Improved Drought Stress Tolerance Research Articles

Ectopic Expression of OsPYL/RCAR7, an ABA Receptor Having Low Signaling Activity, Improves Drought Tolerance without Growth Defects in Rice.

Overexpression of abscisic acid (ABA) receptors has been reported to enhance drought tolerance, but also to cause stunted growth and decreased crop yield. Here, we constructed transgenic rice for all monomeric ABA receptors and observed that only transgenic rice over-expressing OsPYL/RCAR7 showed similar phenotype with wild type, without total yield loss when grown under normal growth condition in a paddy field. Even though transgenic rice over-expressing OsPYL/RCAR7 showed neither an ABA-sensitivity nor an osmotic stress tolerance in plate assay, it showed drought tolerance. We investigated the ABA-dependent interaction with OsPP2CAs and ABA signaling induction by OsPYL/RCAR7. In yeast two hybrid assay, OsPYL/RCAR7 required critically higher ABA concentrations to interact with OsPP2CAs than other ABA receptors, and co-immunoprecipitation assay showed strong interaction under ABA treatment. When ABA-responsive signaling activity was monitored using a transient expression system in rice protoplasts, OsPYL/RCAR7 had the lowest ABA-responsive signaling activity as compared with other ABA receptors. OsPYL/RCAR7 also showed weak suppression of phosphatase activity as compared with other ABA receptors in vitro. Transcriptome analysis of transgenic rice over-expressing OsPYL/RCAR7 suggested that only a few genes were induced similar to control under without exogenous ABA, but a large number of genes was induced under ABA treatment compared with control. We conclude that OsPYL/RCAR7 is a novel functional ABA receptor that has low ABA signaling activity and exhibits high ABA dependence. These results lay the foundation for a new strategy to improve drought stress tolerance without compromising crop growth.

Genome-wide identification of MAPK cascade genes reveals the GhMAP3K14-GhMKK11-GhMPK31 pathway is involved in the drought response in cotton.

The mitogen-activated protein kinase (MAPK) cascade pathway, which has three components, MAP3Ks, MKKs and MPKs, is involved in diverse biological processes in plants. In the current study, MAPK cascade genes were identified in three cotton species, based on gene homology with Arabidopsis. Selection pressure analysis of MAPK cascade genes revealed that purifying selection occurred among the cotton species. Expression pattern analysis showed that some MAPK cascade genes differentially expressed under abiotic stresses and phytohormones treatments, and especially under drought stress. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) experiments showed extensive interactions between different MAPK cascade proteins. Virus-induced gene silencing (VIGS) assays showed that some MAPK cascade modules play important roles in the drought stress response, and the GhMAP3K14-GhMKK11-GhMPK31 signal pathway was demonstrated to regulate drought stress tolerance in cotton. This study provides new information on the function of MAPK cascade genes in the drought response, and will help direct molecular breeding for improved drought stress tolerance in cotton.

A U-box E3 ubiquitin ligase OsPUB67 is positively involved in drought tolerance in rice.

OsPUB67, a U-box E3 ubiquitin ligase, may interact with two drought tolerance negative regulators (OsRZFP34 and OsDIS1) and improve drought tolerance by enhancing the reactive oxygen scavenging ability and stomatal closure. E3 ubiquitin ligases are major components of the ubiquitination cascade and contribute to the biotic and abiotic stress response in plants. In the present study, we show that a rice drought responsive gene, OsPUB67, encoding the U-box E3 ubiquitin ligase was significantly induced by drought, salt, cold, JA, and ABA, and was expressed in nuclei, cytoplasm, and membrane systems. This distribution of expression suggests a significant role for OsPUB67 in a wide range of biological processes and abiotic stress response. Over-expression of OsPUB67 improved drought stress tolerance by enhancing the reactive oxygen scavenging ability and stomatal closure. Bimolecular fluorescence complementation assays revealed that a few E2s interacted with OsPUB67 with unique functional implications in different cell components. Further evidence showed that several E3 ubiquitin ligases interacted with OsPUB67, especially OsRZFP34 and OsDIS1, which are negative regulators of drought tolerance. This interaction on the stomata implied OsPUB67 might function as a heterodimeric ubiquitination complex in response to drought stress. Comprehensive transcriptome analysis revealed OsPUB67 participated in regulating genes involved in the abiotic stress response and transcriptional regulation in an ABA-dependent manner. Our findings revealed OsPUB67 mediated a multilayered complex drought stress tolerance mechanism.

