Telomerase is essential for the maintenance of telomeres, structures located at the ends of linear eukaryotic chromosomes that are crucial for genomic stability. Telomerase has been frequently explored in mammals because of its activity in many types of cancers, but knowledge in plants is rather sketchy despite plants representing useful models due to peculiarities in their telomeres and telomerase biology. We studied in planta complementation of telomerase in Arabidopsis thaliana mutant plants with disrupted expression of the gene encoding the telomerase protein subunit (AtTERT) and significantly shortened telomeres. We found that the upstream region of AtTERT, previously identified as a putative minimal promoter, was essential for reconstitution of telomerase function, as demonstrated by the full or partial recovery of the telomere phenotype in mutants. In contrast, transformation by the full length AtTERT gene construct resulted in more progressive telomere shortening in mutants and even in wild type plants, despite the high level of AtTERT transcript and telomerase activity detected by in vitro assay. Thus, the telomerase protein subunit putative promoter is essential for in planta telomerase reconstitution and restoration of its catalytical activity. Contributions from other factors, including those tissue-specific, for proper telomerase function are discussed.

• Klíčová slova
• Arabidopsis thaliana, Complementation, Promoter, Telomerase, Telomere, in planta,
• MeSH
• Arabidopsis genetika   metabolismus   MeSH
• promotorové oblasti (genetika) genetika   MeSH
• proteiny huseníčku genetika   metabolismus   MeSH
• telomerasa genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• proteiny huseníčku MeSH
• telomerasa MeSH

Recent results suggest that telomerase is involved in many more cellular processes than merely telomere elongation. These include telomere-independent anti-apoptotic, cytoprotective and pro-proliferative effects of telomerase or protection of mitochondrial DNA against oxidative stress. Telomerase also participates in DNA repair and its essential subunits, hTR and hTERT, are able to modulate independently the cell's response to DNA damage. Recent high throughput analyses of gene expression showed that hTERT expression modulates expression of about 300 genes, including genes involved in the regulation of cell cycle progression, proliferation and differentiation. Besides the well-known telomerase catalytic activity of RNA-dependent DNA polymerase, its RNA-dependent RNA polymerase activity was recently described in association with the RNA subunit of mitochondrial RNA processing endoribonuclease, thus suggesting involvement of telomerase in RNA interference processes. These recent discoveries open novel possibilities and entirely unexpected research perspectives, branching off from the mainstream telomere and telomerase research.

• MeSH
• buněčný cyklus fyziologie   MeSH
• lidé MeSH
• mitochondrie enzymologie   MeSH
• nádory enzymologie   MeSH
• oprava DNA fyziologie   MeSH
• oxidační stres fyziologie   MeSH
• poškození DNA fyziologie   MeSH
• regulace genové exprese fyziologie   MeSH
• signální transdukce fyziologie   MeSH
• telomerasa metabolismus   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• telomerasa MeSH

Telomerase and telomerase-generated telomeric DNA sequences are widespread throughout eukaryotes, yet they are not universal. Neither telomerase nor the simple DNA repeats associated with telomerase have been found in some plant and animal species. Telomerase was likely lost from Diptera before the divergence of Diptera and Siphonaptera, some 260 million years ago. Even so, Diptera is one of the most successful animal orders, making up 11% of known animal species. In addition, many species of Coleoptera and Hemiptera seem to lack canonical telomeric repeats at their chromosome ends. These and other insects that appear to lack canonical terminal repeat sequences account for another 10-15% of animal species. Conversely, the silk moth Bombyx mori maintains canonical telomeric sequences at its chromosome ends but seems to lack a functional telomerase. We speculate that a telomere-specific capping complex that recognizes the telomeric repeats and protects chromosome ends is the determining factor in maintaining canonical telomeric sequences and that telomerase is an early and efficacious mechanism for satisfying the needs of capping complex. There are alternate mechanisms for maintaining chromosome ends that do not depend on telomerase, such as recombination found in some human cancer cells and yeast mutants. These mechanisms may maintain the canonical telomeric repeats or allow the terminal sequence to evolve when specificity of the capping complex for terminal repeat sequences is weak.

• MeSH
• delece genu * MeSH
• hmyz enzymologie   genetika   MeSH
• homologní rekombinace MeSH
• koncové repetice MeSH
• molekulární evoluce * MeSH
• telomerasa genetika   MeSH
• telomery metabolismus   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• telomerasa MeSH

Telomerase is a ribonucleoprotein enzyme which elongates the G-rich strand of telomeric DNA to compensate for the progressive reduction in its length due to incomplete replication of chromosome ends, which in human somatic cells leads to cell cycle arrest upon shortening of telomeres to a critical length. To examine the possible involvement of telomerase in metabolism of plant genetic material, we used cells of Nicotiana tabacum strain TBY-2, a stable long-term culture which has kept a constant pattern of restriction fragments from chromosome termini during its 6 month period of cultivation in our laboratory. In a direct assay for telomerase, a 5' end-labeled plant telomeric oligonucleotide 5' (TTTAGGG)(3')6 was elongated in a TBY-2 cell extract, showing a pausing pattern which is a characteristic feature of telomerases from other organisms. The elongation was inhibited by RNase A pretreatment of the extract. We conclude that plant cells possess telomerase which is used for maintenance of their telomeres.

