Two means of transcriptional reactivation within heterochromatin

Probst, Aline V.; Fransz, Paul; Paszkowski, Jerzy; Scheid, Ortrun Mittelsten

doi:10.1046/j.1365-313x.2003.01667.x

Cited by 136 publications

(127 citation statements)

References 40 publications

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“…Surprisingly, images obtained by fluorescent in situ hybridization with probes specific to centromeric 180-bp repeats appear to be very similar for the met1 and WT (Fig. 3D), which is in contrast to the ddm1 (decrease in DNA methylation 1) mutant, where centromeric DNA disperses (13,23). The complete depletion of methylated CpGs and drastic reduction of H3K9 Me in the met1 strain suggest that both modifications are dispensable for maintaining the compact, heterochromatic structures enclosing centromeric DNA.…”

Section: Resultsmentioning

confidence: 91%

Erasure of CpG methylation in Arabidopsis alters patterns of histone H3 methylation in heterochromatin

Tariq

Saze

Probst

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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274

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In mammals and plants, formation of heterochromatin is associated with hypermethylation of DNA at CpG sites and histone H3 methylation at lysine 9. Previous studies have revealed that maintenance of DNA methylation in Neurospora and Arabidopsis requires histone H3 methylation. A feedback loop from DNA methylation to histone methylation, however, is less understood. Its recent examination in Arabidopsis with a partial loss of function in DNA methyltransferase 1 (responsible for maintenance of CpG methylation) yielded conflicting results. Here we report that complete removal of CpG methylation in an Arabidopsis mutant null for DNA maintenance methyltransferase results in a clear loss of histone H3 methylation at lysine 9 in heterochromatin and also at heterochromatic loci that remain transcriptionally silent. Surprisingly, these dramatic alterations are not reflected in heterochromatin relaxation.

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Section: Resultsmentioning

confidence: 91%

Erasure of CpG methylation in Arabidopsis alters patterns of histone H3 methylation in heterochromatin

Tariq

Saze

Probst

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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274

220

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“…These observations are compatible with a model in which etiolated cotyledons with decondensed heterochromatin escape an initial poorly efficient silencing process, which would be compensated by a second more efficient and DNA methylation-dependent system. Although we cannot exclude that expression of the LTR AtGP1 transgene could also be controlled by trans-acting factors superimposing RdDM-based repression, two-layered silencing has nonetheless been identified using mutant plants for the Morpheus' molecule1 (MOM1) putative helicase (70,71) and for the MORC ATPase (72), which are both believed to be involved in DNA or chromosomal remodeling processes. Based on these findings, it is possible that some heterochromatin loci might be sensitive to a position-dependent or condensation-dependent regulatory control during cotyledon development, a process that may relate to the observed relationship between chromatin-based repression and subnuclear positioning of multicopy transgenes (73) and of the FLC gene (66,74).…”

Section: Discussion Nuclear Rearrangements and Increased Transcriptiomentioning

confidence: 99%

Light signaling controls nuclear architecture reorganization during seedling establishment

