Salt Tolerance In Crop Plants Research Articles

An Accurate Representation of the Number of bZIP Transcription Factors in the Triticum aestivum (Wheat) Genome and the Regulation of Functional Genes during Salt Stress.

Climate change is dramatically increasing the overall area of saline soils around the world, which is increasing by approximately two million hectares each year. Soil salinity decreases crop yields and, thereby, makes farming less profitable, potentially causing increased poverty and hunger in many areas. A solution to this problem is increasing the salt tolerance of crop plants. Transcription factors (TFs) within crop plants represent a key to understanding salt tolerance, as these proteins play important roles in the regulation of functional genes linked to salt stress. The basic leucine zipper (bZIP) TF has a well-documented role in the regulation of salt tolerance. To better understand how bZIP TFs are linked to salt tolerance, we performed a genome-wide analysis in wheat using the Chinese spring wheat genome, which has been assembled by the International Wheat Genome Sequencing Consortium. We identified 89 additional bZIP gene sequences, which brings the total of bZIP gene sequences in wheat to 237. The majority of these 237 sequences included a single bZIP protein domain; however, different combinations of five other domains also exist. The bZIP proteins are divided into ten subfamily groups. Using an in silico analysis, we identified five bZIP genes (ABF2, ABF4, ABI5, EMBP1, and VIP1) that were involved in regulating salt stress. By scrutinizing the binding properties to the 2000 bp upstream region, we identified putative functional genes under the regulation of these TFs. Expression analyses of plant tissue that had been treated with or without 100 mM NaCl revealed variable patterns between the TFs and functional genes. For example, an increased expression of ABF4 was correlated with an increased expression of the corresponding functional genes in both root and shoot tissues, whereas VIP1 downregulation in root tissues strongly decreased the expression of two functional genes. Identifying strategies to sustain the expression of the functional genes described in this study could enhance wheat's salt tolerance.

High-affinity potassium transporter from a mangrove tree Avicennia officinalis increases salinity tolerance of Arabidopsis thaliana

Salinity reduces the growth and productivity of crop plants worldwide. Mangroves have evolved efficient ion homeostasis mechanisms to survive under their natural saline growth habitat. Information obtained from them may be utilized for increasing the salt tolerance of crop plants. We identified and characterized a high-affinity potassium transporter gene (AoHKT1) from Avicennia officinalis. The expression of AoHKT1 was induced by NaCl mainly in the leaves. Functional study by heterologous expression of AoHKT1 in Arabidopsis T-DNA insertional mutants athkt1–1 and athkt1–4 revealed that it could enhance the salt tolerance of the mutant plants. This was accompanied by an increase in K+ accumulation in the leaves. AoHKT1 was localized to the plasma membrane in Arabidopsis, and when expressed in yeast, it could complement the functions of both Na+ and K+ transporters. An attempt was made to identify the upstream regulator of AtHKT1, a close homolog of AoHKT1. Using chromatin immunoprecipitation, luciferase assay and yeast one-hybrid assays, WRKY9 was identified as the main transcription factor in the process. Furthermore, this was corroborated by the observation that AtHKT1 levels were significantly reduced in the atwrky9 seedlings. These findings revealed a part of the molecular regulatory mechanism of HKT1 induction in response to salt treatment in Arabidopsis. Our study suggests that AoHKT1 is a potential candidate for generating crop plants with increased salt tolerance.

Halophytes as new model plant species for salt tolerance strategies.

Soil salinity is becoming a growing issue nowadays, severely affecting the world's most productive agricultural landscapes. With intersecting and competitive challenges of shrinking agricultural lands and increasing demand for food, there is an emerging need to build resilience for adaptation to anticipated climate change and land degradation. This necessitates the deep decoding of a gene pool of crop plant wild relatives which can be accomplished through salt-tolerant species, such as halophytes, in order to reveal the underlying regulatory mechanisms. Halophytes are generally defined as plants able to survive and complete their life cycle in highly saline environments of at least 200-500 mM of salt solution. The primary criterion for identifying salt-tolerant grasses (STGs) includes the presence of salt glands on the leaf surface and the Na+ exclusion mechanism since the interaction and replacement of Na+ and K+ greatly determines the survivability of STGs in saline environments. During the last decades or so, various salt-tolerant grasses/halophytes have been explored for the mining of salt-tolerant genes and testing their efficacy to improve the limit of salt tolerance in crop plants. Still, the utility of halophytes is limited due to the non-availability of any model halophytic plant system as well as the lack of complete genomic information. To date, although Arabidopsis (Arabidopsis thaliana) and salt cress (Thellungiella halophila) are being used as model plants in most salt tolerance studies, these plants are short-lived and can tolerate salinity for a shorter duration only. Thus, identifying the unique genes for salt tolerance pathways in halophytes and their introgression in a related cereal genome for better tolerance to salinity is the need of the hour. Modern technologies including RNA sequencing and genome-wide mapping along with advanced bioinformatics programs have advanced the decoding of the whole genetic information of plants and the development of probable algorithms to correlate stress tolerance limit and yield potential. Hence, this article has been compiled to explore the naturally occurring halophytes as potential model plant species for abiotic stress tolerance and to further breed crop plants to enhance salt tolerance through genomic and molecular tools.

