Abstract
Drought stress impacts on seedling establishment, survival and whole-plant productivity. Drought stress responses have been extensively studied at the physiological and molecular level in angiosperms, particularly in agricultural species and the model Arabidopsis thaliana, with the vast majority of work performed on aboveground tissues. Boreal forests are dominated by coniferous tree species and cover vast areas of the terrestrial surface. These areas are predicted to be particularly influenced by ongoing climate change and will be exposed to more frequent and acute drought. The associated impact at all stages of the forest tree life cycle is expected to have large-scale ecological and economic impacts. To provide a comprehensive understanding of the drought response mechanisms of Picea abies seedlings, we assayed the physiological response of needles and transcriptional responses of roots and needles after exposure to mild and severe drought. Shoots and needles showed extensive reversible plasticity for physiological measures indicative of drought response mechanisms, including stomatal conductance (gs) and shoot water potential. Root and needle transcriptional responses contrasted, with an extensive root-specific down-regulation of growth. When we compared the responses of P. abies with previously-characterised A. thaliana drought response genes, we found that the majority of the genes were conserved across lineages. However, in P. abies, transcription factors (TFs) previously identified as belonging to the ABA-dependent pathway had a more limited role and most differentially expressed genes were specific to the stress response of P. abies. These results highlight the importance of profiling both above- and below-ground tissues and provide a comprehensive framework to advance understanding of the drought response mechanism of P. abies.
One sentence summary Analysis of the drought transcriptome of Norway spruce reveals divergent molecular response pathways in conifers.
Author contributions
JCH, VH and NRS planned and designed the study. JCH performed the experiments and analysed the data together with AV, VH and NRS. JCH wrote the initial draft of the manuscript. JCH, AV, VH and NRS edited the manuscript into its final form. All authors read and approved the final manuscript.
Footnotes
Funding: This work was supported by funding from HolmenSkog AB and Berzelii Centre for Forest Biotechnology to VH, and from the Swedish University of Agricultural Science’s Trees and Crops for the Future (TC4F) program to VH and NRS.