The enormous sequence heterogeneity of telomerase RNA (TR) subunits has thus far complicated their characterization in a wider phylogenetic range. Our recent finding that land plant TRs are, similarly to known ciliate TRs, transcribed by RNA polymerase III and under the control of the type-3 promoter, allowed us to design a novel strategy to characterize TRs in early diverging Viridiplantae taxa, as well as in ciliates and other Diaphoretickes lineages. Starting with the characterization of the upstream sequence element of the type 3 promoter that is conserved in a number of small nuclear RNAs, and the expected minimum TR template region as search features, we identified candidate TRs in selected Diaphoretickes genomes. Homologous TRs were then used to build covariance models to identify TRs in more distant species. Transcripts of the identified TRs were confirmed by transcriptomic data, RT-PCR and Northern hybridization. A templating role for one of our candidates was validated in Physcomitrium patens. Analysis of secondary structure demonstrated a deep conservation of motifs (pseudoknot and template boundary element) observed in all published TRs. These results elucidate the evolution of the earliest eukaryotic TRs, linking the common origin of TRs across Diaphoretickes, and underlying evolutionary transitions in telomere repeats.

• MeSH
• genetická transkripce MeSH
• konformace nukleové kyseliny MeSH
• molekulární evoluce * MeSH
• mutace MeSH
• RNA rostlin biosyntéza   chemie   genetika   MeSH
• RNA-polymerasa II metabolismus   MeSH
• RNA-polymerasa III metabolismus   MeSH
• RNA biosyntéza   chemie   genetika   MeSH
• sekvenční seřazení MeSH
• telomerasa biosyntéza   chemie   genetika   MeSH
• telomery chemie   MeSH
• transkriptom MeSH
• Viridiplantae genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• RNA rostlin MeSH
• RNA-polymerasa II MeSH
• RNA-polymerasa III MeSH
• RNA MeSH
• telomerasa MeSH
• telomerase RNA MeSH Prohlížeč

The gene coding for the telomerase reverse transcriptase (TERT) is essential for the maintenance of telomeres. Previously we described the presence of three TERT paralogs in the allotetraploid plant Nicotiana tabacum, while a single TERT copy was identified in the paleopolyploid model plant Arabidopsis thaliana. Here we examine the presence, origin and functional status of TERT variants in allotetraploid Nicotiana species of diverse evolutionary ages and their parental genome donors, as well as in other diploid and polyploid plant species. A combination of experimental and in silico bottom-up analyses of TERT gene copies in Nicotiana polyploids revealed various patterns of retention or loss of parental TERT variants and divergence in their functions. RT-qPCR results confirmed the expression of all the identified TERT variants. In representative plant and green algal genomes, our synteny analyses show that their TERT genes were located in a conserved locus that became advantageous after the divergence of eudicots, and the gene was later translocated in several plant groups. In various diploid and polyploid species, translocation of TERT became fixed in target loci that show ancient synapomorphy.

• Klíčová slova
• Nicotiana, gene evolution, polyploidy, synteny, telomerase,
• MeSH
• Arabidopsis * enzymologie   genetika   MeSH
• genová dávka * MeSH
• polyploidie * MeSH
• proteiny huseníčku * genetika   metabolismus   MeSH
• tabák * enzymologie   genetika   MeSH
• telomerasa * genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• proteiny huseníčku * MeSH
• telomerasa * MeSH
• TERT protein, Arabidopsis MeSH Prohlížeč

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.

• Klíčová slova
• evolution, plant TERT, plant TR., telomerase, telomerase RNA (TR), telomerase reverse transcriptase (TERT),
• MeSH
• biologická evoluce * MeSH
• dějiny 20. století MeSH
• dějiny 21. století MeSH
• Eukaryota klasifikace   genetika   metabolismus   MeSH
• fylogeneze MeSH
• lidé MeSH
• RNA fyziologie   MeSH
• telomerasa chemie   fyziologie   MeSH
• telomery metabolismus   MeSH
• zvířata MeSH
• Check Tag
• dějiny 20. století MeSH
• dějiny 21. století MeSH
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• historické články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• RNA MeSH
• telomerasa MeSH
• telomerase RNA MeSH Prohlížeč

