Gene network analysis predicts the primary regulators of ABA-dependent transcriptional activation and repression in Populus roots

Abstract

Abscisic acid (ABA) acts as a key signalling molecule that mediates plant responses to environmental cues as well as plant growth and development. Stress-induced and developmental changes in ABA content trigger a myriad of post-transcriptional and transcriptional events. Yet, ABA-dependent transcriptional responses are context dependent, and their temporal dynamics in roots under non-stress conditions remain poorly resolved. In this study, we characterised the hallmarks of ABA signalling and responses in the poplar root transcriptome ( Populus nigra L.). We disturbed ABA homeostasis by exogenous ABA treatments, and we combined time-resolved transcriptomics with unsupervised gene network analysis to identify ABA-activated and ABA-inactivated gene co-expression modules. Considering the temporal dynamics of transcriptional events, we predicted the primary targets of the ABA signal, characterised early responding ABA-dependent processes, identified hub genes and revealed their putative functional links. We demonstrated that the properties of a master ABA-activated module induced by exogenous treatments were preserved in the transcriptome response to osmotic stress, revealing a core gene set of ABA-dependent stress responses. Our work sheds light on ABA repression of gene expression, the reprogramming of metabolism and the leaf-senescence pathway. Based on current functional knowledge and phylogenetic information, including poplar-specific features, we proposed a working model of ABA action on root transcriptome in poplar that integrates master genes, key responsive processes, and their putative regulatory architecture.