Genome-wide association study and genomic prediction analyses of drought stress tolerance in China in a collection of off-PVP maize inbred lines

Phenotypic evaluation of the drought-tolerant traits and identification of the genetic markers associated with these traits in diverse germplasms are essential for developing drought-tolerant germplasm through molecular breeding. A collection of 210 off-PVP (no longer subject to Plant Variety Protection) maize inbred lines introduced from the USA (ALs) were genotyped using a low-coverage sequencing method and phenotyped in eight environments (location × year × treatment) in China. The CV of phenotypic data for six target traits varied from 5.34 to 20.69% under well-watered (WW) conditions and from 5.46 to 35.98% under drought-stressed (WS) conditions. ALs exhibited higher grain yield per plot (GY) under the WS conditions and premature characteristic compared with the local checks, which are important breeding targets in drought tolerance. Two subgroups, SS and NSS, were identified in this collection based on population structure analysis, PCA, and an NJ tree. A total of 413 trait-associated SNPs under the WW conditions and 696 SNPs under the WS conditions were detected in a GWAS (genome-wide association study) analysis, with the phenotypic variation explained by each SNP to the target traits varied from 10.02 to 25.40%. In the genomic prediction (GP) analysis, the prediction models incorporating trait-marker associations showed higher prediction accuracies than the prediction models using an equivalent number of randomly selected SNPs for all the six traits evaluated under both the WW and WS conditions. The results observed in this study provide valuable information for understanding the genetic variation of drought stress tolerance in maize, and show great potential to improve drought stress tolerance in maize via genomic selection.

Exogenously applied proline induced changes in key anatomical features and physio-biochemical attributes in water stressed oat (Avena sativa L.) plants.

Oat (Avena sativa) plants grown under 60% field capacity (water-deficit stress) were subjected to proline (40mM) applied as a foliage spray. Water-deficit conditions suppressed plant growth, chlorophyll contents, leaf vascular bundle area, leaf phloem area and leaf midrib thickness, root diameter, root cortex thickness, stem diameter, stem vascular bundle area and stem phloem area. In contrast, water stress caused an increase in leaf proline, hydrogen peroxide, activities of peroxidase and superoxide dismutase enzymes, leaf bulliform cell area, leaf adaxial epidermis thickness, leaf sclerenchyma thickness, root metaxylem area, root epidermis and endodermis area, root stelar diameter, stem sclerenchyma thickness and stem epidermis thickness. However, exogenous application of proline significantly improved the plant growth, leaf proline contents, metaxylem area, mesophyll thickness, root diameter, root cortex thickness, root epidermis, endodermis thickness, stelar diameter, metaxylem area, stem diameter, stem vascular bundle area, stem epidermis area, stem phloem area and stem sclerenchyma thickness. Overall, foliar spray of proline was effective in improving drought stress tolerance which can be attributed to proline-induced significant modulations in physio-biochemical and anatomical features of oat plants.

Drought Stress Tolerance in Wheat and Barley: Advances in Physiology, Breeding and Genetics Research.