Prohexadione calcium enhances rice growth and tillering under NaCl stress.

Salt stress affects crop quality and reduces crop yields, and growth regulators enhance salt tolerance of crop plants. In this report, we examined the effects of prohexadione-calcium (Pro-Ca) on improving rice (Oryza sativa L.) growth and tillering under salt stress. We found that NaCl stress inhibited the growth of two rice varieties and increased malondialdehyde (MDA) levels, electrolyte leakage, and the activities of the antioxidant enzymes. Foliar application of Pro-Ca reduced seedling height and increased stem base width and lodging resistance of rice. Further analyses showed that Pro-Ca application reduced MDA content, electrolyte leakage, and membrane damage in rice leaves under NaCl stress. Pro-Ca enhanced the net photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) of rice seedlings, while increasing the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbic acid peroxidase (APX) at the tillering stage under salt stress. Overall, Pro-Ca improves salt tolerance of rice seedlings at the tillering stage by enhancing lodging resistance, reducing membrane damages, and enhancing photosynthesis and antioxidant capacities of rice seedlings.

Co-application of ACC deaminase-producing rhizobial bacteria and melatonin improves salt tolerance in common bean (Phaseolus vulgaris L.) through ion homeostasis

A comprehensive body of scientific evidence indicates that rhizobial bacteria and melatonin enhance salt tolerance of crop plants. The overall goal of this research was to evaluate the ability of Rhizobium leguminoserum bv phaseoli to suppress salinity stress impacts in common bean treated with melatonin. Treatments included bacterial inoculations (inoculated (RI) and non-inoculated (NI)), different salinity levels (non-saline (NS), 4 (S1) and 8 (S2) dS m−1 of NaCl) and priming (dry (PD), melatonin (PM100) and hydro (PH) priming) with six replications in growing media containing sterile sand and perlite (1:1). The results showed that the bacterial strain had the ability to produce indole acetic acid (IAA), ACC deaminase and siderophore. Plants exposed to salinity stress indicated a significant decline in growth, yield, yield components, nitrogen fixation and selective transport (ST), while showed a significant increase in sodium uptake. However, the combination of PM100 and RI treatments by improving growth, photosynthesis rate and nitrogen fixation positively influenced plant performance in saline conditions. The combined treatment declined the negative impacts of salinity by improving the potassium translocation, potassium to sodium ratio in the shoot and root and ST. In conclusion, the combination of melatonin and ACC deaminase producing rhizobium mitigated the negative effects of salinity. This result is attributed to the increased ST and decreased sodium uptake, which significantly reduced the accumulation of sodium ions in shoot.

Rare alleles from tolerant cultivars are useful for generating salt-tolerant rice

Salinity is a major environmental stress limiting crop yield. The gloomy forecast that by 2025 about 50% of farmland will be severely affected by salinity, coupled with the constantly increasing demand for food, drives home the urgent need to generate salt-tolerant crop plants for ensuring world food security. Salt tolerance is a complex phenomenon regulated by the interplay of multiple genes and factors. Because most of the metabolic activities are sensitive to high levels of Na+ in the cytosol, it is imperative for plants to maintain ion homeostasis in the cells under salt stress.

