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Chromatin features of plant telomeric sequences at terminal vs. internal positions.

Majerová E, Mandáková T, Vu GT, Fajkus J, Lysak MA, Fojtová M - Front Plant Sci (2014)

Bottom Line: Chromatin of genuine telomeres displayed heterochromatic as well as euchromatic marks, while ITRs were just heterochromatic.Telomeric transcripts TERRA (G-rich) and ARRET (C-rich) were identified in both plants and their levels varied among tissues with a maximum in blossoms.Plants with substantially different proportions of internally and terminally located telomeric repeats are instrumental in clarifying the chromatin status of telomeric repeats at distinct chromosome locations.

View Article: PubMed Central - PubMed

Affiliation: Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology and Faculty of Science, Masaryk University Brno, Czech Republic.

ABSTRACT
Epigenetic mechanisms are involved in regulation of crucial cellular processes in eukaryotic organisms. Data on the epigenetic features of plant telomeres and their epigenetic regulation were published mostly for Arabidopsis thaliana, in which the presence of interstitial telomeric repeats (ITRs) may interfere with genuine telomeres in most analyses. Here, we studied the epigenetic landscape and transcription of telomeres and ITRs in Nicotiana tabacum with long telomeres and no detectable ITRs, and in Ballantinia antipoda with large blocks of pericentromeric ITRs and relatively short telomeres. Chromatin of genuine telomeres displayed heterochromatic as well as euchromatic marks, while ITRs were just heterochromatic. Methylated cytosines were present at telomeres and ITRs, but showed a bias with more methylation toward distal telomere positions and different blocks of B. antipoda ITRs methylated to different levels. Telomeric transcripts TERRA (G-rich) and ARRET (C-rich) were identified in both plants and their levels varied among tissues with a maximum in blossoms. Plants with substantially different proportions of internally and terminally located telomeric repeats are instrumental in clarifying the chromatin status of telomeric repeats at distinct chromosome locations.

No MeSH data available.


Northern blot analysis of telomeric RNA in N. tabacum (A) and B. antipoda (B) tissues. Transcription of C-rich (TERRA) and G-rich (ARRET) telomeric strands occurred at similar levels in both plants. The lowest levels of TERRA and ARRET were detected in floral buds, followed by leaves and mature flowers, where they were shifted toward shorter fragments. Due to the strong hybridization signal in B. antipoda blossom samples, expositions for different time intervals were performed (overnight for leaves and buds, 2 h for blossoms) for TERRA, ARRET and Ba493 probes. EtBr – signal of the 25S ribosomal RNA band at the agarose gel stained by ethidium bromide reflects sample loading. Note, that in none set of samples RNA from blossoms was overloaded.
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Figure 6: Northern blot analysis of telomeric RNA in N. tabacum (A) and B. antipoda (B) tissues. Transcription of C-rich (TERRA) and G-rich (ARRET) telomeric strands occurred at similar levels in both plants. The lowest levels of TERRA and ARRET were detected in floral buds, followed by leaves and mature flowers, where they were shifted toward shorter fragments. Due to the strong hybridization signal in B. antipoda blossom samples, expositions for different time intervals were performed (overnight for leaves and buds, 2 h for blossoms) for TERRA, ARRET and Ba493 probes. EtBr – signal of the 25S ribosomal RNA band at the agarose gel stained by ethidium bromide reflects sample loading. Note, that in none set of samples RNA from blossoms was overloaded.

Mentions: RNA isolated from leaves of B. antipoda and N. tabacum plants was analyzed by northern blotting. Membranes were hybridized either with a radioactively labeled pltel-C probe (CCCTAAA)4, which hybridizes to the G-rich telomeric strand and detects TERRA, or a pltel-G probe (TTTAGGG)4, which hybridizes to the C-rich telomeric strand and detects ARRET. In tobacco, both C-rich and G-rich telomeric transcripts were detected at similar levels (Figure 6A, left lines). Taking into consideration that tobacco has no detectable ITRs (Majerova et al., 2011a), transcription of the G-rich telomeric strand (resulting in ARRET transcripts) can be generated by two possible pathways. According to the first scenario, transcription of the G-rich telomeric strand starts within the telomeres using telomeric repeats or hidden non-telomeric sequences as transcription start sites (TSSs). The second hypothesis assumes synthesis of ARRET directly from TERRA by RNA-dependent RNA polymerases.


