Project description:RNA-directed DNA methylation (RdDM) plays an essential role in transposable element (TE) silencing in plants. In the Arabidopsis RdDM pathway, the DDR complex containing DRD1, DMS3, and RDM1, is necessary for recruiting Pol V to transcribe scaffold RNA. Although the role of DDR is known, the mechanism by which the DDR complex is regulated remains unexplored. Here, we demonstrate that the Anaphase Promoting Complex/Cyclosome (APC/C) monitors the assembly of the DDR complex by targeting DMS3 for degradation. We show that a subset of Pol V-dependent RdDM loci are de-repressed in apc/c mutants, accompanied by defective recruitment and transcription of Pol V. APC/C targets DMS3 for ubiquitination and degradation in a D box-dependent manner, and the D-box-mutated DMS3 fails to complement the dms3 mutant. Competitive binding assays shows that the dosage of DMS3 is critical for the assembly of the DDR complex, and in vivo gel filtration analysis shows that the assembly of both DDR and Pol V is compromised in the apc8 mutant. These findings uncover a safeguard role of APC/C-mediated DMS3 degradation in the assembly of the DDR complex, and provide a direct link between selective protein degradation and RdDM.
Project description:RNA-directed DNA methylation (RdDM) plays an essential role in transposable element (TE) silencing in plants. In the Arabidopsis RdDM pathway, the DDR complex containing DRD1, DMS3, and RDM1, is necessary for recruiting Pol V to transcribe scaffold RNA. Although the role of DDR is known, the mechanism by which the DDR complex is regulated remains unexplored. Here, we demonstrate that the Anaphase Promoting Complex/Cyclosome (APC/C) monitors the assembly of the DDR complex by targeting DMS3 for degradation. We show that a subset of Pol V-dependent RdDM loci are de-repressed in apc/c mutants, accompanied by defective recruitment and transcription of Pol V. APC/C targets DMS3 for ubiquitination and degradation in a D box-dependent manner, and the D-box-mutated DMS3 fails to complement the dms3 mutant. Competitive binding assays shows that the dosage of DMS3 is critical for the assembly of the DDR complex, and in vivo gel filtration analysis shows that the assembly of both DDR and Pol V is compromised in the apc8 mutant. These findings uncover a safeguard role of APC/C-mediated DMS3 degradation in the assembly of the DDR complex, and provide a direct link between selective protein degradation and RdDM.
Project description:Chemical cross-linking coupled to mass spectrometry was used to study the A. thaliana DDR complex consisting of DMS3, RMD1 and a peptide from the interaction region of DRD1. Cross-linking was performed using different cross-linking chemistries: disuccinimidyl suberate (DSS) and a combination of adipic acid dihydrazide (ADH) and the coupling reagent, DMTMM.
Project description:During RNA-directed DNA methylation (RdDM), the DDR complex, composed of DRD1, DMS3, and RDM1, is responsible for recruiting DNA polymerase V (Pol V) to silence transposable elements (TEs) in plants. However, how the DDR complex is regulated remains unexplored. Here, we show that the anaphase-promoting complex/cyclosome (APC/C) regulates the assembly of the DDR complex by targeting DMS3 for degradation. We found that a substantial set of RdDM loci was commonly de-repressed in apc/c and pol v mutants, and that the defects in RdDM activity resulted from up-regulated DMS3 protein levels, which finally caused reduced Pol V recruitment. DMS3 was ubiquitinated by APC/C for degradation in a D box-dependent manner. Competitive binding assays and gel filtration analyses showed that a proper level of DMS3 is critical for the assembly of the DDR complex. Consistent with the importance of the level of DMS3, overaccumulation of DMS3 caused defective RdDM activity, phenocopying the apc/c and dms3 mutants. Moreover, DMS3 is expressed in a cell cycle-dependent manner. Collectively, these findings provide direct evidence as to how the assembly of the DDR complex is regulated and uncover a safeguarding role of APC/C in the regulation of RdDM activity.
Project description:Chromosome segregation requires both the separation of sister chromatids and the sustained condensation of chromatids during anaphase. In yeast cells, cohesin is not only required for sister chromatid cohesion but also plays a major role in determining the structure of individual chromatids in metaphase. Separase cleavage is thought to remove all cohesin complexes from chromosomes to initiate anaphase. It is thus not clear how the length and organisation of segregating chromatids are maintained during anaphase in the absence of cohesin. Here we show that degradation of cohesin at the anaphase onset causes aberrant chromatid segregation. Hi-C analysis on segregating chromatids demonstrates that cohesin depletion causes loss of intrachromatid organisation. Surprisingly, TEV-mediated cleavage of cohesin does not dramatically disrupt chromatid organisation in anaphase, explaining why bulk segregation is achieved. In addition, we identified a small pool of cohesin complexes bound to telophase chromosomes in wildtype cells and show that they play a role in the organisation of centromeric regions. Our data demonstrate that in yeast cells, cohesin function is not over in metaphase, but extends to the anaphase period when chromatids are segregating.