Dehydration-responsive Element Research Articles

Studying The Responses of Hordeum vulgare Seedlings to Salinity and Osmotic Stresses: Oxidative Stress/Antioxidants Play Crucial Roles دراسة إستجابات بادرات الشعير للإجهاد الملحي والأسموزي: الإجهاد بالأکسدة ومضاداتها يلعبان دورا هاما

Salinity and osmotic stresses are prime reasons of plant growth and productivity reduction in semi-arid regions and cause complex series of physiological, cellular, and molecular changes. Since osmotic and ionic effects are correlated and initiated by salinity, separating both is an important step in understanding the basis of salt tolerance. Barely seedlings(cultivar Giza 134)were treated with either NaCl(150 mM)or iso-osmotic polyethylene glycol 6000 (19.5% PEG). Treatments were applied two times before sampling and collected after two weeks from emergence. Results showed decreasing of fresh matter in treated seedlings, especially those treated with PEG. Furthermore, significant increase of non-enzymatic antioxidants, oxidative markers in addition to enzymatic antioxidants examined (peroxidase (POX), and polyphenol oxidase (PPO)) was detected with PEG treatment. The osmoregulators including proline (Pro) and glycine betaine(GB) increased in the root tissue, in conjunction with enhancement in the antioxidant status of leaves by applying PEG. Based on molecular analysis using real-time RT-PCR, HvNHX gene (coding for Na+/H+ antiporter) was highly expressed after 48 h from treatment in the roots under salinity, but it was expressed in PEG-treated leaves rather than salt-treated ones, and the opposite was true for HvGORK gene (regulate voltage-gated K+-permeable channels).On the other hand, HvDREB gene(coding for dehydration responsive element binding protein)has recorded higher expression in the roots under PEG treatment compared to control. Taken together, the current study suggests that the studied barley cultivar possesses higher tolerance to salt stress than osmotic stress imposed by PEG, so it could be more suitable for cultivation under salinity conditions.

Genome-wide identification of AP2/EREBP in Fragaria vesca and expression pattern analysis of the FvDREB subfamily under drought stress

BackgroundDrought is a common phenomenon worldwide. It is also one of the main abiotic factors that affect the growth and quality of strawberry. The dehydration-responsive element binding protein (DREB) members that belong to the APETALA2/ethylene-responsive element binding protein (AP2/EREBP) superfamily are unique transcription factors in plants that play important roles in the abiotic stress response.ResultsHere, a total of 119 AP2/EREBP genes were identified in Fragaria vesca, and the AP2/EREBP superfamily was divided into AP2, RAV, ERF, DREB, and soloist subfamilies, containing 18, 7, 61, 32, and one member(s), respectively. The DREB subfamily was further divided into six subgroups (A-1 to A-6) based on phylogenetic analysis. Gene structure, conserved motifs, chromosomal location, and synteny analysis were conducted to comprehensively investigate the characteristics of FvDREBs. Furthermore, transcriptome analysis revealed distinctive expression patterns among the FvDREB genes in strawberry plants exposed to drought stress. The expression of FvDREB6 of the A-2 subgroup was down-regulated in old leaves and up-regulated in young leaves in response to drought. Furthermore, qRT-PCR analysis found that FvDREB8 from the A-2 subgroup had the highest expression level under drought stress. Together, analyses with the expression pattern, phylogenetic relationship, motif, and promoter suggest that FvDREB18 may play a critical role in the regulation of FvDREB1 and FvDREB2 expression.ConclusionsOur findings provide new insights into the characteristics and potential functions of FvDREBs. These FvDREB genes should be further studied as they appear to be excellent candidates for drought tolerance improvement of strawberry.

Investigation of flavonoid expression and metabolite content patterns during seed formation of Artemisia sphaerocephala Krasch.

