Expression of ethylene response factor JERF1 in rice improves tolerance to drought

Ethylene response factor (ERF) proteins regulate a variety of stress responses in plant. JERF1, a tomato ERF protein, can be induced by abscisic acid (ABA). Overexpression of JERF1 enhanced the tolerance of transgenic tobacco to high salt concentration, osmotic stress, and low temperature by regulating the expression of stress-responsive genes by binding to DRE/CRT and GCC-box cis-elements. In this research, we further report that overexpression of JERF1 significantly enhanced drought tolerance of transgenic rice. The overexpression activated the expression of stress-responsive genes and increased the synthesis of the osmolyte proline by regulating the expression of OsP5CS, encoding the proline biosynthesis key enzyme deltal-pyrroline-5-carboxylate synthetase. JERF1 also activated the expression of two ABA biosynthesis key enzyme genes, OsABA2 and Os03g0810800, and increased the synthesis of ABA in rice. Analysis of cis-elements of JERF1-targeted genes pointed to the existence of DRE/CRT and/or GCC box in their promoters, indicating that JERF1 could activate the expression of related genes in rice by binding to these cis-elements. Unlike some other ERF proteins, constructive overexpression of JERF1 did not change the growth and development of transgenic rice, which makes JEFR1 a potentially useful source in breeding for greater tolerance to abiotic stress.     

GbMPK3, a mitogen-activated protein kinase from cotton,enhances drought and oxidative stress tolerance in tobacco

Mitogen-activated protein kinase (MAPK) cascades are highly conserved signaling modules found in all eukaryotes, and play significant roles in developmental and environmental signal transduction. In this study, a MAPK gene (GbMPK3), which showed homologous to AtMPK3 and NtWIPK, was isolated from sea-island cotton (Gossypium barbadense) and induced during multiple abiotic stress treatments including salt, cold, heat, dehydration and oxidative stress. Transgenic tobacco (Nicotiana benthamiana) with constitutively higher expression of GbMPK3 was conferred with enhanced drought tolerance, reduced water loss during drought treatment and improved plant height and survival rates after re-watering. Additionally, the gene expression levels and enzymatic activity of antioxidant enzymes were more strongly induced with depressed hydrogen peroxide accumulation in GbMPK3-overexpressing tobacco compared with wild-type under drought condition. Furthermore, observation of seed germination and leaf morphology showed that tolerance of transgenic plants to methyl viologen was improved due to increased antioxidant enzyme expression, suggesting that GbMPK3 may positively regulate drought tolerance through enhanced reactive oxygen species scavenging ability.     

Ectopic overexpression of tomato JERF3 in tobacco activates downstream gene expression and enhances salt tolerance

Plant Molecular Biology - The ethylene, jasmonic acid and osmotic signaling pathways respond to environmental stimuli and in order to understand how plants adapt to biotic and abiotic stresses it...     

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.     

Evaluation of oxidative stress tolerance in maize (Zea mays L.) seedlings in response to drought

Seedlings of selected six genotypes of maize (Zea mays L.) differing in their drought sensitivity (LM5 and Parkash drought-tolerant and PMH2, JH3459, Paras and LM14 as drought-sensitive) were exposed to 72 h drought stress at two leaf stage. Alterations in their antioxidant pools combined with activities of enzymes involved in defense against oxidative stress were investigated in leaves. Activities of some reactive oxygen species (ROS)-scavenging enzymes, catalase (CAT) and ascorbate peroxidase (APX) were enhanced in tolerant genotypes in response to drought stress. Superoxide dismutase (SOD) activity was significantly decreased in sensitive genotypes, but remained unchanged in tolerant genotypes under stress. Peroxidase (POX) activity was significantly induced in tolerant, as well as sensitive genotypes. Imposition of stress led to increase in H2O2 and malondialdehyde (MDA, a marker for lipid peroxidation) content in sensitive genotypes, while in tolerant genotypes no change was observed. Significant increase in glutathione content was observed in sensitive genotypes. Ascorbic acid pool was induced in both tolerant and sensitive genotypes, but induction was more pronounced in tolerant genotypes. Significant activation of antioxidative defence mechanisms correlated with drought-induced oxidative stress tolerance was the characteristic of the drought tolerant genotypes. These studies provide a mechanism for drought tolerance in maize seedlings.     

