Multivalent H3K9me2 Reader ADCP1 Functions as a plant HP1 to Maintain Epigenetic Silencing

Heterochromatin formation is important for genome stability and transposon silencing. The evolutionally conserved Heterochromatin Protein 1 (HP1) recognizes H3K9me3 and maintains heterochromatin from fission yeast to mammalians. However, it is still questioned about the presence of HP1 protein in plants. Here, we discovered a multivalent H3K9me2 reader ADCP1 in Arabidopsis through biophysical and structural studies, and agenet domain in ADCP1 has the similar function of chromo domain in HP1. We further showed that ADCP1 was essential for heterochromatin maintenance through modulating H3K9me2 and DNA methylation levels. Similar to human HP1alpha and fly HP1a, ADCP1 was also able to mediate heterochromatin phase separation both in vitro and in vivo. Our results demonstrate the plant specific and evolution conserved ADCP1 functions as the HP1 equivalent protein in plant. ADCP1 ChIP performed with GFP antibody using ADCP1-GFP tagged transgenic plants, and Col-0 with no tag as control. H3K9me2 ChIP performed in Col-0 and adcp1-1 mutant and H3 ChIP as positive control. BS-seq perfomed with gDNA of Col-0 and adcp1-1. Total RNAs extracted from Col-0 and adcp1-1 for sequencing.