE. Analysis of the G-overhang structures on plant telomeres: evidence for two distinct telomere architectures. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2000; 23:633-41. [PMID: 10972889 DOI: 10.1046/j.1365-313x.2000.00831.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Telomeres are highly conserved structures essential for maintaining the integrity of eukaryotic genomes. In yeast, ciliates and mammals, the G-rich strand of the telomere forms a 3' overhang on the chromosome terminus. Here we investigate the architecture of telomeres in the dicot plants Silene latifolia and Arabidopsis thaliana using the PENT (primer extension/nick translation) assay. We show that both Arabidopsis and Silene telomeres carry G-overhangs longer than 20-30 nucleotides. However, in contrast to yeast and ciliate telomeres, only half of the telomeres in Silene seedlings possess detectable G-overhangs. PENT reactions using a variety of primers and reaction conditions revealed that the remaining fraction of Silene telomeres carries either no overhangs or overhangs less than 12 nucleotides in length. G-overhangs were observed in Silene seeds and leaves, tissues that lack telomerase activity. These findings suggest that incomplete DNA replication of the lagging strand, rather than synthesis by telomerase, is the primary mechanism for G-overhang synthesis in plants. Unexpectedly, we found that the fraction of telomeres with detectable G-overhangs decreased from 50% in seedlings to 35% in leaves. The difference may reflect increased susceptibility of the G-overhangs to nuclease attack in adult leaves, an event that could act as a precursor for the catabolic processes accompanying leaf senescence
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Affiliation(s)
- K Riha
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, USA
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27
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Oguchi K, Liu H, Tamura K, Takahashi H. Molecular cloning and characterization of AtTERT, a telomerase reverse transcriptase homolog in Arabidopsis thaliana. FEBS Lett 1999; 457:465-9. [PMID: 10471830 DOI: 10.1016/s0014-5793(99)01083-2] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
On the basis of its predicted homology to human telomerase reverse transcriptase (hTERT), a cDNA for Arabidopsis thaliana TERT (AtTERT) has now been isolated from cultured cells. The cDNA contains an open reading frame of 3372 bp, encoding a protein with a predicted size of 131 kDa and isoelectric point of 9.9. The AtTERT protein contains the conserved reverse transcriptase motifs 1, 2 and A-E as well as the TERT-specific T motif. Reverse transcription-polymerase chain reaction analysis and an assay of telomerase activity revealed that both AtTERT mRNA and telomerase activity are abundant in shoot apical meristems but are not detectable in rosette leaves.
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Affiliation(s)
- K Oguchi
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
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