Zinc Oxide Nanoparticles Improve Salt Tolerance in Rice Seedlings by Improving Physiological and Biochemical Indices

Understanding the salinity stress mechanisms is essential for crop improvement and sustainable agriculture. Salinity is prepotent abiotic stress compared with other abiotic stresses that decrease crop growth and development, reducing crop production and creating food security-related threats. Therefore, the input of metal oxide nanoparticles (NPs) such as zinc oxide nanoparticles (ZnO-NPs) can improve salt tolerance in crop plants, especially in the early stage of growth. Therefore, the aim of the current study was to evaluate the impact of ZnO-NPs on inducing salt tolerance in two rice (Oryza sativa L.) genotypes of seedlings. An undocumented rice landrace (Kargi) and salinity tolerance basmati rice (CSR 30) seeds were grown in a hydroponic system for two weeks with and without 50 mg/L concentrations of ZnO-NPs in various doses of NaCl (0, 60, 80, and 100 mM). Both Kargi (15.95–42.49%) and CSR 30 (15.34–33.12%) genotypes showed a reduction in plant height and photosynthetic pigments (chlorophyll a and b, carotenoids, and total chlorophyll), Zn content, and K+ uptake under stress condition, compared with control seedlings. On the other hand, stress upregulated proline, malondialdehyde (MDA), Na+ content, and antioxidant enzyme activities—namely, those of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR)—in both O. sativa genotypes over the control. However, ZnO-NP-treated genotypes (Kargi and CSR 30) restored the photosynthetic pigment accumulation and K+ level, reforming the stomata and trichome morphology, and also increased antioxidant enzymes SOD, APX, CAT, and GR activity, which alleviated the oxidative stress, while reducing the level of MDA, proline, and H2O2 under stress condition. The present findings suggest that adding ZnO-NPs could mitigate the salinity stress in O. sativa by upregulating the antioxidative system and enhancing the cultivation of undocumented landrace (Kargi) and basmati (CSR 30) genotypes of O. sativa in salinity-affected areas.

Expression study of stress-related genes in salinity-treated transgenic Arabidopsis harboring soybean Response Regulator 34

Owing to their sessile nature, plants are easily affected by various extenal factors. Among those, drought and salinity are considered as the most common stresses, which often pose a threat to plant growth and development. Major effects of the drought and salinity are interconnected and drive similar series of molecular changes in plants. These alterations in response to the stress are under the regulation of various signaling pathways, including the engangement of evolutionarily conserved two-component systems (TCSs). Three components with distinct functions can be found in a functional TCS, which are histidine kinases (HKs), histidine-containing phosphotransfer proteins (HPts), and response regulator proteins (RRs). Previous research revealed that the soybean (Glycine max) GmRR34 acts as an important regulatory protein in plants under drought stress conditions. In this project, the investigation on the role of GmRR34 in osmotic stress responses was extended to salinity by examining the expression of a subset of salinity-responsive genes using RT-qPCR method. Our analyses showed that the transgenic Arabidopsis plants ectopically expressing GmRR34 displayed enhanced expression of several important stress-related genes, including Catalase 1 (CAT1), Stromal ascorbate peroxidase 1 (sAPX1), Copper/zinc superoxide dismutase 1 (CSD1), Sodium/hydrogen exchanger 1 (NHX1) and Salt overly sensitive 2 (SOS2). These results indicate that GmRR34-transgenic plants might be more salt-tolerant thanks to stronger activities of antioxidant enzymes and better capacity in maintaining cytosolic ion homeostasis. Therefore, it is highlighted the necessity to perform further studies to fully characterize the GmRR34 biological functions as well as explore its application potential in enhancing the salt tolerance of crop plants.

The Metacaspase TaMCA-Id Negatively Regulates Salt-Induced Programmed Cell Death and Functionally Links With Autophagy in Wheat.

Metacaspases (MCAs), a family of caspase-like proteins, are important regulators of programmed cell death (PCD) in plant defense response. Autophagy is an important regulator of PCD. This study explored the underlying mechanism of the interaction among PCD, MCAs, and autophagy and their impact on wheat response to salt stress. In this study, the wheat salt-responsive gene TaMCA-Id was identified. The open reading frame (ORF) of TaMCA-Id was 1,071 bp, coding 356 amino acids. The predicted molecular weight and isoelectric point were 38,337.03 Da and 8.45, respectively. TaMCA-Id had classic characteristics of type I MCAs domains, a typical N-terminal pro-domain rich in proline. TaMCA-Id was mainly localized in the chloroplast and exhibited nucleocytoplasmictrafficking under NaCl treatment. Increased expression of TaMCA-Id in wheat seedling roots and leaves was triggered by 150 mM NaCl treatment. Silencing of TaMCA-Id enhanced sensitivity of wheat seedlings to NaCl stress. Under NaCl stress, TaMCA-Id-silenced seedlings exhibited a reduction in activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), higher accumulation of H2O2 and , more serious injury to photosystem II (PSII), increase in PCD level, and autophagy activity in leaves of wheat seedlings. These results indicated that TaMCA-Id functioned in PCD through interacting with autophagy under NaCl stress, which could be used to improve the salt tolerance of crop plants.

