The photoreceptor chaperone FHY1 has an independent role in gene modulation and plant development under far-red light [ChIP-seq]

To incorporate the far-red light (FR) signal into a strategy for optimizing plant growth, FAR-RED ELONGATED HYPOCOTYL1 (FHY1) mediates the nuclear translocation of the FR photoreceptor phytochrome A (phyA) and facilitates the association of phyA with the promoters of numerous associated genes crucial for the response to environmental stimuli. However, whether FHY1 plays additional roles following FR irradiation remains elusive. Here, by the global identification of FHY1 chromatin association sites through ChIP-seq analysis and by the comparison of FHY1-associated sites with phyA- associated sites, we demonstrated that nuclear FHY1 can either act independently of phyA or act in association with phyA to activate the expression of distinct target genes. We also determined that phyA can act independently of FHY1 in regulating phyA-specific target genes. Furthermore, we determined that the independent FHY1 nuclear pathway is involved in crucial developmental aspects, as in the case of inhibited seed germination under FR during salt-stress. Notably, the differential presence of cis-elements and transcription factors in common and unique FHY1 and/or phyA associated genes are indicative of the complexity of the independent and coordinated FHY1 and phyA pathways. Our study uncovers new aspects of FHY1 function beyond its currently recognized role in phyA-dependent photomorphogenesis To determine whether phyA and FHY1 associate with the same genes upon FR irradiation, four-day old etiolated 35S: GFP-FHY1 fhy1-1 transgenic seedlings were exposed to 3hr FR. The treated plants were utilized for ChIP-seq analysis with an anti-FHY1 antibody that exhibits high specificity in the detection of FR-induced FHY1-association events. FHY1 associated-DNA samples from three distinct biological replicates and an input DNA sample (as a negative control) were subjected to high-throughput Solexa (Illumina) sequencing.