Abstract
BackgroundDrought is a major environmental constraint to plant growth, development and productivity. Compared with most willows that are generally susceptible to drought, the desert willow Salix psammophila has extraordinary adaptation to drought stress. However, its molecular basis of drought tolerance is still largely unknown.ResultsDuring polyethylene glycol 6000 (PEG 6000)-simulated drought stress, we found that the osmotic adjustment substances were accumulated and the antioxidant enzyme activities were enhanced in S. psammophila roots. A total of 8172 differentially expressed genes were identified in roots of S. psammophila through RNA-Sequencing. Based on K-means clustering, their expression patterns were classified into nine clusters, which were enriched in several stress-related processes including transcriptional regulation, response to various stresses, cell death, etc. Moreover, 672 transcription factors from 45 gene families were differentially expressed under drought stress. Furthermore, a weighted gene co-expression network was constructed, and eight genes were identified as hub genes. We demonstrated the function of two hub genes, magnesium-dependent phosphatase 1 (SpMDP1) and SpWRKY33, through overexpression in Arabidopsis thaliana. Overexpression of the two hub genes enhanced the drought tolerance in transgenic plants, suggesting that the identification of candidate drought tolerance genes in this study was highly efficient and credible.ConclusionsOur study analyzed the physiological and molecular responses to drought stress in S. psammophila, and these results contribute to dissect the mechanism of drought tolerance of S. psammophila and facilitate identification of critical genes involved in drought tolerance for willow breeding.
Highlights
Drought is a major environmental constraint to plant growth, development and productivity
We measured relative water content (RWC), relative electric conductivity (REC), contents of osmotic adjustment substances and activities of antioxidant enzymes of roots to evaluate the physiological responses to drought stress
RNA-Sequencing profiling and global transcriptome changes during drought stress in S. psammophila To further elucidate the molecular basis for drought responses in S. psammophila, a global transcriptomic analysis was performed using RNA-Sequencing. cDNA libraries with two biological replicates at each time point were independently constructed from S. psammophila roots harvested at Approximately 83.50% of total reads were aligned to S. purpurea reference genome version 1.0, a well assembled Salix genome until now (Additional file 1)
Summary
Drought is a major environmental constraint to plant growth, development and productivity. Plants have evolved sophisticated mechanisms to perceive external signal and coordinate metabolic pathways and morphological traits by modulating the expression of genes [5]. Overexpression of some drought-responsive genes (e.g., ethylene response factor 48, calcium-dependent protein kinase 4, NAC5, MYB5, etc.) has demonstrably enhanced drought tolerance in transgenic plants [13,14,15,16]. Large variations occur in transcriptional responses to drought among different plant species [17, 18]. Most researches of drought responses mechanisms have concentrated in crops or model species. Studies on the species-specific molecular mechanisms of drought response are essential for molecular breeding for drought tolerance in forest trees
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