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Ectopic targeting of CG DNA methylation in Arabidopsis with the bacterial SssI methyltransferase.

ABSTRACT: The ability to target epigenetic marks like DNA methylation to specific loci is important in both basic research and in crop plant engineering. However, heritability of targeted DNA methylation, how it impacts gene expression, and which epigenetic features are required for proper establishment are mostly unknown. Here, we show that targeting the CG-specific methyltransferase M.SssI with an artificial zinc finger protein can establish heritable CG methylation and silencing of a targeted locus in Arabidopsis. In addition, we observe highly heritable widespread ectopic CG methylation mainly over euchromatic regions. This hypermethylation shows little effect on transcription while it triggers a mild but significant reduction in the accumulation of H2A.Z and H3K27me3. Moreover, ectopic methylation occurs preferentially at less open chromatin that lacks positive histone marks. These results outline general principles of the heritability and interaction of CG methylation with other epigenomic features that should help guide future efforts to engineer epigenomes.

SUBMITTER: Liu W

PROVIDER: S-EPMC8149686 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Ectopic targeting of CG DNA methylation in Arabidopsis with the bacterial SssI methyltransferase.

Project description:Targeting of epigenetic marks like DNA methylation to specific loci to manipulate gene expression is important in both basic research and in crop plant engineering. However, the extent to which targeted DNA methylation can be heritable is unknown. Here, we show that targeting the CG-specific methyltransferase M.SssI (SssI) from Spiroplasma sp. strain MQ1 with an artificial zinc finger (ZF) protein can establish heritable CG methylation and silencing of the targeted loci in Arabidopsis. This occurs even in the absence of a functional RNA-directed DNA methylation pathway, which is usually required for de novo methylation. In addition to the locus-specific targeted CG methylation, we observed widespread ectopic CG methylation throughout the genome that was highly heritable over generations, even in the absence of the effector transgene. A comparison with other epigenetic features showed that this ectopic methylation occurred preferentially at less open chromatin regions that were lacking in positive epigenetic histone marks. Although ectopic CG methylation was highly enriched over gene body regions, it showed little effect on transcription of these genes. However, we observed a mild but significant reduction in the histone variant H2A.Z and H3K27me3 over genes with ectopic CG methylation. These results outline general principals of the interaction of CG methylation with other epigenomic features that should help guide future efforts to engineer epigenomes.

2021-03-22 | GSE158027 | GEO

Ectopic targeting of CG DNA methylation in Arabidopsis with the bacterial SssI methyltransferase.

Project description:Ectopic targeting of CG DNA methylation in Arabidopsis with the bacterial SssI methyltransferase.

| PRJNA663790 | ENA

CRISPR-based targeting of DNA methylation in Arabidopsis thaliana by a bacterial CG-specific DNA methyltransferase.

Project description:CRISPR-based targeted modification of epigenetic marks such as DNA cytosine methylation is an important strategy to regulate the expression of genes and their associated phenotypes. Although plants have DNA methylation in all sequence contexts (CG, CHG, CHH, where H = A, T, C), methylation in the symmetric CG context is particularly important for gene silencing and is very efficiently maintained through mitotic and meiotic cell divisions. Tools that can directly add CG methylation to specific loci are therefore highly desirable but are currently lacking in plants. Here we have developed two CRISPR-based CG-specific targeted DNA methylation systems for plants using a variant of the bacterial CG-specific DNA methyltransferase MQ1 with reduced activity but high specificity. We demonstrate that the methylation added by MQ1 is highly target specific and can be heritably maintained in the absence of the effector. These tools should be valuable both in crop engineering and in plant genetic research.

| S-EPMC8201958 | biostudies-literature

CRISPR-based targeting of DNA methylation in Arabidopsis thaliana by a bacterial CG specific DNA methyltransferase.

Project description:CRISPR-based targeted modification of epigenetic marks is an important strategy to regulate the expression of genes and their associated phenotypes in plants and animals. The manipulation of DNA cytosine methylation is particularly attractive in plants since DNA methylation changes are often heritable in subsequent plant generations. Although plants have DNA methylation in all sequence contexts (CG, CHG, CHH, where H can be any nucleotide but G), methylation at symmetrical CG sites is the most important for gene silencing, and is also the most efficiently maintained through miotic and meiotic cell divisions. Thus, DNA methylation targeting tools that directly install CG methylation are highly desirable. Here we have developed two CRISPR-based CG specific targeted DNA methylation systems for plants using the DNA methyltransferase MQ1 (SssI) from the bacterium Mollicutes spiroplasma. To reduce off-target effects, we used a variant of the enzyme with reduced catalytic activity. We demonstrate that methylation added by MQ1 is highly target-specific and can be heritably maintained in the absence of the effector. These tools should be valuable both in crop engineering and in plant genetic research.

