Abstract
Although drought stress is one of the most limiting factors in growth and production of Chinese cabbage (Brassica rapa L. ssp. pekinensis), the underlying biochemical and molecular causes are poorly understood. In the present study, to address the mechanisms underlying the drought responses, we analyzed the transcriptome profile of Chinese cabbage grown under drought conditions. Drought stress transcriptionally activated several transcription factor genes, including AP2/ERFs, bHLHs, NACs and bZIPs, and was found to possibly result in transcriptional variation in genes involved in organic substance metabolic processes. In addition, comparative expression analysis of selected BrbZIPs under different stress conditions suggested that drought-induced BrbZIPs are important for improving drought tolerance. Further, drought stress in Chinese cabbage caused differential acclimation responses in glucosinolate metabolism in leaves and roots. Analysis of stomatal aperture indicated that drought-induced accumulation of glucosinolates in leaves directly or indirectly controlled stomatal closure to prevent water loss, suggesting that organ-specific responses are essential for plant survival under drought stress condition. Taken together, our results provide information important for further studies on molecular mechanisms of drought tolerance in Chinese cabbage.
Highlights
Because the increasing world population and worldwide climate change affects agriculture in several ways, an intergovernmental panel on climate change has concluded that increased concentrations of greenhouse gases will lead to dry conditions in the subtropics, creating widespread drought stress in agricultural regions [1]
Based on the difference in copy numbers and similarity of AP2/ERF domains, this family is further divided into five subfamilies, the Apetala2 (AP2), the ethylene responsive element binding factor (ERF), the Related to ABI3/VP1 (RAV), the dehydration-responsive element-binding (DREB) protein, and the Soloist [24], our transcriptome libraries did not contain members of the Soloist subfamily (Figure S4), probably due to its tissue-specific expression
In cluster I, BrbZIP (XP_009111876.1), known as BrbZIP101 [26] exhibited relative higher transcript accumulation in drought-treated leaves and was transiently down-regulated in response to NaCl and wounding stresses, whereas BrbZIPs in cluster II only showed transient down-regulation due to wounding stress. These results indicate that BrbZIPs have divergent functions in response to environmental stresses, and the increased expression of BrbZIP101 might suggest its role as a marker of drought-stress response
Summary
Because the increasing world population and worldwide climate change affects agriculture in several ways, an intergovernmental panel on climate change has concluded that increased concentrations of greenhouse gases will lead to dry conditions in the subtropics, creating widespread drought stress in agricultural regions [1]. Molecules 2018, 23, 1186 cell growth, development, and photosynthesis, and alteration in biosynthetic pathways, antioxidant pathways, and the respiration pathway [5], suggesting that drought tolerance is an outcome of a series of molecular, cellular, physiological, and biochemical processes mediated via induction and/or repression of genes and their regulation through complex transcriptional networks [6]. This indicates that particular attention to drought-stress response genes and drought-stress-induced transcriptional networks will be required for successful yield protection against drought. Our results provide an overview of molecular mechanisms triggered by drought stress in plants, and will be helpful in unraveling the basic mechanisms of environmental stress tolerance
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