Abstract
Drought stress response is a complex trait regulated at transcriptional and post-transcriptional levels in tobacco. Since the 1990s, many studies have shown that miRNAs act in many ways to regulate target expression in plant growth, development and stress response. The recent draft genome sequence of Nicotiana benthamiana has provided a framework for Digital Gene Expression (DGE) and small RNA sequencing to understand patterns of transcription in the context of plant response to environmental stress. We sequenced and analyzed three Digital Gene Expression (DGE) libraries from roots of normal and drought-stressed tobacco plants, and four small RNA populations from roots, stems and leaves of control or drought-treated tobacco plants, respectively. We identified 276 candidate drought responsive genes (DRGs) with sequence similarities to 64 known DRGs from other model plant crops, 82 were transcription factors (TFs) including WRKY, NAC, ERF and bZIP families. Of these tobacco DRGs, 54 differentially expressed DRGs included 21 TFs, which belonged to 4 TF families such as NAC (6), MYB (4), ERF (10), and bZIP (1). Additionally, we confirmed expression of 39 known miRNA families (122 members) and five conserved miRNA families, which showed differential regulation under drought stress. Targets of miRNAs were further surveyed based on a recently published study, of which ten targets were DRGs. An integrated gene regulatory network is proposed for the molecular mechanisms of tobacco root response to drought stress using differentially expressed DRGs, the changed expression profiles of miRNAs and their target transcripts. This network analysis serves as a reference for future studies on tobacco response stresses such as drought, cold and heavy metals.
Highlights
Tobacco, Nicotiana benthamiana, is an important agricultural and economic crop in China [1]
To determine the optimal time to analysis gene expression for drought stress, uniform seedlings of tobacco with six leaves were challenged with 20% PEG6000 to simulate drought and sampled at six durations of stress (3, 6, 12, 24, 48, and 96 h)
PRO and MDA continued to ascend slowly and reached their peak after 96 h. These results suggest that Superoxide dismutase (SOD) activity, PRO and MDA content all significantly increased at 6 and 48 h relative to 3 and 24 h, and the optimal times for drought stress assays were 6 and 48 h
Summary
Nicotiana benthamiana, is an important agricultural and economic crop in China [1]. It is one of the most commonly used species to study molecular plant-microbe interactions [2,3]. Numerous efforts are underway to improve plant productivity, including reduction of yield loss to environmental stress, such as drought, water logging, salt loading, and freezing. These stresses have adverse effects on plant growth, and plant stress responses are regulated by multiple signaling pathways [4,5]. Drought stress increases endogenous abscisic acid (ABA) levels and induces
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