AbstractFlavonoids are a group of phenolic secondary metabolites in plants that have important physiological, ecological and economic value. In this study, using the desert plant Artemisia sphaerocephala Krasch. as the sample material, the content and components of the total flavonoids in its seeds at seven different developmental stages were determined. In addition, the genes involved in flavonoid metabolism were identified by full-length transcriptome sequencing (third-generation sequencing technology based on PacBio RS II). Their expression levels were analysed by RNA-seq short reading sequencing, to reveal the patterns and regulation mechanisms of flavonoid accumulation during seed development. The key results were as follows: the content of total flavonoids in mature seeds was 15.05 mg g−1, including five subclasses: flavonols, chalcones, flavones, flavanones and proanthocyanidins, among which flavonols accounted for 45.78%. The period of rapid accumulation of flavonoids was 40–70 d following anthesis. The high expression of phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL) and UDP-glucose:flavonoids 3-o-glucosyltransferase (UF3GT) promoted the accumulation of total flavonoids, while the high expression of flavonoids 3′-hydroxylase (F3′H) and flavonols synthase (FLS) made flavanols the main component. Transcription factors such as the MYB-bHLH-WDR (MBW) complex and Selenium-binding protein (SBP) directly regulated the structural genes of flavonoid metabolism, while C2H2-type zinc finger (C2H2), Zinc-finger transcription factor (GATA), Dehydration-responsive element binding (DREB), Global Transcription factor Group E protein (GTE), Trihelix DNA-binding factors (Trihelix) and Phytochrome-interacting factor (PIF) indirectly promoted the synthesis of flavonoids through hormones such as brassinoidsteroids (BRs) and abscisic acid (ABA). These results provided valuable resources for the application of related genes in genetics and breeding.

Orchestration of plant development and defense by indirect crosstalk of salicylic acid and brassinosteorid signaling via transcription factor GhTINY2.

Salicylic acid (SA) and brassinosteroids (BRs) are well known to regulate diverse processes of plant development and stress responses, but the mechanisms by which these phytohormones mediate the growth and defense trade-off are largely unclear. In addition, little is known about the roles of DEHYDRATION RESPONSIVE ELEMENT BINDING transcription factors, especially in biotic stress and plant growth. Here, we identified a cotton (Gossypium hirsutum) APETALA2/ETHYLENE RESPONSIVE FACTOR gene GhTINY2 that is strongly induced by Verticillium dahliae. Overexpression of GhTINY2 in cotton and Arabidopsis enhanced tolerance to V. dahliae, while knockdown of expression increased the susceptibility of cotton to the pathogen. GhTINY2 was found to promote SA accumulation and SA signaling transduction by directly activating expression of WRKY51. Moreover, GhTINY2-overexpressing cotton and Arabidopsis showed retardation of growth, increased sensitivity to inhibitors of BR biosynthesis, down-regulation of several BR-induced genes, and up-regulation of BR-repressed genes, while GhTINY2-RNAi cotton showed the opposite effects. We further determined that GhTINY2 negatively regulates BR signaling by interacting with BRASSINAZOLE-RESISTANT 1 (BZR1) and restraining its transcriptional activation of the expression of INDOLE-3-ACETIC ACID INDUCIBLE 19 (IAA19). These findings indicate that GhTINY2 fine-tunes the trade-off between immunity and growth via indirect crosstalk between WRKY51-mediated SA biosynthesis and BZR1-IAA19-regulated BR signaling.

Cellular Phosphorylation Signaling and Gene Expression in Drought Stress Responses: ABA-Dependent and ABA-Independent Regulatory Systems.

Drought is a severe and complex abiotic stress that negatively affects plant growth and crop yields. Numerous genes with various functions are induced in response to drought stress to acquire drought stress tolerance. The phytohormone abscisic acid (ABA) accumulates mainly in the leaves in response to drought stress and then activates subclass III SNF1-related protein kinases 2 (SnRK2s), which are key phosphoregulators of ABA signaling. ABA mediates a wide variety of gene expression processes through stress-responsive transcription factors, including ABA-RESPONSIVE ELEMENT BINDING PROTEINS (AREBs)/ABRE-BINDING FACTORS (ABFs) and several other transcription factors. Seed plants have another type of SnRK2s, ABA-unresponsive subclass I SnRK2s, that mediates the stability of gene expression through the mRNA decay pathway and plant growth under drought stress in an ABA-independent manner. Recent research has elucidated the upstream regulators of SnRK2s, RAF-like protein kinases, involved in early responses to drought stress. ABA-independent transcriptional regulatory systems and ABA-responsive regulation function in drought-responsive gene expression. DEHYDRATION RESPONSIVE ELEMENT (DRE) is an important cis-acting element in ABA-independent transcription, whereas ABA-RESPONSIVE ELEMENT (ABRE) cis-acting element functions in ABA-responsive transcription. In this review article, we summarize recent advances in research on cellular and molecular drought stress responses and focus on phosphorylation signaling and transcription networks in Arabidopsis and crops. We also highlight gene networks of transcriptional regulation through two major regulatory pathways, ABA-dependent and ABA-independent pathways, that ABA-responsive subclass III SnRK2s and ABA-unresponsive subclass I SnRK2s mediate, respectively. We also discuss crosstalk in these regulatory systems under drought stress.