Climate change is a major threat to most of the agricultural crops grown in tropical and sub-tropical areas globally. Drought stress is one of the consequences of climate change that has a negative impact on crop growth and yield. In the past, many simulation models were proposed to predict climate change and drought occurrences, and it is extremely important to improve essential crops to meet the challenges of drought stress which limits crop productivity and production. Wheat and barley are among the most common and widely used crops due to their economic and social values. Many parts of the world depend on these two crops for food and feed, and both crops are vulnerable to drought stress. Improving drought stress tolerance is a very challenging task for wheat and barley researchers and more research is needed to better understand this stress. The progress made in understanding drought tolerance is due to advances in three main research areas: physiology, breeding, and genetic research. The physiology research focused on the physiological and biochemical metabolic pathways that plants use when exposed to drought stress. New wheat and barley genotypes having a high degree of drought tolerance are produced through breeding by making crosses from promising drought-tolerant genotypes and selecting among their progeny. Also, identifying genes contributing to drought tolerance is very important. Previous studies showed that drought tolerance is a polygenic trait and genetic constitution will help to dissect the gene network(s) controlling drought tolerance. This review explores the recent advances in these three research areas to improve drought tolerance in wheat and barley.

Improved drought stress tolerance in Arabidopsis by CRISPR/dCas9 fusion with a Histone AcetylTransferase

Drought episodes decrease plant growth and productivity, which in turn cause high economic losses. Plants naturally sense and respond to water stress by activating specific signalling pathways leading to physiological and developmental adaptations. Genetically engineering genes that belong to these pathways might improve the drought tolerance of plants. The abscisic acid (ABA)-responsive element binding protein 1/ABRE binding factor (AREB1/ABF2) is a key positive regulator of the drought stress response. We investigated whether the CRISPR activation (CRISPRa) system that targets AREB1 might contribute to improve drought stress tolerance in Arabidopsis. Arabidopsis histone acetyltransferase 1 (AtHAT1) promotes gene expression activation by switching chromatin to a relaxed state. Stable transgenic plants expressing chimeric dCas9HAT were first generated. Then, we showed that the CRISPRa dCas9HAT mechanism increased the promoter activity controlling the β-glucuronidase (GUS) reporter gene. To activate the endogenous promoter of AREB1, the CRISPRa dCas9HAT system was set up, and resultant plants showed a dwarf phenotype. Our qRT-PCR experiments indicated that both AREB1 and RD29A, a gene positively regulated by AREB1, exhibited higher gene expression than the control plants. The plants generated here showed higher chlorophyll content and faster stomatal aperture under water deficit, in addition to a better survival rate after drought stress. Altogether, we report that CRISPRa dCas9HAT is a valuable biotechnological tool to improve drought stress tolerance through the positive regulation of AREB1.

Transcriptome-Wide Characterization and Functional Identification of the Aquaporin Gene Family During Drought Stress in Common Vetch.

Aquaporins (AQPs) are transmembrane channels that are essential for the movement of water and other small molecules between biofilms in various physiological processes in plants. In this study, based on transcriptome-wide data, we identified and described a total of 21 AQP genes in common vetch (Vicia sativa subsp. sativa), which is an economically important pasture legume worldwide. Based on phylogenetic analyses, the VsAQPs were sorted into four subfamilies, including four plasma membrane intrinsic proteins (PIPs), six tonoplast intrinsic proteins (TIPs), seven NOD26-like intrinsic proteins, and four small basic intrinsic proteins. Furthermore, chemical and physical properties of these VsAQPs, including the isoelectric point and theoretical molecular weight, were analyzed. Analyses of the AQP signature sequences and key residues indicated the substrate specificity of each VsAQP. A set of VsAQPs was selected for gene expression analysis in a number of tissues and after drought stress treatments using real-time quantitative reverse transcription/polymerase chain reaction assays. Most of the PIPs and TIPs were proposed to have critical roles in regulating the flow of water during drought stress. Heterologous expression experiments in yeast indicated that VsPIP1;2 and VsPIP2;2 are key candidate genes for improving drought stress tolerance. The results reported in this study could be a crucial resource for further practical analyses and for genetic improvement of drought stress tolerance in common vetch.

Genome-Wide Association Studies Reveal Genomic Regions Associated With the Response of Wheat (Triticum aestivum L.) to Mycorrhizae Under Drought Stress Conditions.

