De novo assembly and discovery of drought-responsive genes in eastern white spruce
Since white spruce (Picea glauca) is likely to be most threatened by increasing extreme drought events in the context of climate change, an understanding of acclimation and adaptation to drought stress is of major importance for this widespread North American conifer. Here, we have generated an improved version of the spruce transcriptome, GCAT 4.0, and used RNA-seq to provide the first transcriptome related to short-term drought stress in eastern white spruce. 48 samples were collected for RNA extraction at four time points during a 22-day drought stress experiment with 2-year-old white spruce seedlings. De novo transcriptome assembly and gene expression analysis revealed 33,287 transcripts (18,934 annotated unique genes) with 5,910 drought-responsive genes on all four sampling days. Transcriptomic analyses highlighted the alteration of photosynthesis, cell wall organization or biogenesis processes and water transport while abscisic acid response, osmotic stress, and defense response were up-regulated under drought conditions. Significant changes in the expression of key genes linked to these biological processes, as well as several transcription factors (TFs) associated with signal transduction, growth, oxidative damage and defense responses indicate that they may play key roles in adapting to drought stress in conifers. This study provides first insights into the molecular mechanisms of short-term drought response in white spruce and provides new genetic resources that could pave the way for the development of genetic selection strategies aimed at enhancing the drought resilience of white spruce in the face of climate change.