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FVE promotes RNA-directed DNA methylation by facilitating the association of RNA polymerase V with chromatin [Bisulfite-seq]

ABSTRACT: DNA methylation can be established by RNA-directed DNA methylation (RdDM) in plants. The association of RNA polymerase V (Pol V) with chromatin is a critical step for RdDM. While the SRA-domain-containing proteins SUVH2 and SUVH9 and the DDR complex are known to be required for the association of Pol V with chromatin, it is unknown whether the association of Pol V with chromatin requires other unidentified regulators. Here we found that SUVH9 is able to interact with a conserved histone-interaction protein, FVE, and a previously uncharacterized RRM domain-containing protein, which we named RRM1. We demonstrated that FVE facilitates the association of Pol V with chromatin and thus contributes to DNA methylation at a substantial subset of RdDM target loci, while RRM1 is only slightly involved in RdDM. FVE-dependent RdDM target loci are more abundant in gene-rich chromosome arms than FVE-independent RdDM target loci. FVE was previously shown to be a shared subunit of the RPD3-type histone deacetylase complex and the polycomb-type histone H3K27 trimethyltransferase complex, both of which are involved in transcriptional repression. This study reveals a previously uncharacterized role of FVE in RdDM and suggests that FVE may coordinate RdDM, histone deacetylation, and H3K27 trimethylation, thus ensuring transcriptional silencing of TEs in gene-rich chromosome arms to protect genes from harmful effects of potentially transcribed TEs.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE169178 | GEO | 2021/06/12

REPOSITORIES: GEO

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Project description:RNA-directed DNA methylation (RdDM) in Arabidopsis thaliana depends on the synthesis of non-coding RNAs by nuclear RNA polymerase E (NRPE or Pol V) 1-3, but the mechanism by which Pol V is targeted is unknown. Here we show that genome-wide Pol V association with chromatin redundantly requires the SU(VAR)3-9 homologs, SUVH2 and SUVH9. These proteins resemble histone methyltransferases, however a crystal structure reveals that SUVH9 lacks a peptide-substrate binding cleft and lacks a properly formed S-Adenosyl methionine (SAM) binding pocket necessary for normal catalysis, consistent with a lack of methyltransferase activity for these proteins. SUVH2 and SUVH9 both contain SET- and RING-ASSOCIATED (SRA) domains capable of binding methylated DNA, suggesting that they function to recruit Pol V through DNA methylation. Consistent with this model, mutation of the DNA METHYLTRANSFERASE 1, MET1, causes losses of DNA methylation, a nearly complete loss of Pol V at its normal locations, and redistribution of Pol V to sites that become hypermethylated. By tethering SUVH2 with a zinc finger to an unmethylated epiallele of the homeodomain transcription factor FWA, we demonstrate that SUVH2 is sufficient to both recruit Pol V and establish DNA methylation and gene silencing. Our results suggest that Pol V is recruited to DNA methylation through the methyl-DNA binding SUVH2 and SUVH9 proteins, and our mechanistic findings suggest a means for selectively targeting regions of the plant genome for epigenetic silencing. For wild type plants (ecotype Columbia) and suvh2 suvh9 double mutants whole-genome small RNA (sRNA-seq) and bisulfite sequencing (BS-seq) was performed. For the small RNA sequencing nrpd1 and nrpe1 mutant plants were sequenced in parallel as controls. For the bisulfite sequencing data, the wildtype data and that of the suvh2 and suvh9 single mutants was previously published and is thus not submitted here. 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 wildtype and suvh2 suvh9 mutant plants carrying a C-terminally epitope tagged (3XFLAG) NRPE1. Whole genome ChIP seq was also performed using a gifted endogenous NRPE1 antibody in a wildtype and met1 mutant background. Whole-genome bisulfite sequencing was also performed on fwa-4 epiallele plants transformed with the wild-type SUVH2 protein-coding construct containing a tethering zinc finger targeted to repeats at the fwa gene. For these transgenic libraries a line carrying a FLAG and fwa targeting zinc-finger tagged KRYPTONITE methyltransferase was bisulfite sequenced as a control (“FLAG-ZF-KYP”).

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FVE promotes RNA-directed DNA methylation by facilitating the association of RNA polymerase V with chromatin [Bisulfite-seq]

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