Galactinol synthase confers salt-stress tolerance by regulating the synthesis of galactinol and raffinose family oligosaccharides in poplar

Plants respond to abiotic stress through a series of transcriptional profile and metabolic process modifications through signaling events. Raffinose family oligosaccharides (RFOs) play a role in the regulatory mechanisms of abiotic stress tolerance and are catalyzed by the key enzyme, galactinol synthase (GolS), in plants. The amino acids sequences of GolS of Populus trichocarpa contained the common features of GolS proteins in other plant species, namely, a hydrophobic pentapeptide (APSAA). The PtrGolS3 promoter region contains several cis-elements for stress responses, including abscisic acid responsive element (ABRE), the dehydration and cold responsive elements (DRE/CRT), the low-temperature responsive element (LTRE), and the transcription factor MYB binding sites. Overexpression of AtGolS2 and PtrGolS3 enhanced abiotic stress tolerance along with the expression of stress-related genes in transgenic poplar. In addition, overexpression of AtGolS2 and PtrGolS3 resulted in higher contents of soluble sugars and other stress-associated metabolites (proline, salicylic acid, phenylalanine, and so forth) in two GolS overexpressing poplar lines compared with wild-type poplar under salt stress. Based on these results, a promising PtrGolS candidate gene for metabolic engineering of sugars to improve abiotic stress tolerance in poplar was identified and it may increase the understanding of RFO metabolism in woody plants under short-term salt treatment.

Overexpression of the Panax ginseng MYB4 gene enhances stress tolerance in transgenic Arabidopsis thaliana

The myeloblastosis (MYB) transcription factors are essential for plant stress responses. They can enhance plant tolerance to abiotic stresses (e.g., drought, salinity, and cold) via improved physiological and biochemical responses including the accumulation of metabolites. In this study, we constructed a Panax ginseng MYB4 (PgMYB4) gene expression vector and established the stable transgenic Arabidopsis thaliana lines to study the effects of this gene on plant stress tolerance. The germination rate and seedling taproot length were greater for the PgMYB4-overexpressing plants than for the wild-type plants. Accordingly, the overexpression of PgMYB4 in Arabidopsis enhanced seedling tolerance to drought, salt, and cold conditions. Under drought stress, the relative chlorophyll content decreased less, the proline content increased more, and the water loss rate decreased more in the transgenic plants than in the wild type. The expressions of stress-related genes responsive to dehydration 19A, responsive to dehydration 22, responsive to desiccation 29A, cold-regulated 15A, cold-regulated 47, and pyrroline-5-carboxylate synthase 1 were significantly upregulated in the transgenic Arabidopsis plants. Under high salt stress, the kinesin 1 (KIN1) expression was significantly upregulated in the transgenic plants. In response to the low temperature stress, the dehydration-responsive element binding protein 2A and KIN1 expressions increased dramatically in the transgenic Arabidopsis plants. Thus, PgMYB4 positively regulated the stress tolerance gene networks, which promoted the expression of anti-stress effector genes. This gene may be useful for ginseng breeding programs aiming to develop new cultivars with enhanced stress tolerance.

Genome-wide identification of HSF family in peach and functional analysis of PpHSF5 involvement in root and aerial organ development.

