Transcriptional regulator that binds CpG, CpNpN and CpNpG (N is A, T, or C) islands in promoters regardless the DNA methylation status. Plays probably a role in gene silencing. May associate with histone deacetylase proteins (HDAC). Required for nucleolar dominance that consist in the silencing of rRNA genes inherited from one progenitor in genetic hybrids. Recruited to rRNA genes in a DRM2-dependent manner. Maintains gene silencing by interacting with RNA binding proteins (e.g. NTF2, RPS2C, HDA6 and AGO4) and by regulating DNA methylation status (PubMed:28229965). Homodimer and heterodimer with MBD5 (PubMed:18211904). Interacts with DDM1 via its MBD domain (PubMed:15805479). Interacts with NTF2, RPS2C, HDA6 and AGO4 (PubMed:28229965). Associated with heterochromatin, and particularly at perinucleolar chromocenters and nucleolus organizer regions (NORs) in a DRM2-dependent manner. Expressed in rosette leaves, buds, flowers, stems, mature seeds and roots. The methyl-CpG-binding domain (MBD) functions both in binding to methylated DNA and in protein interactions. Impaired nucleolar dominance (PubMed:19061642). Reduced DNA methylation in some of the targets of RNA-directed DNA methylation (RdDM) and loss of DNA methylation in 180 bp centromeric repeats (PubMed:28229965).