Telomeres are essential structures formed from satellite DNA repeats at the ends of chromosomes in most eukaryotes. Satellite DNA repeat sequences are useful markers for karyotyping, but have a more enigmatic role in the eukaryotic cell. Much work has been done to investigate the structure and arrangement of repetitive DNA elements in classical models with implications for species evolution. Still more is needed until there is a complete picture of the biological function of DNA satellite sequences, particularly when considering non-model organisms. Celebrating Gregor Mendel's anniversary by going to the roots, this review is designed to inspire and aid new research into telomeres and satellites with a particular focus on non-model organisms and accessible experimental and in silico methods that do not require specialized equipment or expensive materials. We describe how to identify telomere (and satellite) repeats giving many examples of published (and some unpublished) data from these techniques to illustrate the principles behind the experiments. We also present advice on how to perform and analyse such experiments, including details of common pitfalls. Our examples are a selection of recent developments and underexplored areas of research from the past. As a nod to Mendel's early work, we use many examples from plants and insects, especially as much recent work has expanded beyond the human and yeast models traditional in telomere research. We give a general introduction to the accepted knowledge of telomere and satellite systems and include references to specialized reviews for the interested reader.

• Klíčová slova
• FISH, NGS, TRAP, eukaryotic tree of life, interstitial telomere sequences, retroelements, satellite, subtelomere structure, telomerase RNA, telomere evolution,
• MeSH
• DNA MeSH
• lidé MeSH
• repetitivní sekvence nukleových kyselin MeSH
• satelitní DNA * MeSH
• sekvence nukleotidů MeSH
• telomery * genetika   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• DNA MeSH
• satelitní DNA * MeSH

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

Telomeres are basic structures of eukaryote genomes. They distinguish natural chromosome ends from double-stranded breaks in DNA and protect chromosome ends from degradation or end-to-end fusion with other chromosomes. Telomere sequences are usually tandemly arranged minisatellites, typically following the formula (TxAyGz)n. Although they are well conserved across large groups of organisms, recent findings in plants imply that their diversity has been underestimated. Changes in telomeres are of enormous evolutionary importance as they can affect whole-genome stability. Even a small change in the telomere motif of each repeat unit represents an important interference in the system of sequence-specific telomere binding proteins. Here, we provide an overview of telomere sequences, considering the latest phylogenomic evolutionary framework of plants in the broad sense (Archaeplastida), in which new telomeric sequences have recently been found in diverse and economically important families such as Solanaceae and Amaryllidaceae. In the family Lentibulariaceae and in many groups of green algae, deviations from the typical plant telomeric sequence have also been detected recently. Ancestry and possible homoplasy in telomeric motifs, as well as extant gaps in knowledge are discussed. With the increasing availability of genomic approaches, it is likely that more telomeric diversity will be uncovered in the future. We also discuss basic methods used for telomere identification and we explain the implications of the recent discovery of plant telomerase RNA on further research about the role of telomerase in eukaryogenesis or on the molecular causes and consequences of telomere variability.

• Klíčová slova
• Allium, Cestrum, Genlisea, circular chromosomes, green algae, linear chromosomes, telomerase, telomeres,
• Publikační typ
• časopisecké články MeSH
• přehledy 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

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

Tandem arrays of TTAGG repeats show a highly conserved location at the telomeres across the phylogenetic tree of arthropods. In giant water bugs Belostoma, the chromosome number changed during speciation by fragmentation of the single ancestral X chromosome, resulting in a multiple sex chromosome system. Several autosome-autosome fusions and a fusion between the sex chromosome pair and an autosome pair resulted in the reduced number in several species. We mapped the distribution of telomeric sequences and interstitial telomeric sequences (ITSs) in Belostoma candidulum (2n = 12 + XY/XX; male/female), B. dentatum (2n = 26 + X1X2Y/X1X1X2X2), B. elegans (2n = 26 + X1X2Y/X1X1X2X2), B. elongatum (2n = 26 + X1X2Y/X1X1X2X2), B. micantulum (2n = 14 + XY/XX), and B. oxyurum (2n = 6 + XY/XX) by FISH with the (TTAGG) n probes. Hybridization signals confirmed the presence of TTAGG repeats in the telomeres of all species examined. The three species with reduced chromosome numbers showed additional hybridization signals in interstitial positions, indicating the occurrence of ITS. From the comparison of all species here analyzed, we observed inverse relationships between chromosome number and chromosome size, and between presence/absence of ITS and chromosome number. The ITS distribution between these closely related species supports the hypothesis that several telomere-telomere fusions of the chromosomes from an ancestral diploid chromosome number 2n = 26 + XY/XX played a major role in the karyotype evolution of Belostoma. Consequently, our study provide valuable features that can be used to understand the karyotype evolution, may contribute to a better understanding of taxonomic relationships, and also elucidate the high plasticity of nuclear genomes at the chromosomal level during the speciation processes.

