Overexpression of TaSTRG gene improves salt and drought tolerance in rice

Metabolome profiling of cacao (Theobroma cacao L.) callus under drought stress conditions induced by polyethylene glycol (PEG) as osmoticant

INTRODUCTION

The cacao tree (Theobroma cacao), a perennial crop that serves as a source of cacao beans, can suffer from drastic climate changes such as irregular rainfall and shorter rainy seasons. The search for hybrids which are capable of producing specific metabolites favoring adaptation in new climatic conditions is a challenge in cacao farming.

OBJECTIVES

We aimed to (1) analyze the metabolic changes in calli of three cacao genotypes during water deficit induced by incubation with polyethylene glycol and (2) assess their response to water deficit stress with regard to somatic embryo differentiation.

METHODS

Metabolic profiling was carried out using 1H-NMR spectroscopy and multivariate data analysis was applied to crude extracts of calli grown in non-stress or water deficit stress conditions.

RESULTS

Water deficit stress influences the capacity of calli to produce embryos. The SCA12 genotype exhibited the best conversion capacity under severe conditions and was considered as tolerant to drought, followed by the SCA6 genotype (mid-tolerant) and the MA12 genotype (sensitive). Fifty-four metabolites were identified in the three cacao genotypes and discriminant metabolites were identified. Metabolites involved in water stress tolerance such as fructose, trans-aconitic acid, leucine, and hydroxybenzene derivatives were observed in SCA12, the tolerant genotype.

CONCLUSION

These results demonstrate the utility of 1H-NMR metabolomics as an essential tool for the analysis of the drought tolerance characteristics of T. cacao.

A meta-analysis highlights the cross-resistance of plants to drought and salt stresses from physiological, biochemical, and growth levels

In nature, drought and salt stresses often occur simultaneously and affect plant growth at multiple levels. However, the mechanisms underlying plant responses to drought and salt stresses and their interactions are still not fully understood. We performed a meta-analysis to compare the effects of drought, salt, and combined stresses on plant physiological, biochemical, morphological and growth traits, analyze the different responses of C3 and C4 plants, as well as halophytes and non-halophytes, and identify the interactive effects on plants. There were numerous similarities in plant responses to drought, salt, and combined stresses. C4 plants had a more effective antioxidant defense system, and could better maintain above-ground growth. Halophytes could better maintain photosynthetic rate (Pn) and relative water content (RWC), and reduce growth as an adaptation strategy. The responses of most traits (Pn, RWC, chlorophyll content, soluble sugar content, H2O2 content, plant dry weight, etc.) to combined stress were less-than-additive, indicating cross-resistance rather than cross-sensitivity of plants to drought and salt stresses. These results are important to improve our understanding of drought and salt cross-resistance mechanisms and further induce resistance or screen-resistant varieties under stress combination.

Wheat (Triticum aestivum. L) Plant U-box E3 ligases TaPUB2 and TaPUB3 enhance ABA response and salt stress resistance in Arabidopsis

Plant U-box E3 ligases (PUBs) are important regulators of responses to various abiotic stress conditions. In this study, we found that wheat (Triticum aestivum. L) PUBs TaPUB2 and TaPUB3 enhanced abscisic acid (ABA) responses and salt tolerance in Arabidopsis. We generated transgenic Arabidopsis lines overexpressing TaPUB2 and TaPUB3 and performed various plant physiological experiments. Overexpression of TaPUB2 and TaPUB3 increased tolerance to salinity stress in an ABA-dependent manner in transgenic plants, as evidenced by germination and survival rates, root length, stomatal aperture regulation, membrane peroxidation, photosynthetic activities, reactive oxygen species scavenging activities and expression of various ABA and salinity stress-related genes. These results demonstrate the functions of PUBs under ABA and salinity stress conditions and provide valuable information for the development of salinity stress-tolerant crop species.

