Project description:In eukaryotes, histone acetylation is a major modification on histone N-terminal tails that is tightly connected to transcriptional activation. HDA6 is a histone deacetylase involved in the transcriptional regulation of genes and transposable elements (TEs) in Arabidopsis thaliana. HDA6 has been shown to participate in several complexes in plants, including a conserved SIN3 complex. Here, we uncover a novel protein complex containing HDA6, several Harbinger transposon-derived proteins (HHP1, SANT1, SANT2, SANT3, and SANT4), and MBD domain-containing proteins (MBD1, MBD2, and MBD4). We show that mutations of all four SANT genes in the sant-null mutant cause increased expression of the flowering repressors FLC, MAF4, and MAF5, resulting in a late flowering phenotype. Transcriptome deep sequencing reveals that while the SANT proteins and HDA6 regulate the expression of largely overlapping sets of genes, TE silencing is unaffected in sant-null mutants. Our global histone H3 acetylation profiling shows that SANT proteins and HDA6 modulate gene expression through deacetylation. Collectively, our findings suggest that Harbinger transposon-derived SANT domain-containing proteins are required for histone deacetylation and flowering time control in plants.
Project description:Histone acetylation is a major epigenetic control mechanism that is tightly linked to the promotion of gene expression. Histone acetylation levels are balanced through the opposing activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Arabidopsis HDAC genes (AtHDACs) compose a large gene family, and distinct phenotypes among AtHDAC mutants reflect the functional specificity of individual AtHDACs. However, the mechanisms underlying this functional diversity are largely unknown. Here, we show that POWERDRESS (PWR), a positive regulator of floral stem cell maintenance, interacts with HDA9 and promotes histone H3 deacetylation possibly by facilitating HDA9 function at target chromatin. The PWR SANT2 domain, which is homologous to that of subunits in animal HDAC complexes, showed specific binding affinity to acetylated histone H3. Three lysine residues (K9, K14 and K27) of H3 retained hyperacetylation status in both pwr and hda9 mutants. Genome wide H3K9 and H3K14 acetylation levels were generally elevated, and a large portion of acetylated targets overlapped between the pwr and hda9 mutants. Comparative analysis revealed a correlation between gene expression and histone H3 acetylation status in the pwr and hda9 mutants. In addition, PWR and HDA9 modulated the AGAMOUS-LIKE 19 (AGL19)-mediated flowering time pathway through histone H3 deacetylation. Finally, PWR was shown to physically interact with HDA9. We therefore propose that PWR acts as a subunit in a complex with HDA9 to negatively regulate the acetylation of specific lysine residues of histone H3 at genomic targets.
Project description:Histone acetylation is a major epigenetic control mechanism that is tightly linked to the promotion of gene expression. Histone acetylation levels are balanced through the opposing activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Arabidopsis HDAC genes (AtHDACs) compose a large gene family, and distinct phenotypes among AtHDAC mutants reflect the functional specificity of individual AtHDACs. However, the mechanisms underlying this functional diversity are largely unknown. Here, we show that POWERDRESS (PWR), a positive regulator of floral stem cell maintenance, interacts with HDA9 and promotes histone H3 deacetylation possibly by facilitating HDA9 function at target chromatin. The PWR SANT2 domain, which is homologous to that of subunits in animal HDAC complexes, showed specific binding affinity to acetylated histone H3. Three lysine residues (K9, K14 and K27) of H3 retained hyperacetylation status in both pwr and hda9 mutants. Genome wide H3K9 and H3K14 acetylation levels were generally elevated, and a large portion of acetylated targets overlapped between the pwr and hda9 mutants. Comparative analysis revealed a correlation between gene expression and histone H3 acetylation status in the pwr and hda9 mutants. In addition, PWR and HDA9 modulated the AGAMOUS-LIKE 19 (AGL19)-mediated flowering time pathway through histone H3 deacetylation. Finally, PWR was shown to physically interact with HDA9. We therefore propose that PWR acts as a subunit in a complex with HDA9 to negatively regulate the acetylation of specific lysine residues of histone H3 at genomic targets.
