Heterochromatin-binding protein that preferentially occupies long transposons and specifically recognizes the histone H3 'Lys-9' methylation (H3K9me) marks, with a stronger affinity for dimethylated H3K9 (H3K9me2) (PubMed:30382101, PubMed:30425322). Required for transcriptional silencing, non-CG DNA methylation (e.g. CHG and CHH regions), and H3K9 dimethylation (H3K9me2) at some loci (PubMed:30382101, PubMed:30425322). Mediates heterochromatin phase separation and chromocenter formation (PubMed:30425322). Enriched in heterochromatin, concentrated in centromeric and pericentromeric regions. Expressed ubiquitously during vegetative stage, in meristems (e.g. root tips and shoot apical meristem), and in ovules and young seeds during reproductive stage. The tandem Agenet domains (AGDs) mediate the specific recognition of the histone 3 lysine 9 dimethylation (H3K9me2) mark. Abnormal transcription up-regulation of some transposable elements (TEs) and of hypermethylated loci (including MU1, GP1, SN1 and ERT7) (PubMed:30382101, PubMed:30425322). Hypomethylated DNA CHG and CHH regions (PubMed:30382101, PubMed:30425322). Reduced H3K9me2 levels (PubMed:30382101). Increased ratio of decondensed nuclei (PubMed:30425322).