PIFs interact with SWC6 to regulate H2A.Z deposition and photomorphogenesis in Arabidopsis

Light is an essential environmental signal perceived by a board range of photoreceptors in plants. Among them, the red/far-red light receptor phytochromes function to promote photomorphogenesis, which is critical to the survival of seedlings after seeds germination. The bHLH transcription factors PHYTOCHROME-INTERACTING FACTORs (PIFs) are the pivotal direct downstream components of phytochromes. H2A.Z is a highly conserved histone variant regulating gene transcription, and its incorporation into nucleosomes is catalyzed by SWR1 complex, in which SWC6 and ARP6 serve as core subunits. Here, we show that PIFs physically interact with SWC6 in vitro and in vivo, leading to the disassociation of HY5 from SWC6. SWC6 and ARP6 regulate hypocotyl elongation partly through PIFs in red light. PIFs and SWC6 co-regulate the expression of auxin-responsive genes such as IAA6, IAA19, IAA20 and IAA29, and repress H2A.Z deposition at IAA6 and IAA19 in red light. Based on previous studies and our findings, we propose that PIFs inhibit photomorphogenesis, at least in part, through repression of H2A.Z deposition at auxin-responsive genes mediated by the interactions of PIFs with SWC6 and promotion of their expression in red light.