Project description:DNA methylation is an epigenetic mark that is associated with transcriptional repression of transposable elements and protein coding genes. Conversely, transcriptionally active regulatory regions are strongly correlated with histone 3 lysine 4 di- and trimethylation (H3K4m2/3). We previously showed that Arabidopsis thaliana plants with mutations in the H3K4m2/m3 demethylase JUMONJI 14 (JMJ14) exhibit a mild reduction in RNA-directed DNA methylation (RdDM) that is associated with an increase in H3K4m2/m3 levels. To determine whether this incomplete RdDM reduction was the result of redundancy with other demethylases, we examined the genetic interaction of JMJ14 with another class of H3K4 demethylases: LYSINE-SPECIFIC DEMETHYLASE 1-LIKE 1 and LYSINE-SPECIFIC DEMETHYLASE 1-LIKE 2 (LDL1 and LDL2). Genome-wide DNA methylation analyses reveal that both families impact RdDM, but not other DNA methylation pathways. ChIP-seq experiments show that regions that exhibit an observable DNA methylation decrease are co-incidental with increases in H3K4m2/m3. Interestingly, the impact on DNA methylation was stronger at DNA-methylated regions adjacent to H3K4m2/m3-marked protein coding genes, suggesting that the activity of H3K4 demethylases may be particularly crucial to prevent spreading of active epigenetic marks. Finally, RNA sequencing analyses indicate that at RdDM targets, the increase of H3K4m2/m3 is not generally associated with transcriptional de-repression. This suggests that the histone mark itselfânot transcriptionâimpacts the extent of RdDM. 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 (âcomplementation replicatesâ).
Project description:RNA-directed DNA methylation (RdDM) is a small interfering RNA (siRNA)-mediated epigenetic modification that contributes to transposon silencing in plants. RdDM requires a complex transcriptional machinery that includes specialized RNA polymerases, named Pol IV and Pol V, as well as chromatin remodelling proteins, transcription factors, RNA binding proteins, and other plant-specific proteins whose functions are not yet clarified. In Arabidopsis thaliana, DICER-LIKE3 and members of the ARGONAUTE4 group of AROGONAUTE (AGO) proteins are involved, respectively, in generating and using 24-nt siRNAs that trigger methylation and transcriptional gene silencing (TGS) of homologous promoter sequences. AGO proteins act in silencing effector complexes by anchoring the 3â and 5â ends of the guide siRNAs at their N-terminal PAZ domain and MID domain, respectively. In addition, many AGO proteins cleave complementary target RNAs through an endonuclease (âslicerâ) activity in their C-terminal PIWI domain. AGO4 is the main AGO protein implicated in the RdDM pathway. Here we report the identification of the related AGO6 in a forward genetic screen for mutants defective in RdDM and TGS in shoot and root apical meristems in Arabidopsis thaliana. The identification of AGO6, and not AGO4, in our screen is consistent with the primary expression of AGO6 in shoot and root growing points and the preferential association of Pol V with AGO6.
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.
Project description:Here we use bisulfite conversion of RNA combined with high-throughput IIlumina sequencing (RBS-seq) to identify single-nucleotide resolution of m5C sites in ribosomal RNAs of all three sub-cellular transcriptomes in Arabidopsis thaliana. m5C sites in rRNAs were also anlyzed in Arabidopsis T-DNA knockouts for the RNA methyltransferases TRM4A, TRM4B, TRDMT1, NSUN5, NOP2A, NOP2B and NOP2C.
Project description:The Microrchidia (MORC) family of ATPases are required for transposable element (TE) silencing and heterochromatin condensation in plants and animals, and C. elegans MORC-1 has been shown to topologically entrap and condense DNA. In Arabidopsis thaliana, mutation of MORCs has been shown to reactivate silent methylated genes and transposons and to decondense heterochromatic chromocenters, despite only minor changes in the maintenance of DNA methylation. Here we provide the first evidence localizing Arabidopsis MORC proteins to specific regions of chromatin and find that MORC4 and MORC7 are closely co-localized with sites of RNA directed DNA methylation (RdDM). We further show that MORC7, when tethered to DNA by an artificial zinc finger, can facilitate the establishment of RdDM. Finally, we show that MORCs are required for the efficient RdDM mediated establishment of DNA methylation and silencing of a newly integrated FWA transgene, even though morc mutations have no effect on the maintenance of preexisting methylation at the endogenous FWA gene. We propose that MORCs function as a molecular tether in RdDM complexes to reinforce RdDM activity for methylation establishment. These findings have implications for MORC protein function in a variety of other eukaryotic organisms.
Project description:The diversity of small RNA-directed DNA methylation (RdDM) mechanisms have been underestimated due to the nearly complete transcriptional silencing of transposable elements (TEs) in the wt Col ecotype of Arabidopsis thaliana. In plants mutant for the SWI/SNF2 histone remodeler DDM1, TEs are globally activated due to loss of genome wide heterochromatin condensation. Activated TEs go through additional non-canonical forms of RdDM. However, the global targets of the non-canonical RdDM pathway are unidentified. In an attempt to identify and contrast the targets of canonical and non-canonical RdDM, we sequenced small RNAs from several RdDM mutants in either the TE-silent or the TE-active (ddm1) contexts.
Project description:DNA methylation in Arabidopsis thaliana is maintained by at least four different enzymes: MET1, CMT3, DRM2, and CMT2. However, DNA methylation is established exclusively by the enzyme DRM2, which acts in the RNA-directed DNA methylation (RdDM) pathway. Some RdDM components belong to gene families and have partially redundant functions, such as DICER-LIKE 2, 3 and 4, and IDN2- LIKE 1 and 2. Traditional mutagenesis screens usually fail to detect genes if they are redundant, since the loss of one gene can be compensated by a related gene. In an effort to circumvent this issue, we utilized co-expression data to identify closely related genes that are co-regulated with genes in the RdDM pathway. Here we report the discovery of two redundant proteins, SNF2-RING-HELICASE-LIKE1 and 2 (FRG1 and 2) that are putative chromatin-related paralogous proteins. Analysis of genome–wide bisulfite sequencing shows that simultaneous mutations of FRG1 and 2 cause broad defects in methylation at RdDM targeted loci. We also show that FRG1 stably associates with Su(var)3-9-related SUVR2, a known RdDM component, in vivo. Combined, our results identify FRG1 and FRG2 as novel components of the RdDM machinery.
Project description:Here we use bisulfite conversion of RNA combined with high-throughput IIlumina sequencing (RBS-seq) to identify single-nucleotide resolution of m5C sites in transfer RNAs of all three sub-cellular transcriptomes of Arabidopsis thaliana. 5-methylcytosine sites in tRNAs were also determined in Arabidopsis T-DNA knockouts for the RNA methyltransferases TRM4A, TRM4B, TRDMT1, NSUN5 and NOP2A.