BackgroundHeat shock factors (HSFs) play important roles during normal plant growth and development and when plants respond to diverse stressors. Although most studies have focused on the involvement of HSFs in the response to abiotic stresses, especially in model plants, there is little research on their participation in plant growth and development or on the HSF (PpHSF) gene family in peach (Prunus persica).MethodsDBD (PF00447), the HSF characteristic domain, was used to search the peach genome and identify PpHSFs. Phylogenetic, multiple alignment and motif analyses were conducted using MEGA 6.0, ClustalW and MEME, respectively. The function of PpHSF5 was confirmed by overexpression of PpHSF5 into Arabidopsis.ResultsEighteen PpHSF genes were identified within the peach genome. The PpHSF genes were nonuniformly distributed on the peach chromosomes. Seventeen of the PpHSFs (94.4%) contained one or two introns, except PpHSF18, which contained three introns. The in silico-translated PpHSFs were classified into three classes (PpHSFA, PpHSFB and PpHSFC) based on multiple alignment, motif analysis and phylogenetic comparison with HSFs from Arabidopsis thaliana and Oryza sativa. Dispersed gene duplication (DSD at 67%) mainly contributed to HSF gene family expansion in peach. Promoter analysis showed that the most common cis-elements were the MYB (abiotic stress response), ABRE (ABA-responsive) and MYC (dehydration-responsive) elements. Transcript profiling of 18 PpHSFs showed that the expression trend of PpHSF5 was consistent with shoot length changes in the cultivar ‘Zhongyoutao 14’. Further analysis of the PpHSF5 was conducted in 5-year-old peach trees, Nicotiana benthamiana and Arabidopsis thaliana, respectively. Tissue-specific expression analysis showed that PpHSF5 was expressed predominantly in young vegetative organs (leaf and apex). Subcellular localization revealed that PpHSF5 was located in the nucleus in N. benthamiana cells. Two transgenic Arabidopsis lines were obtained that overexpressed PpHSF5. The root length and the number of lateral roots in the transgenic seedlings were significantly less than in WT seedlings and after cultivation for three weeks. The transgenic rosettes were smaller than those of the WT at 2–3 weeks. The two transgenic lines exhibited a dwarf phenotype three weeks after transplanting, although there was no significant difference in the number of internodes. Moreover, the PpHSF5-OE lines exhibited enhanced thermotolerance. These results indicated that PpHSF5 might be act as a suppresser of growth and development of root and aerial organs.

Posttranslational regulation of multiple clock-related transcription factors triggers cold-inducible gene expression in Arabidopsis

Cold stress is an adverse environmental condition that affects plant growth, development, and crop productivity. Under cold stress conditions, the expression of numerous genes that function in the stress response and tolerance is induced in various plant species, and the dehydration-responsive element (DRE) binding protein 1/C-repeat binding factor (DREB1/CBF) transcription factors function as master switches for cold-inducible gene expression. Cold stress strongly induces these DREB1 genes. Therefore, it is important to elucidate the mechanisms of DREB1 expression in response to cold stress to clarify the perception and response of cold stress in plants. Previous studies indicated that the central oscillator components of the circadian clock, CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), are involved in cold-inducible DREB1 expression, but the underlying mechanisms are not clear. We revealed that the clock-related MYB proteins REVEILLE4/LHY-CCA1-Like1 (RVE4/LCL1) and RVE8/LCL5 are quickly and reversibly transferred from the cytoplasm to the nucleus under cold stress conditions and function as direct transcriptional activators of DREB1 expression. We found that CCA1 and LHY suppressed the expression of DREB1s under unstressed conditions and were rapidly degraded specifically in response to cold stress, which suggests that they act as transcriptional repressors and indirectly regulate the cold-inducible expression of DREB1s We concluded that posttranslational regulation of multiple clock-related transcription factors triggers cold-inducible gene expression. Our findings clarify the complex relationship between the plant circadian clock and the regulatory mechanisms of cold-inducible gene expression.

Characteristics and phylogeny of DREB gene subfamily in soybeans [Glycine max (L.) Meril

Dehydration responsive element binding proteins (DREB) are transcription factors linked to cis-acting elements of the promoter region, which regulate plant gene expression in response to abiotic stress. In this study, 69 DREB gene sequences of soybean from NCBI belonging to 18 GmDREB (Glycine max DREB) genes of 1 to 8 copies distributed on 17 chromosomes were identified in which GmDREB3 has 8 copies and the rest consisted of 1 to 4 ones. The motif PTPEMAARAYDVAALALKGPSARLNFPEL containing 11 points associated with the promoter of functional genes existed in 4 main types with the most popular one RGRRWKERRWT found in 13/18 DREB proteins was regarded as the popular AP2 domain of DREB protein. The phylogenetic tree based on the nucleotide sequences of GmDREB genes and the amino acid sequences of the AP2 domain expresses the evolution and relationship of the DREB subfamily in soybean. This study provides comprehensive information about the DREB subfamily, which formed the basis for experimental analyses to clarify the function of some members of this subfamily.

