Genome-wide transcriptional adaptation to salt stress in Populus

Background: Adaptation to abiotic stresses is crucial for the survival of perennial plants in a natural environment. However, very little is known about the underlying mechanisms. Here, we adopted a liquid culture system to investigate plant adaptation to repeated salt stress in Populus trees. Results: We first evaluated phenotypic responses and found that plants exhibit better stress tolerance after pretreatment of salt stress. Time-course RNA sequencing (RNA-seq) was then performed to profile changes in gene expression over 12 h of salt treatments. Analysis of differentially expressed genes (DEGs) indicated that significant transcriptional reprogramming and adaptation to repeated salt treatment occurred. Clustering analysis identified two modules of co-expressed genes that were potentially critical for repeated salt stress adaptation, and one key module for salt stress response in general. Gene Ontology (GO) enrichment analysis identified pathways including hormone signaling, cell wall biosynthesis and modification, negative regulation of growth, and epigenetic regulation to be highly enriched in these gene modules. Conclusions: This study illustrates phenotypic and transcriptional adaptation of Populus trees to salt stress, revealing novel gene modules which are potentially critical for responding and adapting to salt stress.