Parallel research on multiple model organisms shows that while some principles of telomere biology are conserved among all eukaryotic kingdoms, we also find some deviations that reflect different evolutionary paths and life strategies, which may have diversified after the establishment of telomerase as a primary mechanism for telomere maintenance. Much more than animals, plants have to cope with environmental stressors, including genotoxic factors, due to their sessile lifestyle. This is, in principle, made possible by an increased capacity and efficiency of the molecular systems ensuring maintenance of genome stability, as well as a higher tolerance to genome instability. Furthermore, plant ontogenesis differs from that of animals in which tissue differentiation and telomerase silencing occur during early embryonic development, and the "telomere clock" in somatic cells may act as a preventive measure against carcinogenesis. This does not happen in plants, where growth and ontogenesis occur through the serial division of apical meristems consisting of a small group of stem cells that generate a linear series of cells, which differentiate into an array of cell types that make a shoot and root. Flowers, as generative plant organs, initiate from the shoot apical meristem in mature plants which is incompatible with the human-like developmental telomere shortening. In this review, we discuss differences between human and plant telomere biology and the implications for aging, genome stability, and cell and organism survival. In particular, we provide a comprehensive comparative overview of telomere proteins acting in humans and in Arabidopsis thaliana model plant, and discuss distinct epigenetic features of telomeric chromatin in these species.

• Klíčová slova
• Arabidopsis, aging, chromatin, epigenetics, human, review, telomerase, telomere,
• MeSH
• chromatin metabolismus   MeSH
• epigeneze genetická MeSH
• lidé MeSH
• rostliny metabolismus   MeSH
• stárnutí buněk genetika   MeSH
• telomerasa metabolismus   MeSH
• telomery metabolismus   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• chromatin MeSH
• telomerasa MeSH

Standard pathways involved in the regulation of telomere stability do not contribute to gradual telomere elongation observed in the course of A. thaliana calli propagation. Genetic and epigenetic changes accompanying the culturing of plant cells have frequently been reported. Here we aimed to characterize the telomere homeostasis during long term callus propagation. While in Arabidopsis thaliana calli gradual telomere elongation was observed, telomeres were stable in Nicotiana tabacum and N. sylvestris cultures. Telomere elongation during callus propagation is thus not a general feature of plant cells. The long telomere phenotype in Arabidopsis calli was correlated neither with changes in telomerase activity nor with activation of alternative mechanisms of telomere elongation. The dynamics of telomere length changes was maintained in mutant calli with loss of function of important epigenetic modifiers but compromised in the presence of epigenetically active drug zebularine. To examine whether the cell culture-induced disruption of telomere homeostasis is associated with the modulated structure of chromosome ends, epigenetic properties of telomere chromatin were analysed. Albeit distinct changes in epigenetic modifications of telomere histones were observed, these were broadly stochastic. Our results show that contrary to animal cells, the structure and function of plant telomeres is not determined significantly by the epigenetic character of telomere chromatin. Set of differentially transcribed genes was identified in calli, but considering the known telomere- or telomerase-related functions of respective proteins, none of these changes per se was apparently related to the elongated telomere phenotype. Based on our data, we propose that the disruption in telomere homeostasis in Arabidopsis calli arises from the interplay of multiple factors, as a part of reprogramming of plant cells to long-term culture conditions.

• Klíčová slova
• Arabidopsis thaliana, Callus, Chromosome stability, Epigenetics, Regenerated plants, Telomere,
• MeSH
• Arabidopsis účinky léků   genetika   metabolismus   MeSH
• chromatin genetika   MeSH
• cytidin analogy a deriváty   farmakologie   MeSH
• druhová specificita MeSH
• ekotyp MeSH
• epigeneze genetická účinky léků   MeSH
• histony metabolismus   MeSH
• homeostáza telomer * účinky léků   MeSH
• messenger RNA genetika   metabolismus   MeSH
• mutace genetika   MeSH
• proteiny huseníčku metabolismus   MeSH
• regenerace účinky léků   MeSH
• rostlinné geny MeSH
• tabák genetika   MeSH
• techniky tkáňových kultur * MeSH
• telomerasa metabolismus   MeSH
• telomery metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• chromatin MeSH
• cytidin MeSH
• histony MeSH
• messenger RNA MeSH
• proteiny huseníčku MeSH
• pyrimidin-2-one beta-ribofuranoside MeSH Prohlížeč
• telomerasa MeSH

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.