Evolution and identification of DREB transcription factors in the wheat genome: modeling, docking and simulation of DREB proteins associated with salt stress

Soil salinity and the resulting salt stress it imposes on crop plants is a major problem for modern agriculture. Understanding how salt tolerance mechanisms in plants are regulated is therefore important. One regulatory mechanism is the APETALA2/Ethylene Responsive Factor (AP2/ERF) transcription factor family, including dehydration responsive element binding (DREB) transcription factors. By binding to DNA, specifically upstream of genes that play roles in salt tolerance pathways, DREB proteins upregulate expression of these genes. DREB in Triticum aestivum (wheat) cluster in sub-groups and in this study by scanning the recently extended predicted proteome of wheat for DREB, we increased the number of members of this sub-family. Using the wheat genome, we identified 576 genes coding for the AP2 domain of which 508 were identified to have one AP2 domain, a characteristic of the DREB/ERF subfamily. We confirmed the existing four sub-groups by sequence-based phylogenetic analyses but also identified 32 new DREB subfamily members, not belonging to any known sub-group. Transcription factor profile inference analysis identified two genes, TraesCS2B02G002700 and TraesCS2D02G015200, being homologous to DREB1A of Arabidopsis thaliana. Based on molecular simulation (25 ns) analysis, TraesCS2B02G002700 with a CCGAC motif was observed to interact very stably with DNA. In silico mutational analysis at the 19th position in the DREB domain of TraesCS2B02G002700-DNA complex indicated this as a stable part for recognizing and forming interaction with DNA. Moreover, six target genes were predicted having an upstream CCGAC motif regulated by TraesCS2B02G002700. Our study provides an overall framework for exploring the transcription factors in plants and identifying e.g. potential salt stress target genes. Communicated by Ramaswamy H. Sarma

Co-overexpression of AtDREB1A and BcZAT12 increases drought tolerance and fruit production in double transgenic tomato (Solanum lycopersicum) plants

Drought is the major problem in agricultural production due to loss of moisture content in soil as well as climate variations. Our main aim is to enhance drought tolerance and yield potential in the present study pyramided Arabidopsis thaliana Dehydration Responsive Element Binding1A (AtDREB1A) and Brasica caranata Zinc finger proteins (BcZAT12) transcription factor genes driven by ectopic promoter rd29 A of Arabidopsis thaliana and Brassica carinata lea1, respectively. Co-overexpression of both the genes provides tolerance to multiple abiotic stresses but the AtDREB1A overexpression has been reported to cause retarded growth and dwarf phenotype; however BcZAT12 overexpressing transgenic plants does not show retarded growth and dwarf phenotype. Co-overexpressing of AtDREB1A and BcZAT12 in five (DZ1-DZ5) double transgenic (DT) tomato lines has been observed under 0, 07, 14 and 21 Days of Water Deficit (DWD). The DT plants showed enhanced drought tolerance and yield potential than single transgenic (ST) and non transgenic (NT) plants. Furthermore, AtDREB1A and BcZAT12 co-overexpressed plants showed reduced level of electrolyte leakage (EL), hydrogen peroxide and membrane lipid peroxidation and elevated level of relative water content (RWC), proline, chlorophyll color index (CCI) and photosynthetic efficiency as compared to ST and NT. The plant growth and yield attributes were improved by the co-overexpression of AtDREB1A and BcZAT12 in DT plants. The transcript analysis showed the increased level of DREB1A, ZAT12 and P5CS genes expression which were higher in DT tomato plants, and indicate that both the genes induce together in the DT plants. The present study which is first report of co-overexpressing AtDREB1A and BcZAT12 in tomato will provide a base for genetic engineering in plants through the multigenic transgenic approach to cope against various biotic and abiotic stresses.