Impact of Nanomaterials on the Regulation of Gene Expression and Metabolomics of Plants under Salt Stress

Plant salinity resistance results from a combination of responses at the physiological, molecular, cellular, and metabolic levels. This article focuses on plant stress tolerance mechanisms for controlling ion homeostasis, stress signaling, hormone metabolism, anti-oxidative enzymes, and osmotic balance after nanoparticle applications. Nanoparticles are used as an emerging tool to stimulate specific biochemical reactions related to plant ecophysiological output because of their small size, increased surface area and absorption rate, efficient catalysis of reactions, and adequate reactive sites. Regulated ecophysiological control in saline environments could play a crucial role in plant growth promotion and survival of plants under suboptimal conditions. Plant biologists are seeking to develop a broad profile of genes and proteins that contribute to plant salt resistance. These plant metabolic profiles can be developed due to advancements in genomic, proteomic, metabolomic, and transcriptomic techniques. In order to quantify plant stress responses, transmembrane ion transport, sensors and receptors in signaling transduction, and metabolites involved in the energy supply require thorough study. In addition, more research is needed on the plant salinity stress response based on molecular interactions in response to nanoparticle treatment. The application of nanoparticles as an aspect of genetic engineering for the generation of salt-tolerant plants is a promising area of research. This review article addresses the use of nanoparticles in plant breeding and genetic engineering techniques to develop salt-tolerant crops.

Identification and development of novel salt-responsive candidate gene based SSRs (cg-SSRs) and MIR gene based SSRs (mir-SSRs) in bread wheat (Triticum aestivum)

Salt stress adversely affects the global wheat production and productivity. To improve salinity tolerance of crops, identification of robust molecular markers is highly imperative for development of salt-tolerant cultivars to mimic yield losses under saline conditions. In this study, we mined 171 salt-responsive genes (including 10 miRNAs) from bread wheat genome using the sequence information of functionally validated salt-responsive rice genes. Salt-stress, tissue and developmental stage-specific expression analysis of RNA-seq datasets revealed the constitutive as well as the inductive response of salt-responsive genes in different tissues of wheat. Fifty-four genotypes were phenotyped for salt stress tolerance. The stress tolerance index of the genotypes ranged from 0.30 to 3.18. In order to understand the genetic diversity, candidate gene based SSRs (cg-SSRs) and MIR gene based SSRs (miR-SSRs) were mined from 171 members of salt-responsive genes of wheat and validated among the contrasting panels of 54 tolerant as well as susceptible wheat genotypes. Among 53 SSR markers screened, 10 cg-SSRs and 8 miR-SSRs were found to be polymorphic. Polymorphic information content between the wheat genotypes ranged from 0.07 to 0.67, indicating the extant of wide genetic variation among the salt tolerant and susceptible genotypes at the DNA level. The genetic diversity analysis based on the allelic data grouped the wheat genotypes into three separate clusters of which single group encompassing most of the salt susceptible genotypes and two of them containing salt tolerance and moderately salt tolerance wheat genotypes were in congruence with penotypic data. Our study showed that both salt-responsive genes and miRNAs based SSRs were more diverse and can be effectively used for diversity analysis. This study reports the first extensive survey on genome-wide analysis, identification, development and validation of salt-responsive cg-SSRs and miR-SSRs in wheat. The information generated in the present study on genetic divergence among genotypes having a differential response to salt will help in the selection of suitable lines as parents for developing salt tolerant cultivars in wheat.

The Impact of Drought in Plant Metabolism: How to Exploit Tolerance Mechanisms to Increase Crop Production