In the majority of wheat growing areas worldwide, the incidence of drought stress has increased significantly resulting in a negative impact on plant development and grain yield. Arbuscular mycorrhizal symbiosis is known to improve drought stress tolerance of wheat. However, quantitative trait loci (QTL) involved in the response to drought stress conditions in the presence of mycorrhizae are largely unknown. Therefore, a diverse set consisting of 94 bread wheat genotypes was phenotyped under drought stress and well watered conditions in the presence and absence of mycorrhizae. Grain yield and yield components, drought stress related traits as well as response to mycorrhizae were assessed. In parallel, wheat accessions were genotyped by using the 90k iSelect chip, resulting in a set of 15511 polymorphic and mapped SNP markers, which were used for genome-wide association studies (GWAS). In general, drought stress tolerance of wheat was significantly increased in the presence of mycorrhizae compared to drought stress tolerance in the absence of mycorrhizae. However, genotypes differed in their response to mycorrhizae under drought stress conditions. Several QTL regions on different chromosomes were detected associated with grain yield and yield components under drought stress conditions. Furthermore, two genome regions on chromosomes 3D and 7D were found to be significantly associated with the response to mycorrhizae under drought stress conditions. Overall, the results reveal that inoculation of wheat with mycorrhizal fungi significantly improves drought stress tolerance and that QTL regions associated with the response to mycorrhizae under drought stress conditions exist in wheat. Further research is necessary to validate detected QTL regions. However, this study may be the starting point for the identification of candidate genes associated with drought stress tolerance and response to mycorrhizae under drought stress conditions. Maybe in future, these initial results will help to contribute to use mycorrhizal fungi effectively in agriculture and combine new approaches i.e., use of genotypic variation in response to mycorrhizae under drought stress conditions with existing drought tolerance breeding programs to develop new drought stress tolerant genotypes.

Isolation and characterization of MbWRKY1, a WRKY transcription factor gene from Malus baccata (L.) Borkh involved in drought tolerance

WRKY transcription factors are involved in stress responses in plants; however, their roles in abiotic stresses are still not well known in Malus plants. In the present study, a WRKY gene was isolated from Malus baccata (L.) Borkh and designated as MbWRKY1. Subcellular localization revealed that MbWRKY1 was localized in the nucleus. The expression levels of MbWRKY1 were up-regulated by dehydration, salinity, and ABA treatments in M. baccata seedlings. When MbWRKY1 was introduced into tobacco, it improved drought stress tolerance in transgenic plants. Under the drought treatment, transgenic plants had higher contents of chlorophyll, proline, relative water, AsA, and GSH than wild-type (WT) plants. Compared with WT plants, the overexpression of MbWRKY1 in transgenic tobacco also led to decreased levels of H2O2, MDA, and elecrolyte leakage when dealing with drought stress. There were increased activities of POD, CAT, SOD, and APX in transgenic tobaccos, especially when dealing with drought treatment. Moreover, the MbWRKY1 transgenic plants enhanced the expressions of oxidative stress response (NtPOD, NtCAT, NtSOD, and NtAPX) and stress-related genes (NtP5CS and NtLEA5) when dealing with drought stress. These results suggest that the MbWRKY1 gene plays a positive regulatory role in drought stress response.

Penconazole and calcium improves drought stress tolerance and oil quality in canola

ABSTRACTIn this study, the effects of penconazole (PEN) and calcium (Ca) on growth amelioration and quality of seed oil in canola (Brassica napus L.) under drought stress were investigated. Drought stress reduced the growth parameters (fresh weight and dry weight) in canola; however the application of PEN and Ca improved these parameters under drought condition. Inducing effect of Ca on protein content was more prominent than PEN. Proline content increased under drought stress and PEN and Ca treatment caused more induction it under drought. PEN and Ca alleviated the negative effects of drought stress in canola by inducing antioxidant defense. The application of PEN and Ca caused a significant reduction in lipid peroxidation and hydrogen peroxide and mitigation of the drought induced oxidative stress. Drought stress induced protein content, total phenol, flavonol content, soluble sugar, palmitic acid and palmitoloic acid, and reduced flavonoid content, oleic acid, linolenic acid, and linolonoic acid in canola seed. PEN and Ca increased palmitic acid, linoleic acid (Omega-6), linolenic acid (Omega-3), oleic acid, protein, and soluble sugar. Our results indicated that application of PEN and Ca enables canola plants to withstand the deleterious impact of drought stress and caused improvement of antioxidant capacity, essential fatty acids (linolenic acid and linolonoic acid) and oil quality in canola seed.

