Overexpression of NtGCN2 improves drought tolerance in tobacco by regulating proline accumulation, ROS scavenging ability, and stomatal closure

Genome-wide identification of hormone biosynthetic and metabolism genes in the 2OGD family of tobacco and JOX genes silencing enhances drought tolerance in plants

Phytohormones play crucial roles in regulation of plant growth and tolerance to abiotic stresses. The 2-oxoglutarate-dependent dioxygenase (2OGD) superfamily responds to hormone biosynthesis and metabolism in plants. However, the Nt2OGD family in tobacco has not been fully explored. In this study, we identify 126 members of the Nt2OGD family, and 60 of them are involved in hormone biosynthesis and metabolism process (Nt2OGD-Hs), including 1-aminocyclopropane-1-carboxylic acid oxidases (ACO), dioxygenases for auxin oxidation (DAO), gibberellin (GA) 20-oxidases and 3-oxidases (GA20ox and GA3ox), carbon-19 and carbon-20 GA 2-oxidases (C19-GA2ox and C20-GA2ox), lateral branching oxidoreductases (LBO), jasmonate-induced oxygenases (JOX), downy mildew resistant 6, and DMR6-like oxygenases (DMR6/DLO). Gene duplication analysis suggests the segmental duplication and whole genome duplication (WGD) might be a potential mechanism for the expansion of this family. Expression analysis reveals that most of Nt2OGD-Hs show tissue-specific expression patterns, and some of them respond to environmental conditions. Of Nt2OGD-Hs, the expression of NtJOX3 and NtJOX5, which are involved in JA metabolism, exhibits remarkable changes during drought treatments. Silencing of NtJOX3 or NtJOX5 increases tobacco tolerance to drought stress. Furthermore, knocking out OsJOX3 and OsJOX4, respectively in rice, result in high tolerance to drought. Taken together, our work comprehensively identifies the Nt2OGD family in tobacco and provides new insights into roles of the JA pathway in drought tolerance in plants.

NtGCN2 confers cadmium tolerance in Nicotiana tabacum L. by regulating cadmium uptake, efflux, and subcellular distribution

General control non-derepressible-2 (GCN2) is widely expressed in eukaryotes and responds to biotic and abiotic stressors. However, the precise function and mechanism of action of GCN2 in response to cadmium (Cd) stress in Nicotiana tabacum L. (tobacco) remains unclear. We investigated the role of NtGCN2 in Cd tolerance and explored the mechanism by which NtGCN2 responds to Cd stress in tobacco by exposing NtGCN2 transgenic tobacco lines to different concentrations of CdCl2. NtGCN2 was activated under 50 μmol·L-1 CdCl2 stress and enhanced the Cd tolerance and photosynthetic capacities of tobacco by increasing chlorophyll content and antioxidant capacity by upregulating NtSOD, NtPOD, and NtCAT expression and corresponding enzyme activities and decreasing malondialdehyde and O2·- contents. NtGCN2 enhanced the osmoregulatory capacity of tobacco by elevating proline (Pro) and soluble sugar contents and maintaining low levels of relative conductivity. Finally, NtGCN2 enhanced Cd tolerance in tobacco by reducing Cd uptake and translocation, promoting Cd efflux, and regulating Cd subcellular distribution. In conclusion, NtGCN2 improves the tolerance of tobacco to Cd through a series of mechanisms, namely, increasing antioxidant, photosynthetic, and osmoregulation capacities and regulating Cd uptake, translocation, efflux, and subcellular distribution. This study provides a scientific basis for further exploration of the role of NtGCN2 in plant responses to Cd stress and enhancement of the Cd stress signaling network in tobacco.

Overexpression of the WRKY transcription factor gene NtWRKY65 enhances salt tolerance in tobacco (Nicotiana tabacum)

BACKGROUND

Salt stress severely inhibits plant growth, and the WRKY family transcription factors play important roles in salt stress resistance. In this study, we aimed to characterize the role of tobacco (Nicotiana tabacum) NtWRKY65 transcription factor gene in salinity tolerance.

