The Arabidopsis thaliana salt tolerance gene SOS1 encodes a putative Na+/H+ antiporter

AtSERK1 and BAK1/AtSERK3 positively regulate seed germination in response to saline condition in Arabidopsis

Salt stress adversely affects plants by inhibiting seed germination, growth, and development throughout their life cycle. Abscisic acid (ABA) is a primary plant hormone that regulates seed dormancy under environmental stresses. The salt-overly sensitive (SOS) pathway regulates ion homeostasis in seedlings grown under saline conditions. Recently, sos mutants have been reported to exhibit higher seed germination rates than wild-type plants under salt conditions. Previously, BRI1-associated receptor kinase 1 (BAK1) was demonstrated to be involved in ABA-induced stomatal closure under drought conditions. In the present study, we demonstrated that bak1 and atserk1 mutants exhibited stronger inhibition of seed germination on salt-containing media than wild-type plants, and the degree of inhibition was greater in atserk1 mutants. However, seedling growth after germination was not different among the genotypes. RNA-sequencing analysis of salt-treated atserk1 seeds revealed that the number of differentially expressed genes (DEGs) induced by salt stress was lower in atserk1 than in wild-type plants. However, most DEGs in atserek1 were involved in signal transduction with phosphorelay events, suggesting that AtSERKs may function post-transcriptionally to regulate seed germination. Furthermore, bak1/sos2 or atserk1/sos2 double mutant analyses showed that AtSERKs act downstream of SOS2 in the salt-induced inhibition of seed germination. Taken together, these results suggest that both AtSERKs and SOS proteins work together to regulate the balance between seed germination and maintenance of seed dormancy under saline conditions.

LbHKT1;1 Negatively Regulates Salt Tolerance of Limonium bicolor by Decreasing Salt Secretion Rate of Salt Glands

The HKT-type proteins have been extensively studied and have been shown to play important roles in long-distance Na+ transport, maintaining ion homoeostasis and improving salt tolerance in plants. However, there have been no reports on the types, characteristics and functions of HKT-type proteins in Limonium bicolor, a recretohalophyte species with the typical salt gland structure. In this study, five LbHKT genes were identified in L. bicolor, all belonging to subfamily 1 (HKT1). There are many cis-acting elements related to abiotic/biotic stress response on the promoters of the LbHKT genes. LbHKT1;1 was investigated in detail. Subcellular localization results showed that LbHKT1;1 is targeted to the plasma membrane. Functional analysis in yeast showed that LbHKT1;1 has a higher tolerance than AtHKT1;1 under high Na+ conditions. Silencing and overexpression of the LbHKT1;1 gene in L. bicolor showed that LbHKT1;1 negatively regulates salt secretion by the salt glands. Further experiments showed that LbbZIP52 can specifically bind to the ABRE element in the LbHKT1;1 promoter and regulate the expression of the LbHKT1;1 gene and is involved in the negative regulation of the salt secretion capacity of L. bicolor. This study demonstrates for the first time that the HKT-type protein is involved in salt secretion by salt glands and provides a new perspective on the function of HKT-type proteins under salt stress conditions.

Enhancing wheat resilience to salt stress through an integrative nanotechnology approach with chitosan proline and chitosan glycine

Salt stress significantly limits wheat production worldwide, jeopardizing food security and sustainable agriculture. Developing strategies to enhance wheat's resilience to salinity is critical for maintaining yield in affected regions. This study investigates the potential of chitosan-proline (Cs-Pro) and chitosan-glycine (Cs-Gly) nanoparticles in mitigating salt stress in salt-tolerant Heydari and salt-sensitive Sepahan wheat cultivars, with a special question on genotype-dependent differences. Plants were treated with nanoparticles at concentrations of 0, 200, and 400 mg L⁻¹ under salt stress levels of 0, 200, and 400 mM NaCl. The salt-tolerant Heydari cultivar exhibited superior adaptability to saline conditions, in addition reacted more positively to nanoparticle treatments. Results demonstrated significant physiological improvements, including increased relative water content (RWC), enhanced chlorophyll content and elevated proline levels, especially after 400 mg L⁻¹ Cs-Pro treatment. Oxidative stress markers, such as malondialdehyde (MDA) and hydrogen peroxide, were substantially reduced, while antioxidant enzyme activity was boosted. Certain stress-responsive genes (e.g., TaADC, TaPxPAO, TaSAMDC, TaSPDS, TaSOS1, TaNHX1) were upregulated, highlighting the importance of ionic balance and polyamine metabolism in improved stress tolerance. The application of Cs-Pro and Cs-Gly nanoparticles presents a promising approach to enhance wheat's salinity tolerance by improving physiological, biochemical, and molecular responses.