Bourbousse

Mestiri

Zabulon

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

103

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The spatial organization of chromatin can be subject to extensive remodeling in plant somatic cells in response to developmental and environmental signals. However, the mechanisms controlling these dynamic changes and their functional impact on nuclear activity are poorly understood. Here, we determined that light perception triggers a switch between two different nuclear architectural schemes during Arabidopsis postembryonic development. Whereas progressive nucleus expansion and heterochromatin rearrangements in cotyledon cells are achieved similarly under light and dark conditions during germination, the later steps that lead to mature nuclear phenotypes are intimately associated with the photomorphogenic transition in an organ-specific manner. The light signaling integrators DE-ETIOLATED 1 and CONSTITUTIVE PHOTOMORPHOGENIC 1 maintain heterochromatin in a decondensed state in etiolated cotyledons. In contrast, under light conditions cryptochrome-mediated photoperception releases nuclear expansion and heterochromatin compaction within conspicuous chromocenters. For all tested loci, chromatin condensation during photomorphogenesis does not detectably rely on DNA methylation-based processes. Notwithstanding, the efficiency of transcriptional gene silencing may be impacted during the transition, as based on the reactivation of transposable element-driven reporter genes. Finally, we report that global engagement of RNA polymerase II in transcription is highly increased under light conditions, suggesting that cotyledon photomorphogenesis involves a transition from globally quiescent to more active transcriptional states. Given these findings, we propose that light-triggered changes in nuclear architecture underlie interplays between heterochromatin reorganization and transcriptional reprogramming associated with the establishment of photosynthesis. plant development | photomorphogenesis | light signaling | nuclear organization | heterochromatin C hromatin allows dense packaging of chromosomal DNA into a small and constrained nuclear space. It also serves as a structural framework for regulatory processes that control the functional status of genome domains with variable sizes, notably by dynamically influencing the subnuclear partitioning of generich and repeat-rich domains within euchromatic and heterochromatic regions, respectively (reviewed in refs. 1-3). These chromatin-based processes impact plasticity in the regulation of nuclear programs during both vegetative and reproductive phases of the plant life cycle (recently reviewed in refs. 4-8). In many cases, such events combine local chromatin variations with prominent changes in nuclear architecture and higher-order chromatin organization.Spatial chromatin organization is well exemplified by the extreme cases of transcriptionally silent chromocenters that contain the majority of ribosomal DNA repeats, such as the (peri)centromeric domains of mice and several plant species that include transposable elements (TE) and non-TE repeated sequences (9,

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“…Although MOM1 mediates H3K9 dimethylation at a few target loci shared by RdDM and MOM1 (Numa et al, 2010), the involvement of MOM1 in transcriptional silencing at the whole-genome level is independent of changes not only in DNA methylation but also in histone H3K9 dimethylation (Probst et al, 2003;Vaillant et al, 2006). To understand how MOM1 contributes to transcriptional silencing, a series of truncated MOM1 sequences were transformed into the mom1 mutant for complementation assays (Caikovski et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

The SUMO E3 Ligase-Like Proteins PIAL1 and PIAL2 Interact with MOM1 and Form a Novel Complex Required for Transcriptional Silencing

et al. 2016

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The mechanism by which MORPHEUS' MOLECULE1 (MOM1) contributes to transcriptional gene silencing has remained elusive since the gene was first identified and characterized. Here, we report that two Arabidopsis thaliana PIAS (PROTEIN INHIBITOR OF ACTIVATED STAT)-type SUMO E3 ligase-like proteins, PIAL1 and PIAL2, function redundantly to mediate transcriptional silencing at MOM1 target loci. PIAL1 and PIAL2 physically interact with each other and with MOM1 to form a high molecular mass complex. In the absence of either PIAL2 or MOM1, the formation of the high molecular mass complex is disrupted. We identified a previously uncharacterized IND (interacting domain) in PIAL1 and PIAL2 and demonstrated that IND directly interacts with MOM1. The CMM2 (conserved MOM1 motif 2) domain of MOM1 was previously shown to be required for the dimerization of MOM1. We demonstrated that the CMM2 domain is also required for the interaction of MOM1 with PIAL1 and PIAL2. We found that although PIAL2 has SUMO E3 ligase activity, the activity is dispensable for PIAL2's function in transcriptional silencing. This study suggests that PIAL1 and PIAl2 act as components of the MOM1-containing complex to mediate transcriptional silencing at heterochromatin regions.

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Two means of transcriptional reactivation within heterochromatin

Cited by 136 publications

References 40 publications

Erasure of CpG methylation in Arabidopsis alters patterns of histone H3 methylation in heterochromatin

Erasure of CpG methylation in Arabidopsis alters patterns of histone H3 methylation in heterochromatin

Light signaling controls nuclear architecture reorganization during seedling establishment

The SUMO E3 Ligase-Like Proteins PIAL1 and PIAL2 Interact with MOM1 and Form a Novel Complex Required for Transcriptional Silencing

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