Plants are often exposed to unfavorable environmental conditions, for instance abiotic stresses, which dramatically alter distribution of plant species among ecological niches and limit the yields of crop species. Among these, drought stress is one of the most impacting factors which alter seriously the plant physiology, finally leading to the decline of the crop productivity. Drought stress causes in plants a set of morpho-anatomical, physiological and biochemical changes, mainly addressed to limit the loss of water by transpiration with the attempt to increase the plant water use efficiency. The stomata closure, one of the first consistent reactions observed under drought, results in a series of consequent physiological/biochemical adjustments aimed at balancing the photosynthetic process as well as at enhancing the plant defense barriers against drought-promoted stress (e.g., stimulation of antioxidant systems, accumulation of osmolytes and stimulation of aquaporin synthesis), all representing an attempt by the plant to overcome the unfavorable period of limited water availability. In view of the severe changes in water availability imposed by climate change factors and considering the increasing human population, it is therefore of outmost importance to highlight: (i) how plants react to drought; (ii) the mechanisms of tolerance exhibited by some species/cultivars; and (iii) the techniques aimed at increasing the tolerance of crop species against limited water availability. All these aspects are necessary to respond to the continuously increasing demand for food, which unfortunately parallels the loss of arable land due to changes in rainfall dynamics and prolonged period of drought provoked by climate change factors. This review summarizes the most updated findings on the impact of drought stress on plant morphological, biochemical and physiological features and highlights plant mechanisms of tolerance which could be exploited to increase the plant capability to survive under limited water availability. In addition, possible applicative strategies to help the plant in counteracting unfavorable drought periods are also discussed.

Involvement of OsGF14b Adaptation in the Drought Resistance of Rice Plants

BACKGROUND

Drought stress is one of the major abiotic stresses that restrict plant growth and development. 14-3-3 proteins have been validated to regulate many biological processes in plants. Previous research demonstrated that OsGF14b plays different roles in panicle and leaf blast resistance. In this study, we researched the function of OsGF14b in drought resistance in rice.

FINDINGS

Here, we report that OsGF14b was strongly induced by soil drought stress. In comparison with wild type (WT), the osgf14b mutant exhibited improved resistance to drought and osmotic stress by changing the content of stress-relevant parameters, complementation of the osgf14b mutant restored the drought sensitivity to WT levels, whereas the OsGF14b-overexpression lines exhibited enhanced sensitivity to drought and osmotic stress. The osgf14b mutant plants were hypersensitive to abscisic acid (ABA), while the OsGF14b-overexpression plants showed reduced sensitivity to ABA. Furthermore, mutation and overexpression of OsGF14b affected the expression of stress-related genes under normal growth conditions and/or drought stress conditions.

CONCLUSIONS

We have demonstrated that OsGF14b is involved in the drought resistance of rice plants, partially in an ABA-dependent manner.

OsERF101, an ERF family transcription factor, regulates drought stress response in reproductive tissues

An ERF transcription factor OsERF101 is predominantly expressed in rice reproductive tissues and plays an important role in improving rice seed setting rate under drought stress. Drought reduces grain yield due to the cumulative damage effects to plant vegetative and reproductive developmental processes. However, the genes involved in these processes are still not completely understood. In this study, we identified a gene named OsERF101 as an important positive regulator in the adaptive responses to dehydration stress during the reproductive and vegetative stages. This gene encodes a member of APETALA2/Ethylene-Responsive Element Binding Protein (AP2/EREBP) family. OsERF101 was predominantly expressed in flowers, particularly in the tapetum and microspores under normal growth conditions. It was induced by drought, PEG6000 and abscisic acid (ABA) in leaves. During the vegetative stage, OsERF101-overexpression plants were more resistant to osmotic stress caused by PEG6000 compared to the control plants. They also had higher survival and seed setting rates than wild type when subjected to reproductive-stage drought stress. Further physiological analysis revealed that the pollen fertility was improved in the overexpression lines, while the knockout mutant and RNAi lines showed reduced pollen fertility and compromised drought tolerance during the reproductive stage. The increased proline content and peroxidase activity in OsERF101-overexpression plants might contribute to the improved drought-tolerance of plants. In addition, OsERF101-overexpression plants displayed ABA susceptible phenotype, in which the expression levels of ABA-responsive genes RD22, LEA3, and PODs were up-regulated. Taken together, our results indicate that OsERF101 is a gene that regulates dehydration responses during the vegetative and reproductive stages.

Characterization of Salt-Induced Epigenetic Segregation by Genome-Wide Loss of Heterozygosity and its Association with Salt Tolerance in Rice (Oryza sativa L.)