How salt stress-responsive proteins regulate plant adaptation to saline conditions.

An overview is presented of recent advances in our knowledge of candidate proteins that regulate various physiological and biochemical processes underpinning plant adaptation to saline conditions. Salt stress is one of the environmental constraints that restrict plant distribution, growth and yield in many parts of the world. Increased world population surely elevates food demands all over the globe, which anticipates to add a great challenge to humanity. These concerns have necessitated the scientists to understand and unmask the puzzle of plant salt tolerance mechanisms in order to utilize various strategies to develop salt tolerant crop plants. Salt tolerance is a complex trait involving alterations in physiological, biochemical, and molecular processes. These alterations are a result of genomic and proteomic complement readjustments that lead to tolerance mechanisms. Proteomics is a crucial molecular tool that indicates proteins expressed by the genome, and also identifies the functions of proteins accumulated in response to salt stress. Recently, proteomic studies have shed more light on a range of promising candidate proteins that regulate various processes rendering salt tolerance to plants. These proteins have been shown to be involved in photosynthesis and energy metabolism, ion homeostasis, gene transcription and protein biosynthesis, compatible solute production, hormone modulation, cell wall structure modification, cellular detoxification, membrane stabilization, and signal transduction. These candidate salt responsive proteins can be therefore used in biotechnological approaches to improve tolerance of crop plants to salt conditions. In this review, we provided comprehensive updated information on the proteomic data of plants/genotypes contrasting in salt tolerance in response to salt stress. The roles of salt responsive proteins that are potential determinants for plant salt adaptation are discussed. The relationship between changes in proteome composition and abundance, and alterations observed in physiological and biochemical features associated with salt tolerance are also addressed.

Proteome responses of pearl millet genotypes under salinity

Soil salinity is a major problem worldwide, and plants counteract the salt-stress with various cellular strategies. A vast advancement has been achieved for elucidation of abiotic stress-tolerance mechanisms using high-throughput methods of proteomics. In the present study, two pearl millet genotypes with contrasting salt-stress tolerance were selected on the basis of our previous study for large-scale screening of 33 pearl millet accessions, showing differences in their morpho-physiological parameters and stress-related gene expression under salinity. They were subjected to comparative whole proteome analysis after treatment with 150 mm NaCl. We have observed 295 and 315 protein spots on Sypro-Ruby stained 2-DE gels for the tolerant (Tol) and sensitive (Sen) accessions, respectively, in the range of 12-200 kDa MW and 4-7 pI. Data obtained for differential protein expression indicated that maximum proteins exhibited reduced expression in the sensitive accession, while most of them were highly upregulated salt-induced proteins in the tolerant accession. The present study provided a possible insight into the regulatory mechanism of salinity-stress tolerance at whole proteome level. The tolerant genotype of pearl millet can be used as a potential source of novel candidate genes responsible for imparting salinity-stress tolerance. It can further be exploited to develop salt-tolerant crop plants through biotechnological interventions.

Adaptive Mechanisms of Halophytes and Their Potential in Improving Salinity Tolerance in Plants.

Soil salinization, which is aggravated by climate change and inappropriate anthropogenic activities, has emerged as a serious environmental problem, threatening sustainable agriculture and future food security. Although there has been considerable progress in developing crop varieties by introducing salt tolerance-associated traits, most crop cultivars grown in saline soils still exhibit a decline in yield, necessitating the search for alternatives. Halophytes, with their intrinsic salt tolerance characteristics, are known to have great potential in rehabilitating salt-contaminated soils to support plant growth in saline soils by employing various strategies, including phytoremediation. In addition, the recent identification and characterization of salt tolerance-related genes encoding signaling components from halophytes, which are naturally grown under high salinity, have paved the way for the development of transgenic crops with improved salt tolerance. In this review, we aim to provide a comprehensive update on salinity-induced negative effects on soils and plants, including alterations of physicochemical properties in soils, and changes in physiological and biochemical processes and ion disparities in plants. We also review the physiological and biochemical adaptation strategies that help halophytes grow and survive in salinity-affected areas. Furthermore, we illustrate the halophyte-mediated phytoremediation process in salinity-affected areas, as well as their potential impacts on soil properties. Importantly, based on the recent findings on salt tolerance mechanisms in halophytes, we also comprehensively discuss the potential of improving salt tolerance in crop plants by introducing candidate genes related to antiporters, ion transporters, antioxidants, and defense proteins from halophytes for conserving sustainable agriculture in salinity-prone areas.

