Expressing class I wheat NHX (TaNHX2) gene in eggplant (Solanum melongena L.) improves plant performance under saline condition

Cytochrome P450 SmCYP78A7a positively functions in eggplant response to salt stress via forming a positive feedback loop with SmWRKY11

Accumulating salinity in soil critically affected growth, development, and yield in plant. However, the mechanisms of plant against salt stress largely remain unknown. Herein, we identified a gene named SmCYP78A7a, which encoded a cytochrome P450 monooxygenase and belonged to the CYP78A sub-family, and its transcript level was significantly up-regulated by salt stress and down-regulated by dehydration stress. SmCYP78A7a located in the endoplasmic reticulum. Silencing of SmCYP78A7a enhanced susceptibility of eggplant to salt stress, and significantly down-regulated the transcript levels of salt stress defense related genes SmGSTU10 and SmWRKY11 as well as increased hydrogen peroxide (H2O2) content and decreased catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) enzyme activities. In addition, SmCYP78A7a transient expression enhanced eggplant tolerance to salt stress. By chromatin immunoprecipitation PCR (ChIP-PCR), luciferase reporter assay, and electrophoretic mobility shift assay (EMSA), SmWRKY11 activated SmCYP78A7a expression by directly binding to the W-box 6-8 (W-box 6, W-box 7, and W-box 8) within SmCYP78A7a promoter to confer eggplant tolerance to salt stress. In summary, our finds reveal that SmCYP78A7a positively functions in eggplant response to salt stress via forming a positive feedback loop with SmWRKY11, and provide a new insight into regulatory mechanisms of eggplant to salt stress.

Overexpression of a 'Beta' MYB Factor Gene, VhMYB15, Increases Salinity and Drought Tolerance in Arabidopsis thaliana

'Beta' is a hybrid of Vitis riparia L. and V. labrusca and has a strong ability to adapt to adverse growth environments and is mainly cultivated and used as a resistant rootstock. At present, the most extensively studied MYB TFs are R2R3-type, which have been found to be involved in plant growth, development, and stress response processes. In the present research, VhMYB15, a key transcription factor for abiotic stress tolerance, was screened by bioinformatics in 'Beta' rootstock, and its function under salinity and drought stresses was investigated. VhMYB15 was highly expressed in roots and mature leave under salinity and drought stresses. Observing the phenotype and calculating the survival rate of plants, it was found that VhMYB15-overexpressing plants exhibited relatively less yellowing and wilting of leaves and a higher survival rate under salinity and drought stresses. Consistent with the above results, through the determination of stress-related physiological indicators and the expression analysis of stress-related genes (AtSOS2, AtSOS3, AtSOS1, AtNHX1, AtSnRK2.6, AtNCED3, AtP5CS1, and AtCAT1), it was found that transgenic Arabidopsis showed better stress tolerance and stronger adaptability under salinity and drought stresses. Based on the above data, it was preliminarily indicated that VhMYB15 may be a key factor in salinity and drought regulation networks, enhancing the adaptability of 'Beta' to adverse environments.

Tolerance and adaptation mechanism of Solanaceous crops under salinity stress

Solanaceous crops act as a source of food, nutrition and medicine for humans. Soil salinity is a damaging environmental stress, causing significant reductions in cultivated land area, crop productivity and quality, especially under climate change. Solanaceous crops are extremely vulnerable to salinity stress due to high water requirements during the reproductive stage and the succulent nature of fruits and tubers. Salinity stress impedes morphological and anatomical development, which ultimately affect the production and productivity of the economic part of these crops. The morpho-physiological parameters such as root-to-shoot ratio, leaf area, biomass production, photosynthesis, hormonal balance, leaf water content are disturbed under salinity stress in Solanaceous crops. Moreover, the synthesis and signalling of reactive oxygen species, reactive nitrogen species, accumulation of compatible solutes, and osmoprotectant are significant under salinity stress which might be responsible for providing tolerance in these crops. The regulation at the molecular level is mediated by different genes, transcription factors, and proteins, which are vital in the tolerance mechanism. The present review aims to redraw the attention of the researchers to explore the mechanistic understanding and potential mitigation strategies against salinity stress in Solanaceous crops, which is an often-neglected commodity.