In a breeding effort to develop salt tolerant (ST) rice varieties by designed QTL pyramiding, large numbers of progenies derived from four crosses between salt- or drought- tolerant BC2F5 IR64 introgression lines, were subjected to severe salt stress, resulting in 422 ST plants. The progeny testing of the selected F3 lines under more severe salt stress resulted in identification of 16 promising homozygous lines with high levels of ST. Genetic characterization of the 422 ST F3 progeny and 318 random F2 plants from the same four crosses using 105 segregating SSR markers lead to three interesting discoveries: (1) salt stress can induce genome-wide epigenetic segregation (ES) characterized by complete loss of heterozygosity (LOH) and nearly complete loss of an allele (LOA) in the F3 progenies of four rice populations in a single generation; (2) ∼25% of the stress-induced ES loci were transgenerational and inherited from their salt- and drought- selected parents; and (3) the salt-induced LOH and LOA loci (regions) appeared to contain genes/alleles associated with ST and/or drought tolerance. 32 genomic regions that showed one or more types of salt-induced ES in the random and salt-selected progenies from these crosses. The same or different types of ES were detected with two large genomic regions on chromosomes 1 and 6 where more and the strongest ES were found across different populations. 14 genomic regions were found where the salt-induced ES regions were overlapping with QTL affecting ST related traits. The discovery of the three types of salt-induced ES showed several interesting characteristics and had important implications in evolution and future breeding for developing stress-resilient rice and crops.

Expression of cold and drought regulatory protein (CcCDR) of pigeonpea imparts enhanced tolerance to major abiotic stresses in transgenic rice plants

Transgenic rice expressing pigeonpea Cc CDR conferred high-level tolerance to different abiotic stresses. The multiple stress tolerance observed in CcCDR -transgenic lines is attributed to the modulation of ABA-dependent and-independent signalling-pathway genes. Stable transgenic plants expressing Cajanus cajan cold and drought regulatory protein encoding gene (CcCDR), under the control of CaMV35S and rd29A promoters, have been generated in indica rice. Different transgenic lines of CcCDR, when subjected to drought, salt, and cold stresses, exhibited higher seed germination, seedling survival rates, shoot length, root length, and enhanced plant biomass when compared with the untransformed control plants. Furthermore, transgenic plants disclosed higher leaf chlorophyll content, proline, reducing sugars, SOD, and catalase activities, besides lower levels of MDA. Localization studies revealed that the CcCDR-GFP fusion protein was mainly present in the nucleus of transformed cells of rice. The CcCDR transgenics were found hypersensitive to abscisic acid (ABA) and showed reduced seed germination rates as compared to that of control plants. When the transgenic plants were exposed to drought and salt stresses at vegetative and reproductive stages, they revealed larger panicles and higher number of filled grains compared to the untransformed control plants. Under similar stress conditions, the expression levels of P5CS, bZIP, DREB, OsLEA3, and CIPK genes, involved in ABA-dependent and-independent signal transduction pathways, were found higher in the transgenic plants than the control plants. The overall results amply demonstrate that the transgenic rice expressing CcCDR bestows high-level tolerance to drought, salt, and cold stress conditions. Accordingly, the CcCDR might be deployed as a promising candidate gene for improving the multiple stress tolerance of diverse crop plants.

MID1 plays an important role in response to drought stress during reproductive development

Drought during rice reproductive development results in yield loss. It is important to understand the functions of drought-responsive genes in reproductive tissues for improving rice yield under water-deficit conditions. We show here that MID1 (MYB Important for Drought Response1), encoding a putative R-R-type MYB-like transcription factor, can improve rice yield under drought. MID1 was primarily expressed in root and leaf vascular tissues, with low level in the tapetum, and was induced by drought and other abiotic stresses. Compared with wild type, MID1-overexpressing plants were more tolerant to drought at both vegetative and reproductive stages and produced more grains under water stress. MID1-overexpressing plants exhibited less severe anther defects such as deformed anther locules, abnormal tapetum, degenerated microspores and expanded middle layer, with improved pollen fertility and higher seed setting rate. MID1 was localized to the nucleus and could activate gene expression in yeast, and its homologs were identified in many other plants with high levels sequence similarity. In addition, candidate MID1-regulated genes were analyzed using RNA-seq and qRT-PCR, including genes crucial for stress responses and anther development, with altered expressions in the florets of MID1-overexpressing plants and RNAi lines. Furthermore, MID1 could bind to the promoters of two drought-related genes (Hsp17.0 and CYP707A5) and one anther developmental gene (KAR) according to ChIP-qPCR data. Our findings suggest that MID1 is a transcriptional regulator that promotes rice male development under drought by modulating the expressions of drought-related and anther developmental genes and provide valuable information for crop improvement.

