An Arabidopsis mitochondrial uncoupling protein confers tolerance to drought and salt stress in transgenic tobacco plants

Background

Plants are challenged by a large number of environmental stresses that reduce productivity and even cause death. Both chloroplasts and mitochondria produce reactive oxygen species under normal conditions; however, stress causes an imbalance in these species that leads to deviations from normal cellular conditions and a variety of toxic effects. Mitochondria have uncoupling proteins (UCPs) that uncouple electron transport from ATP synthesis. There is evidence that UCPs play a role in alleviating stress caused by reactive oxygen species overproduction. However, direct evidence that UCPs protect plants from abiotic stress is lacking.

Methodology/Principal Findings

Tolerances to salt and water deficit were analyzed in transgenic tobacco plants that overexpress a UCP (AtUCP1) from Arabidopsis thaliana. Seeds of AtUCP1 transgenic lines germinated faster, and adult plants showed better responses to drought and salt stress than wild-type (WT) plants. These phenotypes correlated with increased water retention and higher gas exchange parameters in transgenic plants that overexpress AtUCP1. WT plants exhibited increased respiration under stress, while transgenic plants were only slightly affected. Furthermore, the transgenic plants showed reduced accumulation of hydrogen peroxide in stressed leaves compared with WT plants.

Conclusions/Significance

Higher levels of AtUCP1 improved tolerance to multiple abiotic stresses, and this protection was correlated with lower oxidative stress. Our data support previous assumptions that UCPs reduce the imbalance of reactive oxygen species. Our data also suggest that UCPs may play a role in stomatal closure, which agrees with other evidence of a direct relationship between these proteins and photosynthesis. Manipulation of the UCP protein expression in mitochondria is a new avenue for crop improvement and may lead to crops with greater tolerance for challenging environmental conditions.     

Overexpression of monodehydroascorbate reductase in transgenic tobacco confers enhanced tolerance to ozone,salt and polyethylene glycol stresses

Ascorbate (AsA) is a major antioxidant and free-radical scavenger in plants. Monodehydroascorbate reductase (MDAR; EC 1.6.5.4) is crucial for AsA regeneration and essential for maintaining a reduced pool of AsA. To examine whether an overexpressed level of MDAR could minimize the deleterious effects of environmental stresses, we developed transgenic tobacco plants overexpressing Arabidopsis thaliana MDAR gene (AtMDAR1) in the cytosol. Incorporation of the transgene in the genome of tobacco plants was confirmed by PCR and Southern-blot analysis and its expression was confirmed by Northern- and Western-blot analyses. These transgenic plants exhibited up to 2.1-fold higher MDAR activity and 2.2-fold higher level of reduced AsA compared to non-transformed control plants. The transgenic plants showed enhanced stress tolerance in term of significantly higher net photosynthesis rates under ozone, salt and polyethylene glycol (PEG) stresses and greater PSII effective quantum yield under ozone and salt stresses. Furthermore, these transgenic plants exhibited significantly lower hydrogen peroxide level when tested under salt stress. These results demonstrate that an overexpressed level of MDAR properly confers enhanced tolerance against ozone, salt and PEG stress.     

Overexpression of the Malus hupehensis MhNPR1 gene increased tolerance to salt and osmotic stress in transgenic tobacco

Earlier, we have reported that overexpression of Malus hupehensis Non-expressor of pathogenesis related gene 1 (MhNPR1) gene in tobacco could induce the expression of pathogenesis-related genes and enhance resistance to fungus Botrytis cinerea. In this study, we showed that MhNPR1 can be induced by NaCl, PEG6000, low temperature (4 °C), abscisic acid and apple aphids’ treatments in M. hupehensis. Heterogonous expression of MhNPR1 gene in tobacco conferred enhanced resistance to NaCl at the stage of seed germination, and conferred resistance to mannitol at the stage of seed germination and to PEG6000 at the stage of seedlings. Furthermore, overexpression of MhNPR1 in transgenic tobacco led to higher expression levels of osmotic-stress related genes compared with wild-type plants. This was the first report of a novel function of NPR1 that overexpression of MhNPR1 gene has a positive effect on salt and osmotic stress in tobacco, which differs from the function that overexpressing of AtNPR1 gene has a negative effect on dehydration and salt stress in rice.     

Ectopic overexpression of AtHDG11 in tall fescue resulted in enhanced tolerance to drought and salt stress

Tall fescue (Festuca arundinacea Schreb.) is a cool-season perennial grass, which has been conventionally grown in the temperate area. However, as a major type of cool-season turf grass, its growth has been extended to the sub-tropical climate or even to the transitional climate between the sub-tropical and the tropical, and, in some cases, to heavily salinized lands. The extended growth imposes a serious challenge to its tolerance to the abiotic stress, particularly to drought, salt and high temperature. Here, we report a successful introduction of Arabidopsis AtHDG11 into the tall fescue via Agrobacterium-mediated transformation. The ectopic overexpression of AtHDG11 under the control of CaMV 35S promoter with four enhancers resulted in significantly enhanced tolerance to drought and salt stress. No obvious adverse effects on growth and development were observed in the transgenic plants. The enhanced stress tolerance was associated with a more extensive root system, a lower level of malondialdehyde, a nearly normal Na⁺/K⁺ ratio, a higher level of proline and a kinetically accelerated induction of SOD and CAT activities observed in the transgenic plants during drought and/or salt stress, indicating that an enhanced ROS scavenging capability might play a significant role in the acquired tolerance to the abiotic stress. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Ya-Jun Cao and Qiang Wei contributed equally to this work.     

