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RNA polymerase IV is essential for tomato embryo development through mediating non-CG methylation [sRNA-seq]

ABSTRACT: Background: Plant-unique RNA polymerase IV (Pol IV) governs the establishment of small RNA-directed DNA methylation (RdDM) and contributes to the maintenance of transposable element (TE) silencing. Pol IV-dependent RdDM is highly active during embryonic development, and its absence occasionally reduces seed sets in species with high TE content. However, the mechanism underlying embryonic development failure due to the loss of Pol IV-RdDM remains largely unclear. Results: Here, we report that the loss-of-function of SlNRPD1, encoding the largest subunit of the Pol IV complex leads to aberrant embryogenesis in tomato (Solanum lycopersicum). The slnrpd1 mutants show non-CG hypomethylation and a burst of 21/22-nt sRNA from the distal chromatin region. We found that non-CG hypomethylation at the gene body region is generally associated with the activation of transcription, and knocking out DEMETER-like DNA demethylases cannot reverse slnrpd1 embryo lethality. mCHH hypomethylation in slnrpd1 disrupts gene expression related to auxin and WUSCHEL-related homeobox (WOX) signaling. TE reactivation in slnrpd1 mainly affects the expression of a limited number of nearby genes rather than contributing to excessive sRNA. Conclusion: We conclude that Pol IV-mediated RdDM is essential for tomato embryogenesis via non-CG methylation. mCHH hypomethylation in the slnrpd1 embryo leads to abnormal auxin/WOX signaling and TE reactivation which probably disrupts the tissue and organ initiation. This study provides new insights into the epigenetic regulation of gene and TE expression during embryogenesis. Keywords: DNA methylation, RdDM, NRPD1, Embryogenesis, Tomato

ORGANISM(S): Solanum lycopersicum

PROVIDER: GSE246017 | GEO | 2024/10/01

REPOSITORIES: GEO

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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”).

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RNA polymerase IV is essential for tomato embryo development through mediating non-CG methylation [sRNA-seq]

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