RESULTS

This study characterized the role of tobacco (Nicotiana tabacum) NtWRKY65 transcription factor gene in salinity tolerance using four NtWRKY65 overexpression lines. NtWRKY65 is localized to the nucleus, has transactivation activity, and is upregulated by NaCl treatment. Salinity treatment resulted in the overexpressing transgenic tobacco lines generating significantly longer roots, with larger leaf area, higher fresh weight, and greater chlorophyll content than those of wild type (WT) plants. Moreover, the overexpressing lines showed elevated antioxidant enzyme activity, reduced malondialdehyde content, and leaf electrolyte leakage. In addition, the Na+ content significantly decreased, and the K+/Na+ ratio was increased in the NtWRKY65 overexpression lines compared to those in the WT. These results suggest that NtWRKY65 overexpression enhances salinity tolerance in transgenic plants. RNA-Seq analysis of the NtWRKY65 overexpressing and WT plants revealed that NtWRKY65 might regulate the expression of genes involved in the salt stress response, including cell wall component metabolism, osmotic stress response, cellular oxidant detoxification, protein phosphorylation, and the auxin signaling pathway. These results were consistent with the morphological and physiological data. These findings indicate that NtWRKY65 overexpression confers enhanced salinity tolerance.

CONCLUSIONS

Our results indicated that NtWRKY65 is a critical regulator of salinity tolerance in tobacco plants.

Ectopic expression of HaPEPC1 from the desert shrub Haloxylon ammodendron confers drought stress tolerance in Arabidopsis thaliana

Phosphoenolpyruvate carboxylase (PEPC) plays a crucial role in the initial carbon fixation process in C4 plants. However, its nonphotosynthetic functions in Haloxylon ammodendron, a C4 perennial xerohalophytic shrub, are still poorly understood. Previous studies have reported the involvement of PEPC in plant responses to abiotic stresses such as drought and salt stress. However, the underlying mechanism of PEPC tolerance to drought stress has not been determined. In this study, we cloned the C4-type PEPC gene HaPEPC1 from H. ammodendron and investigated its biological function by generating transgenic Arabidopsis plants with ectopic expression of HaPEPC1. Our results showed that, compared with WT (wild-type) plants, ectopic expression of HaPEPC1 plants exhibited significantly greater germination rates and chlorophyll contents. Furthermore, under drought stress, the transgenic plants presented increased root length, fresh weight, photosynthetic capacity, and antioxidant enzyme activities, particularly ascorbate peroxidase and peroxidase. Additionally, the transgenic plants exhibited reduced levels of malondialdehyde, H2O2 (hydrogen peroxide), and O2- (superoxide radical). Transcriptome analysis indicated that ectopic expression of HaPEPC1 primarily regulated the expression of genes associated with the stress defence response, glutathione metabolism, and abscisic acid (ABA) synthesis and signalling pathways in response to drought stress. Taken together, these findings suggest that the ectopic expression of HaPEPC1 enhances the reduction of H2O2 and O2- in transgenic plants, thereby improving reactive oxygen species (ROS) scavenging capacity and enhancing drought tolerance. Therefore, the HaPEPC1 gene holds promise as a candidate gene for crop selection aimed at enhancing drought tolerance.

The positive impact of the NtTAS14-like1 gene on osmotic stress response in Nicotiana tabacum

KEY MESSAGE

NtTAS14-like1 enhances osmotic tolerance through coordinately activating the expression of osmotic- and ABA-related genes. Osmotic stress is one of the most important limiting factors for tobacco (Nicotiana tabacum) growth and development. Dehydrin proteins are widely involved in plant adaptation to osmotic stress, but few of these proteins have been functionally characterized in tobacco. Here, to identify genes required for osmotic stress response in tobacco, an encoding dehydrin protein gene NtTAS14-like1 was isolated based on RNA sequence data. The expression of NtTAS14-like1 was obviously induced by mannitol and abscisic acid (ABA) treatments. Knock down of NtTAS14-like1 expression reduced osmotic tolerance, while overexpression of NtTAS14-like1 conferred tolerance to osmotic stress in transgenic tobacco plants, as determined by physiological analysis of the relative electrolyte leakage and malonaldehyde accumulation. Further expression analysis by quantitative real-time PCR indicated that NtTAS14-like1 participates in osmotic stress response possibly through coordinately activating osmotic- and ABA-related genes expression, such as late embryogenesis abundant (NtLEA5), early responsive to dehydration 10C (NtERD10C), calcium-dependent protein kinase 2 (NtCDPK2), ABA-responsive element-binding protein (NtAREB), ABA-responsive element-binding factor 1 (NtABF1), dehydration-responsive element-binding genes (NtDREB2A), xanthoxin dehydrogenase/reductase (NtABA2), ABA-aldehyde oxidase 3 (NtAAO3), 9-cis-epoxycarotenoid dioxygenase (NtNCED3). Together, this study will facilitate to improve our understandings of molecular and functional properties of plant TAS14 proteins and to improve genetic evidence on the involvement of the NtTAS14-like1 in osmotic stress response of tobacco.