Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

Molecular mechanism of action of plant DRM de novo DNA methyltransferases

ABSTRACT: DNA methylation is a conserved epigenetic gene regulation mechanism. DOMAINS REARRANGED METHYLTRANSFERASE (DRM) is a key de novo methyltransferase in plants, but how DRM acts mechanistically is poorly understood. Here, we report the crystal structure of the methyltransferase domain of tobacco DRM (NtDRM) and reveal a molecular basis for its rearranged structure. NtDRM forms a functional homo-dimer critical for catalytic activity. We also show that Arabidopsis DRM2 exists in complex with the siRNA effector ARGONAUTE4 (AGO4) and preferentially methylates one DNA strand, likely the strand acting as the template for non-coding Pol V RNA transcripts. This strand-biased DNA methylation is also positively correlated with strand-biased siRNA accumulation. These data suggest a model in which DRM2 is guided to target loci by AGO4-siRNA and involves base-pairing of associated siRNAs with nascent RNA transcripts. Whole-genome bisulfite sequencing was done for a wildtype line (ecotype Col) as well as various transgenic lines in a drm2 mutant background (ecotype Col). Each transgenic line expressed a version of the DRM2 protein that was either wildtype or carried induced mutations in order to test the function of various domains in the DRM2 protein. Two sets of whole-genome bisulfite were performed (130615 or 131216) and comparisons were mainly done within sets although comparisons can also be done between sets. The drm2 mutant methylome was also analyzed in this study using a previously published whole-genome bisulfite library (GSE39901).

ORGANISM(S): Arabidopsis thaliana

SUBMITTER: Christopher Hale

PROVIDER: E-GEOD-54944 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Molecular mechanism of action of plant DRM de novo DNA methyltransferases.

Zhong Xuehua X Du Jiamu J Hale Christopher J CJ Gallego-Bartolome Javier J Feng Suhua S Vashisht Ajay A AA Chory Joanne J Wohlschlegel James A JA Patel Dinshaw J DJ Jacobsen Steven E SE

Cell 20140501 5

DNA methylation is a conserved epigenetic gene-regulation mechanism. DOMAINS REARRANGED METHYLTRANSFERASE (DRM) is a key de novo methyltransferase in plants, but how DRM acts mechanistically is poorly understood. Here, we report the crystal structure of the methyltransferase domain of tobacco DRM (NtDRM) and reveal a molecular basis for its rearranged structure. NtDRM forms a functional homodimer critical for catalytic activity. We also show that Arabidopsis DRM2 exists in complex with the small ...[more]

PMID: 24855943

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Project description:In Arabidopsis, CHG DNA methylation is controlled by the H3K9 methylation mark through a self-reinforcing loop between DNA methyltransferase CHROMOMETHYLASE3 (CMT3) and H3K9 histone methyltransferase KRYPTONITE/SUVH4 (KYP). We report on the structure of KYP in complex with methylated DNA, substrate H3 peptide and cofactor SAH, thereby defining the spatial positioning of the SRA domain relative to the SET domain. The methylated DNA is bound by the SRA domain with the 5mC flipped out of the DNA, while the H3(1-15) peptide substrate binds between the SET and post-SET domains, with the epsilon-ammonium of K9 positioned adjacent to bound SAH. These structural insights complemented by in vivo functional data on key mutants of residues lining the 5mC and H3K9-binding pockets within KYP, establish how methylated DNA recruits KYP to the histone substrate. Together, the structures of KYP and previously reported CMT3 complexes provide insights into molecular mechanisms linking DNA and histone methylation. Plants homozygous for null mutations in the KRYPTONITE H3K9 methyltransferase were stably transformed with transgenes encoding the wildtype KYP protein or transgenes carrying induced point mutations in the KYP active site. The resulting lines were assayed for DNA methylation by whole-genome bisulfite sequencing to learn the efficiency with which wildtype and mutant versions of the KYP protein could restore DNA methylation lost in a kyp mutant. Samples 7 and 8 were run as single Illumina lanes and as such were compared to a previous Col sample (GSM881756), this Col sample was realigned to the TAIR10 genome for this study and as such updated processed files are available with this submission. These samples were used to define kyp mutant CHG context DMRs that were complemented upon introduction of the wildtype KYP protein. Samples 1-6 were run as multiplexed samples and were used to assay the degree of complementation for various point mutants. All plants are in the Col ecotype background.

Project description:DNA methylation is a mechanism of epigenetic gene regulation and genome defense conserved in many eukaryotic organisms. In Arabidopsis, the DNA methyltransferase DRM2 controls RNA-directed DNA methylation in a pathway that also involves the plant specific RNA Polymerase V (Pol V). The Arabidopsis genome also encodes an evolutionarily conserved but catalytically inactive DNA methyltransferase DRM3. Here, we show that DRM3 has moderate effects on global RNA-directed DNA methylation and small RNA abundance throughout the genome, and DRM3 protein physically interacts with Pol V. In drm3 mutants, we observe a lower level of Pol V-dependent transcripts, even though Pol V chromatin occupancy is increased at many sites in the genome. These findings suggest that DRM3 acts to promote Pol V transcriptional elongation or assist in the stabilization of Pol V transcripts, and shed further light on the mechanism of RNA-directed DNA methylation. For wildtype plants as well as drm3, drm2, and nrpe1 mutants ChIP-seq was carried out using an endogenous NRPE1 antibody given to us by the Craig Pikaard lab. Two biological replicates of ChIP-seq were also carried out using anti-Flag resin on wildtype and drm3 plants carrying a Flag epitope tagged version of NRPE1. Small RNA sequencing was carried out on Col, drm3, drm2, and nrpe1 plants. Finally, whole-genome bisulfite sequencing analysis was carried out on previously published datasets (as detailed below) which were realigned using a newer genome version and mapping protocol. As such the updated processed files are part of this submission. Please note that the drm2, drm3, and nrpe1 mutant libraries used in this study were previously published (GSE39901), as were the 2 other Col replicates used (GSE36129) as below and thus duplicated sample records were created for the convenient retrieval of the complete raw data from SRA; Bisulfite_seq-Col_1 - GSM881756 Bisulfite_seq-Col_2 - GSM1193638 Bisulfite_seq-drm3 - GSM981017 Bisulfite_seq-drm2 - GSM981015 Bisulfite_seq-nrpe1- GSM981040

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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”).

Dataset Information

Molecular mechanism of action of plant DRM de novo DNA methyltransferases

Publications

Molecular mechanism of action of plant DRM de novo DNA methyltransferases.

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