Maintenance of H3K9me2 heterochromatin in the pollen vegetative nucleus requires ARID1 nuclear body formation

Chromatin de-condensation in plants usually accompanies a decrease in heterochromatin markers such as H3K9me2, H3K27me1, and H2A.W. However, H3K9 methyltransferases are detected primarily in the vegetative nucleus. This finding raises two questions: whether heterochromatin persists in the vegetative nucleus, and by what mechanism it is regulated.

Here, we show that the vegetative nucleus harbors a basal level of H3K9me2, and that ARID1, an integrator coordinating pollen mitosis and heterochromatin reprogramming during sperm cell formation, promotes the maintenance of this basal level via its C-terminal tail-mediated nuclear body formation. The heterochromatin nature of ARID1 nuclear bodies is further confirmed by their colocalization with H2A.W and H3K27me1. Domain truncation analysis reveals that nuclear body formation of ARID1 depends on its C-terminal forty-nine amino acids.