SmRAV1, an AP2 and B3 Transcription Factor, Positively Regulates Eggplant's Response to Salt Stress

Salt stress is a lethal abiotic stress threatening global food security on a consistent basis. In this study, we identified an AP2 and B3 domain-containing transcription factor (TF) named SmRAV1, and its expression levels were significantly up-regulated by NaCl, abscisic acid (ABA), and hydrogen peroxide (H2O2) treatment. High expression of SmRAV1 was observed in the roots and sepal of mature plants. The transient expression assay in Nicotiana benthamiana leaves revealed that SmRAV1 was localized in the nucleus. Silencing of SmRAV1 via virus-induced gene silencing (VIGS) decreased the tolerance of eggplant to salt stress. Significant down-regulation of salt stress marker genes, including SmGSTU10 and SmNCED1, was observed. Additionally, increased H2O2 content and decreased catalase (CAT) enzyme activity were recorded in the SmRAV1-silenced plants compared to the TRV:00 plants. Our findings elucidate the functions of SmRAV1 and provide opportunities for generating salt-tolerant lines of eggplant.

SmWRKY11 acts as a positive regulator in eggplant response to salt stress

Salt stress is one of the most threatening abiotic stresses to plants, which can seriously affect plant growth, development, reproduction, and yield. However, the mechanisms of plant against salt stress largely remain unclear. Herein, SmWRKY11, an assumed WRKY transcription factor, was functionally characterized in eggplant against salt stress. SmWRKY11 was significantly up-regulated by salt, dehydration stress, and ABA treatment. SmWRKY11 located in the nucleus, and the Plant_zn_clust conserved domain exhibited transcriptional activation activity. Silencing of SmWRKY11 enhanced the susceptibility of eggplant to salt stress, accompanied by significantly down-regulation of transcript expression levels of salt stress defense-related genes SmNCED1, SmGSTU10, and positive regulator of salt stress response SmERF1 as well as increase of hydrogen peroxide (H2O2) content and decrease of the enzyme activities of catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). In addition, silencing of SmERF1 also could significantly down-regulate SmWRKY11 expression in eggplant response to salt stress. By luciferase reporter assay and chromatin immunoprecipitation PCR assay, SmERF1 expression was found to be indirectly activated by SmWRKY11. These data indicate that SmWRKY11 acts as a positive regulator by forming positive feedback loop with SmERF1 via an indirect regulatory manner in eggplant response to salt stress.

Wheat adaptation to environmental stresses under climate change: Molecular basis and genetic improvement

Wheat (Triticum aestivum) is a staple food for about 40% of the world's population. As the global population has grown and living standards improved, high yield and improved nutritional quality have become the main targets for wheat breeding. However, wheat production has been compromised by global warming through the more frequent occurrence of extreme temperature events, which have increased water scarcity, aggravated soil salinization, caused plants to be more vulnerable to diseases, and directly reduced plant fertility and suppressed yield. One promising option to address these challenges is the genetic improvement of wheat for enhanced resistance to environmental stress. Several decades of progress in genomics and genetic engineering has tremendously advanced our understanding of the molecular and genetic mechanisms underlying abiotic and biotic stress responses in wheat. These advances have heralded what might be considered a "golden age" of functional genomics for the genetic improvement of wheat. Here, we summarize the current knowledge on the molecular and genetic basis of wheat resistance to abiotic and biotic stresses, including the QTLs/genes involved, their functional and regulatory mechanisms, and strategies for genetic modification of wheat for improved stress resistance. In addition, we also provide perspectives on some key challenges that need to be addressed.

