Local changes in chromatin accessibility and transcriptional networks underlying the nitrate response in Arabidopsis roots.

Transcriptional regulation, determined by chromatin structure and regulatory elements interacting at promoter regions, is a key step in plant responses to environmental cues. Nitrate (NO₃^-) is a nutrient signal that regulates the expression of hundreds of genes in Arabidopsis thaliana. Here we integrate mRNA-seq, genome-wide RNA polymerase II (RNPII), ChIP-Seq and DNase-seq data sets to establish the relationship between RNPII occupancy and chromatin accessibility in response to NO₃^- treatments in Arabidopsis root organs. Genomic footprinting allowed us to identify in vivo regulatory elements controlling gene expression in response to NO₃^- treatments. NO₃^--modulated TF footprints are important for a rapid increase in RNPII occupancy and transcript accumulation over time. We mapped key TF regulatory interactions and functionally validated the role of NAP, a NAC-domain containing TF, as a new regulatory factor in NO₃^- transport. Our strategy provides a comprehensive view of transcriptional networks in response to a nutrient signal in Arabidopsis roots.