2021-05-19 | GSE149840 | GEO

Cytosine-to-uracil deamination by SssI DNA methyltransferase.

Project description:The prokaryotic DNA(cytosine-5)methyltransferase M.SssI shares the specificity of eukaryotic DNA methyltransferases (CG) and is an important model and experimental tool in the study of eukaryotic DNA methylation. Previously, M.SssI was shown to be able to catalyze deamination of the target cytosine to uracil if the methyl donor S-adenosyl-methionine (SAM) was missing from the reaction. To test whether this side-activity of the enzyme can be used to distinguish between unmethylated and C5-methylated cytosines in CG dinucleotides, we re-investigated, using a sensitive genetic reversion assay, the cytosine deaminase activity of M.SssI. Confirming previous results we showed that M.SssI can deaminate cytosine to uracil in a slow reaction in the absence of SAM and that the rate of this reaction can be increased by the SAM analogue 5'-amino-5'-deoxyadenosine. We could not detect M.SssI-catalyzed deamination of C5-methylcytosine ((m5)C). We found conditions where the rate of M.SssI mediated C-to-U deamination was at least 100-fold higher than the rate of (m5)C-to-T conversion. Although this difference in reactivities suggests that the enzyme could be used to identify C5-methylated cytosines in the epigenetically important CG dinucleotides, the rate of M.SssI mediated cytosine deamination is too low to become an enzymatic alternative to the bisulfite reaction. Amino acid replacements in the presumed SAM binding pocket of M.SssI (F17S and G19D) resulted in greatly reduced methyltransferase activity. The G19D variant showed cytosine deaminase activity in E. coli, at physiological SAM concentrations. Interestingly, the C-to-U deaminase activity was also detectable in an E. coli ung (+) host proficient in uracil excision repair.

| S-EPMC3804486 | biostudies-literature

Lowering DNA binding affinity of SssI DNA methyltransferase does not enhance the specificity of targeted DNA methylation in E. coli.

Project description:Targeted DNA methylation is a technique that aims to methylate cytosines in selected genomic loci. In the most widely used approach a CG-specific DNA methyltransferase (MTase) is fused to a sequence specific DNA binding protein, which binds in the vicinity of the targeted CG site(s). Although the technique has high potential for studying the role of DNA methylation in higher eukaryotes, its usefulness is hampered by insufficient methylation specificity. One of the approaches proposed to suppress methylation at unwanted sites is to use MTase variants with reduced DNA binding affinity. In this work we investigated how methylation specificity of chimeric MTases containing variants of the CG-specific prokaryotic MTase M.SssI fused to zinc finger or dCas9 targeting domains is influenced by mutations affecting catalytic activity and/or DNA binding affinity of the MTase domain. Specificity of targeted DNA methylation was assayed in E. coli harboring a plasmid with the target site. Digestions of the isolated plasmids with methylation sensitive restriction enzymes revealed that specificity of targeted DNA methylation was dependent on the activity but not on the DNA binding affinity of the MTase. These results have implications for the design of strategies of targeted DNA methylation.

| S-EPMC8316445 | biostudies-literature

RNAi, DRD1, and histone methylation actively target developmentally important non-CG DNA methylation in arabidopsis.