Functional study of a salt-inducible TaSR gene in Triticum aestivum

The gene expression chip of a salt-tolerant wheat mutant under salt stress was used to clone a salt-induced gene with unknown functions. This gene was designated as TaSR (Triticum aestivum salt-response gene) and submitted to GenBank under accession number EF580107. Quantitative polymerase chain reaction (PCR) analysis showed that gene expression was induced by salt stress. Arabidopsis and rice (Oryza sativa) plants expressing TaSR presented higher salt tolerance than the controls, whereas AtSR mutant and RNA interference rice plants were more sensitive to salt. Under salt stress, TaSR reduced Na(+) concentration and improved cellular K(+) and Ca(2+) concentrations; this gene was also localized on the cell membrane. β-Glucuronidase (GUS) staining and GUS fluorescence quantitative determination were conducted through fragmentation cloning of the TaSR promoter. Salt stress-responsive elements were detected at 588-1074 bp upstream of the start codon. GUS quantitative tests of the full-length promoter in different tissues indicated that promoter activity was highest in the leaf under salt stress. Bimolecular fluorescence complementation and yeast two-hybrid screening further showed the correlation of TaSR with TaPRK and TaKPP. In vitro phosphorylation of TaSR and TaPRK2697 showed that TaPRK2697 did not phosphorylate TaSR. This study revealed that the novel TaSR may be used to improve plant tolerance to salt stress.

Isolation and molecular characterization of ERF1, an ethylene response factor gene from durum wheat (Triticum turgidum L. subsp. durum), potentially involved in salt-stress responses

As food crop, wheat is of prime importance for human society. Nevertheless, our understanding of the genetic and molecular mechanisms controlling wheat productivity conditions has been, so far, hampered by the lack of sufficient genomic resources. The present work describes the isolation and characterization of TdERF1, an ERF gene from durum wheat (Triticum turgidum L. subsp. durum). The structural features of TdERF1 supported the hypothesis that it is a novel member of the ERF family in durum wheat and, considering its close similarity to TaERF1 of Triticum aestivum, it probably plays a similar role in mediating responses to environmental stresses. TdERF1 displayed an expression pattern that discriminated between two durum wheat genotypes contrasted with regard to salt-stress tolerance. The high number of cis-regulatory elements related to stress responses present in the TdERF1 promoter and the ability of TdERF1 to regulate the transcription of ethylene and drought-responsive promoters clearly indicated its potential role in mediating plant responses to a wide variety of environmental constrains. TdERF1 was also regulated by abscisic acid, ethylene, auxin, and salicylic acid, suggesting that it may be at the crossroads of multiple hormone signalling pathways. Four TdERF1 allelic variants have been identified in durum wheat genome, all shown to be transcriptionally active. Interestingly, the expression of one allelic form is specific to the tolerant genotype, further supporting the hypothesis that this gene is probably associated with the susceptibility/tolerance mechanism to salt stress. In this regard, the TdERF1 gene may provide a discriminating marker between tolerant and sensitive wheat varieties.