Genetic modification strategies for enhancing plant resilience to abiotic stresses in the context of climate change

Enhancing the resilience of plants to abiotic stresses, such as drought, salinity, heat, and cold, is crucial for ensuring global food security challenge in the context of climate change. The adverse effects of climate change, characterized by rising temperatures, shifting rainfall patterns, and increased frequency of extreme weather events, pose significant threats to agricultural systems worldwide. Genetic modification strategies offer promising approaches to develop crops with improved abiotic stress tolerance. This review article provides a comprehensive overview of various genetic modification techniques employed to enhance plant resilience. These strategies include the introduction of stress-responsive genes, transcription factors, and regulatory elements to enhance stress signaling pathways. Additionally, the manipulation of hormone signaling pathways, osmoprotectant accumulation, and antioxidant defense mechanisms is discussed. The use of genome editing tools, such as CRISPR-Cas9, for precise modification of target genes related to stress tolerance is also explored. Furthermore, the challenges and future prospects of genetic modification for abiotic stress tolerance are highlighted. Understanding and harnessing the potential of genetic modification strategies can contribute to the development of resilient crop varieties capable of withstanding adverse environmental conditions caused by climate change, thereby ensuring sustainable agricultural productivity and food security.

Arbuscular mycorrhizal fungi affect the expression of PxNHX gene family, improve photosynthesis and promote Populus simonii×P. nigra growth under saline-alkali stress

INTRODUCTION

Saline-alkali stress seriously endangers the normal growth of Populus simonii×P. nigra. Arbuscular mycorrhizal (AM) fungi can enhance the saline-alkali tolerance of plants by establishing a symbiotic relationship with them.

METHODS

In this study, a pot experiment was conducted to simulate a saline-alkali environment where Populus simonii×P. nigra were inoculated with Funneliformis mosseae to explore their effects on the saline-alkali tolerance of Populus simonii×P. nigra.

RESULTS AND DISCUSSION

Our results show that a total of 8 NHX gene family members are identified in Populus simonii×P. nigra. F. mosseae regulate the distribution of Na+ by inducing the expression of PxNHXs. The pH value of poplar rhizosphere soil is reduced, result in the promote absorption of Na⁺ by poplar, that ultimately improved the soil environment. Under saline-alkali stress, F. mosseae improve the chlorophyll fluorescence and photosynthetic parameters of poplar, promote the absorption of water, K⁺ and Ca²⁺, thus increase the plant height and fresh weight of aboveground parts, and promote the growth of poplar. Our results provide a theoretical basis for further exploring the application of AM fungi to improve the saline-alkali tolerance of plants.

Genetic manipulation for abiotic stress resistance traits in crops

Abiotic stresses are major limiting factors that pose severe threats to agricultural production. Conventional breeding has significantly improved crop productivity in the last century, but traditional breeding has reached its maximum capacity due to the multigenic nature of abiotic stresses. Alternatively, biotechnological approaches could provide new opportunities for producing crops that can adapt to the fast-changing environment and still produce high yields under severe environmental stress conditions. Many stress-related genes have been identified and manipulated to generate stress-tolerant plants in the past decades, which could lead to further increase in food production in most countries of the world. This review focuses on the recent progress in using transgenic technology and gene editing technology to improve abiotic stress tolerance in plants, and highlights the potential of using genetic engineering to secure food and fiber supply in a world with an increasing population yet decreasing land and water availability for food production and fast-changing climate that will be largely hostile to agriculture.

Salt stress triggers augmented levels of Na+, K+ and ROS alters salt-related gene expression in leaves and roots of tall wheatgrass (Agropyron elongatum)