• Klíčová slova
• plant, shelterin, telomerase, telomere, telomeric proteins, telomeric repeat binding (TRB),
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Telomerase-reverse transcriptase (TERT) plays an essential catalytic role in maintaining telomeres. However, in animal systems telomerase plays additional non-telomeric functional roles. We previously screened an Arabidopsis cDNA library for proteins that interact with the C-terminal extension (CTE) TERT domain and identified a nuclear-localized protein that contains an RNA recognition motif (RRM). This RRM-protein forms homodimers in both plants and yeast. Mutation of the gene encoding the RRM-protein had no detectable effect on plant growth and development, nor did it affect telomerase activity or telomere length in vivo, suggesting a non-telomeric role for TERT/RRM-protein complexes. The gene encoding the RRM-protein is highly expressed in leaf and reproductive tissues. We further screened an Arabidopsis cDNA library for proteins that interact with the RRM-protein and identified five interactors. These proteins are involved in numerous non-telomere-associated cellular activities. In plants, the RRM-protein, both alone and in a complex with its interactors, localizes to nuclear speckles. Transcriptional analyses in wild-type and rrm mutant plants, as well as transcriptional co-analyses, suggest that TERT, the RRM-protein, and the RRM-protein interactors may play important roles in non-telomeric cellular functions.

• Klíčová slova
• BiFC, MODIFIER OF snc1, metallothionein 2A, nuclear poly(A)-binding protein, oxidation-related zinc finger 2 protein, putative nuclear DNA-binding protein G2p, telobox, telomerase,
• Publikační typ
• časopisecké články MeSH

A comparative approach in biology is needed to assess the universality of rules governing this discipline. In plant telomere research, most of the key principles were established based on studies in only single model plant, Arabidopsis thaliana. These principles include the absence of telomere shortening during plant development and the corresponding activity of telomerase in dividing (meristem) plant cells. Here we examine these principles in Physcomitrella patens as a representative of lower plants. To follow telomerase expression, we first characterize the gene coding for the telomerase reverse transcriptase subunit PpTERT in P. patens, for which only incomplete prediction has been available so far. In protonema cultures of P. patens, growing by filament apical cell division, the proportion of apical (dividing) cells was quantified and telomere length, telomerase expression and activity were determined. Our results show telomere stability and demonstrate proportionality of telomerase activity and expression with the number of apical cells. In addition, we analyze telomere maintenance in mre11, rad50, nbs1, ku70 and lig4 mutants of P. patens and compare the impact of these mutations in double-strand-break (DSB) repair pathways with earlier observations in corresponding A. thaliana mutants. Telomere phenotypes are absent and DSB repair kinetics is not affected in P. patens mutants for DSB factors involved in non-homologous end joining (NHEJ). This is compliant with the overall dominance of homologous recombination over NHEJ pathways in the moss, contrary to the inverse situation in flowering plants.

• MeSH
• Arabidopsis genetika   MeSH
• chromozomy rostlin genetika   MeSH
• DNA rostlinná genetika   MeSH
• dvouřetězcové zlomy DNA MeSH
• fenotyp MeSH
• fylogeneze MeSH
• homeostáza telomer genetika   MeSH
• homologní rekombinace MeSH
• mechy genetika   metabolismus   MeSH
• molekulární sekvence - údaje MeSH
• mutace MeSH
• oprava DNA * MeSH
• rostlinné proteiny genetika   metabolismus   MeSH
• sekvence aminokyselin MeSH
• sekvence nukleotidů MeSH
• sekvenční analýza DNA MeSH
• sekvenční seřazení MeSH
• telomerasa genetika   metabolismus   MeSH
• telomery genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA rostlinná MeSH
• rostlinné proteiny MeSH
• telomerasa MeSH