Stress-inducible expression of AtDREB1A transcription factor greatly improves drought stress tolerance in transgenic indica rice

The cultivation of rice (Oryza sativa L.), a major food crop, requires ample water (30 % of the fresh water available worldwide), and its productivity is greatly affected by drought, the most significant environmental factor. Much research has focussed on identifying quantitative trait loci, stress-regulated genes and transcription factors that will contribute towards the development of climate-resilient/tolerant crop plants in general and rice in particular. The transcription factor DREB1A, identified from the model plant Arabidopsis thaliana, has been reported to enhance stress tolerance against drought stress. We developed transgenic rice plants with AtDREB1A in the background of indica rice cultivar Samba Mahsuri through Agrobacterium-mediated transformation. The AtDREB1A gene was stably inherited and expressed in T1 and T2 plants and in subsequent generations, as indicated by the results of PCR, Southern blot and RT-PCR analyses. Expression of AtDREB1A was induced by drought stress in transgenic rice lines, which were highly tolerant to severe water deficit stress in both the vegetative and reproductive stages without affecting their morphological or agronomic traits. The physiological studies revealed that the expression of AtDREB1A was associated with an increased accumulation of the osmotic substance proline, maintenance of chlorophyll, increased relative water content and decreased ion leakage under drought stress. Most of the homozygous lines were highly tolerant to drought stress and showed significantly a higher grain yield and spikelet fertility relative to the nontransgenic control plants under both stressed and unstressed conditions. The improvement in drought stress tolerance in combination with agronomic traits is very essential in high premium indica rice cultivars, such as Samba Mahsuri, so that farmers can benefit in times of seasonal droughts and water scarcity.

Overexpression of GsCBRLK from Glycine soja enhances tolerance to salt stress in transgenic alfalfa (Medicago sativa)

GsCBRLK encodes a novel plant-specific calcium-dependent calmodulin-binding receptor-like kinase from Glycine soja Siebold & Zucc. In our previous study, GsCBRLK was found to be a positive regulator of plant tolerance to salt and abscisic acid (ABA) stress. In this study we transformed alfalfa (Medicago sativa L.) with GsCBRLK to assess whether forage legumes overexpressing GsCBRLK adapt to saline soils. Results showed that transgenic alfalfa plants overexpressing GsCBRLK exhibited enhanced salt tolerance. Transgenic alfalfa grew well in the presence of 300mM NaCl for 15 days, whereas wild-type (WT) plants exhibited severe chlorosis and growth retardation. Although transgenic alfalfa grew slowly and even had yellow leaves under the 400mM NaCl treatment, most of the WT plants exhibited more severe chlorosis and did not survive. In addition, samples from transgenic and WT plants treated with 300mM NaCl for 0, 3, 6, 9, 12, and 15 days were selected for physiological analysis. Lower membrane leakage and malondialdehyde (MDA) content were observed in transgenic alfalfa compared with WT plants during salt treatment. The reduction of chlorophyll content in transgenic alfalfa was less than that in WT plants. Furthermore, the plants that overexpressed GsCBRLK showed enhanced superoxide dismutase (SOD) activity, less of a Na+ increase, and a greater K+ decrease than WT plants. These results indicated that the overexpression of GsCBRLK confers enhanced tolerance to salt stress in transgenic alfalfa.

The rice OsDIL gene plays a role in drought tolerance at vegetative and reproductive stages

Drought is one of the critical factors limiting reproductive yields of rice and other crops globally. However, little is known about the molecular mechanism underlying reproductive development under drought stress in rice. To explore the potential gene function for improving rice reproductive development under drought, a drought induced gene, Oryza sativa Drought-Induced LTP (OsDIL) encoding a lipid transfer protein, was identified from our microarray data and selected for further study. OsDIL was primarily expressed in the anther and mainly responsive to abiotic stresses, including drought, cold, NaCl, and stress-related plant hormone abscisic acid (ABA). Compared with wild type, the OsDIL-overexpressing transgenic rice plants were more tolerant to drought stress during vegetative development and showed less severe tapetal defects and fewer defective anther sacs when treated with drought at the reproductive stage. The expression levels of the drought-responsive genes RD22, SODA1, bZIP46 and POD, as well as the ABA synthetic gene ZEP1 were up-regulated in the OsDIL-overexpression lines but the ABA degradation gene ABAOX3 was down-regulated. Moreover, overexpression of OsDIL lessened the down-regulation by drought of anther developmental genes (OsC4, CYP704B2 and OsCP1), providing a mechanism supporting pollen fertility under drought. Overexpression of OsDIL significantly enhanced drought resistance in transgenic rice during reproductive development, while showing no phenotypic changes or yield penalty under normal conditions. Therefore, OsDIL is an excellent candidate gene for genetic improvement of crop yield in adaption to unfavorable environments.