Halophyte based Mediterranean agriculture in the contexts of food insecurity and global climate change

The loss of agro-biodiversity, climate changes and food insecurity are major challenges in the Mediterranean countries with potentially multidimensional consequences. With respect to salinity, approximately 18 million ha, corresponding to 25 % of total irrigated land in the Mediterranean area, are salt affected. Intensive cropping and the excessive use of expensive inputs such as water and fertilizers aggravate this situation. Understanding how we could improve crop productivity in salinized environments is therefore critical to face these challenges. Our comprehension of fundamental physiological mechanisms in plant salt stress adaptation has greatly advanced over the last decades. However, many of these mechanisms have been linked to salt tolerance in simplified experimental systems whereas they have been rarely functionally proven in real agricultural contexts. The sustainability of farming systems in salt affected Mediterranean soils can be effectively achieved by the use of salt-tolerant halophyte plants even more effective through the use of intercropping, crop rotation and aquaponics.. Moreover, if these halophyte plants are removed from the soil to grow other species, pressure on generating salt-tolerant crop plants would be reduced and much healthier crop plants would be cultivated in less stressed saline soils. This paper will focus on the sustainable practices based on the cultivation of halophytes in saline soils by highlighting some experimental activities carried out at laboratory and field levels in the last few years.

Alleviation of Salt-Induced Adverse Effects on Gas Exchange, Photosynthetic Pigments Content and Chloroplast Ultrastructure in Gerbera Jamesonii L. by Exogenous Salicylic Acid Application

Aims: The effects of exogenously applied salicylic acid (SA) on gas exchange characteristics, photosynthetic pigments and chloroplast ultrastructure were investigated in gerbera at their reproductive stage under salt-stressed conditions.
 Methodology: A pot experiment was conducted under glasshouse conditions at the Zhejiang University, Hangzhou, China, (30° N/120° E) between February 2008 and March 2009.Plants, pretreated with foliar applications of 0, 0.5, and 1.0 mmoldm-3 SA at the onset of flower initiation were irrigated with 100 mmoldm-3NaCl(aq) for two weeks, starting after three days from the SA pretreatment. Control did not receive either NaCl or SA.Photosynthetic rate, gas exchange, photosynthetic pigments content and chloroplast ultrastructure were investigated against treatments. All data were subjected to analysis of variance (ANOVA) and Generalized Linear Model (GLM) using SAS statistical software. Pearson’s correlation test was carried out to study the relationships among the parameters. The means were compared using Duncan’s multiple range test (DMRT). For all the tests, P< .05 was considered statistically significant.
 Results: Salt stress adversely affected the gas exchange characteristics, photosynthetic pigment contents and chloroplast ultrastructure. SA application significantly increased the net photosynthesis, stomatal conductivity, intra-cellular CO2 content and transpiration rate but decreased the stomatal limitation, compared to those of untreated salt-stressed plants. Further, the enhanced photosynthetic pigment contents and notably undamaged chloroplast ultrastructure were evident of the ameliorative effects of SA on photosynthetic system under salt stress. Of the two concentrations tested, 0.5 mmoldm-3 SA concentration seemed to have greater effect throughout the experiment showing no significant variation from control in some attributes (chlorophyll contents and chloroplast ultrastructure).
 Conclusion: Responses of plants pretreated with SA spraying and significant correlation among them plausibly suggest SA-induced enhancement of photosynthetic system as another target for conferring salt tolerance in crop plants.

