Comparative transcriptome profiling of a desert evergreen shrub, Ammopiptanthus mongolicus, in response to drought and cold stresses

Background: The molecular mechanisms involved in plant tolerance to either drought or cold have been extensively studied in many plant species. However, few studies have focused on their comparisons especially using non-model plants with strong tolerance to both stresses. Ammopiptanthus mongolicus (Maxim. ex Kom.) Cheng f. is the only evergreen broadleaf shrub grown in the central Asian desert and it has very strong cold and drought tolerance. To provide further insights into plant tolerance, the transcriptome profiles of drought-and cold-treated A. mongolicus seedlings were analyzed using Illumina technology and differentially expressed genes (DEGs) were compared. Results: A comprehensive transcriptome of A. mongolicus was sequenced using pooled mRNA extracted from drought-, cold-stressed and unstressed seedlings as well as leaves from naturally grown shrub. These sequences were assembled into 86058 unigenes, of which 51014 unigenes had an annotated function and 2440 encoded transcription factors (TFs). Transcriptome profiles were analyzed in A. mongolicus seedlings after drought and cold treatments at three time points (2, 8 and 24 h). Between 3917 and 6102 unigenes were identified as DEGs at a single time point in both stresses. Among these DEGs 2028 and 2026 DEGs were common across the three time points of drought and cold treatments respectively, and 971 DEGs were co-regulated by both stresses. Functional enrichment analyses identified many common or specific biological processes and gene sets in response to drought and cold stresses. The most pronounced findings are that flavonoid biosynthesis genes were enriched in the DEGs co-up-regulated by both stresses; while membrane protein genes and genes related to chloroplast were abundant in the DEGs specifically up-regulated by drought or cold, respectively. Furthermore, the DREB, ERF, NAC and WRKY TFs were predominantly co-up-regulated by both stresses. Conclusions: The present study provides the most comprehensive transcriptome resource and the first dynamic transcriptome profiles of A. mongolicus under drought and cold stresses. This information will deepen our understanding of plant tolerance to drought and cold. The up-regulated DEGs will be valuable for further investigations of key genes and molecular mechanisms involved in the adaptation of A. mongolicus to harsh environments.