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HDA6 Regulates Locus-Directed
Heterochromatin Silencing in Cooperation with MET1


Heterochromatin silencing is pivotal for genome stability in eukaryotes. In

Arabidopsis, a plant-specific mechanism called

RNA–directed DNA methylation (RdDM) is involved in heterochromatin

silencing. Histone deacetylase HDA6 has been identified as a component of such

machineries; however, its endogenous targets and the silencing mechanisms have

not been analyzed globally. In this study, we investigated the silencing

mechanism mediated by HDA6. Genome-wide transcript profiling revealed that the

loci silenced by HDA6 carried sequences corresponding to the RDR2-dependent

24-nt siRNAs, however their transcript levels were mostly unaffected in the

rdr2 mutant. Strikingly, we observed significant overlap of

genes silenced by HDA6 to those by the CG DNA methyltransferase MET1.

Furthermore, regardless of dependence on RdDM pathway, HDA6 deficiency resulted

in loss of heterochromatic epigenetic marks and aberrant enrichment for

euchromatic marks at HDA6 direct targets, along with ectopic expression of these

loci. Acetylation levels increased significantly in the hda6

mutant at all of the lysine residues in the H3 and H4 N-tails, except H4K16.

Interestingly, we observed two different CG methylation statuses in the

hda6 mutant. CG methylation was sustained in the

hda6 mutant at some HDA6 target loci that were surrounded

by flanking DNA–methylated regions. In contrast, complete loss of CG

methylation occurred in the hda6 mutant at the HDA6 target loci

that were isolated from flanking DNA methylation. Regardless of CG methylation

status, CHG and CHH methylation were lost and transcriptional derepression

occurred in the hda6 mutant. Furthermore, we show that HDA6

binds only to its target loci, not the flanking methylated DNA, indicating the

profound target specificity of HDA6. We propose that HDA6 regulates

locus-directed heterochromatin silencing in cooperation with MET1, possibly

recruiting MET1 to specific loci, thus forming the foundation of silent

chromatin structure for subsequent non-CG methylation.


Vyšlo v časopise: HDA6 Regulates Locus-Directed Heterochromatin Silencing in Cooperation with MET1. PLoS Genet 7(4): e32767. doi:10.1371/journal.pgen.1002055
Kategorie: Research Article
prolekare.web.journal.doi_sk: https://doi.org/10.1371/journal.pgen.1002055

Souhrn

Heterochromatin silencing is pivotal for genome stability in eukaryotes. In

Arabidopsis, a plant-specific mechanism called

RNA–directed DNA methylation (RdDM) is involved in heterochromatin

silencing. Histone deacetylase HDA6 has been identified as a component of such

machineries; however, its endogenous targets and the silencing mechanisms have

not been analyzed globally. In this study, we investigated the silencing

mechanism mediated by HDA6. Genome-wide transcript profiling revealed that the

loci silenced by HDA6 carried sequences corresponding to the RDR2-dependent

24-nt siRNAs, however their transcript levels were mostly unaffected in the

rdr2 mutant. Strikingly, we observed significant overlap of

genes silenced by HDA6 to those by the CG DNA methyltransferase MET1.

Furthermore, regardless of dependence on RdDM pathway, HDA6 deficiency resulted

in loss of heterochromatic epigenetic marks and aberrant enrichment for

euchromatic marks at HDA6 direct targets, along with ectopic expression of these

loci. Acetylation levels increased significantly in the hda6

mutant at all of the lysine residues in the H3 and H4 N-tails, except H4K16.

Interestingly, we observed two different CG methylation statuses in the

hda6 mutant. CG methylation was sustained in the

hda6 mutant at some HDA6 target loci that were surrounded

by flanking DNA–methylated regions. In contrast, complete loss of CG

methylation occurred in the hda6 mutant at the HDA6 target loci

that were isolated from flanking DNA methylation. Regardless of CG methylation

status, CHG and CHH methylation were lost and transcriptional derepression

occurred in the hda6 mutant. Furthermore, we show that HDA6

binds only to its target loci, not the flanking methylated DNA, indicating the

profound target specificity of HDA6. We propose that HDA6 regulates

locus-directed heterochromatin silencing in cooperation with MET1, possibly

recruiting MET1 to specific loci, thus forming the foundation of silent

chromatin structure for subsequent non-CG methylation.


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