Chromatin features of plant telomeric sequences at terminal vs. internal positions.

Majerová E, Mandáková T, Vu GT, Fajkus J, Lysak MA, Fojtová M - Front Plant Sci (2014)

Northern blot analysis of telomeric RNA in N. tabacum (A) and B. antipoda (B) tissues. Transcription of C-rich (TERRA) and G-rich (ARRET) telomeric strands occurred at similar levels in both plants. The lowest levels of TERRA and ARRET were detected in floral buds, followed by leaves and mature flowers, where they were shifted toward shorter fragments. Due to the strong hybridization signal in B. antipoda blossom samples, expositions for different time intervals were performed (overnight for leaves and buds, 2 h for blossoms) for TERRA, ARRET and Ba493 probes. EtBr – signal of the 25S ribosomal RNA band at the agarose gel stained by ethidium bromide reflects sample loading. Note, that in none set of samples RNA from blossoms was overloaded.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4219495&req=5

Figure 6: Northern blot analysis of telomeric RNA in N. tabacum (A) and B. antipoda (B) tissues. Transcription of C-rich (TERRA) and G-rich (ARRET) telomeric strands occurred at similar levels in both plants. The lowest levels of TERRA and ARRET were detected in floral buds, followed by leaves and mature flowers, where they were shifted toward shorter fragments. Due to the strong hybridization signal in B. antipoda blossom samples, expositions for different time intervals were performed (overnight for leaves and buds, 2 h for blossoms) for TERRA, ARRET and Ba493 probes. EtBr – signal of the 25S ribosomal RNA band at the agarose gel stained by ethidium bromide reflects sample loading. Note, that in none set of samples RNA from blossoms was overloaded.
Mentions: RNA isolated from leaves of B. antipoda and N. tabacum plants was analyzed by northern blotting. Membranes were hybridized either with a radioactively labeled pltel-C probe (CCCTAAA)4, which hybridizes to the G-rich telomeric strand and detects TERRA, or a pltel-G probe (TTTAGGG)4, which hybridizes to the C-rich telomeric strand and detects ARRET. In tobacco, both C-rich and G-rich telomeric transcripts were detected at similar levels (Figure 6A, left lines). Taking into consideration that tobacco has no detectable ITRs (Majerova et al., 2011a), transcription of the G-rich telomeric strand (resulting in ARRET transcripts) can be generated by two possible pathways. According to the first scenario, transcription of the G-rich telomeric strand starts within the telomeres using telomeric repeats or hidden non-telomeric sequences as transcription start sites (TSSs). The second hypothesis assumes synthesis of ARRET directly from TERRA by RNA-dependent RNA polymerases.

Bottom Line: Chromatin of genuine telomeres displayed heterochromatic as well as euchromatic marks, while ITRs were just heterochromatic.Telomeric transcripts TERRA (G-rich) and ARRET (C-rich) were identified in both plants and their levels varied among tissues with a maximum in blossoms.Plants with substantially different proportions of internally and terminally located telomeric repeats are instrumental in clarifying the chromatin status of telomeric repeats at distinct chromosome locations.

View Article: PubMed Central - PubMed

Affiliation: Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology and Faculty of Science, Masaryk University Brno, Czech Republic.

ABSTRACT
Epigenetic mechanisms are involved in regulation of crucial cellular processes in eukaryotic organisms. Data on the epigenetic features of plant telomeres and their epigenetic regulation were published mostly for Arabidopsis thaliana, in which the presence of interstitial telomeric repeats (ITRs) may interfere with genuine telomeres in most analyses. Here, we studied the epigenetic landscape and transcription of telomeres and ITRs in Nicotiana tabacum with long telomeres and no detectable ITRs, and in Ballantinia antipoda with large blocks of pericentromeric ITRs and relatively short telomeres. Chromatin of genuine telomeres displayed heterochromatic as well as euchromatic marks, while ITRs were just heterochromatic. Methylated cytosines were present at telomeres and ITRs, but showed a bias with more methylation toward distal telomere positions and different blocks of B. antipoda ITRs methylated to different levels. Telomeric transcripts TERRA (G-rich) and ARRET (C-rich) were identified in both plants and their levels varied among tissues with a maximum in blossoms. Plants with substantially different proportions of internally and terminally located telomeric repeats are instrumental in clarifying the chromatin status of telomeric repeats at distinct chromosome locations.

No MeSH data available.