Impact of the overexpression of the StDREB1 transcription factor on growth parameters, yields, and chemical composition of tubers from greenhouse and field grown potato plants.

Potato plants are often exposed to biotic and abiotic stresses that negatively impact their growth, development, and yield. Plants respond to different stresses by inducing large numbers of stress-responsive genes, which can be either functional or regulatory genes. Among regulatory genes, Dehydration Responsive Element Binding (DREB) genes are considered as one of the main groups of transcriptional regulators. The overexpression of these factors in several transgenic plants leads to enhancement of abiotic stress tolerance. However, a number of reports showed that the overexpression of DREB factors under control of constitutive promoter, affects their morphology and production. Therefore, it becomes interesting to evaluate the effect of the overexpression of this StDREB1 transcription factor on plant growth, morphology, yield and tuber composition under both greenhouse and field culture conditions. To our knowledge, there is no available data on the effect of DREBA-4 overexpression on potato plants morphology and yield. Indeed, most studies focused on DREB genes from A-1 and A-2 groups for other plant species. Our results showed that StDREB1, a A-4 group of DREB gene from potato (Solanum tuberosum L.), overexpressing plants did not show any growth retardation. On the contrary, they seem to be more vigorous, and produced higher tuber weight in greenhouse and field culture than the wild type (WT) plants. Moreover, the overexpression of StDREB1 transcription factor seemed to have an effect on tuber quality in terms of dry matter, starch contents and reducing sugars in comparison to the WT tubers. These data suggest that the StDREB1 gene from A-4 group of DREB subfamily can be a good candidate in potato breeding for stress tolerance.

Transgenic chickpea (Cicer arietinum L.) harbouring AtDREB1a are physiologically better adapted to water deficit

BackgroundChickpea (Cicer arietinum L.) is the second most widely grown pulse and drought (limiting water) is one of the major constraints leading to about 40–50% yield losses annually. Dehydration responsive element binding proteins (DREBs) are important plant transcription factors that regulate the expression of many stress-inducible genes and play a critical role in improving the abiotic stress tolerance. Transgenic chickpea lines harbouring transcription factor, Dehydration Responsive Element-Binding protein 1A from Arabidopsis thaliana (AtDREB1a gene) driven by stress inducible promoter rd29a were developed, with the intent of enhancing drought tolerance in chickpea. Performance of the progenies of one transgenic event and control were assessed based on key physiological traits imparting drought tolerance such as plant water relation characteristics, chlorophyll retention, photosynthesis, membrane stability and water use efficiency under water stressed conditions.ResultsFour transgenic chickpea lines harbouring stress inducible AtDREB1a were generated with transformation efficiency of 0.1%. The integration, transmission and regulated expression were confirmed by Polymerase Chain Reaction (PCR), Southern Blot hybridization and Reverse Transcriptase polymerase chain reaction (RT-PCR), respectively. Transgenic chickpea lines exhibited higher relative water content, longer chlorophyll retention capacity and higher osmotic adjustment under severe drought stress (stress level 4), as compared to control. The enhanced drought tolerance in transgenic chickpea lines were also manifested by undeterred photosynthesis involving enhanced quantum yield of PSII, electron transport rate at saturated irradiance levels and maintaining higher relative water content in leaves under relatively severe soil water deficit. Further, lower values of carbon isotope discrimination in some transgenic chickpea lines indicated higher water use efficiency. Transgenic chickpea lines exhibiting better OA resulted in higher seed yield, with progressive increase in water stress, as compared to control.ConclusionsBased on precise phenotyping, involving non-invasive chlorophyll fluorescence imaging, carbon isotope discrimination, osmotic adjustment, higher chlorophyll retention and membrane stability index, it can be concluded that AtDREB1a transgenic chickpea lines were better adapted to water deficit by modifying important physiological traits. The selected transgenic chickpea event would be a valuable resource that can be used in pre-breeding or directly in varietal development programs for enhanced drought tolerance under parched conditions.

Physiological and molecular responses for long term salinity stress in common fig (Ficus carica L.).

The online version contains supplementary material available at (10.1007/s12298-020-00921-z).