In turfgrass breeding, competent grass ecotypes are preferably identified for their resistance to salinity condition. This research was designed to explore genes that induce salt resistance (NHX1, NHX2, HKT1;4, SnRK2.4 and NAC9) and their role in physiological modifications of six tall wheatgrass ecotypes (Agropyron elongatum L.). The sites of sample collection were characterized by different levels of salinity, i.e. low (EC: 4 dS m-1 and pH: 6.5), moderate (EC: 7 dS m-1 and pH: 6.5) and high (EC: 12 dS m-1 and pH: 7.5). This study was designed as a split-plot in a randomized complete block where salinity treatments served as the whole-plot factor and ecotypes served as the subplot factor. The ecotypes were screened for their resistance to salinity, based on visual symptoms, salt injury index, physiological features and biochemical parameters. The results revealed that ecotype 'AE5' was most resistant to salinity than other ecotypes, whereas 'AE3' was the most susceptible. To understand why these differences occurred, measurements were aimed at revealing mRNA levels that resulted from genes responsible for salt resistance. Our results demonstrated that salinity-resistant ecotypes showed high expression levels of several genes, i.e. NHX1, NHX2, HKT1;4, SnRK2.4 and NAC9 in the leaves and roots. These results were corroborated by a decrease (by 1.5-2.5 times) in stress markers, namely, superoxide anion (O2-), hydrogen peroxide (H2O2) and malondialdehyde (MDA), as well as an increase (by 0.5-7 times) in enzymatic and non-enzymatic antioxidant activity in salinity-resistant ecotypes when the plants were exposed to salinity. We observed higher values of initial root length and lateral root density (21% and 18%, respectively) in salinity-resistant ecotypes under salinity condition, compared to other ecotypes. There were lower expression levels of NHX1 and NHX2 in the roots, which were 3.2 and 2.1 times less, respectively, compared to the leaves. This implied that NHX1 and NHX2 expressions can lead to the sequestration of Na+ in the leaves during salinity condition. The current research revealed that HKT1;4 was more able to restrict Na + accumulation, compared to the actions of NHX1 and NHX2 genes. The over-expression of HKT1;4 in 'AE5' allowed a better maintenance of root growth during salinity condition. The expression of NAC9 had an increase of 2.1-fold which correlated with an increase in the amount of antioxidant enzymes. In general, the location of sample collection explained the differences in gene expression, especially regarding the extent to which plants respond to salinity condition. Ultimately, these differences can define physiological features in salinity-resistant and salinity-susceptible ecotypes of tall wheatgrass.

The red seaweed Kappaphycus alvarezii antiporter gene (KaNa+/H+) confers abiotic stress tolerance in transgenic tobacco

BACKGROUND

Plant establishment, growth, development and productivity are adversely affected by abiotic stresses that are dominant characteristics of environmentally challenged/degraded habitats created in the Anthropocene. Crop breeding for climate resilience properties is need of the hour to sustain the crop productivity. We report on the characterization of Kappaphycus alvarezii (a red seaweed) Na+/H+ antiporter gene (KaNa+/H+) for enhanced salt and osmotic stress tolerance.

METHODS

The KaNa+/H+ antiporter gene was cloned and over-expressed in tobacco under the control of CaMV35S promoter. Transgenic analysis was carried out to assess the stress tolerance ability of tobacco over-expressing KaNa+/H+ antiporter gene.

RESULTS

Over-expression of KaNa+/H+ gene improved the seed germination and seed vigor index under stress. Transgenic plants grew better and exhibited delayed leaf senescence. Improved K+/Na+, carotenoid/total chlorophyll and relative water content; lower accumulation of reactive oxygen species (ROS), MDA and Na+; lower electrolyte leakage; better membrane stability index and accumulation of K+, photosynthetic pigment, starch, sugar, free amino acid, proline and polyphenol contents indicated better physiological health of the transgenic tobacco under stress. Transgenic tobacco exhibited higher photosynthesis, photosystem II efficiency, electron transfer rate, photochemical quenching and activity of water splitting complex. Compared with control tobacco, transgenic tobacco exhibited higher expression of stress-defence genes under stress and better recovery after long-term osmotic stress.

CONCLUSIONS

Lower Na+ cytotoxicity, lower accumulation of ROS and maintenance of the membrane integrity helped transgenic tobacco to maintain the physiological functioning under stress. Present results established K. alvarezii as a potential gene resource and the KaNa+/H+ antiporter gene as a potential candidate gene in molecular breeding of crops for development of the degraded land.

