Overexpression of the wheat salt tolerance-related gene TaSC enhances salt tolerance in Arabidopsis

A novel gene named TaSC was cloned from salt-tolerant wheat. Northern blot showed that the expression of TaSC in salt-tolerant wheat was up-regulated after salt stress. Real-time quantitative PCR analyses showed that TaSC expression was induced by salt and ABA in wheat. Localization analysis showed that TaSC proteins were localized to the plasma membrane in transgenic Arabidopsis thaliana. The overexpression of TaSC in Col-0 and atsc (SALK_072220) Arabidopsis strains resulted in increased salt tolerance of the transgenic plants. TaSC overexpression in Col-0 and atsc signi?cantly up-regulated the expression of AtFRY1, AtSAD1, and AtCDPK2. AtCDPK2 overexpression in atsc rescued the salt-sensitive phenotype of atsc. The TaSC gene may improve plant salt tolerance by acting via the CDPK pathway.     

Salt tolerance in crop plants: new approaches through tissue culture and gene regulation

Recent approaches to study of salinity tolerance in crop plants have ranged from genetic mapping to molecular characterization of gene products induced by salt/drought stress. Transgenic plant design has allowed to test the effects of overexpression of specific prokaryotic or plant genes that are known to be up-regulated by salt/drought stress. This review summarizes current progress in the field in the context of adaptive metabolic and physiological responses to salt stress and their potential role in long term tolerance. Specifically considered are gene activation by salt, in view of proposed avenues for improved salt tolerance and the need to ascertain the additional influences of developmental regulation of such genes. Discussion includes the alternate genetic strategy we have pursued for improving salinity tolerance in alfalfa (Medicago sativa L.) and rice (Oryza sativa L.). This strategy combines single-step selection of salt-tolerant cells in culture, followed by regeneration of salt-tolerant plants and identification of genes important in conferring salt tolerance. We have postulated that activation or improved expression of a subset of genes encoding functions that are particularly vulnerable under conditions of salt-stress could counteract the molecular effects of such stress and could provide incremental improvements in tolerance. We have proceeded to identify the acquired specific changes in gene regulation for our salt-tolerant mutant cells and plants. One particularly interesting and novel gene isolate from the salt-tolerant cells is Alfin1, which encodes a putative zinc-finger regulatory protein, expressed predominantly in roots. We have demonstrated that this protein binds DNA in a sequence specific manner and may be potentially important in gene regulation in roots in response to salt and an important marker for salt tolerance in crop plants.     

Effect of aspartic acid on physiological characteristics and gene expression of salt exclusion in Tartary buckwheat under salt stress

Salt-tolerant variety Chuanqiao No. 1 and salt-sensitive variety Chuanqiao No. 2 of Tartary buckwheat were used as experimental materials. The effect of aspartic acid on seed germination, physiological characteristics of seedlings and gene expression of salt exclusion in Tartary buckwheat were studied under NaCl stress of 150 mM. The results showed that the aspartic acid treatment could restore the seed germination rate and root vigor of seedlings to the control with non-damage level in salt-tolerant Tartary buckwheat variety under salt stress, and the salt-sensitive variety was increased greatly. Spraying aspartic acid had some protective effects on cell membrane of leaves in Tartary buckwheat under salt stress, and the protective effects were more obviously on salt-sensitive variety, and that could restore the activity of SOD and CAT of leaves to the control level in salt-tolerant Tartary buckwheat variety under salt stress, and the activity of antioxidant enzymes in salt-sensitive variety was increased significantly. The relative expression of FtNHX1 and FtSOS1 genes was increased significantly under salt stress, and that of FtNHX1 gene in salt-tolerant and salt-sensitive varieties was reached the maximum expression level at 12 h and 24 h respectively, while that of FtSOS1 gene in salt-tolerant and salt-sensitive varieties was reached the maximum expression level at 12 h, and the salt-tolerant variety was increased greatly. After spraying aspartic acid, the relative expression of FtNHX1 and FtSOS1 genes was increased more obviously. The relative expression of FtNHX1 gene in salt-tolerant and salt-sensitive varieties was reached the maximum expression level at 12 h, while that of FtSOS1 gene was reached the maximum expression level at 12 h and 24 h respectively, and that in salt-tolerant variety was increased especially more, indicating that spraying aspartic acid on gene expression of salt exclusion in salt-tolerant variety of Tartary buckwheat has a better effect under salt stress.     