• MeSH
• buněčné linie MeSH
• DNA rostlinná chemie   MeSH
• elektroforéza v polyakrylamidovém gelu MeSH
• jedovaté rostliny * MeSH
• molekulární sekvence - údaje MeSH
• pankreatická ribonukleasa metabolismus   MeSH
• sekvence nukleotidů MeSH
• tabák enzymologie   genetika   MeSH
• telomerasa metabolismus   MeSH
• telomery chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA rostlinná MeSH
• pankreatická ribonukleasa MeSH
• telomerasa MeSH

Telomerase is an enzyme that adds repeats of DNA sequences to the ends of chromosomes, thereby preventing their shortening. Telomerase activity is associated with proliferative status of cells, organismal development, and aging. We report an analysis of telomerase activity and telomere length in the honeybee, Apis mellifera. Telomerase activity was found to be regulated in a development and caste-specific manner. During the development of somatic tissues of larval drones and workers, telomerase activity declined to 10 % of its level in embryos and remained low during pupal and adult stages but was upregulated in testes of late pupae, where it reached 70 % of the embryo level. Upregulation of telomerase activity was observed in the ovaries of late pupal queens, reaching 160 % of the level in embryos. Compared to workers and drones, queens displayed higher levels of telomerase activity. In the third larval instar of queens, telomerase activity reached the embryo level, and an enormous increase was observed in adult brains of queens, showing a 70-fold increase compared to a brain of an adult worker. Southern hybridization of terminal TTAGG fragments revealed a high variability of telomeric length between different individuals, although the same pattern of hybridization signals was observed in different tissues of each individual.

• Klíčová slova
• Apis mellifera, Insects, Longevity, Telomerase, Telomere,
• MeSH
• chromozomy hmyzu genetika   metabolismus   MeSH
• hmyzí proteiny genetika   metabolismus   MeSH
• homeostáza telomer fyziologie   MeSH
• telomerasa genetika   metabolismus   MeSH
• telomery genetika   metabolismus   MeSH
• včely genetika   metabolismus   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• hmyzí proteiny MeSH
• telomerasa MeSH

Kings and queens of termites, like queens of other advanced eusocial insects, are endowed with admirable longevity, which dramatically exceeds the life expectancies of their non-reproducing nest-mates and related solitary insects. In the quest to find the mechanisms underlying the longevity of termite reproductives, we focused on somatic maintenance mediated by telomerase. This ribonucleoprotein is well established for pro-longevity functions in vertebrates, thanks primarily to its ability of telomere extension. However, its participation in lifespan regulation of insects, including the eusocial taxa, remains understudied. Here, we report a conspicuous increase of telomerase abundance and catalytic activity in the somatic organs of primary and secondary reproductives of the termite Prorhinotermes simplex and confirm a similar pattern in two other termite species. These observations stand in contrast with the telomerase downregulation characteristic for most adult somatic tissues in vertebrates and also in solitary insects and non-reproducing castes of termites. At the same time, we did not observe caste-specific differences in telomere lengths that might explain the differential longevity of termite castes. We conclude that although the telomerase activation in termite reproductives is in line with the broadly assumed association between telomerase and longevity, its direct phenotypic impact remains to be elucidated.

• Klíčová slova
• kings and queens, longevity, social insects, telomerase, telomeres, termites,
• MeSH
• dlouhověkost MeSH
• Isoptera * MeSH
• rozmnožování MeSH
• telomerasa * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• telomerasa * MeSH

To elucidate the molecular nature of evolutionary changes of telomeres in the plant order Asparagales, we aimed to characterize telomerase RNA subunits (TRs) in these plants. The unusually long telomere repeat unit in Allium plants (12 nt) allowed us to identify TRs in transcriptomic data of representative species of the Allium genus. Orthologous TRs were then identified in Asparagales plants harbouring telomere DNA composed of TTAGGG (human type) or TTTAGGG (Arabidopsis-type) repeats. Further, we identified TRs across the land plant phylogeny, including common model plants, crop plants, and plants with unusual telomeres. Several lines of functional testing demonstrate the templating telomerase function of the identified TRs and disprove a functionality of the only previously reported plant telomerase RNA in Arabidopsis thaliana. Importantly, our results change the existing paradigm in plant telomere biology which has been based on the existence of a relatively conserved telomerase reverse transcriptase subunit (TERT) associating with highly divergent TRs even between closely related plant taxa. The finding of a monophyletic origin of genuine TRs across land plants opens the possibility to identify TRs directly in transcriptomic or genomic data and/or predict telomere sequences synthesized according to the respective TR template region.

