Epigenetic memory marks determine epiallele stability at loci targeted by de novo DNA methylation
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ABSTRACT:
ORGANISM(S): Arabidopsis thaliana
PROVIDER: GSE140566 | GEO | 2020/04/17
REPOSITORIES: GEO
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2017-01-09 | GSE89591 | GEO
Project description:Transgenerationally heritable epialleles are defined by the stable propagation of alternative transcriptional states through mitotic and meiotic cell cycles. Given that the propagation of DNA methylation at CpG sites, mediated in Arabidopsis by MET1, plays a central role in epigenetic inheritance, we examined genome-wide DNA methylation in partial and complete loss-of-function met1 mutants. We interpreted the data in relation to transgenerational epiallelic stability and provide evidence that DNA sequence features such as density of CpGs and genomic repetitiveness of the loci largely determine their susceptibility to epiallelic switching. The importance of this rule was confirmed by analyses of common epialleles in natural Arabidopsis accessions and verified in rice.
2017-01-09 | GSE89586 | GEO
Project description:DNA methylation is an epigenetic modification that plays critical roles in gene silencing, development, and the maintenance of genome integrity. In Arabidopsis, DNA methylation is established by DOMAINS REARRANGED METHYLTRANSFERASE 2 (DRM2) and is targeted by 24 nt small interfering RNAs (siRNAs) through a pathway termed RNA-directed DNA methylation (RdDM)1. This pathway requires two plant-specific RNA polymerases: Pol-IV, which functions to initiate siRNA biogenesis and Pol-V, which functions in the downstream DNA methyltransferase targeting phase of the RdDM pathway to generate scaffold transcripts that recruit downstream RdDM factors1,2. To understand the mechanisms controlling Pol-IV targeting we investigated the function of SAWADEE HOMEODOMAIN HOMOLOG 1 (SHH1)3,4, a Pol-IV interacting protein3. Here we show that SHH1 acts upstream in the RdDM pathway to enable siRNA production from a large subset of the most active RdDM targets and that SHH1 is required for Pol-IV occupancy at these same loci. We also show that the SHH1 SAWADEE domain is a novel chromatin binding module that adopts a unique tandem Tudor-like fold and functions as a dual lysine reader, probing for both unmethylated K4 and methylated K9 modifications on the histone 3 (H3) tail. Finally, we show that key residues within both lysine binding pockets of SHH1 are required in vivo to maintain siRNA and DNA methylation levels as well as Pol-IV occupancy at RdDM targets, demonstrating a central role for methyl H3K9 binding in SHH1 function and providing the first insights into the mechanism of Pol-IV targeting. Given the parallels between methylation systems in plants and mammals1,5, a further understanding of this early targeting step may aid in our ability to control the expression of endogenous and newly introduced genes, which has broad implications for agriculture and gene therapy. For wild type plants (ecotype Columbia) and RdDM mutants whole-genome small RNA (sRNA-seq) and bisulfite sequencing (BS-seq) was performed. The Col and nrpe1 BS-seq libraries were previously reported (GSE39247) and so are not part of this submission. In addition, two replicates of whole genome chromatin immunoprecipitation (ChIP-seq) was performed on wild type (ecotype Columbia) plants as a negative control with experimentals consiting of nrpd1 mutant plants carrying a C-terminally epitope tagged (3XFLAG) NRPD1. Whole-genome bisulfite sequencing and small RNA sequencing was also performed on shh1 mutant plants transformed with the wild-type SHH1 protein-coding construct as well as multiple constructs containing point mutations. For these complementation libraries a separate shh1 mutant and Col control line were sequenced (“complementation replicates”).
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2018-12-31 | GSE47722 | GEO
Project description:DNA methylation in Arabidopsis thaliana is maintained by at least four different enzymes MET1, CMT3, DRM2 and CMT2. However, new methylation patterns are established exclusively by the enzyme DRM2, which acts within a pathway termed RNA-directed DNA methylation (RdDM). Some RdDM components belong to gene families and have partially redundant functions (i.e. DICER LIKE 2, 3 and 4 and IDN2 PARALOG 1 and 2). Traditional screens, which usually affect single genes, usually fail to detect genes if they are redundant, since the loss of one gene is compensated by a related gene. In an effort to circumvent this caveat, we utilized co-expression data to identify closely related genes that are co-regulated with genes in the RdDM pathway. We report the discovery of two redundant proteins, SNF2-RING-HELICASE1 and 2 (FRINGE1 and 2) that are putative chromatin-related paralogous proteins. Analysis of genome–wide bisulfite sequencing shows that simultaneous mutations of FRINGE1 and 2 cause broad defects in methylation at RdDM targeted loci. We also show that FRINGE1 stably associates with Su(var)3-9-related SUVR2, a known RdDM component, in vivo. Combined our results identify FRINGE1 and FRINGE2 as novel components of the RdDM machinery. One fringe 1/2 sample analyzed.
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