Histone deacetylase complex 1 facilitates hypocotyl elongation by attenuating acetylation and transcription via a PIF4-dependent process.

Photomorphogenesis is a transitional response occurring when seedlings are exposed to light. Upon red-light exposure, this process depends on the nuclear translocation of phytochrome B (phyB) and its interaction with downstream components. Histone deacetylase complex 1 (HDC1) is a member of the histone deacetylation complex (HDAC) that regulates the sensitivity of Arabidopsis seedlings to environmental cues. Here, we show that HDC1 is a positive regulator of hypocotyl elongation when plants are exposed to red light. By employing protein interaction assays and mutant combinations, we demonstrate that HDC1 interacts with PIF4 and regulates its abundance. Chromatin immunoprecipitation sequencing (ChIP-seq) reveals that HDC1 modulates the expression of growth-promoting genes by deacetylating promoter regions and that HDC1 is required for PIF4 association over DNA targets. Altogether, our findings explore the connection between red-light signaling and chromatin states and assign another function to a member of the HDAC complex in plants.