Chromatin accessibility dynamics insight into crosstalk between regulatory landscapes in poplar responses to multiple treatments.

The perennial trees develop and coordinates endogenous response signaling pathways, including their crosstalk and convergence, to cope with various environmental stresses which occur simultaneously in most cases. These processes are involved in gene transcriptional regulations that depend on dynamic interactions between regulatory proteins and corresponding chromatin regions, but the mechanisms remain poorly understood in trees. In this study, we detected chromatin regulatory landscapes of poplar under abscisic acid (ABA), methyl jasmonate (MeJA), salicylic acid (SA) and sodium chloride (NaCl) treatment, respectively, through integrating ATAC-seq and RNA-seq data. Our results showed that the degree of chromatin accessibility for a given gene is closely related to its expression level. However, unlike the gene expression that shows treatment-specific response patterns, changes in chromatin accessibility exhibit high similarities under these treatments. We further proposed and experimentally validated that a homologous gene copy of RD26 (RESPONSIVE TO DESICCATION 26) mediates the crosstalk between JA and NaCl signaling pathways by directly regulating the stress-responsive genes, and that circadian clock-related transcription factors like RVE8 (REVEILLE8) play a central role in response of poplar to these treatments. Overall, our study provides a chromatin insight into the molecular mechanism of transcription regulatory networks in response to different environmental stresses, and raises the key roles of the circadian clock of poplar to adapt to adverse environments.