Project description:Cytosine DNA methylation protects eukaryotic genomes by silencing transposons and harmful DNAs, but also regulates gene expression during normal development. Loss of CG methylation in the Arabidopsis thaliana met1 and ddm1 mutants causes varied and stochastic developmental defects that are often inherited independently of the original met1 or ddm1 mutation. Loss of non-CG methylation in plants with combined mutations in the DRM and CMT3 genes also causes a suite of developmental defects. We show here that the pleiotropic developmental defects of drm1 drm2 cmt3 triple mutant plants are fully recessive, and unlike phenotypes caused by met1 and ddm1, are not inherited independently of the drm and cmt3 mutations. Developmental phenotypes are also reversed when drm1 drm2 cmt3 plants are transformed with DRM2 or CMT3, implying that non-CG DNA methylation is efficiently re-established by sequence-specific signals. We provide evidence that these signals include RNA silencing though the 24-nucleotide short interfering RNA (siRNA) pathway as well as histone H3K9 methylation, both of which converge on the putative chromatin-remodeling protein DRD1. These signals act in at least three partially intersecting pathways that control the locus-specific patterning of non-CG methylation by the DRM2 and CMT3 methyltransferases. Our results suggest that non-CG DNA methylation that is inherited via a network of persistent targeting signals has been co-opted to regulate developmentally important genes.

| S-EPMC1472700 | biostudies-literature

DNA conformational dynamics in the context-dependent non-CG CHH methylation by plant methyltransferase DRM2.

Project description:DNA methylation provides an important epigenetic mechanism that critically regulates gene expression, genome imprinting, and retrotransposon silencing. In plants, DNA methylation is prevalent not only in a CG dinucleotide context but also in non-CG contexts, namely CHG and CHH (H = C, T, or A) methylation. It has been established that plant non-CG DNA methylation is highly context dependent, with the +1- and +2-flanking sequences enriched with A/T nucleotides. How DNA sequence, conformation, and dynamics influence non-CG methylation remains elusive. Here, we report structural and biochemical characterizations of the intrinsic substrate preference of DOMAINS REARRANGED METHYLTRANSFERASE 2 (DRM2), a plant DNA methyltransferase responsible for establishing all cytosine methylation and maintaining CHH methylation. Among nine CHH motifs, the DRM2 methyltransferase (MTase) domain shows marked substrate preference toward CWW (W = A or T) motifs, correlating well with their relative abundance in planta. Furthermore, we report the crystal structure of DRM2 MTase in complex with a DNA duplex containing a flexible TpA base step at the +1/+2-flanking sites of the target nucleotide. Comparative structural analysis of the DRM2-DNA complexes provides a mechanism by which flanking nucleotide composition impacts DRM2-mediated DNA methylation. Furthermore, the flexibility of the TpA step gives rise to two alternative DNA conformations, resulting in different interactions with DRM2 and consequently temperature-dependent shift of the substrate preference of DRM2. Together, this study provides insights into how the interplay between the conformational dynamics of DNA and temperature as an environmental factor contributes to the context-dependent CHH methylation by DRM2.

| S-EPMC10711165 | biostudies-literature

CRISPR-based targeting of DNA methylation in Arabidopsis thaliana by a bacterial CG specific DNA methyltransferase.

Project description:CRISPR-based targeting of DNA methylation in Arabidopsis thaliana by a bacterial CG specific DNA methyltransferase.

| PRJNA630258 | ENA

A model of pulldown alignments from SssI-treated DNA improves DNA methylation prediction.

Project description:BackgroundProtein pulldown using Methyl-CpG binding domain (MBD) proteins followed by high-throughput sequencing is a common method to determine DNA methylation. Algorithms have been developed to estimate absolute methylation level from read coverage generated by affinity enrichment-based techniques, but the most accurate one for MBD-seq data requires additional data from an SssI-treated Control experiment.ResultsUsing our previous characterizations of Methyl-CpG/MBD2 binding in the context of an MBD pulldown experiment, we build a model of expected MBD pulldown reads as drawn from SssI-treated DNA. We use the program BayMeth to evaluate the effectiveness of this model by substituting calculated SssI Control data for the observed SssI Control data. By comparing methylation predictions against those from an RRBS data set, we find that BayMeth run with our modeled SssI Control data performs better than BayMeth run with observed SssI Control data, on both 100 bp and 10 bp windows. Adapting the model to an external data set solely by changing the average fragment length, our calculated data still informs the BayMeth program to a similar level as observed data in predicting methylation state on a pulldown data set with matching WGBS estimates.ConclusionIn both internal and external MBD pulldown data sets tested in this study, BayMeth used with our modeled pulldown coverage performs better than BayMeth run without the inclusion of any estimate of SssI Control pulldown, and is comparable to - and in some cases better than - using observed SssI Control data with the BayMeth program. Thus, our MBD pulldown alignment model can improve methylation predictions without the need to perform additional control experiments.

| S-EPMC6700779 | biostudies-literature

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