The wheat gene <Emphasis Type="Italic">TaST</Emphasis> can increase the salt tolerance of transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

On the basis of the results of gene chip analysis of the salt-tolerant wheat mutant RH8706-49 under conditions of salt stress, we identified and cloned an unknown salt-induced gene TaST (Triticum aestivum salt-tolerant). Real-time quantitative PCR analysis showed that the expression of the gene was induced by salt stress. Transgenic Arabidopsis plants overexpressing the TaST gene showed higher salt tolerance than the wild-type controls. Subcellular localization studies revealed that the protein encoded by this gene was in the nucleus. In comparison with wild-type controls, transgenic Arabidopsis plants accumulated more Ca²⁺, soluble sugar, and proline and less Na⁺ under salt stress. Real-time quantitative PCR analysis showed that Arabidopsis plants overexpressing TaST also showed increased expression of many stress-related genes. All these findings indicated that TaST can enhance the salt tolerance of transgenic Arabidopsis plants.     

Effective salt criteria in callus-cultured tomato genotypes

Na+, Cl-, K+, Ca2+, and proline contents, the rate of lipid peroxidation level in terms of malondialdehyde (MDA) and chlorophyll content, and the changes in the activity of antioxidant enzymes, such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), ascorbate peroxidase (APX: EC 1.11.1.11), and glutathione reductase (GR: EC 1.6.4.2), in tissues of five tomato cultivars in salt tolerance were investigated in a callus culture. The selection of effective parameters used in these tomato genotypes and to find out the use of in vitro tests in place of in vivo salt tolerance tests were investigated. As a material, five different tomato genotypes during a 10-day time period were used, and 150 mM NaCl was applied at callus plant tissue. The exposure to NaCl induced a significant increase in MDA content in both salt-resistant and salt-sensitive cultivars. But the MDA content was higher in salt-sensitive cultivars. The chlorophyll content was more decreased in salt-sensitive than in salt-resistant ones. The proline amount was more increased in salt-sensitive than in salt-resistant ones. It has been reported that salt-tolerant plants, besides being able to regulate the ion and water movements, also exhibit a strong antioxidative enzyme system for effective removal of ROS. The degree of damage depends on the balance between the formation of ROS and its removal by the antioxidative scavenging system that protects against them. Exclusion or inclusion of Na+, Cl-, K+, and Ca2+, antioxidant enzymes and MDA concentration play a key protective role against stress, and this feature at the callus plant tissue used as an identifier for tolerance to salt proved to be an effective criterion.     

ACC氧化酶基因AhACOs对花生耐盐性的影响

ACC氧化酶(ACC oxidase,ACO)是催化乙烯合成的关键酶之一,乙烯参与植物的盐胁迫反应过程,而盐胁迫严重影响花生产量。本研究通过对AhACOs基因的克隆及功能验证,探究AhACOs在花生盐胁迫响应中的生物学功能,为花生耐盐品种的选育提供基因资源。以花生耐盐突变体M29的cDNA为模板扩增得到基因AhACO1和AhACO2,与植物表达载体pCAMBIA super1300重组后,通过农杆菌介导的花粉管注射法将重组质粒转化到花育22号中。收获后切取籽仁远胚端部分子叶,利用PCR检测筛选阳性籽仁。利用qRT-PCR分析AhACOs基因表达量,通过毛细管柱气相色谱法检测植株的乙烯释放量。阳性籽仁和对照籽仁种植21 d后浇盐水,观察其表型变化。结果发现,盐胁迫后,转基因植株生长状况好于对照组花育22号,并且其叶绿素相对含量SPAD(soil and plant analyzer development)值和净光合速率(net photosynthesis rate,Pn)均高于对照组花生。另外,AhACO1和AhACO_(2)转基因植株的乙烯释放量分别为对照组花生的2.79倍和1.87倍。这些结果表明AhACO1和AhACO2可显著提高花生的耐盐能力。     

Salt and oxidative stress: similar and specific responses and their relation to salt tolerance in Citrus