Overexpression of AtPYL5 under the control of guard cell specific promoter improves drought stress tolerance in Arabidopsis

PYR/PYLs function as ABA receptors and are key regulators during plant drought stress response. Previously we screened drought tolerance of Arabidopsis ABA receptors PYR/PYLs under the control of five different promoters. In this study, we characterized drought stress tolerance of AtPYL5 transgene under the control of one guard cell specific promoter, pGC1. pGC1::AtPYL5 transgenic Arabidopsis exhibited reduced transpiration rate and decreased water loss after drought treatment. Transformation of pGC1::AtPYL5 in Arabidopsis also decreased oxidative stress damage and improved photosynthesis under drought stress condition. These results indicated that pGC1::AtPYL5 construct is effective and might pave new way to develop genetically engineered plants to improve drought stress tolerance.

Overexpression of a SBP-Box Gene (VpSBP16) from Chinese Wild Vitis Species in Arabidopsis Improves Salinity and Drought Stress Tolerance.

Salinity and drought are two major abiotic stresses that limit grape productivity. Responses to stress in grape are known to be regulated by several families of transcription factors. However, little is known about the role of grape Squamosa promoter binding protein (SBP)-box transcription factor genes in response to abiotic stress. To better understand the functions of the grape SBP-box genes in abiotic stress tolerance, a full-length complementary DNA (cDNA) sequence of the putative SBP-box transcription factor gene, VpSBP16 was amplified from Chinese wild grapevine Vitis pseudoreticulata clone “Baihe-35-1”. We observed that the VpSBP16 protein fused to the green fluorescent protein (GFP) reporter accumulated in the nucleus when transiently expressed in onion epidermal cells. Moreover, VpSBP16 was shown to have transcriptional activation activity using a yeast trans-activation assay. We performed a VpSBP16 functional analysis through the characterization of transgenic Arabidopsis thaliana plants constitutively over-expressing VpSBP16. The transgenic lines had longer roots and the seeds had a higher germination rate than the wild type (WT) under osmotic stress. In addition, the accumulation of reactive oxygen species (ROS) of transgenic seedlings was significantly lower than WT in the transgenic lines, as was electrolyte leakage. VpSBP16 overexpression also elevated expression levels of stress-response genes involved in the salt overly sensitive (SOS) pathway. These results indicate that overexpression VpSBP16 in A. thaliana enhances tolerance of salt and drought stress during seed germination, as well in seedlings and mature plants, by regulating SOS and ROS signaling cascades.

Isolation and characterization of MbWRKY2 gene involved in enhanced drought tolerance in transgenic tobacco

ABSTRACTPlant-specific WRKY transcription factors are widely involved in abiotic stress responses. In this study, a WRKY gene was isolated from Malus baccata (L.) Borkh and designated it as MbWRKY2. Subcellular localization showed that MbWRKY2 was localized in the nucleus. The expression levels of MbWRKY2 were up-regulated by abiotic stresses in M. baccata. When MbWRKY2 was introduced into tobacco, it improved drought stress tolerance in transgenic plants. The transgenic tobaccos had the higher contents of chlorophyl, proline, relative water content, AsA, and GSH, increased activities of CAT, APX, SOD, and POD, and decreased levels of MDA, H2O2, and electrolyte leakage than wild-type, especially when dealt with dehydration treatment. Moreover, the MbWRKY2-OE plants enhanced the expression of oxidative stress response and stress-related genes involved in osmotic adjustment and membrane protection. These results suggest that MbWRKY2 gene plays a positive regulatory role in drought stress response.

