The HAF2 protein shapes histone acetylation levels of PRR5 and LUX loci in Arabidopsis.

The histone acetyltransferase HAF2 facilitates H3 acetylation deposition at the PRR5 and LUX promoters to contribute to robust circadian oscillation. The circadian clock ensures synchronization of endogenous rhythmic processes with environmental cycles. Multi-layered regulation underlies precise circadian oscillation, and epigenetic regulation is emerging as a crucial scheme for robust circadian maintenance. Here, we report that HISTONE ACETYLTRANSFERASE OF THE TAFII250 FAMILY 2 (HAF2) is involved in circadian homeostasis. The HAF2 gene is activated at midday, and its temporal expression is shaped by CIRCADIAN CLOCK-ASSOCIATED 1. The midday-activated HAF2 protein stimulates H3 acetylation (H3ac) deposition at the PRR5 and LUX loci, contributing to establishment of the raising phase. These results indicate that epigenetic waves in circadian networks underlie temporal compartmentalization of circadian components and stable maintenance of circadian oscillation.