Trichoderma asperellum 22043: Inoculation Promotes Salt Tolerance of Tomato Seedlings Through Activating the Antioxidant System and Regulating Stress-Resistant Genes

Salt stress poses a major threat to plant growth, and breeding for salt-tolerant varieties is not always successful to ameliorate this threat. In the present experiment, the effect of T. asperellum 22043 inoculation on the growth of salt-stressed tomatoes and the mechanisms by which it improves salt tolerance were investigated. It was observed that tomato plants treated with T. asperellum 22043 spore suspension under salt tress (50 and 100 mM NaCl) consistently exhibited higher seeds germination, seedling survival rate, plant height, and chlorophyll content, but lower malondialdehyde and proline contents than the plants treated without the Trichoderma. T. asperellum 22043 effectively improved the stress resistance of tomato through regulating the transcriptional levels of reactive oxygen species (ROS) scavenging enzyme gene expression to modulate the activity of ROS scavenging enzymes and the expression of the genes related to transporter and aquaporin to maintain the balance of cell Na+. In conclusion, T. asperellum 22043 can enhance tomato seedlings' salt tolerance by activating the antioxidant system and regulating the expression of stress-resistant genes.

Salt stress activates the CDK8-AHL10-SUVH2/9 module to dynamically regulate salt tolerance in Arabidopsis

Salt stress has devastating effects on agriculture, yet the key regulators modulating the transcriptional dynamics of salt-responsive genes remain largely elusive in plants. Here, we discover that salt stress substantially induces the kinase activity of Mediator cyclin-dependent kinase 8 (CDK8), which is essential for its positive role in regulating salt tolerance. CDK8 is identified to phosphorylate AT-hook motif nuclear-localized protein 10 (AHL10) at serine 314, leading to its degradation under salt stress. Consistently, AHL10 is found to negatively regulate salt tolerance. Transcriptome analysis further indicates that CDK8 regulates over 20% of salt-responsive genes, half of which are co-regulated by AHL10. Moreover, AHL10 is revealed to recruit SU(VAR)3-9 homologs (SUVH2/9) to AT-rich DNA sequences in the nuclear matrix-attachment regions (MARs) of salt-responsive gene promoters, facilitating H3K9me2 deposition and repressing salt-responsive genes. Our study thereby has identified the CDK8-AHL10-SUVH2/9 module as a key molecular switch controlling transcriptional dynamics in response to salt stress.

RGF Gene Family Analysis and Functional Evidence for RGF8-Mediated Salt Stress Tolerance in Brassica Species

Brassica napus L. is a vital oil crop and exhibits notable salt tolerance, making the enhancement of this trait crucial for cultivation in saline soils. Uncovering its underlying mechanism may further heighten the salt tolerance of B. napus. In this study, we conducted a genome-wide analysis of the Root Meristem Growth Factor (RGF) gene family in Brassica species and identified BnaRGF8 as a key regulator of salt tolerance. Under 200 mM NaCl treatment, all RGF genes were induced, with BnaRGF8 showing the greatest upregulation. This response was consistently observed across 10 genotypes, indicating a universal trend in B. napus. Functional characterization revealed that chemically synthesized BnaRGF8 alleviated salt-induced growth inhibition by restoring primary root elongation and lateral root formation. Additionally, BnaRGF8 preserved membrane integrity and maintained cell division under salt stress, establishing itself as a novel anti-salt peptide in B. napus.

Genome-wide identification of SlIQMs and the regulatory effect of calcium on tomato seedlings under drought stress and phytohormone treatment

KEY MESSAGE

SlIQMs were identified, exogenous calcium and phytohormones induced their expression. SlIQMs's function were verified by VIGS. Calcium synergistically promoted seedling growth with ABA, IAA, MeJA and antagonized growth inhibition with GA3 or SA. The IQM genes, are crucial members of the calmodulin-binding protein family, play pivotal roles in plant growth and stress response. However, the existence and impact of IQM in tomato remain unclear. This study demonstrates that the SlIQMs are randomly distributed across the 4 chromosomes of tomato and exclusively located within the nucleus. Phylogenetic analysis classifies the SlIQMs into 3 distinct subclasses. Analysis of cis-acting elements reveals that SlIQMs may function in stress or hormone process. Quantitative reverse-transcriptase PCR analysis further testified that polyethylene glycol (PEG), abscisic acid (ABA), indole acetic acid (IAA), gibberellin (GA3), methyl jasmonate (MeJA), and salicylic acid (SA) induce expression levels of SlIQM1/2/3/5/6/7. Furthermore, exogenous calcium significantly alleviates detrimental effects on seedlings growth leaded by drought stress. Moreover, the relationships between hormones and calcium were explored. The results showed that calcium synergistically promoted the seedlings growth with ABA, IAA and MeJA, however antagonistic effects on inhibiting growth are observed between calcium and GA3 or SA. The virus-induced silencing of 6 candidate genes caused growth inhibition of tomato seedlings under drought stress and phytohormone treatment. These findings lay the foundation for a comprehensive study of the structure and biological function of SlIQM genes and the interaction between calcium and different plant hormones on plant growth.