• MeSH
• Allium genetika   MeSH
• Arabidopsis genetika   MeSH
• chřestotvaré genetika   MeSH
• fylogeneze * MeSH
• genom rostlinný genetika   MeSH
• lidé MeSH
• molekulární evoluce * MeSH
• RNA genetika   MeSH
• telomerasa genetika   MeSH
• telomery genetika   MeSH
• vyšší rostliny genetika   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• RNA MeSH
• telomerasa MeSH
• telomerase RNA MeSH Prohlížeč

Most eukaryotic organisms employ a telomerase complex for the maintenance of chromosome ends. The core of this complex is composed of telomerase reverse transcriptase (TERT) and telomerase RNA (TR) subunits. The TERT reverse transcriptase (RT) domain synthesises telomeric DNA using the TR template sequence. The other TERT domains contribute to this process in different ways. In particular, the TERT RNA-binding domain (TRBD) interacts with specific TR motif(s). Using a yeast 3-hybrid system, we show the critical role of Arabidopsis thaliana (At) TRBD and embryophyta-conserved KRxR motif in the unstructured linker preceding the TRBD domain for binding to the recently identified AtTR subunit. We also show the essential role of the predicted P4 stem and pseudoknot AtTR structures and provide evidence for the binding of AtTRBD to pseudoknot and KRxR motif stabilising interaction with the P4 stem structure. Our results thus provide the first insight into the core part of the plant telomerase complex.

• Klíčová slova
• A.thaliana telomerase, AtTERT, AtTR, Protein-RNA interactions, Yeast three-hybrid,
• MeSH
• Arabidopsis * genetika   enzymologie   MeSH
• konformace nukleové kyseliny MeSH
• proteiny huseníčku * genetika   metabolismus   chemie   MeSH
• RNA rostlin genetika   metabolismus   MeSH
• RNA metabolismus   genetika   MeSH
• techniky dvojhybridového systému MeSH
• telomerasa * genetika   metabolismus   chemie   MeSH
• vazba proteinů MeSH
• Publikační typ
• časopisecké články MeSH

The activity of telomerase in plant cells is precisely regulated in response to changes in cell division rate. To explore this regulatory mechanism, the effect on telomerase activity of protein extracts from nuclei of telomerase-negative tissues was examined. An inhibition of telomerase activity was found which was species-non-specific. This inhibition was due to proteins which form salt-stable, sequence-specific complexes with the G-rich telomeric strand and reduce its accessibility, as shown by gel retardation and by terminal transferase (TdT) extension of G-rich telomeric and non-telomeric (substrate) primers. A 40 kDa polypeptide was detected by SDS-PAGE after cross-linking the complex formed by extracts from tobacco leaf nuclei. Such proteins may be involved in regulation of telomerase activity in plants.

• MeSH
• buněčné jádro metabolismus   MeSH
• DNA vazebné proteiny farmakologie   MeSH
• jedovaté rostliny MeSH
• rostlinné extrakty farmakologie   MeSH
• rostliny enzymologie   ultrastruktura   MeSH
• substrátová specifita MeSH
• tabák MeSH
• telomerasa antagonisté a inhibitory   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA vazebné proteiny MeSH
• rostlinné extrakty MeSH
• telomerasa MeSH

Telomerase, telomeric DNA and associated proteins together represent a complex, finely tuned and functionally conserved mechanism that ensures genome integrity by protecting and maintaining chromosome ends. Changes in its components can threaten an organism's viability. Nevertheless, molecular innovation in telomere maintenance has occurred multiple times during eukaryote evolution, giving rise to species/taxa with unusual telomeric DNA sequences, telomerase components or telomerase-independent telomere maintenance. The central component of telomere maintenance machinery is telomerase RNA (TR) as it templates telomere DNA synthesis, its mutation can change telomere DNA and disrupt its recognition by telomere proteins, thereby leading to collapse of their end-protective and telomerase recruitment functions. Using a combination of bioinformatic and experimental approaches, we examine a plausible scenario of evolutionary changes in TR underlying telomere transitions. We identified plants harbouring multiple TR paralogs whose template regions could support the synthesis of diverse telomeres. In our hypothesis, formation of unusual telomeres is associated with the occurrence of TR paralogs that can accumulate mutations, and through their functional redundancy, allow for the adaptive evolution of the other telomere components. Experimental analyses of telomeres in the examined plants demonstrate evolutionary telomere transitions corresponding to TR paralogs with diverse template regions.

• Klíčová slova
• evolution, land plants, mechanism of telomere transitions, telomerase RNA paralogs, unusual telomere DNA,
• MeSH
• RNA genetika   metabolismus   MeSH
• rostliny metabolismus   MeSH
• telomerasa * genetika   metabolismus   MeSH
• telomery genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• RNA MeSH
• telomerasa * MeSH
• telomerase RNA MeSH Prohlížeč