Abstract
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.
Highlights
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
We found that ectopic recruitment of MORC7 to the FWA promoter was sufficient to cause de novo DNA methylation and transcriptional gene silencing, and this was dependent on functional RNA-directed DNA methylation (RdDM)
We identified 3440 and 6119 clear peaks for MORC4 and MORC7, respectively (MACS2, q value < 0.01, fold enrichment >2) with 80% of MORC4 peaks overlapping with MORC7 peaks (Fig. 1a, b, Supplementary Fig. 1b)
Summary
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. 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. The plant-specific RNA-directed DNA methylation (RdDM) pathway is required for both de novo and maintenance. RNAs (dsRNAs) by RNA-DEPENDENT RNA POLYMERASE 2 (RDR2)[11,12] These dsRNAs are further cleaved by DICER-LIKE 3 (DCL3) into 24-nt siRNAs13, and are subsequently loaded onto the effector proteins ARGONAUTE 4 (AGO4), AGO6, or AGO914
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