Abstract
Heterochromatin Protein 1 (HP1) recognizes histone H3 lysine 9 methylation (H3K9me) through its conserved chromodomain and maintains heterochromatin from fission yeast to mammals. However, in Arabidopsis, Like Heterochromatin Protein 1 (LHP1) recognizes and colocalizes genome-wide with H3K27me3, and is the functional homolog of Polycomb protein. This raises the question whether genuine HP1 homologs exist in plants. Here, we report on the discovery of ADCP1, a plant-specific triple tandem Agenet protein, as a multivalent H3K9me reader in Arabidopsis, and establish that ADCP1 is essential for heterochromatin formation and transposon silencing through modulating H3K9 and DNA methylation levels. Structural studies revealed the molecular basis underlying H3K9me-specific recognition by tandem Agenet of ADCP1. Similar to human HP1α and fly HP1a, ADCP1 mediates heterochromatin phase separation. Our results demonstrate that despite its distinct domain compositions, ADCP1 convergently evolves as an HP1-equivalent protein in plants to regulate heterochromatin formation.
Highlights
Heterochromatin Protein 1 (HP1) recognizes histone H3 lysine 9 methylation (H3K9me) through its conserved chromodomain and maintains heterochromatin from fission yeast to mammals
We report on the discovery of Agenet Domain Containing Protein 1 (ADCP1) as a multivalent histone H3K9 methylation reader in plants, and outline its functional roles in mediating heterochromatin phase separation, H3K9 and CHG/CHH DNA methylation maintenance, as well as transposon silencing
Our results suggest that ADCP1 and HP1 are functionally equivalent and have been convergently evolved with similar histone reader activity and multivalent feature for heterochromatin regulation
Summary
Heterochromatin Protein 1 (HP1) recognizes histone H3 lysine 9 methylation (H3K9me) through its conserved chromodomain and maintains heterochromatin from fission yeast to mammals. Heterochromatin mediates various functions such as transposon silencing and nuclear organization.[1,2] The formation and functional maintenance of heterochromatin require Heterochromatin Protein 1 (HP1).[3] HP1 recognizes histone H3 lysine 9 trimethylation (H3K9me3) through its chromodomain and this interaction can be switched off by phosphorylation at adjacent H3 serine 10 (H3S10ph).[4,5,6,7] The chromo shadow domain of HP1 mediates dimerization of HP1 and its association with a repertoire of proteins.[8] HP1 was reported to mediate heterochromatin phase separation in flies and humans.[9,10] As an H3K9me[3] reader, HP1 is conserved from fission yeast to mammals. Our results suggest that ADCP1 and HP1 are functionally equivalent and have been convergently evolved with similar histone reader activity and multivalent feature for heterochromatin regulation
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