Signal Transduction in Cereal Plants Struggling with Environmental Stresses: From Perception to Response

Cereal plants under abiotic or biotic stressors to survive unfavourable conditions and continue growth and development, rapidly and precisely identify external stimuli and activate complex molecular, biochemical, and physiological responses. To elicit a response to the stress factors, interactions between reactive oxygen and nitrogen species, calcium ions, mitogen-activated protein kinases, calcium-dependent protein kinases, calcineurin B-like interacting protein kinase, phytohormones and transcription factors occur. The integration of all these elements enables the change of gene expression, and the release of the antioxidant defence and protein repair systems. There are still numerous gaps in knowledge on these subjects in the literature caused by the multitude of signalling cascade components, simultaneous activation of multiple pathways and the intersection of their individual elements in response to both single and multiple stresses. Here, signal transduction pathways in cereal plants under drought, salinity, heavy metal stress, pathogen, and pest attack, as well as the crosstalk between the reactions during double stress responses are discussed. This article is a summary of the latest discoveries on signal transduction pathways and it integrates the available information to better outline the whole research problem for future research challenges as well as for the creative breeding of stress-tolerant cultivars of cereals.

Approaches Involved in the Vegetable Crops Salt Stress Tolerance Improvement: Present Status and Way Ahead

Salt stress is one of the most important abiotic stresses as it persists throughout the plant life cycle. The productivity of crops is prominently affected by soil salinization due to faulty agricultural practices, increasing human activities, and natural processes. Approximately 10% of the total land area (950 Mha) and 50% of the total irrigated area (230 Mha) in the world are under salt stress. As a consequence, an annual loss of 12 billion US$ is estimated because of reduction in agriculture production inflicted by salt stress. The severity of salt stress will increase in the upcoming years with the increasing world population, and hence the forced use of poor-quality soil and irrigation water. Unfortunately, majority of the vegetable crops, such as bean, carrot, celery, eggplant, lettuce, muskmelon, okra, pea, pepper, potato, spinach, and tomato, have very low salinity threshold (ECt, which ranged from 1 to 2.5 dS m-1 in saturated soil). These crops used almost every part of the world and lakes' novel salt tolerance gene within their gene pool. Salt stress severely affects the yield and quality of these crops. To resolve this issue, novel genes governing salt tolerance under extreme salt stress were identified and transferred to the vegetable crops. The vegetable improvement for salt tolerance will require not only the yield influencing trait but also target those characters or traits that directly influence the salt stress to the crop developmental stage. Genetic engineering and grafting is the potential tool which can improve salt tolerance in vegetable crop regardless of species barriers. In the present review, an updated detail of the various physio-biochemical and molecular aspects involved in salt stress have been explored.

Genome-wide association study reveals a genomic region on 5AL for salinity tolerance in wheat

Soil salinity is a major threat to crop productivity and quality worldwide. In order to reduce the negative effects of salinity stress, it is important to understand the genetic basis of salinity tolerance. Identifying new salinity tolerance QTL or genes is crucial for breeders to pyramid different tolerance mechanisms to improve crop adaptability to salinity. Being one of the major cereal crops, wheat is known as a salt-sensitive glycophyte and subject to substantial yield losses when grown in the presence of salt. In this study, both pot and tank experiments were conducted to investigate the genotypic variation present in 328 wheat varieties in their salinity tolerance at the vegetative stage. A Genome-Wide Association Studies (GWAS) were carried out to identify QTL conferring salinity tolerance through a mixed linear model. Six, five and eight significant marker-trait associations (MTAs) were identified from pot experiments, tank experiments and average damage scores, respectively. These markers are located on the wheat chromosomes 1B, 2B, 2D, 3A, 4B, and 5A. These tolerance alleles were additive in their effects and, when combined, increased tolerance to salinity. Candidate genes identified in these QTL regions encoded a diverse class of proteins involved in salinity tolerance in plants. A Na⁺/H⁺ exchanger and a potassium transporter on chromosome 5A (IWB30519) will be of a potential value for improvement of salt tolerance of wheat cultivars using marker assisted selection programs. Some useful genotypes, which showed consistent tolerance in different trials, can also be effectively used in breeding programs.

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.