SOS2 phosphorylates FREE1 to regulate multi-vesicular body trafficking and vacuolar dynamics under salt stress

Salt stress causes ion toxicity in plant cells and limits plant growth and crop productivity. Sodium ions (Na+) are transported out of the cell and sequestered in the vacuole for detoxification under salt stress. The salt excretion system is controlled by the SALT OVERLY SENSITIVE (SOS) pathway, which consists of the calcium sensors SOS3 and SOS3-LIKE CALCIUM-BINDING PROTEIN 8, the protein kinase SOS2, and the plasma membrane Na+/H+ antiporter SOS1. Although much is known about salt responses in plants at the molecular level, it remains unclear if and how plants respond to salt stress through endomembrane remodelling. In this study, we describe a mechanism of salt tolerance in Arabidopsis (Arabidopsis thaliana) involving the modulation of FREE1 levels, which impacts multivesicular body (MVB) trafficking. Specifically, the ESCRT-I (endosomal sorting complex required for transport-I) component FREE1 (FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING 1) regulates vacuole fragmentation to enhance salt tolerance. SOS2 phosphorylates FREE1, leading to its degradation and affecting MVB maturation, thereby reducing MVB-vacuole fusion and regulating endomembrane dynamics in response to salt stress. These findings highlight the adaptive role of the plant endomembrane system in coping with salt stress.

Salinity survival: molecular mechanisms and adaptive strategies in plants

Soil salinity is a significant environmental challenge that threatens plant growth and development, adversely affecting global food crop production. This underscores the critical need to elucidate the molecular mechanisms underlying plant salt tolerance, which has profound implications for agricultural advancement. Recent progress in plant salt tolerance has greatly improved our understanding of the molecular mechanisms of plant responses to salt stress and precision design breeding as an effective strategy for developing new salt-tolerant crop varieties. This review focuses on the model plant species Arabidopsis thaliana and important crops, namely, wheat (Triticum aestivum), maize (Zea mays), and rice (Oryza sativa). It summarizes current knowledge on plant salt tolerance, emphasizing key aspects such as the perception and response to salt stress, Na+ transport, Na+ compartmentalization and clearance, changes in reactive oxygen species induced by salt stress, and regulation of plant stem cell development under salt stress conditions. The review might provide new and valuable information for understanding the molecular mechanisms of plant response and adaptation to salt stress.

SALT OVERLY SENSITIVE2 and AMMONIUM TRANSPORTER1;1 contribute to plant salt tolerance by maintaining ammonium uptake

Soil salinity is a severe threat to agriculture and plant growth. Under high salinity conditions, ammonium (NH4+) is the predominant inorganic nitrogen source used by plants due to limited nitrification. However, how ammonium shapes the plant response to salt stress remains a mystery. Here, we demonstrate that the growth of Arabidopsis (Arabidopsis thaliana) seedlings is less sensitive to salt stress when provided with ammonium instead of nitrate (NO3-), a response that is mediated by ammonium transporters (AMTs). We further show that the kinase SALT OVERLY SENSITIVE2 (SOS2) physically interacts with and activates AMT1;1 by directly phosphorylating the nonconserved serine residue Ser-450 in the C-terminal region. In agreement with the involvement of SOS2, ammonium uptake was lower in sos2 mutants grown under salt stress relative to the wild type. Moreover, AMT-mediated ammonium uptake enhanced salt-induced SOS2 kinase activity. Together, our study demonstrates that SOS2 activates AMT1;1 to fine-tune and maintain ammonium uptake and optimize the plant salt stress response.

Current progress in deciphering the molecular mechanisms underlying plant salt tolerance

Enhancing crop salt tolerance through genetics and genomics is important for food security. It is environmentally friendly and cost-effective in maintaining crop production in farmlands affected by soil salinization and can also facilitate the utilization of marginal saline land. Despite the limited success achieved so far, it is becoming possible to bridge the gap between fundamental research and crop breeding owing to a deeper understanding of plant salt tolerance at both physiological and molecular levels. Therefore, we review the recent key progress in identifying the molecular mechanisms contributing to plant salt tolerance with a focus on balancing growth and salt resilience. With the accruing knowledge and the rapidly evolving tools (e.g. genome editing and artificial intelligence), it is reasonable to expect the future salt-tolerant crops in a few decades.

