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.
- 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
Characterization of protein-protein and protein-DNA interactions is critical to understand mechanisms governing the biology of cells. Here we describe optimized methods and their mutual combinations for this purpose: bimolecular fluorescence complementation (BiFC), co-immunoprecipitation (Co-IP), yeast two-hybrid systems (Y2H), and chromatin immunoprecipitation (ChIP). These improved protocols detect trimeric complexes in which two proteins of interest interact indirectly via a protein sandwiched between them. They also allow isolation of low-abundance chromatin proteins and confirmation that proteins of interest are associated with specific DNA sequences, for example telomeric tracts. Here we describe these methods and their application to map interactions of several telomere- and telomerase-associated proteins and to purify a sufficient amount of chromatin from Arabidopsis thaliana for further investigations (e.g., next-generation sequencing, hybridization).
- MeSH
- Arabidopsis genetika metabolismus MeSH
- buněčné jádro metabolismus MeSH
- chromatin metabolismus MeSH
- chromatinová imunoprecipitace metody MeSH
- DNA rostlinná metabolismus MeSH
- DNA vazebné proteiny izolace a purifikace metabolismus MeSH
- imunoprecipitace metody MeSH
- mapování interakce mezi proteiny metody MeSH
- optické zobrazování metody MeSH
- proteiny huseníčku genetika metabolismus MeSH
- techniky dvojhybridového systému MeSH
- telomerasa metabolismus MeSH
- telomery metabolismus MeSH
- vazba proteinů MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Telomerase maturation and recruitment to telomeres is regulated by several telomerase- and telomere-associated proteins. Among a number of proteins, human Pontin and Reptin play critical roles in telomerase biogenesis. Here we characterized plant orthologues of Pontin and Reptin, RuvBL1 and RuvBL2a, respectively, and show association of Arabidopsis thaliana RuvBL1 (AtRuvBL1) with the catalytic subunit of telomerase (AtTERT) in the nucleolus in vivo. In contrast to mammals, interactions between AtTERT and AtRuvBL proteins in A. thaliana are not direct and they are rather mediated by one of the Arabidopsis thaliana Telomere Repeat Binding (AtTRB) proteins. We further show that plant orthologue of dyskerin, named AtCBF5, is indirectly associated with AtTRB proteins but not with the AtRuvBL proteins in the plant nucleus/nucleolus, and interacts with the Protection of telomere 1 (AtPOT1a) in the nucleolus or cytoplasmic foci. Our genome-wide phylogenetic analyses identify orthologues in RuvBL protein family within the plant kingdom. Dysfunction of AtRuvBL genes in heterozygous T-DNA insertion A. thaliana mutants results in reduced telomerase activity and indicate the involvement of AtRuvBL in plant telomerase biogenesis.
- MeSH
- Arabidopsis genetika metabolismus MeSH
- buněčné jadérko metabolismus MeSH
- DNA-helikasy metabolismus MeSH
- fylogeneze MeSH
- jaderné proteiny MeSH
- katalytická doména MeSH
- proteiny huseníčku genetika metabolismus MeSH
- proteiny vázající RNA metabolismus MeSH
- proteiny vázající telomery metabolismus MeSH
- telomerasa metabolismus MeSH
- telomery metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Recently we characterised TRB1, a protein from a single-myb-histone family, as a structural and functional component of telomeres in Arabidopsis thaliana. TRB proteins, besides their ability to bind specifically to telomeric DNA using their N-terminally positioned myb-like domain of the same type as in human shelterin proteins TRF1 or TRF2, also possess a histone-like domain which is involved in protein-protein interactions e.g., with POT1b. Here we set out to investigate the genome-wide localization pattern of TRB1 to reveal its preferential sites of binding to chromatin in vivo and its potential functional roles in the genome-wide context. Our results demonstrate that TRB1 is preferentially associated with promoter regions of genes involved in ribosome biogenesis, in addition to its roles at telomeres. This preference coincides with the frequent occurrence of telobox motifs in the upstream regions of genes in this category, but it is not restricted to the presence of a telobox. We conclude that TRB1 shows a specific genome-wide distribution pattern which suggests its role in regulation of genes involved in biogenesis of the translational machinery, in addition to its preferential telomeric localization.
- MeSH
- Arabidopsis genetika metabolismus MeSH
- genová knihovna MeSH
- histony metabolismus MeSH
- molekulární sekvence - údaje MeSH
- nukleotidové motivy MeSH
- promotorové oblasti (genetika) genetika MeSH
- proteiny huseníčku genetika metabolismus MeSH
- proteiny vázající telomery genetika metabolismus MeSH
- proteosyntéza MeSH
- ribozomy genetika MeSH
- sekvence nukleotidů MeSH
- sekvenční analýza DNA MeSH
- sekvenční analýza hybridizací s uspořádaným souborem oligonukleotidů MeSH
- telomery metabolismus MeSH
- vazba proteinů MeSH
- výpočetní biologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem 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.
Telobox is a Myb-related DNA-binding domain which is present in a number of yeast, plant and animal proteins. Its capacity to bind preferentially double-stranded telomeric DNA has been used in numerous studies to search for candidate telomeric proteins in various organisms, including plants. Here we provide an overview of these studies with a special emphasis on plants, where a specific subfamily of the proteins possessing the N-terminally positioned telobox is present in addition to more common C-terminal telobox proteins. We further demonstrate the presence of a telobox protein (CpTBP1) in Cestrum parqui, a plant lacking typical telomeres and telomerase. The protein shows nuclear localisation and association with chromatin. The role of this protein in ancestral and current telomere structure is discussed in the evolutionary context. Altogether, the present overview shows the importance of the telobox domain in a search for candidate telomere proteins but at the same time warns against oversimplified identification of any telobox protein with telomere structure without appropriate evidence of its telomeric localisation and function.
- MeSH
- Cestrum metabolismus MeSH
- DNA vazebné proteiny genetika metabolismus MeSH
- DNA metabolismus MeSH
- fylogeneze MeSH
- molekulární sekvence - údaje MeSH
- proteiny vázající telomery genetika metabolismus MeSH
- rostlinné proteiny chemie metabolismus MeSH
- sekvence aminokyselin MeSH
- telomery metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
Chromosome stability is conditioned by functional chromatin structure of chromosome ends - telomeres. Organisation and regulation of telomere maintenance represent a complex process whose details still remain enigmatic, especially in plants. Several telomere-binding or telomere-associated proteins and distinct epigenetic marks have been shown to influence telomere length and telomerase activity. HMGB proteins play important role in dynamic changes of chromatin structure and are involved in regulation of cellular processes of key importance, such as replication, transcription, recombination and DNA-repair. HMGB proteins in plants are more diversified than in other eukaryotes. Here, we summarise the roles of plant HMGB proteins in regulation of chromatin structure and dynamics and report on the newly identified role of AtHMGB1 protein in the regulation of plant telomere length. Astonishingly, contrary to mice mHMGB1 homologue, AtHMGB1 does not affect telomerase activity and AtHMGB1 loss or overexpression does not cause any obvious changes in chromatin architecture.
