Photoperiodic Regulation of Flowering Time through Periodic Histone Deacetylation of the Florigen Gene <i>FT</i>

<div><p>The developmental transition from a vegetative to a reproductive phase (i.e., flowering) is timed by the seasonal cue day length or photoperiod in many plant species. Through the photoperiod pathway, inductive day lengths trigger the production of a systemic flowering signal, florigen, to provoke the floral transition. FLOWERING LOCUS T (FT), widely conserved in angiosperms, is a major component of the mobile florigen. In the long-day plant <i>Arabidopsis</i>, <i>FT</i> expression is rhythmically activated by the output of the photoperiod pathway <i>CONSTANS</i> (<i>CO</i>), specifically at the end of long days. How <i>FT</i> expression is modulated at an adequate level in response to the long-day cue to set a proper flowering time remains unknown. Here, we report a periodic histone deacetylation mechanism for the photoperiodic modulation of <i>FT</i> expression. We have identified a plant-unique core structural component of an <i>Arabidopsis</i> histone deacetylase (HDAC) complex. In long days, this component accumulates at dusk, and is recruited by a MADS-domain transcription factor to the <i>FT</i> locus specifically at the end of the day, leading to periodic histone deacetylation of <i>FT</i> chromatin at dusk. Furthermore, we found that at the end of long days CO activity not only activates <i>FT</i> expression but also enables HDAC-activity recruitment to <i>FT</i> chromatin to dampen the level of <i>FT</i> expression, and so prevent precocious flowering in response to the inductive long-day cue. These results collectively reveal a periodic histone deacetylation mechanism for the day-length control of flowering time in higher plants.</p>