Profile and Time-Scale Dynamics of Differentially Expressed Genes in Transcriptome of Populus davidiana Under Drought Stress

The genus Populus contains 25–35 species of deciduous flowering plants in the family Salicaceae. It has evolved to overcome various environmental stresses including drought stress through changes in physiological processes such a stomatal movement, photosynthesis, stress signaling, defense responses, and overall growth rate. In this study, we performed RNA-seq-based transcriptome profiling of Populus davidiana in response to drought stress induced by 10% PEG at two time points (6 and 12 h). We generated over 527 million reads by applying Populus trichocarpa as reference genome. Assembly of the reads yielded 32,650 genes and 75,820 transcripts; of these, after quantile normalization, a total of 997 genes were identified with dynamic expression over time, classifying them into nine different clusters. Among them, 550 genes responded significantly to drought stress treatment after 6 h (108 genes up-regulated and 201 genes down-regulated) and 12 h (161 up-regulated and 80 down-regulated) respectively, with at least twofold change in their expression. Based on analysis of these genes, we found several differentially expressed genes (DEGs) involved in cellular transport, transcriptional regulation, protein modification, regulation of cellular redox state, and those involved in response to other stresses. We also validated RNA-seq-mediated transcriptome data by RT-qPCR analysis of eight randomly selected DEGs. It showed significantly high correlation coefficient (0.95) suggesting high reliability of RNA-seq analysis. This study presents the first RNA-seq mediated transcriptome profile of P. davidiana in response to drought stress, providing critical information necessary for understanding the mechanisms underpinning drought stress tolerance in forest trees and other plant species.