Enhanced tolerance to drought and salt stresses in transgenic faba bean (Vicia faba L.) plants by heterologous expression of the PR10a gene from potato

We report for the first time that expression of potato PR10a gene in faba bean causes enhanced tolerance to drought and salinity. Grain legumes such as soybean (Glycine max L. Merrill), pea (Pisum sativum L.) and faba bean (Vicia faba L.) are staple sources of protein for human and animal nutrition. Among grain legumes, faba bean is particularly sensitive to abiotic stress (in particular osmotic stress due to lack of water or enhanced soil salinity) and often suffers from severe yield losses. Many stress responsive genes have been reported with an effect on improving stress tolerance in model plants. Pathogenesis-related proteins are expressed by all plants in response to pathogen infection and, in many cases, in response to abiotic stresses as well. The PR10a gene isolated from the potato cultivar Desiree was selected for this study due to its role in enhancing salt and/or drought tolerance in potato, and transferred into faba bean cultivar Tattoo by Agrobacterium tumefaciens-mediated transformation system based upon direct shoot regeneration after transformation of meristematic cells derived from embryo axes. The transgene was under the control of the constitutive mannopine synthase promoter (p-MAS) in a dicistronic binary vector, which also contained luciferase (Luc) gene as scorable marker linked by internal ribosome entry site elements. Fertile transgenic faba bean plants were recovered. Inheritance and expression of the foreign genes were demonstrated by PCR, RT-PCR, Southern blot and monitoring of Luciferase activity. Under drought condition, after withholding water for 3 weeks, the leaves of transgenic plants were still green, while non-transgenic plants (WT) wilted and turned brown. Twenty-four hours after re-watering, the leaves of transgenic plants remained green, while WT plants did not recover. Moreover, the transgenic lines displayed higher tolerance to NaCl stress. Our results suggested that introducing a novel PR10a gene into faba bean could be a promising approach to improve its drought and salt tolerance ability, and that MAS promoter is not only constitutive, but also wound-, auxin/cytokinin- as well as stress-inducible.

Function of the wheat TaSIP gene in enhancing drought and salt tolerance in transgenic Arabidopsis and rice

Microarray analysis of a salt-tolerant wheat mutant identified a gene of unknown function that was induced by exposure to high levels of salt and subsequently denoted TaSIP (Triticum aestivum salt-induced protein). Quantitative PCR analysis revealed that TaSIP expression was induced not only by salt, but also by drought, abscisic acid (ABA), and other environmental stress factors. Transgenic rice plants that expressed an RNA interference construct specific for a rice gene homologous to TaSIP was more susceptible to salt stress than wild-type rice plants. Subcellular localization studies showed that the TaSIP localized to the cell membrane. Under conditions of salt and drought stress, transgenic Arabidopsis plants that overexpressed TaSIP showed superior physiological properties compared with control plants, including lower Na(+) content and upregulation of several stress resistance genes. Staining of transgenic tissues with β-glucuronidase (GUS) failed to indicate tissue-specific activity of the full-length TaSIP promoter. Quantitative analysis of GUS fluorescence in transgenic plants treated with ABA or salt stress revealed that the region 1,176-1,410 bp from the start codon contained an ABA-responsive element and that the region 579-1,176 bp from the start codon upstream of the exon contained a salt-stress-responsive element. Based on these results, we conclude that the key part of the TaSIP gene is the region of its promoter involved in salt tolerance.