WRKY9 transcription factor regulates cytochrome P450 genes CYP94B3 and CYP86B1, leading to increased root suberin and salt tolerance in Arabidopsis

Salinity affects crop productivity worldwide and mangroves growing under high salinity exhibit adaptations such as enhanced root apoplastic barrier to survive under such conditions. We have identified two cytochrome P450 family genes, AoCYP94B3 and AoCYP86B1 from the mangrove tree Avicennia officinalis and characterized them using atcyp94b3 and atcyp86b1, which are mutants of their putative Arabidopsis orthologs and the corresponding complemented lines with A. officinalis genes. CYP94B3 and CYP86B1 transcripts were induced upon salt treatment in the roots of both A. officinalis and Arabidopsis. Both AoCYP94B3 and AoCYP86B1 were localized to the endoplasmic reticulum. Heterologous expression of 35S::AoCYP94B3 and 35S::AoCYP86B1 in their respective Arabidopsis mutants (atcyp94b3 and atcyp86b1) increased the salt tolerance of the transgenic seedlings by reducing the amount of Na+ accumulation in the shoots. Moreover, the reduced root suberin phenotype of atcyp94b3 was rescued in the 35S::AoCYP94B3;atcyp94b3 transgenic Arabidopsis seedlings. Gas-chromatography and mass spectrometry analyses showed that the amount of suberin monomers (C-16 ω-hydroxy acids, C-16 α, ω-dicarboxylic acids and C-20 eicosanol) were increased in the roots of 35S::AoCYP94B3;atcyp94b3 Arabidopsis seedlings. Using chromatin immunoprecipitation and electrophoretic mobility shift assays, we identified AtWRKY9 as the upstream regulator of AtCYP94B3 and AtCYP86B1 in Arabidopsis. In addition, atwrky9 showed suppressed expression of AtCYP94B3 and AtCYP86B1 transcripts, and reduced suberin in the roots. These results show that AtWRKY9 controls suberin deposition by regulating AtCYP94B3 and AtCYP86B1, leading to salt tolerance. Our data can be used for generating salt-tolerant crop plants in the future.

Bioinformatic analysis of promoter, motifs and CpG islands of genes encoding potassium transporters in crop plants

ABSTRACT Potassium transporter genes are essential for plant salt stress tolerance. Identification of gene regulatory elements is vital for the recognition of gene expression patterns. Thus, understanding gene regulatory systems of potassium transporter genes is useful to improve the salt tolerance of crop plants. The present study was aimed at in silico analysis of promoter and regulatory elements of potassium transporter genes in coffee, peanut, soybean, maize, sorghum and potato crops. A total of 19 potassium transporter genes were identified, and the transcription start site (TSS), conserved motif, CpG islands were analysed using various computational tools. The highest promoter prediction score (1) was obtained in one gene sequence (LOC113728271) for Coffea arabica transcription start site, whereas the lowest score (0.8) was recorded in one gene sequence (LOC8065633) for Sorghum bicolor transcription start site. The analysis also showed that 66% of the genes contained more than one transcription start site whereas 63.16% had only one transcription start site. Five motifs were identified. Motif 1 was found as the common promoter motif residing on 78.95% of potassium transporter promoter sequences with an E-value of 3.4e − 002.C2H2 zinc finger transcription factors are predicted to bind to these conserved motifs with high statistical probability (2.28e − 03). Very few CpG islands were observed both in the promoter and body region of the gene sequences using two algorithms. The present study could contribute for better understanding of gene expression and the improvement of crops’ tolerance to environmental stresses through molecular assisted breeding or genetic engineering techniques.

TaPUB15, a U‐Box E3 ubiquitin ligase gene from wheat, enhances salt tolerance in rice

AbstractPlant U‐box (PUB) E3 ubiquitin ligases play essential roles in response to environmental stresses and hormone signaling, but little is known about them in wheat (Triticum aestivum L.). We characterized a U‐box E3 ubiquitin ligase gene, TaPUB15, which is conserved in wheat cultivars. TaPUB15 was expressed in multiple tissues, and the expression was much higher in roots than in other tissues. Transcription of TaPUB15 was induced by salt, abscisic acid, 4°C, and polyethylene glycol (PEG). Overexpression of TaPUB15‐D led to improve salt tolerance in transgenic rice, along with more roots in transgenic rice. Ion flux assays showed that transgenic rice plants had improved salt tolerance and maintained low Na+/K+ ratios under salinity stress. Gene expression assays indicated that several salt stress‐related genes were significantly upregulated in transgenic rice relative to the wild type. These results from transgenic rice were also verified in transgenic Arabidopsis. Our data showed that TaPUB15 plays crucial roles in enhancing salt tolerance in crop plants and served a valuable gene resource for promoting the breeding of salt‐tolerant wheat in the future.