Salt damage to plants has been attributed to a combination of several factors including mainly osmotic stress and the accumulation of toxic ions. Recent findings in our laboratory showed that phospholipid hydroperoxide glutathione peroxidase (PHGPX), an enzyme active in the cellular antioxidant system, was induced by salt in citrus cells and mainly in roots of plants. Following this observation we studied the two most important enzymes active in elimination of reactive oxygen species, namely, superoxide dismutase (SOD) and ascorbate peroxidase (APX), to determine whether a general oxidative stress is induced by salt. While Cu/Zn-SOD activity and cytosolic APX protein level were similarly induced by salt and methyl viologen, the response of PHGPX and other APX isozymes was either specific to salt or methyl viologen, respectively. Unlike PHGPX, cytosolic APX and Cu/Zn-SOD were not induced by exogenously added abscisic acid. Salt induced a significant increase in SOD activity which was not matched by the subsequent enzyme APX. We suggest that the excess of H₂O₂ interacts with lipids to form hydroperoxides which in turn induce and are removed by PHGPX. Ascorbate peroxidase seems to be a key enzyme in determining salt tolerance in citrus as its constitutive activity in salt-sensitive callus is far below the activity observed in salt-tolerant callus, while the activities of other enzymes involved in the defence against oxidative stress, namely SOD, glutathione reductase and PHGPX, are essentially similar. Received: 10 January 1997 / Accepted: 28 May 1997     

耐盐杂草稻3个锌指蛋白基因家族的实时定量分析

利用在300余份来源于辽宁、吉林、黑龙江、内蒙古、江苏等地的杂草稻材料中筛选出耐高盐杂草稻材料WR03-12。通过RT-PCR的方法得到盐胁迫下WR03-12与盐敏感栽培稻‘越光’幼苗的cDNA第一链,对3个锌指蛋白基因家族的6个基因表达情况进行了荧光实时定量分析。结果表明,2个C2C2型锌指蛋白基因SRZ1与SRZ2受到高盐胁迫的负向诱导,WR03-12受负向诱导程度要小于‘越光’;2个TFIIIA型锌指蛋白基因ZFP18与ZFP245受到盐胁迫的正向诱导,WR03-12受诱导程度也小于‘越光’;具有A20锌指结构的基因AACZ1基因在越光中不受盐诱导,而在WR03-12中受短时间诱导后,第7天已经恢复到胁迫前水平。具有AN1锌指结构的基因AACZ2在‘越光’与WR03-12中均不受盐胁迫诱导,且表达水平没有显著差别。杂草稻WR03-12与‘越光’对于盐胁迫的应答机制可能在转录调控方面存在差别。     

Identification of early salt stress response genes in tomato root by suppression subtractive hybridization and microarray analysis

High salinity is one of the most serious threats to crop production. To understand the molecular basis of plant responses to salt stress better, suppression subtractive hybridization (SSH) and microarray approaches were combined to identify the potential important or novel genes involved in the early stage of tomato responses to severe salt stress. First, SSH libraries were constructed for the root tissue of two cultivated tomato (Solanum lycopersicum) genotypes: LA2711, a salt-tolerant cultivar, and ZS-5, a salt-sensitive cultivar, to compare salt treatment and non-treatment plants. Then a subset of clones from these SSH libraries were used to construct a tomato cDNA array and microarray analysis was carried out to verify the expression changes of this set of clones upon a high concentration of salt treatment at various time points compared to the corresponding non-treatment controls. A total of 201 non-redundant genes that were differentially expressed upon 30 min of severe salt stress either in LA2711 or ZS-5 were identified from microarray analysis; most of these genes have not previously been reported to be associated with salt stress. The diversity of the putative functions of these genes indicated that salt stress resulted in a complex response in tomato plants.     

Coordinate Gene Response to Salt Stress in Lophopyrum elongatum

Lophopyrum elongatum is a highly salt-tolerant relative of wheat. A previous study showed that the abundance of a number of mRNA species is enhanced or reduced in the roots of the L. elongatum × Triticum aestivum amphiploid by salt stress. Eleven genes with enhanced expression in the roots of salt-stressed L. elongatum plants have been cloned as cDNAs. The clones were used as probes to characterize temporal expression of these genes in roots after initiation of salt (250 mm NaCl) stress. All 11 genes are induced within 2 h after exposure to 250 mm NaCl and reached peak expression after 6 h. The decline of gene expression distinguished two groups, one in which mRNA concentrations returned to basal levels by 24 h and the other in which this occurred between 3 and 7 d. One of the 11 clones was found to be homologous to a multigene family of abscisic acid-induced genes, rab and dhn, identified in other species. We suggest that the coordinate expression of this large number of genes reflects the existence of a highly specific early response to salt stress. We refer to this response as the “early salt stress response.”