Project description:Although the interplay of covalent histone acetylation/deacetylation and ATP-dependent chromatin remodeling is crucial for the regulation of chromatin structure and gene expression in eukaryotes, the underlying molecular mechanism in plants remains largely unclear. Here we show a direct interaction between Arabidopsis SWI3B, an essential subunit of the SWI/SNF chromatin-remodeling complex, and the RPD3/HDA1-type histone deacetylase HDA6 both in vitro and in vivo. Furthermore, SWI3B and HDA6 co-repress the transcription of a subset of transposons. Both SWI3B and HDA6 maintain transposon silencing by decreasing histone H3 acetylation but increasing histone H3 lysine 9 di-methylation, DNA methylation and nucleosome occupancy. Our findings reveal that SWI3B and HDA6 may act in the same corepressor complex to maintain transposon silencing in Arabidopsis.
Project description:Polyploidy is a widespread phenomenon in flowering plant species. Polyploid plants frequently exhibit considerable transcriptomic alterations after whole-genome duplication (WGD). It is known that the transcriptomic response to tetraploidization is ecotype-dependent in Arabidopsis. Nevertheless, the biological significance and the underlying mechanism are unknown. Here, we showed that 4x Col-0 and 4x Ler presented different flowering times, with a delayed flowering time in 4x Col-0 but not in 4x Ler. We found that the expression of FLOWERING LOCUS C (FLC), the major repressor of flowering, was significantly increased in 4x Col-0 but subtle change in 4x Ler. Moreover, the level of a repressive epigenetic mark, trimethylation of histone H3 at lysine 27 (H3K27me3), was significantly decreased in 4x Col-0 but not in 4x Ler, potentially leading to different transcription levels of FLC and flowering time in 4x Col-0 and 4x Ler. Apart from the FLC locus, hundreds of genes showed differentially H3K27me3 alterations in 4x Col-0 and 4x Ler. Comparably, LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) and transcription factors required for H3K27me3 deposition presented differential transcriptional changes between 4x Col and Ler, potentially account for differential H3K27me3 alterations in 4x Col-0 and Ler. Last, we found that the natural 4x Arabidopsis ecotype Wa-1 presented early flowering time, associated with low expression and high H3K27me3 of FLC. Taken together, our results showed a role of H3K27me3 alterations in response to genome duplication in Arabidopsis autopolyploids and that flowering time variation potentially functions in autopolyploid speciation.
Project description:We show that in Arabidopsis SIN3 LIKE (SNL)family genes encoding a scoffold protein for assembly of histone deacetylase complex, directly regulate the expression of an FT activator and three FT repressors to regulate the transition to flowering in short days and long days, respectively. Under inductive long days, SNLs including SIN3 LIKE 1(SNL1) to SNL5, function in partial redundancy to repress the expression of three AP2 family transcription factors that repress FT expression, and thus mediate long-day induction of FT expression and promote the transitiion to flowering. In contrast, under non-inductive short days SNLs act to inhibit the floral transition, partly through direct repression of a MADS box transcriptional factor that promotes FT expression. Thus, our results reveal that SNLs, through histone deacetylation, play a novel dual role for the control of flowering in the long-day plant Arabidopsis: inhibiting flowering when the day length is shorter and promoting the floral transition when days become longer than a threshold length.
Project description:Histone modifications are essential for chromatin activity and play an important role in many biological processes. Trimethylation of histone H3K27 (H3K27me3) is a repressive modification established by Polycomb repressive complex 2 (PRC2). Although the presence of the histone H3 serine 28 phosphorylation (H3S28ph) modification at adjacent amino acid residues has both positive and negative effects on Polycomb silencing in mammals, little is known about the effect of H3S28ph on H3K27me3-mediated gene silencing in plants. In this study, we show that mutating H3S28A in Arabidopsis causes a dominant-negative effect that leads to an early-flowering phenotype by promoting the expression of flowering-promoting genes independently of abnormal cell division. While H3S28ph levels decreased due to the H3S28A mutation, H3K27me3 levels at the same loci did not increase. Moreover, we observed decreased H3K27me3 levels at some known PRC2 target genes in H3.3S28A transgenic lines, rather than the expected enhanced H3K27me3-mediated silencing. In line with the reduced H3K27me3 levels, the expression of the PRC2 catalytic subunits CLF and SWN decreased. Taken together, these data demonstrate that H3.3S28 is required for PRC2-dependent H3K27me3-mediated silencing in Arabidopsis, suggesting that H3S28 has a non-canonical function in H3K27me3-mediated gene silencing.