Hormone-treatment (ABA, SA) timecourse of Arabidopsis thaliana root

To differentiate between possible explanations for this, gene expression was profiled using bulk RNA-seq in response to hormone-induced stress. Abscisic Acid (ABA) treatment time-course data revealed that TFs known to activate transcription in response to ABA were significantly up-regulated, and most target genes of these TFs were upregulated as well - with the exception being target genes with TFBSs exclusively in coding sequence, which showed no significant expression change.

Salicylic acid (SA) treatment further confirmed that target genes of known SA-responsive activators were induced only when TFBSs were found outside the coding region. However a key SA-responsive repressor (ABR1) showed strong repression of genes with CDS binding sites, suggesting a mechanism for rapid antagonistic response. Moreover, integration with chromatin accessibility data from the same tissues revealed strong links between constitutive TFBS accessibility and stress-induced target gene expression, suggesting that rapid, tissue-wide regulatory responses might preferentially operate through constitutively accessible sites primarily located close to transcription start sites.