Gene encoding vesicle-associated membrane protein-associated protein from <Emphasis Type="Italic">Triticum aestivum</Emphasis> (<Emphasis Type="Italic">TaVAP</Emphasis>) confers tolerance to drought stress

Abiotic stresses like drought, salinity, high and low temperature, and submergence are major factors that limit the crop productivity. Hence, identification of genes associated with stress response in crops is a prerequisite for improving their tolerance to adverse environmental conditions. In an earlier study, we had identified a drought-inducible gene, vesicle-associated membrane protein-associated protein (TaVAP), in developing grains of wheat. In this study, we demonstrate that TaVAP is able to complement yeast and Arabidopsis mutants, which are impaired in their respective orthologs, signifying functional conservation. Constitutive expression of TaVAP in Arabidopsis imparted tolerance to water stress conditions without any apparent yield penalty. Enhanced tolerance to water stress was associated with maintenance of higher relative water content, photosynthetic efficiency, and antioxidant activities. Compared to wild type, the TaVAP-overexpressing plants showed enhanced lateral root proliferation that was attributed to higher endogenous levels of IAA. These studies are the first to demonstrate that TaVAP plays a critical role in growth and development in plants, and is a potential candidate for improving the abiotic stress tolerance in crop plants.     

Ectopic expression of ADP ribosylation factor 1 (SaARF1) from smooth cordgrass (Spartina alterniflora Loisel) confers drought and salt tolerance in transgenic rice and Arabidopsis

Salinity and drought are two very important abiotic stressors that negatively impact the growth and yield of all sensitive crop plants. Genes from halophytes have been shown to be useful to engineer crop plants that can survive under adverse soil and water conditions. The present report establishes, for the first time, the physiological role of a class one ADP ribosylation factor gene (SaARF1) from the halophyte Spartina alterniflora (smooth cordgrass) in imparting salinity and drought stress tolerance when expressed in both monocot (rice) and dicot (Arabidopsis) systems. The Arabidopsis and rice plants overexpressing ARF1 are many-fold more tolerant to salt and drought than wild-type (WT) plants. The transgenics exhibited improved growth and productivity relative to WT through tissue tolerance by maintaining higher relative water content and membrane stability, and higher photosynthetic yield by retaining higher chlorophyll concentration and fluorescence under stress conditions compared to WT. These findings indicated that genes from halophyte resources can be useful to engineer and improve salt and drought stress tolerance in both monocot and dicot plants.     

Overexpression of <Emphasis Type="Italic">Zm-HINT1</Emphasis> Confers Salt and Drought Tolerance in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Histidine triad nucleotide-binding protein 1 (HINT1) is highly conserved in many species and plays important roles in various biological processes. However, little is known about the responses of HINT1 to abiotic stress in plants. Salt and drought stress are major limiting factors for plant growth and development, and their negative effects on crop productivity may threaten the world’s food supply. Previously, we identified a maize gene, Zm-HINT1, which encodes a 138-amino-acid protein containing conserved domains including the HIT motif, helical regions, and β-strands. Here, we demonstrate that overexpression of Zm-HINT1 in Arabidopsis confers salt and drought tolerance to plants. Zm-HINT1 significantly regulated Na⁺ and K⁺ accumulation in plants under salt stress. The improve tolerance characteristics of Arabidopsis plants that were overexpressing Zm-HINT1 led to increased survival rates after salt and drought treatments. Compared with control plants, those plants that overexpressed Zm-HINT1 showed increased proline content and superoxide dismutase activity, as well as lower malondialdehyde and hydrogen peroxide accumulation under salt and drought treatments. The expression patterns of stress-responsive genes in Arabidopsis plants that overexpressed Zm-HINT1 significantly differed from those in control lines. Taken together, these results suggest that Zm-HINT1 has potential applications in breeding and genetic engineering strategies that are designed to produce new crop varieties with improved salt and drought tolerance.     