Although telomere-binding proteins constitute an essential part of telomeres, in vivo data indicating the existence of a structure similar to mammalian shelterin complex in plants are limited. Partial characterization of a number of candidate proteins has not identified true components of plant shelterin or elucidated their functional mechanisms. Telomere repeat binding (TRB) proteins from Arabidopsis thaliana bind plant telomeric repeats through a Myb domain of the telobox type in vitro, and have been shown to interact with POT1b (Protection of telomeres 1). Here we demonstrate co-localization of TRB1 protein with telomeres in situ using fluorescence microscopy, as well as in vivo interaction using chromatin immunoprecipitation. Classification of the TRB1 protein as a component of plant telomeres is further confirmed by the observation of shortening of telomeres in knockout mutants of the trb1 gene. Moreover, TRB proteins physically interact with plant telomerase catalytic subunits. These findings integrate TRB proteins into the telomeric interactome of A. thaliana.

• Klíčová slova
• Arabidopsis thaliana, plant shelterin, telomerase, telomere, telomere protein interaction, telomere repeat binding (TRB),
• MeSH
• Arabidopsis enzymologie   genetika   MeSH
• proteiny huseníčku metabolismus   MeSH
• proteiny vázající telomery metabolismus   MeSH
• telomerasa metabolismus   MeSH
• telomery metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• proteiny huseníčku MeSH
• proteiny vázající telomery MeSH
• telomerasa MeSH

Telomere repeats are added onto chromosome ends by telomerase, consisting of two main core components: a catalytic protein subunit (telomerase reverse trancriptase, TERT), and an RNA subunit (telomerase RNA, TR). Here, we report for the first time evidence that HMGB1 (a chromatin-associated protein in mammals, acting as a DNA chaperone in transcription, replication, recombination, and repair) can modulate cellular activity of mammalian telomerase. Knockout of the HMGB1 gene (HMGB1 KO) in mouse embryonic fibroblasts (MEFs) results in chromosomal abnormalities, enhanced colocalization of γ-H2AX foci at telomeres, and a moderate shortening of telomere lengths. HMGB1 KO MEFs also exhibit significantly (>5-fold) lower telomerase activity than the wild-type MEFs. Correspondingly, enhanced telomerase activity is observed upon overexpression of HMGB1 in MEFs. HMGB1 physically interacts with both TERT and TR, as well as with active telomerase complex in vitro. However, direct interaction of HMGB1 with telomerase is most likely not accountable for the observed higher telomerase activity in HMGB1-containing cells, as revealed from the inability of purified HMGB1 protein to stimulate telomerase activity in vitro. While no transcriptional silencing of TERT is observed in HMGB1 KO MEFs, levels of TR are diminished (~3-fold), providing possible explanation for the observed lower telomerase activity in HMGB1 KO cells. Interestingly, knockout of the HMGB2 gene elevates telomerase activity (~3-fold) in MEFs, suggesting that the two closely related proteins of the HMGB family, HMGB1 and HMGB2, have opposite effects on telomerase activity in the cell. The ability of HMGB1 to modulate cellular activity of telomerase and to maintain telomere integrity can help to understand some aspects of the protein involvement in chromosome stability and cancer.

• MeSH
• buněčné linie MeSH
• chromozomální aberace MeSH
• down regulace MeSH
• fibroblasty cytologie   metabolismus   MeSH
• fluorescenční mikroskopie MeSH
• fragmentace DNA MeSH
• genový knockout * MeSH
• histony genetika   metabolismus   MeSH
• hybridizace in situ fluorescenční MeSH
• myši MeSH
• poškození DNA MeSH
• protein HMGB1 genetika   metabolismus   MeSH
• protein HMGB2 genetika   metabolismus   MeSH
• replikace DNA MeSH
• RNA genetika   metabolismus   MeSH
• telomerasa genetika   metabolismus   MeSH
• telomery metabolismus   patologie   MeSH
• zvířata MeSH
• Check Tag
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• gamma-H2AX protein, mouse MeSH Prohlížeč
• histony MeSH
• protein HMGB1 MeSH
• protein HMGB2 MeSH
• RNA MeSH
• telomerasa MeSH
• telomerase RNA MeSH Prohlížeč
• Tert protein, mouse MeSH Prohlížeč