Molecular cloning and functional analysis of MbWRKY3 involved in improved drought tolerance in transformed tobacco

ABSTRACTPlant-specific WRKY transcription factors were involved in stress responses and ABA signaling. In the present study, a WRKY gene is isolated from Malus baccata (L.) Borkh and designated as MbWRKY3. Subcellular localization revealed that MbWRKY3 was localized onto nucleus. The MbWRKY3 expression levels were up-regulated by salinity, drought, and ABA treatments in M. baccata. When MbWRKY3 was introduced into tobaccos, it improved drought stress tolerance in transgenic plants. Compared to WT, the transgenic tobaccos had the higher levels of relative water content, and proline and chlorophyll contents, decreased levels of electrolyte leakage, MDA, and H2O2, increased activities of the reactive oxygen species-related enzymes (SOD, CAT, and POD), and greater up-regulations of the corresponding genes (NtSOD, NtCAT, and NtPOD), especially when dealt with drought stress. These results suggest that MbWRKY3 gene plays a positive regulatory role in drought stress response.

Silencing of OsGRXS17 in rice improves drought stress tolerance by modulating ROS accumulation and stomatal closure

Glutaredoxins (GRXs) modulate redox-dependent signaling pathways and have emerged as key mediators in plant responses to environmental stimuli. Here we report that RNAi-mediated suppression of Oryza sativa GRXS17 (OsGRXS17) improved drought tolerance in rice. Gene expression studies showed that OsGRXS17 was present throughout the plant and that transcript abundance increased in response to drought stress and abscisic acid (ABA) treatment. Localization studies, utilizing GFP-OsGRXS17 fusion proteins, indicated that OsGRXS17 resides in both the cytoplasm and the nuclear envelope. Under drought stress conditions, rice plants with reduced OsGRXS17 expression showed lower rates of water loss and stomatal conductance, higher relative water content, and enhanced survival compared to wild-type controls. Further characterization of the OsGRXS17 down-regulated plants revealed an elevation in H2O2 production within the guard cells, increased sensitivity to ABA, and a reduction in stomatal apertures. The findings demonstrate a critical link between OsGRXS17, the modulation of guard cell H2O2 concentrations, and stomatal closure, expanding our understanding of the mechanisms governing plant responses to drought.

Drought stress‐induced changes in starch yield and physiological traits in potato

AbstractDrought stress is an important limitation for potato (Solanum tuberosum L.) production as potato depends on appropriate water availability for high yields of good quality. Therefore, especially in the background of climate change, it is an important goal in potato breeding to improve drought stress tolerance. In this study, 34 European starch potato cultivars were evaluated for drought stress tolerance by growing under well‐watered and long‐term drought stress conditions in rainout shelters in 2 years’ pot trials. Besides yield, six physiological traits, that is free proline content, osmolality, total soluble sugar content, chlorophyll content (SPAD), cell membrane stability and crude protein content, were determined in leaves sampled during vegetative growth and during flowering to investigate their association with drought tolerance. ANOVA revealed significant treatment effects for all physiological traits and increased genotypic effects at flowering. The sensitivity of physiological traits to drought was significantly higher during flowering than during vegetative growth. Drought stress decreased starch yield significantly (p < .001), on average by 55%. Starch yield was significantly influenced by genotype and genotype × treatment interactions. Stress tolerance index (STI) calculated from starch yield ranged from 0.26 (sensitive) to 0.76 (tolerant) with significant genotype effects (p ≤ .001). STI correlated positively with cell membrane stability (r = .59) and crude protein content (r = .38) and negatively with osmolality (r = −.57) and total soluble sugar content (r = −.71). These contrary correlations suggest a dual adaptation strategy in potato under long‐term drought stress conditions including increased membrane stability combined with an increased osmolality due to an increased soluble sugar content.