ABA Inducible Rice Protein Phosphatase 2C Confers ABA Insensitivity and Abiotic Stress Tolerance in Arabidopsis

Arabidopsis PP2C belonging to group A have been extensively worked out and known to negatively regulate ABA signaling. However, rice (Oryza sativa) orthologs of Arabidopsis group A PP2C are scarcely characterized functionally. We have identified a group A PP2C from rice (OsPP108), which is highly inducible under ABA, salt and drought stresses and localized predominantly in the nucleus. Genetic analysis revealed that Arabidopsis plants overexpressing OsPP108 are highly insensitive to ABA and tolerant to high salt and mannitol stresses during seed germination, root growth and overall seedling growth. At adult stage, OsPP108 overexpression leads to high tolerance to salt, mannitol and drought stresses with far better physiological parameters such as water loss, fresh weight, chlorophyll content and photosynthetic potential (Fv/Fm) in transgenic Arabidopsis plants. Expression profile of various stress marker genes in OsPP108 overexpressing plants revealed interplay of ABA dependent and independent pathway for abiotic stress tolerance. Overall, this study has identified a potential rice group A PP2C, which regulates ABA signaling negatively and abiotic stress signaling positively. Transgenic rice plants overexpressing this gene might provide an answer to the problem of low crop yield and productivity during adverse environmental conditions.     

JcLEA,a Novel LEA-Like Protein from Jatropha curcas,Confers a High Level of Tolerance to Dehydration and Salinity in Arabidopsis thaliana

Jatropha curcas L. is a highly drought and salt tolerant plant species that is typically used as a traditional folk medicine and biofuel crop in many countries. Understanding the molecular mechanisms that underlie the response to various abiotic environmental stimuli, especially to drought and salt stresses, in J. curcas could be important to crop improvement efforts. In this study, we cloned and characterized the gene for a late embryogenesis abundant (LEA) protein from J. curcas that we designated JcLEA. Sequence analyses showed that the JcLEA protein belongs to group 5, a subgroup of the LEA protein family. In young seedlings, expression of JcLEA is significantly induced by abscisic acid (ABA), dehydration, and salt stress. Subcellular localization analysis shows that that JcLEA protein is distributed in both the nucleus and cytoplasm. Moreover, based on growth status and physiological indices, the overexpression of JcLEA in transgenic Arabidopsis plants conferred increased resistance to both drought and salt stresses compared to the WT. Our data suggests that the group 5 JcLEA protein contributes to drought and salt stress tolerance in plants. Thus, JcLEA is a potential candidate gene for plant genetic modification.     

Isolation and characterization of two sorbitol transporter gene promoters in micropropagated apple plants (Malus?×?domestica) regulated by drought stress

The role of polyol transporters in stress tolerance in plants have been elucidated by many studies. Sorbitol transporter genes MdSOT3, MdSOT4 and MdSOT5 in apple plants, which are important for sorbitol loading and unloading, are regulated by drought stress. To further confirm the role of sorbitol transporters in stress tolerance, the constructs harboring MdSOT3 and MdSOT5 genes were introduced into wild type Arabidopsis plants (Col-0) and the Arabidopsis transformed with MdSOT3 or MdSOT5 performed higher drought stress tolerance compared to WT. In order to further understand how sorbitol transporters are involved in drought tolerance in apple plants, upstream regions of sorbitol transporter genes were isolated from apple plant source leaves by Anchored PCR from genomic DNA obtained, and then were used to drive expression of the GUS reporter in tobacco plants. The results showed that the longest fragments of MdSOT3 and MdSOT5 promoters induced the highest GUS activity under drought stress conditions. Additionally, fragments of these promoters that contain cis-acting elements known to be involved in stress response also induced GUS activity under drought stress. Taken together, our data suggest that increased MdSOT3 and MdSOT5 activity, through cis-acting elements in the promoters of these genes, play important roles in imparting tolerance to drought in micropropagated apple plants.     

毛尖紫萼藓干旱胁迫cDNA文库的构建

干旱胁迫是影响植物生长发育的主要环境因素,严重影响农作物的产量。解决这个问题的有效途径是培育和利用优良的抗旱品种。应用比较功能基因组学方法筛选抗旱相关基因,并通过基因工程培育抗旱品种已成为植物遗传资源与品种改良研究的重要内容。毛尖紫萼藓（Grimmia pilifera）是典型旱生藓类,生长在向阳的裸岩上,具有很强的抗旱能力,是很好的抗旱基因资源。本研究采用SMART技术构建毛尖紫萼藓干旱cDNA文库,文库滴度为2.8×10⁵ pfu·mL^-1,重组率为91.7%,插入片段大小为500~2 000 bp,平均为800 bp。通过测序我们获得了1 045条ESTs,其中高质量的996条,通过拼接获得875个Unigenes,为进一步筛选抗旱相关基因奠定了基础。     

OsASR5 enhances drought tolerance through a stomatal closure pathway associated with ABA and H2O2 signalling in rice