Characterization of Differentially Expressed Genes under Salt Stress in Olive

Climate change, currently taking place worldwide and also in the Mediterranean area, is leading to a reduction in water availability and to groundwater salinization. Olive represents one of the most efficient tree crops to face these scenarios, thanks to its natural ability to tolerate moderate salinity and drought. In the present work, four olive cultivars (Koroneiki, Picual, Royal de Cazorla and Fadak86) were exposed to high salt stress conditions (200 mM of NaCl) in greenhouse, in order to evaluate their tolerance level and to identify key genes involved in salt stress response. Molecular and physiological parameters, as well as plant growth and leaves’ ions Na⁺ and K⁺ content were measured. Results of the physiological measurements showed Royal de Cazorla as the most tolerant cultivar, and Fadak86 and Picual as the most susceptible ones. Ten candidate genes were analyzed and their complete genomic, CDS and protein sequences were identified. The expression analysis of their transcripts through reverse transcriptase quantitative PCR (RT-qPCR) demonstrated that only OeNHX7, OeP5CS, OeRD19A and OePetD were upregulated in tolerant cultivars, thus suggesting their key role in the activation of a salt tolerance mechanism.

The NAC-type transcription factor GmNAC20 improves cold, salinity tolerance, and lateral root formation in transgenic rice plants

NAC-type transcription factors are crucial players in the abiotic stress responses of plants. Soybean NAC-type transcription factor GmNAC20 was transformed into rice genome via Agrobacterium method of transformation to improve abiotic stress tolerance. Integration and expression of GmNAC20 were verified by the DNA blot hybridization, immunoblotting, RT-PCR, and quantitative RT-PCR in T3 generation of transgenic rice plants. Significant expression of GmNAC20 was found in transgenic plants under salinity, cold, and IAA treatments. The transgenic rice plants expressing GmNAC20 displayed enhanced salinity and cold stress tolerance via upregulating the abiotic stress-responsive genes. Furthermore, T3 transgenic plants retained relative water content, chlorophyll content with enhanced accumulation of proline content than wild-type plants under salinity, and cold stress environments. The decrease in MDA content and electrolyte leakage with a significant increase in antioxidant enzyme activities were noticed in transgenic rice plants under either salinity or cold stress conditions, compared to wild-type plants. Overexpression of GmNAC20 in rice plants also induced the lateral root formation, associated with upregulation of auxin signaling-related genes. Taken together, our results indicated that GmNAC20 acts as a positive regulator for conferring salinity and cold tolerance in rice plants and appropriate candidate for improving salinity and cold stress in other important food crops.

Gene structure of three kinds of vacuolar-type Na+/H+ antiporters including TaNHX2 transcribed in bread wheat

The vacuolar-type sodium/proton antiporter is considered to play an important role in withstanding salt stress by transporting sodium ions into vacuoles. In this study, the gene structures of three kinds of vacuolar-type antiporters transcribed in bread wheat under salt stress were analyzed. After spraying 0.5 M NaCl to seedlings of wheat cultivar Chinese Spring, 1,392~1,400 bp cDNA fragments were isolated by RT-PCR using primers designed from common regions in rice OsNHX1 and Atriplex subcordata AgNHX1. Next, the entire structure of the genomic DNA and cDNA were determined via CapFishing-5’ Rapid Amplification of cDNA Ends (RACE), 3’RACE, and genomic PCR cloning. As a result, 3 kinds of vacuolar-type Na⁺/H⁺ antiporter genes, TaNHXa (genome DNA 4,255 bp, cDNA 2,414 bp, 539 a.a.), TaNHXb (gDNA 4,167 bp, cDNA 1,898 bp, 539 a.a.) and TaNHXc (gDNA 4,966 bp, cDNA 1,928 bp, 547 a.a.), were identified. They encode 12 transmembrane domains containing third domain’s amyloid binding sites (FFIYLLPP), characteristic of the vacuolar-type Na⁺/H⁺ antiporter, binding to the cell vacuolar membrane. TaNHXa, b and c consisting of 14 exons and 13 introns were 22~55 % longer than A. thaliana AtNHX1 in total length. TaNHXa (TaNHX2) showed homogeneity with OsNHX1, while TaNHXb and c were phylogenetically independent.