Fluidization of membrane lipids enhances the tolerance of Saccharomyces cerevisiae to freezing and salt stress

Unsaturated fatty acids play an essential role in the biophysical characteristics of cell membranes and determine the proper function of membrane-attached proteins. Thus, the ability of cells to alter the degree of unsaturation in their membranes is an important factor in cellular acclimatization to environmental conditions. Many eukaryotic organisms can synthesize dienoic fatty acids, but Saccharomyces cerevisiae can introduce only a single double bond at the Delta(9) position. We expressed two sunflower (Helianthus annuus) oleate Delta(12) desaturases encoded by FAD2-1 and FAD2-3 in yeast cells of the wild-type W303-1A strain (trp1) and analyzed their effects on growth and stress tolerance. Production of the heterologous desaturases increased the content of dienoic fatty acids, especially 18:2Delta(9,12), the unsaturation index, and the fluidity of the yeast membrane. The total fatty acid content remained constant, and the level of monounsaturated fatty acids decreased. Growth at 15 degrees C was reduced in the FAD2 strains, probably due to tryptophan auxotrophy, since the trp1 (TRP1) transformants that produced the sunflower desaturases grew as well as the control strain did. Our results suggest that changes in the fluidity of the lipid bilayer affect tryptophan uptake and/or the correct targeting of tryptophan transporters. The expression of the sunflower desaturases, in either Trp(+) or Trp(-) strains, increased NaCl tolerance. Production of dienoic fatty acids increased the tolerance to freezing of wild-type cells preincubated at 30 degrees C or 15 degrees C. Thus, membrane fluidity is an essential determinant of stress resistance in S. cerevisiae, and engineering of membrane lipids has the potential to be a useful tool of increasing the tolerance to freezing in industrial strains.     

Over-expression of ascorbate peroxidase in tobacco chloroplasts enhances the tolerance to salt stress and water deficit

The role of APX (ascorbate peroxidase) in protection against oxidative stress was examined using transgenic tobacco plants. The full length cDNA, coding Arabidopsis thaliana L. APX fused downstream to the chloroplast transit sequence from A. thaliana glutathione reductase, was cloned into appropriate binary vector and mobilized into Agrobacterium tumefaciens C58C2. Leaf discs were infected with the Agrobacterium and cultured on medium supplied with kanamycin. The incorporation of the gene in tobacco genome was confirmed by Southern dot blot hybridization. Transgenic lines were generated, and the line Chl-APX5 shown to have 3.8-fold the level of APX activity in the wild-type plants. The isolated chloroplasts from this line showed higher APX activity. During early investigation, this line showed enhanced tolerance to the active oxygen-generating paraquat and sodium sulphite. The first generation of this line, also, showed enhanced tolerance to salt, PEG and water stresses, as determined by net photosynthesis. The present data indicate that overproducing the cytosolic APX in tobacco chloroplasts reduces the toxicity of H₂O₂.     

The ethylene response factor AtERF98 enhances tolerance to salt through the transcriptional activation of ascorbic acid synthesis in Arabidopsis

Ascorbic acid (AsA) is an important antioxidant in plants, and its biosynthesis is finely regulated through developmental and environmental cues; however, the regulatory mechanism remains unclear. In this report, the knockout and knockdown mutants of Arabidopsis AtERF98 decreased the AsA level, whereas the overexpression of AtERF98 increased it, which suggests that AtERF98 plays an important role in regulating AsA biosynthesis. AtERF98-overexpressing plants showed enhanced expression of AsA synthesis genes in the d-mannose/l-galactose (d-Man/l-Gal) pathway and the myo-inositol pathway gene MIOX4, as well as of AsA turnover genes. In contrast, AtERF98 mutants showed decreased expression of AsA synthesis genes in the d-Man/l-Gal pathway but not of the myo-inositol pathway gene or AsA turnover genes. In addition, the role of AtERF98 in regulating AsA production was significantly impaired in the d-Man/l-Gal pathway mutant vtc1-1, but the expression of the myo-inositol pathway gene or AsA turnover genes was not affected, which indicates that the regulation of AtERF98 in AsA synthesis is primarily mediated by the d-Man/l-Gal pathway. Transient expression and chromatin immunoprecipitation assays further showed that AtERF98 binds to the promoter of VTC1, which indicates that AtERF98 modulates AsA biosynthesis by directly regulating the expression of the AsA synthesis genes. Moreover, the knockout mutant aterf98-1 displayed decreased salt-induced AsA synthesis and reduced tolerance to salt. The supplementation of exogenous AsA increased the salt tolerance of aterf98-1; coincidently, the enhanced salt tolerance of AtERF98-overexpressing plants was impaired in vtc1-1. Thus, our data provide evidence that the regulation of AtERF98 in AsA biosynthesis contributes to enhanced salt tolerance in Arabidopsis.     