Drought is one of the major abiotic stresses that directly implicate plant growth and crop productivity. Although many genes in response to drought stress have been identified, genetic improvement to drought resistance especially in food crops is showing relatively slow progress worldwide. Here, we reported the isolation of abscisic acid, stress and ripening (ASR) genes from upland rice variety, IRAT109 (Oryza sativa L. ssp. japonica), and demonstrated that overexpression of OsASR5 enhanced osmotic tolerance in Escherichia coli and drought tolerance in Arabidopsis and rice by regulating leaf water status under drought stress conditions. Moreover, overexpression of OsASR5 in rice increased endogenous ABA level and showed hypersensitive to exogenous ABA treatment at both germination and postgermination stages. The production of H₂O₂, a second messenger for the induction of stomatal closure in response to ABA, was activated in overexpression plants under drought stress conditions, consequently, increased stomatal closure and decreased stomatal conductance. In contrast, the loss‐of‐function mutant, osasr5, showed sensitivity to drought stress with lower relative water content under drought stress conditions. Further studies demonstrated that OsASR5 functioned as chaperone‐like protein and interacted with stress‐related HSP40 and 2OG‐Fe (II) oxygenase domain containing proteins in yeast and plants. Taken together, we suggest that OsASR5 plays multiple roles in response to drought stress by regulating ABA biosynthesis, promoting stomatal closure, as well as acting as chaperone‐like protein that possibly prevents drought stress‐related proteins from inactivation.     

Overexpression of <Emphasis Type="Italic">MeDREB1D</Emphasis> confers tolerance to both drought and cold stresses in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

Cassava (Manihot esculenta) is an important tropical crop with extraordinary tolerance to drought stress but few reports on it. In this study, MeDREB1D was significantly and positively induced by drought stress. Two allelic variants of the gene named MeDREB1D(R-2) and MeDREB1D(Y-3) were identified. Overexpressing MeDREB1D(R-2) and MeDREB1D(Y-3) in Arabidopsis resulted in stronger tolerance to drought and cold stresses. Under drought stress, transgenic plants had more biomass, higher survival rates and less MDA content than wild-type plants. Under cold stress, transgenic plants also had higher survival rates than wild-type plants. To further characterize the molecular function of MeDREB1D, we conducted an RNA-Seq analysis of transgenic and wild-type Arabidopsis plants. The results showed that the Arabidopsis plants overexpressing MeDREB1D led to changes in downstream genes. Several POD genes, which may play a vital role in drought and cold tolerance, were up-regulated in transgenic plants. In brief, these results suggest that MeDREB1D can simultaneously improve plant tolerance to drought and cold stresses.     

Overexpression of a wheat phospholipase D gene,TaPLDα, enhances tolerance to drought and osmotic stress in Arabidopsis thaliana

Phospholipase D (PLD) is crucial for plant responses to stress and signal transduction, however, the regulatory mechanism of PLD in abiotic stress is not completely understood; especially, in crops. In this study, we isolated a gene, TaPLDα, from common wheat (Triticum aestivum L.). Analysis of the amino acid sequence of TaPLDα revealed a highly conserved C2 domain and two characteristic HKD motifs, which is similar to other known PLD family genes. Further characterization revealed that TaPLDα expressed differentially in various organs, such as roots, stems, leaves and spikelets of wheat. After treatment with abscisic acid (ABA), methyl jasmonate, dehydration, polyethylene glycol and NaCl, the expression of TaPLDα was up-regulated in shoots. Subsequently, we generated TaPLDα-overexpressing transgenic Arabidopsis lines under the control of the dexamethasone-inducible 35S promoter. The overexpression of TaPLDα in Arabidopsis resulted in significantly enhanced tolerance to drought, as shown by reduced chlorosis and leaf water loss, higher relative water content and lower relative electrolyte leakage than the wild type. Moreover, the TaPLDα-overexpressing plants exhibited longer roots in response to mannitol treatment. In addition, the seeds of TaPLDα-overexpressing plants showed hypersensitivity to ABA and osmotic stress. Under dehydration, the expression of several stress-related genes, RD29A, RD29B, KIN1 and RAB18, was up-regulated to a higher level in TaPLDα-overexpressing plants than in wild type. Taken together, our results indicated that TaPLDα can enhance tolerance to drought and osmotic stress in Arabidopsis and represents a potential candidate gene to enhance stress tolerance in crops.     