Engineering salinity tolerance in plants: progress and prospects.

There is a need to integrate conceptual framework based on the current understanding of salt stress responses with different approaches for manipulating and improving salt tolerance in crop plants. Soil salinity exerts significant constraints on global crop production, posing a serious challenge for plant breeders and biotechnologists. The classical transgenic approach for enhancing salinity tolerance in plants revolves by boosting endogenous defence mechanisms, often via a single-gene approach, and usually involves the enhanced synthesis of compatible osmolytes, antioxidants, polyamines, maintenance of hormone homeostasis, modification of transporters and/or regulatory proteins, including transcription factors and alternative splicing events. Occasionally, genetic manipulation of regulatory proteins or phytohormone levels confers salinity tolerance, but all these may cause undesired reduction in plant growth and/or yields. In this review, we present and evaluate novel and cutting-edge approaches for engineering salt tolerance in crop plants. First, we cover recent findings regarding the importance of regulatory proteins and transporters, and how they can be used to enhance salt tolerance in crop plants. We also evaluate the importance of halobiomes as a reservoir of genes that can be used for engineering salt tolerance in glycophytic crops. Additionally, the role of microRNAs as critical post-transcriptional regulators in plant adaptive responses to salt stress is reviewed and their use for engineering salt-tolerant crop plants is critically assessed. The potentials of alternative splicing mechanisms and targeted gene-editing technologies in understanding plant salt stress responses and developing salt-tolerant crop plants are also discussed.

Inorganic fertilizer and salt tolerance in Sorghum bicolor (L.) moench ssp. bicolor

In many cases, increased salt tolerance has been shown to correlate with increased nitrogen (N) fertilizer in some plants. It was hypothesized that increased fertilizer would increase salt tolerance in Sorghum bicolor (L.) Moench ssp. bicolor (“milo”). In this study, three fertilizer treatments (containing 0, 50, and 150 lbs N acre−1) and four salinity treatments (0, 40, 80, and 120 mM) were applied to S. bicolor. Weekly measures of chlorophyll concentration, height, stomatal conductance, and photosynthesis were conducted for 4 weeks of treatment. Biomass was measured following 4 weeks of treatment. Plant biomass, height, and chlorophyll concentration were reduced by increasing salinity. Any salinity of at least 40 mM reduced the height of plants, regardless of fertilizer concentration. Plant biomass was increased at 50 lbs N acre−1 but was decreased at 150 lbs N acre−1. Contrary to the hypothesis, increased fertilizer decreased many aspects of growth and performance in S. bicolor. There was a statistical interaction between salt and fertilizer for photosynthesis and stomatal conductance. Photosynthesis and stomatal conductance in 0 mM salt remained high across all fertilizer treatments, but were low across all fertilizer treatments in 120 mM salt. Photosynthesis and stomatal conductance in 40 and 80 mM salt treatments were high in low fertilizer concentrations and became lower in high fertilizer concentrations. This indicates that increased fertilizer does not always increase salt tolerance in crop plants and is indicative of a more complex interaction between plant and soil conditions.

Deletion of the N-terminal domain of the yeast vacuolar (Na+ ,K+ )/H+ antiporter Vnx1p improves salt tolerance in yeast and transgenic Arabidopsis.

Cation/proton antiporters play a major role in the control of cytosolic ion concentrations in prokaryotes and eukaryotes organisms. In yeast, we previously demonstrated that Vnx1p is a vacuolar monovalent cation/H+ exchanger showing Na+ /H+ and K+ /H+ antiporter activity. We have also shown that disruption of VNX1 results in an almost complete abolishment of vacuolar Na+ /H+ exchange, but yeast cells overexpressing the complete protein do not show improved salinity tolerance. In this study, we have identified an autoinhibitory N-terminal domain and have engineered a constitutively activated version of Vnx1p, by removing this domain. Contrary to the wild type protein, the activated protein has a pronounced effect on yeast salt tolerance and vacuolar pH. Expression of this truncated VNX1 gene also improves Arabidopsis salt tolerance and increases Na+ and K+ accumulation of salt grown plants thus suggesting a biotechnological potential of activated Vnx1p to improve salt tolerance of crop plants.