Expression profiling of DREB1 and evaluation of vegetation indices in contrasting wheat genotypes exposed to drought stress

DREBs, the Dehydration Responsive Element binding proteins belonging to the superfamily of AP2/ERF plant transcription factors regulate diverse processes of plant development and stress responses. The expression level of DREB1 transcription factor gene was examined under drought in wheat genotypes of Azerbaijani origin differing in drought resistance: two tetraploid wheat (Triticum durum Desf.), cultivars Barakatli 95 (tolerant), Garagylchyg 2 (sensitive) and two hexaploid wheat (Triticum aestivum L.), cultivars Azamatli 95 (less sensitive), Giymatli 2/17 (sensitive), as well as German hexaploid winter wheat cultivar Batis and the synthetic hexaploid wheat accession Syn022L. The seeds were sown in pots in control and drought blocks inside the growth chamber and 12-day-old seedlings were exposed to drought stress. These genotypes were thoroughly phenotyped for variability of vegetation indices like NDVI, SR, OSAVI, ARI1, GM2 and PRI using spectro-radiometer PolyPen RP400 & RP410 under control and drought stress. In tetraploid genotypes and synthetic wheat accession, the vegetation indices were less affected by drought than in hexaploids and the response to stress recovery was faster. Drought sensitive genotypes experienced lower vegetation indices as compared to the tolerant ones. The expression of DREB1 gene was analyzed at 7 days after stress, when the visible stress-related traits were observed. The transcript level was determined by qRT-PCR using the elongation factor 1 alpha (Elf1-α) gene as an internal control. There was no genotypic difference in the basal expression of DREB1 under control conditions. Overall, the transcript levels were significantly increased among all genotypes exposed to drought stress. Futher, under drought stress the expression level of DREB1 in tolerant genotypes increased more than in drought sensitive ones. The German wheat cultivar Batis revealed the highest up-regulation of DREB1 under drought stress conditions. These data will help to screen drought stress tolerance at large scale among the diverse wheat gene pool non-invasively using digital phenotyping.

Transcription factors as key molecular target to strengthen the drought stress tolerance in plants.

Amid apprehension of global climate change, crop plants are inevitably confronted with a myriad of abiotic stress factors during their growth that inflicts a serious threat to their development and overall productivity. These abiotic stresses comprise extreme temperature, pH, high saline soil, and drought stress. Among different abiotic stresses, drought is considered the most calamitous stressor with its serious impact on the crops' yield stability. The development of climate-resilient crops that withstands reduced water availability is a major focus of the scientific fraternity to ensure the food security of the sharply increasing population. Numerous studies aim to recognize the key regulators of molecular and biochemical processes associated with drought stress tolerance response. A few potential candidates are now considered as promising targets for crop improvement. Transcription factors act as a key regulatory switch controlling the gene expression of diverse biological processes and, eventually, the metabolic processes. Understanding the role and regulation of the transcription factors will facilitate the crop improvement strategies intending to develop and deliver agronomically-superior crops. Therefore, in this review, we have emphasized the molecular avenues of the transcription factors that can be exploited to engineer drought tolerance potential in crop plants. We have discussed the molecular role of several transcription factors, such as basic leucine zipper (bZIP), dehydration responsive element binding (DREB), DNA binding with one finger (DOF), heat shock factor (HSF), MYB, NAC, TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP), and WRKY. We have also highlighted candidate transcription factors that can be used for the development of drought-tolerant crops.

Characterization of the DREBA4-Type Transcription Factor (SlDREBA4), Which Contributes to Heat Tolerance in Tomatoes.

Dehydration-responsive element binding (DREB) transcription factors play crucial regulatory roles in abiotic stress. The only DREB transcription factor in tomato (Solanum lycopersicum), SlDREBA4 (Accession No. MN197531), which was determined to be a DREBA4 subfamily member, was isolated from cv. Microtom using high-temperature-induced digital gene expression (DGE) profiling technology. The constitutive expression of SlDREBA4 was detected in different tissues of Microtom plants. In addition to responding to high temperature, SlDREBA4 was up-regulated after exposure to abscisic acid (ABA), cold, drought and high-salt conditions. Transgenic overexpression and silencing systems revealed that SlDREBA4 could alter the resistance of transgenic Microtom plants to heat stress by altering the content of osmolytes and stress hormones, and the activities of antioxidant enzymes at the physiologic level. Moreover, SlDREBA4 regulated the downstream gene expression of many heat shock proteins (Hsp), as well as calcium-binding protein enriched in the pathways of protein processing in endoplasmic reticulum (ko04141) and plant-pathogen interaction (ko04626) at the molecular level. SlDREBA4 also induces the expression of biosynthesis genes in jasmonic acid (JA), salicylic acid (SA), and ethylene (ETH), and specifically binds to the DRE elements (core sequence, A/GCCGAC) of the Hsp genes downstream from SlDREBA4. This study provides new genetic resources and rationales for tomato heat-tolerance breeding and the heat-related regulatory mechanisms of DREBs.