Functional Genomics of Drought Tolerance in Bioenergy Crops

With predicted global changes in temperature and precipitation, drought will increasingly impose a challenge to biomass production. Most of the bioenergy crops have some degree of drought susceptibility as revealed for example through measures of low water-use efficiency (WUE). It is imperative to improve drought tolerance and WUE in bioenergy crops for sustainable biomass production in arid and semi-arid regions. Genetics and functional genomics can play critical roles in generating knowledge to inform and aid genetic improvement for drought tolerance in bioenergy crops. The molecular aspects of drought response have been extensively investigated in model plants like Arabidopsis, yet our understanding of the molecular mechanisms underlying drought tolerance in bioenergy crops is limited. Plants in general exhibit various responses to drought stress depending on species and genotype. A rational strategy for studying drought tolerance in bioenergy crops is to translate the knowledge from model plants relative to the unique features associated with individual bioenergy species and genotypes. In this review, we summarize the general knowledge concerning drought responsive pathways, with a focus on the identification of commonality and specialty in drought responsive mechanisms among alternate species and genotypes. We describe the genomic resources developed for bioenergy crops and discuss genetic and epigenetic regulation of drought responses. We also examine comparative and evolutionary genomics as a means to leverage the ever-increasing genomics resources and provide new insights beyond what is known from studies on individual species. Finally, we outline future opportunities for studying drought tolerance using the emerging technologies.     

Transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> Plants Expressing Grape Glutathione S-Transferase Gene (<Emphasis Type="Italic">VvGSTF13</Emphasis>) Show Enhanced Tolerance to Abiotic Stress

Although glutathione S-transferase (GST, EC 2.5.1.18) is thought to play important roles in abiotic stress, limited information is available regarding the function of its gene in grapes. In this study, a GST gene from grape, VvGSTF13, was cloned and functionally characterized. Transgenic Arabidopsis plants containing this gene were normal in terms of growth and maturity compared with control plants but had enhanced resistance to salt, drought, and methyl viologen stress. The increased tolerance of the transgenic plants correlated with changes in activities of antioxidative enzymes. Our results indicate that the gene from grape plays a positive role in improving tolerance to salinity, drought, and methyl viologen stresses in Arabidopsis.     

Overexpression of three orthologous glutathione S-transferases from Populus increased salt and drought resistance in Arabidopsis

Glutathione S-transferases (GSTs) are multifunctional proteins and play a role in detoxification of xenobiotics as well as prevention of oxidative damage. This study exogenously overexpressed PtGSTF4 from Populus trichocarpa and its two orthologs from Populus yatungensis and Populus euphratica in Arabidopsis thaliana, respectively. To elucidate the function of three GSTF4 proteins in stress response, we compared germination and seedling growth in transgenic Arabidopsis with salt and drought treatments. All three Populus GSTF4 genes overexpressed Arabidopsis showed enhanced resistance to salt stress and drought. GSTF4 transgenic plants accumulated less hydrogen peroxide and more chlorophylls and decreased levels of lipid peroxidation under salt stress and drought comparing to the mock control plants. The difference observed by GSH and GSSG measurements indicated GSTF4 proteins may involve in glutathione-dependent peroxide scavenging which lead to reduced oxidative damage. The Arabidopsis transformed with the GSTF4 gene form P. euphratica showed higher germination rate and different performance of affecting GSSG contents comparing with the other two orthologous GST genes under NaCl treatment. These results suggested three Populus GSTF4 orthologs may have functional divergence in stress responding. This study provides insights into molecular mechanisms that underlie salt and drought stress tolerance of Phi GSTs and gives evidence for the functional divergence among orthologs in vivo.     

Evidence for the role of wheat eukaryotic translation initiation factor 3 subunit g (TaeIF3g) in abiotic stress tolerance

The gene encoding eIF3g (TaeIF3g), one of the 11 subunits of eukaryotic translation initiation factor 3 (eIF3), was cloned from wheat for carrying out its functional analysis. Transgenic expression of TaeIF3g enhanced the tolerance of TaeIF3g-overexpressing parental yeast cells and Arabidopsis plants under different abiotic stress conditions. Compared to untransformed plants, TaeIF3g-overexpressing Arabidopsis thaliana plants exhibited significantly higher survival rate, soluble proteins and photosynthetic efficiency, and enhanced protection against photooxidative stress under drought conditions. This study provides first evidence that TaeIF3g imparts stress tolerance and could be a potential candidate gene for developing crop plants tolerant to abiotic stress.