HOS15 Interacts with the Histone Deacetylase HDA9 and the Evening Complex to Epigenetically Regulate the Floral Activator .

In plants, seasonal inputs such as photoperiod and temperature modulate the plant's internal genetic program to regulate the timing of the developmental transition from vegetative to reproductive growth. This regulation of the floral transition involves chromatin remodeling, including covalent modification of histones. Here, we report that HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 15 (HOS15), a WD40 repeat protein, associates with a histone deacetylase complex to repress transcription of the ()-mediated photoperiodic flowering pathway in Arabidopsis (). Loss of function of HOS15 confers early flowering under long-day conditions because elevated expression. LUX ARRHYTHMO (LUX), a DNA binding transcription factor and component of the Evening Complex (EC), is important for the binding of HOS15 to the promoter. In wild type, HOS15 associates with the EC components LUX, EARLY FLOWERING 3 (ELF3), and ELF4 and the histone deacetylase HDA9 at the promoter, resulting in histone deacetylation and reduced expression. In the mutant, the levels of histone acetylation are elevated at the promoter, resulting in increased expression. Our data suggest that the HOS15-EC-HDA9 histone-modifying complex regulates photoperiodic flowering via the transcriptional repression of .