• Klíčová slova
• chromosomal fusion, interstitial telomeric repeats, karyotype evolution, telomere FISH,
• Publikační typ
• časopisecké články MeSH

In all eukaryotes, the highly repeated 35S ribosomal DNA (rDNA) sequences encoding 18S-5.8S-26S ribosomal RNA (rRNA) typically show high levels of intragenomic uniformity due to homogenisation processes, leading to concerted evolution of 35S rDNA repeats. Here, we compared 35S rDNA divergence in several seed plants using next generation sequencing and a range of molecular and cytogenetic approaches. Most species showed similar 35S rDNA homogeneity indicating concerted evolution. However, Cycas revoluta exhibits an extraordinary diversity of rDNA repeats (nucleotide sequence divergence of different copies averaging 12 %), influencing both the coding and non-coding rDNA regions nearly equally. In contrast, its rRNA transcriptome was highly homogeneous suggesting that only a minority of genes (<20 %) encode functional rRNA. The most common SNPs were C > T substitutions located in symmetrical CG and CHG contexts which were also highly methylated. Both functional genes and pseudogenes appear to cluster on chromosomes. The extraordinary high levels of 35S rDNA diversity in C. revoluta, and probably other species of cycads, indicate that the frequency of repeat homogenisation has been much lower in this lineage, compared with all other land plant lineages studied. This has led to the accumulation of methylation-driven mutations and pseudogenisation. Potentially, the reduced homology between paralogs prevented their elimination by homologous recombination, resulting in long-term retention of rDNA pseudogenes in the genome.

• Klíčová slova
• Concerted evolution, Cycadales, Cytosine methylation, Living fossil, rDNA,
• MeSH
• Cycas genetika   MeSH
• DNA rostlinná genetika   MeSH
• genetická transkripce genetika   MeSH
• hybridizace in situ fluorescenční MeSH
• jednonukleotidový polymorfismus genetika   MeSH
• mezerníky ribozomální DNA genetika   MeSH
• ribozomální DNA genetika   MeSH
• RNA ribozomální 18S genetika   MeSH
• RNA ribozomální 5.8S genetika   MeSH
• RNA ribozomální genetika   MeSH
• sekvence nukleotidů MeSH
• sekvenční analýza DNA MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA rostlinná MeSH
• mezerníky ribozomální DNA MeSH
• ribozomální DNA MeSH
• RNA ribozomální 18S MeSH
• RNA ribozomální 5.8S MeSH
• RNA ribozomální MeSH
• RNA, ribosomal, 26S MeSH Prohlížeč

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

Telomeres are nucleoprotein structures that distinguish native chromosomal ends from double-stranded breaks. They are maintained by telomerase that adds short G-rich telomeric repeats at chromosomal ends in most eukaryotes and determines the TnAmGo sequence of canonical telomeres. We employed an experimental approach that was based on detection of repeats added by telomerase to identify the telomere sequence type forming the very ends of chromosomes. Our previous studies that focused on the algal order Chlamydomonadales revealed several changes in telomere motifs that were consistent with the phylogeny and supported the concept of the Arabidopsis-type sequence being the ancestral telomeric motif for green algae. In addition to previously described independent transitions to the Chlamydomonas-type sequence, we report that the ancestral telomeric motif was replaced by the human-type sequence in the majority of algal species grouped within a higher order clade, Caudivolvoxa. The Arabidopsis-type sequence was apparently retained in the Polytominia clade. Regarding the telomere sequence, the Chlorogonia clade within Caudivolvoxa bifurcates into two groups, one with the human-type sequence and the other group with the Arabidopsis-type sequence that is solely formed by the Chlorogonium species. This suggests that reversion to the Arabidopsis-type telomeric motif occurred in the common ancestral Chlorogonium species. The human-type sequence is also synthesized by telomerases of algal strains from Arenicolinia, Dunaliellinia and Stephanosphaerinia, except a distinct subclade within Stephanosphaerinia, where telomerase activity was not detected and a change to an unidentified telomeric motif might arise. We discuss plausible reasons why changes in telomeric motifs were tolerated during evolution of green algae.

• Klíčová slova
• 18S rDNA phylogeny, Green algae, TRAP, Telomerase activity, Telomere evolution,
• MeSH
• aminokyselinové motivy genetika   MeSH
• fylogeneze MeSH
• repetitivní sekvence nukleových kyselin genetika   MeSH
• ribozomální DNA genetika   MeSH
• RNA ribozomální 18S genetika   MeSH
• sekvence nukleotidů MeSH
• sekvenční analýza DNA MeSH
• telomerasa genetika   MeSH
• telomery genetika   MeSH
• Volvocida genetika   MeSH
• zkracování telomer genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ribozomální DNA MeSH
• RNA ribozomální 18S MeSH
• 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