Comparative proteomic analysis of salt response proteins in seedling roots of two wheat varieties

A comparative proteomic analysis was made of salt response in seedling roots of wheat cultivars Jing-411 (salt tolerant) and Chinese Spring (salt sensitive) subjected to a range of salt stress concentrations (0.5%, 1.5% and 2.5%) for 2 days. One hundred and ninety eight differentially expressed protein spots (DEPs) were located with at least two-fold differences in abundance on 2-DE maps, of which 144 were identified by MALDI-TOF-TOF MS. These proteins were involved primarily in carbon metabolism (31.9%), detoxification and defense (12.5%), chaperones (5.6%) and signal transduction (4.9%). Comparative analysis showed that 41 DEPs were salt responsive with significant expression changes in both varieties under salt stress, and 99 (52 in Jing-411 and 47 in Chinese Spring) were variety specific. Only 15 and 9 DEPs in Jing-411 and Chinese Spring, respectively, were up-regulated in abundance under all three salt concentrations. All dynamics of the DEPs were analyzed across all treatments. Some salt responsive DEPs, such as guanine nucleotide-binding protein subunit beta-like protein, RuBisCO large subunit-binding protein subunit alpha and pathogenesis related protein 10, were up-regulated significantly in Jing-411 under all salt concentrations, whereas they were down-regulated in salinity-stressed Chinese Spring.

Rice plants expressing the moss sodium pumping ATPase PpENA1 maintain greater biomass production under salt stress

High cytosolic concentrations of Na+ inhibit plant growth and development. To maintain low cytosolic concentrations of Na+ , higher plants use membrane-bound transporters that drive the efflux of Na+ or partition Na+ ions from the cytosol, either to the extracellular compartment or into the vacuole. Bryophytes also use an energy-dependent Na+ pumping ATPase, not found in higher plants, to efflux Na+ . To investigate whether this transporter can increase the salt tolerance of crop plants, Oryza sativa has been transformed with the Physcomitrella patens Na+ pumping ATPase (PpENA1). When grown in solutions containing 50 mm NaCl, plants constitutively expressing the PpENA1 gene are more salt tolerant and produce greater biomass than controls. Transgenics and controls accumulate similar amounts of Na+ in leaf and root tissues under stress, which indicates that the observed tolerance is not because of Na+ exclusion. Moreover, inductively coupled plasma analysis reveals that the concentration of other ions in the transformants and the controls is similar. The transgenic lines are developmentally normal and fertile, and the transgene expression levels remain stable in subsequent generations. GFP reporter fusions, which do not alter the ability of PpENA1 to complement a salt-sensitive yeast mutant, indicate that when it is expressed in plant tissues, the PpENA1 protein is located in the plasma membrane. PpENA1 peptides are found in plasma membrane fractions supporting the plasma membrane targeting. The results of this study demonstrate the utility of PpENA1 as a potential tool for engineering salinity tolerance in important crop species.

GsCBRLK, a calcium/calmodulin-binding receptor-like kinase, is a positive regulator of plant tolerance to salt and ABA stress

Calcium/calmodulin-dependent kinases play vital roles in protein phosphorylation in eukaryotes, yet little is known about the phosphorylation process of calcium/calmodulin-dependent protein kinase and its role in stress signal transduction in plants. A novel plant-specific calcium-dependent calmodulin-binding receptor-like kinase (GsCBRLK) has been isolated from Glycine soja. A subcellular localization study using GFP fusion protein indicated that GsCBRLK is localized in the plasma membrane. Binding assays demonstrated that calmodulin binds to GsCBRLK with an affinity of 25.9 nM in a calcium-dependent manner and the binding motif lies between amino acids 147 to169 within subdomain II of the kinase domain. GsCBRLK undergoes autophosphorylation and Myelin Basis Protein phosphorylation in the presence of calcium. It was also found that calcium/calmodulin positively regulates GsCBRLK kinase activity through direct interaction between the calmodulin-binding domain and calmodulin. So, it is likely that GsCBRLK responds to an environmental stimulus in two ways: by increasing the protein expression level and by regulating its kinase activity through the calcium/calmodulin complex. Furthermore, cold, salinity, drought, and ABA stress induce GsCBRLK gene transcripts. Over-expression of GsCBRLK in transgenic Arabidopsis resulted in enhanced plant tolerance to high salinity and ABA and increased the expression pattern of a number of stress gene markers in response to ABA and high salt. These results identify GsCBRLK as a molecular link between the stress- and ABA-induced calcium/calmodulin signal and gene expression in plant cells.