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.
Project description:DNA replication requires the faithful propagation of both genetic and epigenetic information. There is evidence that DNA polymerases play a role in transcriptional silencing, but the extent of their contribution and how it relates to heterochromatin maintenance is unclear. Analyzing a new hypomorphic pol2a mutant allele, we find that POL2A, the catalytic subunit of the DNA polymerase epsilon, maintains heterochromatin silencing and nuclear organization. We also found that POL2 inhibits DNA methylation and histone H3 lysine 9 methylation, which both correlate with 24-nucleotide small RNA accumulation. In this experiment, we sequenced small-RNA libraries generated from immature inflorescences of pol2a-10 and pol2a-12 mutants and wild-type plants.
Project description:Propagation of patterns of gene expression through the cell cycle requires prompt restoration of epigenetic marks after the twofold dilution caused by DNA replication. Here, we show that the transcriptional repressive mark histone H3K27 trimethylation (H3K27me3) is restored in replicating plant cells through DNA replication-coupled modification of histone variant H3.1. Plants evolved a mechanism for efficient K27 trimethylation on H3.1, which is essential for inheritance of the silencing memory from mother to daughter cells. We illustrate how this mechanism establishes H3K27me3 mediated silencing during the developmental transition to flowering. Our study reveals transmission of H3K27me3 in plant cells through cell divisions, enabling H3K27me3 to function as an epigenetic mark.
Project description:Propagation of patterns of gene expression through the cell cycle requires prompt restoration of epigenetic marks after the twofold dilution caused by DNA replication. Here, we show that the transcriptional repressive mark histone H3K27 trimethylation (H3K27me3) is restored in replicating plant cells through DNA replication-coupled modification of histone variant H3.1. Plants evolved a mechanism for efficient K27 trimethylation on H3.1, which is essential for inheritance of the silencing memory from mother to daughter cells. We illustrate how this mechanism establishes H3K27me3 mediated silencing during the developmental transition to flowering. Our study reveals transmission of H3K27me3 in plant cells through cell divisions, enabling H3K27me3 to function as an epigenetic mark.
Project description:chip in silencing suppressor plants or in mirna plants-Transcriptional and post-transcriptional changes in Arabidopsis plants that constitutively express suppressors of RNA silencing
Project description:Histone chaperones and chromatin remodelers control nucleosome dynamics, essential for transcription, replication, and DNA repair. The histone chaperone Anti-Silencing Factor 1 (ASF1) plays a central role in facilitating CAF-1-mediated replication-dependent H3.1 deposition and HIRA-mediated replication-independent H3.3 deposition in yeast and metazoans. Whether ASF1 function is evolutionarily conserved in plants is unknown. Here, we show that Arabidopsis ASF1 proteins display an exclusive preference for the H3.3-depositing HIRA complex. Simultaneous mutation of both Arabidopsis ASF1 genes caused a decrease in chromatin density and ectopic H3.1 occupancy at loci typically enriched with H3.3. Genetic, transcriptomic, and proteomic data indicate that ASF1 proteins strongly prefer the HIRA complex over CAF-1. asf1 mutants also displayed an increase in spurious Pol II transcriptional initiation, and showed defects in the maintenance of gene body CG DNA methylation and in the distribution of histone modifications. Furthermore, ectopic targeting of ASF1 caused excessive histone deposition, less accessible chromatin, and gene silencing. These findings reveal the importance of ASF1-mediated H3.3-H4 deposition via the HIRA pathway for proper epigenetic regulation of the genome.
Project description:DNA methylation on N6-adenine (6mA), the most prevalent DNA modification in prokaryotes, has recently been found as a potentially new epigenetic mark in several unicellular and multicellular eukaryotes. However, the distribution patterns and potential functions of 6mA in land plants, which are primary producers for most ecosystems, remain completely unknown. Here we report global profiling of 6mA sites at single-nucleotide resolution in the genomes of Arabidopsis thaliana Columbia-0 (Col), using single-molecule real-time sequencing. DNA methylome analysis shows that 6mA sites are widely distributed across the Col genomes and enriched over the pericentromeric heterochromatin regions. Nearly 30% of 6mA sites are present in gene bodies with a trend of enrichment around the transcriptional start site. In addition to a common consensus 6mA site found in other eukaryotes, novel 6mA sites were found, indicating that 6mA could evolve new functions in land plants. Further analysis of 6mA methylome and RNA-sequencing data demonstrates that 6mA positively correlates with the gene expression level in Col plants. Consistently, DNA affinity chromatography coupled with mass spectrometry reveals that histone variants associated with actively expressed genes interact with 6mA DNA. Our results uncover 6mA as a DNA mark associated with actively expressed genes in Arabidopsis, indicating that 6mA could serve as a potentially novel epigenetic mark in land plants.