Overexpression of Pp14-3-3 from Pyrus pyrifolia fruit increases drought and salt tolerance in transgenic tobacco plant

Drought and salinity are the major abiotic stresses, which reduce agricultural productivity. In plants, 14-3-3s function as regulators of many target proteins through direct protein-protein interactions and play an important role during response to abiotic stresses. Here we report that CaMV 35S promoter driven overexpression of a Pyrus pyrifolia 14-3-3 gene, Pp14-3-3, improves drought and NaCl tolerance in T1 generation plants of transgenic tobacco (Nicotiana tabacum L. cv Xanthi). Under drought and NaCl stresses, the Pp14-3-3 was largely expressed in T1 transgenic tobacco lines, and compared with the wild-type (WT), transgenic tobacco plants showed relatively normal growth condition. In addition, the levels of membrane lipid peroxidation in T1 transgenic lines were definitely lower than that in WT according to the significantly decreased content of malondialdehyde. Meanwhile, the T1 transgenic tobacco lines showed significantly slower superoxide anion production rate than the WT under abiotic stress. Moreover, both the glutathione S-transferase (GST) and ascorbate peroxidase (APX) activities in T1 transgenic lines were markedly higher than those in WT. GSTs and APXs are important components of plant antioxidant system, and the results of present study suggested that Pp14-3-3 should play a crucial role in reducing oxidative damage caused by drought and salt stresses.     

Overexpression of PtAnnexin1 from Populus trichocarpa enhances salt and drought tolerance in transgenic poplars

Tree Genetics & Genomes - High numbers of endemic plants exist in subtropical China, but there have been few investigations of the phylogeography and dynamic history for endemic tree species in...     

Salinity and drought tolerance of mannitol-accumulating transgenic tobacco

Tobacco plants (Nicotiana tabacum L.) were transformed with a mannitol-1-phosphate dehydrogenase gene resulting in mannitol accumulation. Experiments were conducted to determine whether mannitol provides salt and/or drought stress protection through osmotic adjustment. Non-stressed transgenic plants were 20–25% smaller than non-stressed, non-transformed (wild-type) plants in both salinity and drought experiments. However, salt stress reduced dry weight in wild-type plants by 44%, but did not reduce the dry weight of transgenic plants. Transgenic plants adjusted osmotically by 0.57 MPa, whereas wild-type plants did not adjust osmotically in response to salt stress. Calculations of solute contribution to osmotic adjustment showed that mannitol contributed only 0-003-0-004 MPa to the 0.2 MPa difference in full turgor osmotic potential (π_o) between salt-stressed transgenic and wild-type plants. Assuming a cytoplasmic location for mannitol and that the cytoplasm constituted 5% of the total water volume, mannitol accounted for only 30–40% of the change in π_o of the cytoplasm. Inositol, a naturally occurring polyol in tobacco, accumulated in response to salt stress in both transgenic and wild-type plants, and was 3-fold more abundant than mannitol in transgenic plants. Drought stress reduced the leaf relative water content, leaf expansion, and dry weight of transgenic and wild-type plants. However, π_o was not significantly reduced by drought stress in transgenic or wild-type plants, despite an increase in non-structural carbohydrates and mannitol in droughted plants. We conclude that (1) mannitol was a relatively minor osmolyte in transgenic tobacco, but may have indirectly enhanced osmotic adjustment and salt tolerance; (2) inositol cannot substitute for mannitol in this role; (3) slower growth of the transgenic plants, and not the presence of mannitol per se, may have been the cause of greater salt tolerance, and (4) mannitol accumulation was enhanced by drought stress but did not affect π_o or drought tolerance.     

Overexpression of the acerola (Malpighia glabra) monodehydroascorbate reductase gene in transgenic tobacco plants results in increased ascorbate levels and enhanced tolerance to salt stress

Monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) is a key enzyme of the ascorbate (AsA)-glutathione cycle that maintains reduced pools of AsA and serves as an important antioxidative enzyme. Previously, we have cloned MDHAR cDNA from acerola (Malpighia glabra), a plant that accumulates abundant amount of AsA. In this study, MDHAR cDNA from acerola was introduced into tobacco plants using an Agrobacterium-mediated gene delivery system. Transgenic tobacco plants accumulated greater amounts of AsA and showed higher MDHAR activity than the control plants. Lipid peroxidation and chlorophyll degradation, which were stimulated in control plants, were restrained in transgenic plants subjected to salt stress. These results indicate that overexpression of acerola MDHAR imparts greater tolerance to salt stress.     