Reassessing the role of ion homeostasis for improving salinity tolerance in crop plants

Soil salinity is a constraint for major agricultural crops leading to severe yield loss, which may increase with the changing climatic conditions. Disruption in the cellular ionic homeostasis is one of the primary responses induced by elevated sodium ions (Na⁺ ). Therefore, unraveling the mechanism of Na⁺ uptake and transport in plants along with the characterization of the candidate genes facilitating ion homeostasis is obligatory for enhancing salinity tolerance in crops. This review summarizes the current advances in understanding the ion homeostasis mechanism in crop plants, emphasizing the role of transporters involved in the regulation of cytosolic Na⁺ level along with the conservation of K⁺ /Na⁺ ratio. Furthermore, expression profiles of the candidate genes for ion homeostasis were also explored under various developmental stages and tissues of Oryza sativa based on the publicly available microarray data. The review also gives an up-to-date summary on the efforts to increase salinity tolerance in crops by manipulating selected stress-associated genes. Overall, this review gives a combined view on both the ionomic and molecular background of salt stress tolerance in plants.

Plant NHX Antiporters: From Function to Biotechnological Application, with Case Study

Salt stress is one of the major abiotic stresses that negatively affect crops worldwide. Plants have evolved a series of mechanisms to cope with the limitations imposed by salinity. Molecular mechanisms, including the upregulation of cation transporters such as the Na+/H+ antiporters, are one of the processes adopted by plants to survive in saline environments. NHX antiporters are involved in salt tolerance, development, cell expansion, growth performance and disease resistance of plants. They are integral membrane proteins belonging to the widely distributed CPA1 sub-group of monovalent cation/H+ antiporters and provide an important strategy for ionic homeostasis in plants under saline conditions. These antiporters are known to regulate the exchange of sodium and hydrogen ions across the membrane and are ubiquitous to all eukaryotic organisms. With the genomic approach, previous studies reported that a large number of proteins encoding Na+/H+ antiporter genes have been identified in many plant species and successfully introduced into desired species to create transgenic crops with enhanced tolerance to multiple stresses. In this review, we focus on plant antiporters and all the aspects from their structure, classification, function to their in silico analysis. On the other hand, we performed a genome-wide search to identify the predicted NHX genes in Argania spinosa L. We highlighted for the first time the presence of four putative NHX (AsNHX1-4) from the Argan tree genome, whose phylogenetic analysis revealed their classification in one distinct vacuolar cluster. The essential information of the four putative NHXs, such as gene structure, subcellular localization and transmembrane domains was analyzed.

Salinity tolerance in barley during germination- homologs and potential genes

Salinity affects more than 6% of the world's total land area, causing massive losses in crop yield. Salinity inhibits plant growth and development through osmotic and ionic stresses; however, some plants exhibit adaptations through osmotic regulation, exclusion, and translocation of accumulated Na+ or Cl-. Currently, there are no practical, economically viable methods for managing salinity, so the best practice is to grow crops with improved tolerance. Germination is the stage in a plant's life cycle most adversely affected by salinity. Barley, the fourth most important cereal crop in the world, has outstanding salinity tolerance, relative to other cereal crops. Here, we review the genetics of salinity tolerance in barley during germination by summarizing reported quantitative trait loci (QTLs) and functional genes. The homologs of candidate genes for salinity tolerance in Arabidopsis, soybean, maize, wheat, and rice have been blasted and mapped on the barley reference genome. The genetic diversity of three reported functional gene families for salt tolerance during barley germination, namely dehydration-responsive element-binding (DREB) protein, somatic embryogenesis receptor-like kinase and aquaporin genes, is discussed. While all three gene families show great diversity in most plant species, the DREB gene family is more diverse in barley than in wheat and rice. Further to this review, a convenient method for screening for salinity tolerance at germination is needed, and the mechanisms of action of the genes involved in salt tolerance need to be identified, validated, and transferred to commercial cultivars for field production in saline soil.

