Project description:Heterochromatic condensates (chromocenters) are critical for maintaining the silencing of heterochromatin. However, it is a riddle why the presence of chromocenters is variable across species. Here, we reveal that variations in the plant heterochromatin protein ADCP1 confer a diversity in chromocenter formation via phase separation. ADCP1 physically interacts with the high mobility group protein HMGA to form a complex and mediates heterochromatin condensation by multivalent interactions. The loss of intrinsically disordered regions (IDRs) in ADCP1 homologues during evolution has led to the absence of prominent chromocenter in various plant species, and introduction of IDR-containing ADCP1 with HMGA promotes heterochromatin condensation and retrotransposon silencing. Moreover, plants in the Cucurbitaceae group have evolved an IDR-containing chimera of ADCP1 and HMGA, which enables formation of chromocenters remarkably. Together, our work uncovers a coevolved mechanism of phase separation in packing heterochromatin and constraining retrotransposons.