Overexpression of plant uncoupling mitochondrial protein in transgenic tobacco increases tolerance to oxidative stress

An Arabidopsis thaliana cDNA clone encoding a plant uncoupling mitochondrial protein (AtPUMP1) was overexpressed in transgenic tobacco plants. Analysis of the AtPUMP1 mRNA content in the transgenic lines, determined by Northernblot, revealed variable levels of transgene expression. Antibody probing ofWestern blots of mitochondrial proteins from three independent transgenic lines showed significant accumulation of AtPUMP1 in this organelle. Overproduction of AtPUMP1 in transgenic tobacco plants led to a significantincrease in tolerance to oxidative stress promoted by exogenous hydrogen peroxide as compared to wild-type control plants. These results provide thefirst biological evidence for a role of PUMP in protection of plant cells against oxidative stress damage.     

Overexpression of the PtSOS2 gene improves tolerance to salt stress in transgenic poplar plants

In higher plants, the salt overly sensitive (SOS) signalling pathway plays a crucial role in maintaining ion homoeostasis and conferring salt tolerance under salinity condition. Previously, we functionally characterized the conserved SOS pathway in the woody plant Populus trichocarpa. In this study, we demonstrate that overexpression of the constitutively active form of PtSOS2 (PtSOS2TD), one of the key components of this pathway, significantly increased salt tolerance in aspen hybrid clone Shanxin Yang (Populus davidiana × Populus bolleana). Compared to the wild‐type control, transgenic plants constitutively expressing PtSOS2TD exhibited more vigorous growth and produced greater biomass in the presence of high concentrations of NaCl. The improved salt tolerance was associated with a decreased Na⁺ accumulation in the leaves of transgenic plants. Further analyses revealed that plasma membrane Na⁺/H⁺ exchange activity and Na⁺ efflux in transgenic plants were significantly higher than those in the wild‐type plants. Moreover, transgenic plants showed improved capacity in scavenging reactive oxygen species (ROS) generated by salt stress. Taken together, our results suggest that PtSOS2 could serve as an ideal target gene to genetically engineer salt‐tolerant trees.     

Overexpression of Camellia sinensis H1 histone gene confers abiotic stress tolerance in transgenic tobacco

Key message

Overexpression of CsHis in tobacco promoted chromatin condensation, but did not affect the phenotype. It also conferred tolerance to low-temperature, high-salinity, ABA, drought and oxidative stress in transgenic tobacco.

Abstract

H1 histone, as a major structural protein of higher-order chromatin, is associated with stress responses in plants. Here, we describe the functions of the Camellia sinensis H1 Histone gene (CsHis) to illustrate its roles in plant responses to stresses. Subcellular localization and prokaryotic expression assays showed that the CsHis protein is localized in the nucleus, and its molecular size is approximately 22.5 kD. The expression levels of CsHis in C. sinensis leaves under various conditions were investigated by qRT-PCR, and the results indicated that CsHis was strongly induced by various abiotic stresses such as low-temperature, high-salinity, ABA, drought and oxidative stress. Overexpression of CsHis in tobacco (Nicotiana tabacum) promoted chromatin condensation, while there were almost no changes in the growth and development of transgenic tobacco plants. Phylogenetic analysis showed that CsHis belongs to the H1C and H1D variants of H1 histones, which are stress-induced variants and not the key variants required for growth and development. Stress tolerance analysis indicated that the transgenic tobacco plants exhibited higher tolerance than the WT plants upon exposure to various abiotic stresses; the transgenic plants displayed reduced wilting and senescence and exhibited greater net photosynthetic rate (Pn), stomatal conductance (Gs) and maximal photochemical efficiency (Fv/Fm) values. All the above results suggest that CsHis is a stress-induced gene and that its overexpression improves the tolerance to various abiotic stresses in the transgenic tobacco plants, possibly through the maintenance of photosynthetic efficiency.     

Overexpression of Ks-type dehydrins gene OeSRC1 from Olea europaea increases salt and drought tolerance in tobacco plants

Molecular Biology Reports - Agricultural production is greatly affected by environmental stresses, such as cold, drought and high-salinity. It is possible to produce tolerant genotypes by...     

Manipulation of monoubiquitin improves salt tolerance in transgenic tobacco

Ubiquitin (Ub) is regarded as a stress protein involved in many stress responses. In this paper, sense and antisense transgenic tobacco plants, as well as the wild type and vector control, were used to study the role of Ub in salt tolerance of plants. In sense Ta-Ub2 transgenic tobacco plants, there was higher expression of Ub protein conjugates than in the wild type and vector control, but the reverse trend was observed in antisense Nt-Ub1 transgenic plants. The germination rate of tobacco seed, growth status and photosynthesis of the tobacco plants suggested that over-expressing Ub promoted the growth of transgenic tobacco plants and enhanced their salt tolerance, but the opposite effect was seen in plants with repressed Ub expression. Changes in antioxidant capacity may be one of the mechanisms underlying Ub-regulated salt tolerance. Furthermore, improved tolerance to a combination of stresses was also observed in the sense transgenic tobacco plants. These findings imply that Ub is involved in the tolerance of plants to abiotic stress.