A Glycine max sodium/hydrogen exchanger enhances salt tolerance through maintaining higher Na+ efflux rate and K+/Na+ ratio in Arabidopsis

BACKGROUND

Soybean (Glycine max (L.)) is one the most important oil-yielding cash crops. However, the soybean production has been seriously restricted by salinization. It is therefore crucial to identify salt tolerance-related genes and reveal molecular mechanisms underlying salt tolerance in soybean crops. A better understanding of how plants resist salt stress provides insights in improving existing soybean varieties as well as cultivating novel salt tolerant varieties. In this study, the biological function of GmNHX1, a NHX-like gene, and the molecular basis underlying GmNHX1-mediated salt stress resistance have been revealed.

RESULTS

We found that the transcription level of GmNHX1 was up-regulated under salt stress condition in soybean, reaching its peak at 24 h after salt treatment. By employing the virus-induced gene silencing technique (VIGS), we also found that soybean plants became more susceptible to salt stress after silencing GmNHX1 than wild-type and more silenced plants wilted than wild-type under salt treatment. Furthermore, Arabidopsis thaliana expressing GmNHX1 grew taller and generated more rosette leaves under salt stress condition compared to wild-type. Exogenous expression of GmNHX1 resulted in an increase of Na+ transportation to leaves along with a reduction of Na+ absorption in roots, and the consequent maintenance of a high K+/Na+ ratio under salt stress condition. GmNHX1-GFP-transformed onion bulb endothelium cells showed fluorescent pattern in which GFP fluorescence signals enriched in vacuolar membranes. Using the non-invasive micro-test technique (NMT), we found that the Na+ efflux rate of both wild-type and transformed plants after salt treatment were significantly higher than that of before salt treatment. Additionally, the Na+ efflux rate of transformed plants after salt treatment were significantly higher than that of wild-type. Meanwhile, the transcription levels of three osmotic stress-related genes, SKOR, SOS1 and AKT1 were all up-regulated in GmNHX1-expressing plants under salt stress condition.

CONCLUSION

Vacuolar membrane-localized GmNHX1 enhances plant salt tolerance through maintaining a high K+/Na+ ratio along with inducing the expression of SKOR, SOS1 and AKT1. Our findings provide molecular insights on the roles of GmNHX1 and similar sodium/hydrogen exchangers in regulating salt tolerance.

Improved salinity tolerance and growth performance in transgenic sunflower plants via ectopic expression of a wheat antiporter gene (TaNHX2)

Sunflower (Helianthus annuus. L) is one of the principal oil seed crops affected by the salinity stress, which limits the oil content and crop yield of sunflower plants. The acclimatization of plants to abiotic stresses such as salinity tolerance is mainly mediated by the vacuolar Na⁺/H⁺ antiporters (NHX) by tagging Na⁺ into vacuoles from the cytosol. We show here that the over-expression of wheat TaNHX2 gene in transgenic sunflower conferred improved salinity stress tolerance and growth performance. Transgenic sunflower plants were produced by infecting the embryonic axis ex-plants with Agrobacterium tumefaciens strain EHA105 containing a pBin438-TaNHX2 binary vector that carried a wheat antiporter (TaNHX2) gene under the control of a double CaMV 35S promoter with NPT II gene as a selectable marker. PCR analysis of T₀ and T₁ transgenic plants confirmed the integration of TaNHX2 in sunflower genome. Stable integration and expression of TaNHX2 in sunflower genome was further verified by Southern hybridization and semi-quantitative RT-PCR analyses. As compared to the non-transformed plants, TaNHX2 expressing transgenic plants showed better growth performance and accumulated higher Na⁺, K⁺ contents in leaves and roots under salt stress (200 mM NaCl). Transgenic sunflower plants displayed improved protection against cell damage exhibiting stable relative water content, chlorophyll content, increased proline accumulation and improved reactive oxygen species (ROS) scavenging because of higher activities of the antioxidant enzymes like superoxide dismutase and ascorbate peroxidase, along with decreased production of hydrogen peroxide, free oxygen radical and malondialdehyde (MDA) under salt stress (200 mM NaCl). Taken together, our findings suggest that TaNHX2 expression in sunflower plants contributed towards improving growth performance under sodium chloride stress.