Catalytically inactive DNA methyltransferase that acts as regulatory factor for DRM2-mediated DNA methylation. Required for maintenance of non-CpG DNA methylation. Required for normal establishment and maintenance of RNA-directed DNA methylation (RdDM) and accumulation of specific repeat-associated small interfering RNAs (siRNAs) (PubMed:21060858, PubMed:25316414, PubMed:25561521). Required for nucleolus organizer region (NOR) nuclear organization during interphase (PubMed:25316414). Acts downstream of the production of siRNAs. May promote RNA polymerase V (Pol V) transcriptional elongation or assist in the stabilization of Pol V transcripts (PubMed:25561521). Interacts with Pol V. Colocalizes with AGO4 in perinucleolar region. Belongs to the class I-like SAM-binding methyltransferase superfamily. DRM-methyltransferase family. Lacks the conserved tripeptide Ser-Pro-Cys in position 672 necessary for the methyltransferase activity in DRM protein (AC Q9M548).