新疆胀果甘草幼苗耐盐性及对NaCl胁迫的离子响应

以盐碱荒漠草甸药用植物胀果甘草(Glycyrrhiza inflata)为材料, 采用水培法研究了盐处理(50、100、200、300 mmol·L^-1NaCl) 28天后幼苗株高、生物量、含水量、根粗、甘草酸含量和不同器官的离子含量及离子的选择吸收、运输能力, 并对丙二醛、脯氨酸含量进行测定, 以确定其耐盐范围及耐盐方式。结果表明, 低盐浓度对胀果甘草幼苗生长无显著影响, 只有较高盐浓度(≥200 mmol·L^-1 NaCl)使幼苗总生物量、株高、甘草酸含量显著降低; 根据耐盐系数与盐浓度的拟合方程, 确定适宜幼苗生长的盐浓度范围为0-278.17 mmol·L^-1。随盐浓度上升, 植株选择性吸收K⁺、Ca²⁺、Mg²⁺, 而抑制Na⁺进入体内, 幼苗对进入植株体内的Na⁺在不同盐浓度下采取了不同的分配策略, 低盐浓度下(0-100 mmol·L^-1), 植株体内Na⁺主要积累在根中, 避免了叶中Na⁺的过多积累, 其盐适应机制以耐盐方式为主; 高盐浓度下(≥200 mmol·L^-1 NaCl), Na⁺主要积累在下部叶, 并通过叶片脱落的方式带走体内的盐分, 其盐适应机制以避盐方式为主。盐胁迫下, 幼苗能促进K⁺而抑制Na⁺向上部叶的运输, 使上部叶拒Na喜K, 维持了较高的K⁺/Na⁺比值, 有利于幼苗生长; 同时, 地下根系能通过积累Ca²⁺、Mg²⁺和合成脯氨酸、甘草酸, 以提高渗透调节能力, 缓解Na⁺毒害, 使根的生长不受影响, 有利于保证幼苗在盐环境中吸收维持生长的必要养分, 这是胀果甘草幼苗具有较强耐盐性的原因。以上结果说明, 胀果甘草幼苗通过对盐离子的吸收和运输调控、离子区域化和渗透调节, 以耐盐和避盐两种方式适应盐碱荒漠环境。     

An alfalfa (Medicago sativa L.) ethylene response factor gene, MsERF11, enhances salt tolerance in transgenic Arabidopsis

A novel orthologue of ethylene response factor gene, MsERF11, was isolated from alfalfa in this study. It has an open reading frame of 807?bp, encoding a predicted polypeptide of 268 amino acids. Sequence similarity analysis clearly suggested that MsERF11 encoded an ethylene response factor protein. The results of transient expression of MsERF11 in onion epidermal cells indicated that MsERF11 is a nuclear protein. The expression pattern of MsERF11 gene was analyzed by real-time quantitative PCR and a higher level of expression was observed in leaves than was observed in roots, stems, flower buds and flowers. Furthermore, the expression was induced by PEG6000, NaCl, Al(2)(SO(4))(3) and six different hormones. Over-expressing MsERF11 resulted in enhanced tolerances to salt stress in transgenic Arabidopsis plants. This research indicates that MsERF11 has the potential to be used for improving crop's salt tolerance in areas where salinity is a limiting factor for agricultural productivity. Key message MsERF11 was isolated from alfalfa. Its expression was induced by different abiotic stresses and hormones. Over-expressing MsERF11 resulted in enhanced salt tolerance in transgenic Arabidopsis plants.