Nitric oxide and selenium nanoparticles confer changes in growth, metabolism, antioxidant machinery, gene expression, and flowering in chicory (Cichorium intybus L.): potential benefits and risk assessment.

This experiment was conducted to provide a better insight into the plant responses to nitric oxide (NO) and selenium nanoparticle (nSe). Chicory seedlings were sprayed with nSe (0, 4, and 40 mg l-1), and/or NO (0 and 25 μM). NO and/or nSe4 improved shoot and root biomass by an average of 32%. The nSe40 adversely influenced shoot and root biomass (mean = 26%), exhibiting moderate toxicity partly relieved by NO. The nSe and NO treatments transcriptionally stimulated the dehydration response element B1A (DREB1A) gene (mean = 29.6-fold). At the transcriptional level, nSe4 or NO moderately upregulated phenylalanine ammonia-lyase (PAL) and hydroxycinnamoyl-CoA quinate transferase (HCT1) genes (mean = sevenfold). The nSe4 + NO, nSe40, and nSe40 + NO groups drastically induced the expression of PAL and HCT1 genes (mean = 30-fold). With a similar trend, hydroxycinnamoyl-CoA Quinate/shikimate hydroxycinnamoyl transferase (HQT1) gene was also upregulated in response to nSe and/or NO (mean = 25-fold). The activities of nitrate reductase and catalase enzymes were also induced in the nSe- and/or NO-treated seedlings. Likewise, the application of these supplements associated with an increase in ascorbate concentration (mean = 31.5%) reduced glutathione (mean = 35%). NO and/or nSe enhanced the PAL activity (mean = 36.4%) and soluble phenols (mean = 40%). The flowering was also influenced by the supplements in dose and compound dependent manner exhibiting the long-time responses. It appears that the nSe-triggered signaling can associate with a plethora of developmental, physiological, and molecular responses at least in part via the fundamental regulatory roles of transcription factors, like DREB1A as one the most significant genes for conferring tolerance in crops.

DREB2 Family Transcription Factors Promote the Expression of Phytocystatin1 in Arabidopsis thaliana During Seed Germination

Phytocystatins (PhyCYSs) are plant-specific proteinaceous inhibitors of cysteine proteases (CPs) that regulate protein turnover and defense responses. Here, we characterized a member of the PhyCYS gene family in Arabidopsis thaliana, AtCYS1, during seed germination. AtCYS1 transcript level and AtCYS1 promoter-driven β-glucuronidase (GUS) activity gradually increased during germination, as measured by quantitative reverse transcription PCR (qRT-PCR) and GUS staining assays, respectively. The level and activity of the AtCYS1 protein were up-regulated during germination, as shown by western blot and CP inhibitory activity analyses, respectively. In addition, a canonical dehydration-responsive element (DRE) was identified in the AtCYS1 promoter. Electrophoretic mobility shift assays (EMSAs) revealed that the DRE-binding factor 2C (DREB2C) binds directly to the AtCYS1 promoter. Transient transactivation assays using Arabidopsis leaf protoplasts showed that DREB2A and DREB2C act as transcriptional activators of AtCYS1. In DREB2C overexpression lines, AtCYS1 protein levels were elevated, while the endogenous CP activity was reduced. However, AtCYS1 overexpression lines (35S:AtCYS1) and the cys1-1 null mutant, characterized by a quantitative imbalance in the AtCYS1 protein level, showed delayed germination under normal growth conditions. These results suggest that DREB2 proteins act as transcriptional activators of the AtCYS1 gene, and an imbalance in the level of AtCYS1 inhibits seed germination.