Drought stress-induced Picea abies transcriptome changes in the context of functional interactions

Molecular responses to drought stress have been mainly studied in deciduous tree species although conifers dominate boreal forests. Here, we analysed the transcriptional response of Picea abies (L.) H. Karst. needles after exposure to severe drought by quantitative RNA-sequencing. In total, 2,402 differentially expressed genes (DEGs) were identified, of which 1,186 were up- and 1,216 downregulated. The upregulated DEGs are mainly involved in responses to stress, nitrogen compound, water deprivation, and abscisic acid as well as in channel activity. Although only one bZIP was identified among the DEGs, several other transcription factors involved in ABA-dependent pathways such as MYB, bHLH and WRKY showed differential expression. AP2/EREBP transcription factors related to ABA-independent pathways were also identified as DEGs. A functional interaction network of the 40 most connected Arabidopsis thaliana homologs of all Picea abies DEGs placed the two top-hubs P5CS1 and P5CS2 in the center. P5CS1 is the key enzyme in the biosynthesis of proline known to be accumulated in plants under abiotic stress. Lignin synthesis and DNA-related processes, among others, are overrepresented in this network. Our data highlight interesting gene targets for functional studies and natural genetic variation analyses to support the future identification and selection of potential drought tolerant trees.