Exogenous applications of Polyamines modulate drought responses in wheat through osmolytes accumulation, increasing free polyamine levels and regulation of polyamine biosynthetic genes

Polyamines (PAs) can improve drought stress tolerance in plants; however, very limited information is available on the mechanism of action of exogenous application by different methods under drought stress in wheat. The present study investigates the mechanism through which seed priming and foliar spraying with PAs protect wheat plants from drought stress. 10 days old wheat seedlings were exposed to drought stress by withholding water alone or with 100 μM PAs solutions (putrescine, Put; spermine, Spm; and mixture of Put and Spm for 10 h seed-priming or three foliar sprays during withholding water. Drought stress impaired the wheat growth and altered the osmoprotectants, endogenous PAs levels, PAs biosynthetic genes expression and weight of 1000 grains compared to the corresponding control values. Exogenously applied PAs improved cell water status, accumulated osmoprotectants and PAs and up-regulated PAs biosynthetic genes, ADC, arginine decarboxylase; DHS, deoxyhypusine synthase; ODC, ornithine decarboxylase and SAMDC, S-adenosyl methionine decarboxylase. Put significantly regulate the endogenous PAs by both methods of application, however, Spm and mixture of Put and Spm could positively regulate the endogenous PAs and the biosynthetic gene expression by foliar spraying rather than seed priming. The data provide evidence that maintenance of water economy through stabilized cellular structure is an important strategy of drought tolerance by PAs in wheat.

Systematic analysis of the G-box Factor 14-3-3 gene family and functional characterization of GF14a in Brachypodium distachyon

The 14-3-3 proteins are highly conserved and ubiquitously found in eukaryotes. Plant 14-3-3 proteins are involved in many signaling pathways to regulate plant growth and development. Here we identified seven Brachypodium distachyon 14-3-3 genes and analyzed the evolution, gene structure and expression profiles of these genes. Several cis-elements involved in stress response and hormone pathway were found in the promoter region of 14-3-3 genes. Results of gene expression analysis showed that these genes were induced by abiotic stresses or hormone treatments. Transgenic Arabidopsis overexpressing BdGF14a exhibited increased leaf water content (LWC) and decreased electrolyte leakage (EL) and showed improved drought stress tolerance. BdGF14a transgene significantly up-regulated expression levels of DREB1A and DREB1B, but slightly elevated ABI1 expression. These results indicated that BdGF14a functioned as a positive regulator in plant response to drought stress mainly via ABA independent pathway.

De novo assembly and analysis of the Pugionium cornutum (L.) Gaertn. transcriptome and identification of genes involved in the drought response

Pugionium cornutum (L.) Gaertn. is a xerophytic plant species widely distributed in sandy and desert habitats in northwest China. However, the molecular mechanism of drought tolerance in P. cornutum has received little attention. At present, there is limited available transcriptome information for P. cormutum in public databases. Illumina sequencing was used to identify drought-responsive genes and to further characterize the molecular basis of drought tolerance in P. cornutum. In total, 51,385 unigenes with an average length of 825.32bp were obtained by de novo transcriptome assembly. Among these unigenes, 35,276 were annotated with gene descriptions, conserved domains, gene ontology terms, and metabolic pathways. In addition, the results showed that differentially expressed genes (DEGs) were mainly involved in photosynthesis, nitrogen metabolism, and plant hormone signal transduction pathways, notably ascorbate and aldarate metabolism, which could be an alternative pathway to enhance antioxidant capacity in P. cornutum in response to drought stress. These results provide an important clue about the effects of accumulation of ROS on ascorbic acid biosynthesis in P. cornutum. In addition, we found that transcription of most genes involved in ascorbic acid metabolism was altered under drought stress. Additionally, 93 drought-inducible transcription factor genes were identified in the DEGs under drought conditions; these included DREB, AP2/EREBP, B-2a, ERF2, MYB and Zinc finger family. The results of this study provide further insight into the molecular mechanisms of stress tolerance in P. cornutum, and also identify some attractive candidate genes and valuable information for improving drought stress tolerance in other species through genetic engineering.