How abscisic acid collaborates in Brassica napus responses to salt and drought stress: An in silico approach

Canola (Brassica napus sp.), the most important oily seed product in the world, is affected largely by salinity and drought stresses due to its ability to be planted in arid and semiarid regions. Therefore, studying potent genes involved in salt/drought stress response in canola would help improve abiotic stress tolerance. In this study, genes involved in response to salt and drought stresses in B. napus were investigated via sequence-read archive databases at different time points. The results were analyzed by the GALAXY server to detect DEGs. DEGs associated with short-, medium- and long-term salinity and drought stress were identified via extensive meta-analysis and robust rank aggregation methods. Subsequently, Gene Ontology (GO) analysis of the identified robust DEGs was performed via BLAST2GO. By constructing a protein-protein interaction (PPI) network with Cytoscape software, the hub genes associated with each line of salt and drought stress response were identified. Among all DEGs, HAI2 and DREB1B, which are hub genes, were selected for validation by qRT‒PCR in salt/drought-tolerant and salt/drought-sensitive cultivars of canola, Okapi and RGS, respectively, under salt and drought treatments. Fine-tuning affected the manner and time of contribution of each Abscisic Acid (ABA)-dependent and ABA-independent signaling pathway in response to salinity and drought tolerant and sensitive canola cultivars. Furthermore, the identification of hub genes through meta-analysis provided insight into the molecular responses of canola to salinity/drought stresses and the engineering of abiotic stress tolerance in canola for industrial cultivation of canola in poor-quality lands.

Typical tetra-mediated signaling and plant architectural changes regulate salt-stress tolerance in indica rice genotypes

Upon exposure to salt stress, calcium signaling in plants activates various stress-responsive genes and proteins along with enhancement in antioxidant defense to eventually regulate the cellular homeostasis for reducing cytosolic sodium levels. The coordination among the calcium signaling molecules and transporters plays a crucial role in salinity tolerance. In the present study, twenty-one diverse indigenous rice genotypes were evaluated for salt tolerance during the early seedling stage, and out of that nine genotypes were further selected for physio-biochemical study. Further analysis identified potential salt-tolerant and salt-sensitive genotypes with tolerant lines exhibiting lower Na+/K+ ratio. Plant phenotype clearly documented the root architectural changes among the most salt-tolerant and sensitive genotypes, while the histo-biochemical DAB and NBT staining and in-gel SOD activity clearly revealed the differential ROS accumulation between the contrasting genotypes and their antioxidant activity. Ultrastructural study depicted stronger UV autofluorescence in the hypodermal and vascular bundle regions, while phloroglucinol staining displayed intense coloration in the vascular bundle region of Bhutmuri, the salt-tolerant genotype, compared to Manipuri Black, the salt-sensitive one showing differential lignification among the contrasting genotype to combat salt stress. Based on expression study, our proposed model depicted immediate upregulation (short-term) of OsSOS3 and OsNHX1 along with gradual upregulation of OsHKT and downregulation of OsSOS1 throughout the stress period to protect the tolerant plant through signaling cascade, while the inadequate upregulation of OsSOS3, OsNHX1, and OsHKT under early stress, coupled with poor coordination between the expression of OsSOS1 and OsSOS3 genes, makes the plant salt sensitive.

Genome-wide identification, characterization, and functional analysis of the CHX, SOS, and RLK genes in Solanum lycopersicum under salt stress

The cation/proton exchanger (CHX), salt overly sensitive (SOS), and receptor-like kinase (RLK) genes play significant roles in the response to salt stress in plants. This study is the first to identify the SOS gene in Solanum lycopersicum (tomato) through genome-wide analysis under salt stress conditions. Quantitative reverse transcription PCR (qRT-PCR) results indicated that the expression levels of CHX, SOS, and RLK genes were upregulated, with fold changes of 1.83, 1.49, and 1.55, respectively, after 12 h of exposure to salt stress. Genome-wide analysis revealed 21 CHX, 5 SOS, and 86 RLK genes in S. lycopersicum. CHX genes were found on chromosomes 2, 3, 4, 5, 6, 7, 8, 9, 11, and 12 of S. lycopersicum. SOS genes were found on chromosomes 1, 4, 6, and 10. RLK genes were found on all chromosomes of S. lycopersicum. The Ka/Ks ratios indicate that the CHX, SOS, and RLK genes have been primarily influenced by purifying selection. This suggests that these genes have faced strong environmental pressures throughout their evolution. Purifying selection typically results in a decrease in genetic diversity. The estimated duplication time for CHX paralogous gene pairs ranged from approximately 26.965 to 245.413 million years ago (Mya), while the duplication time for SOS paralogous gene pairs ranged from around 116.682 to 275.631 Mya. For RLK paralogous gene pairs, the duplication time varied from approximately 27.689 to 239.376 Mya. Synteny analysis of the CHX, SOS, and RLK genes demonstrated collinear relationships with orthologous genes in Arabidopsis thaliana, but no collinearity orthologous relationships in Oryza sativa (rice). Furthermore, the analysis revealed that there were 6 orthologous SlCHX genes, 2 orthologous SlSOS genes, and 44 orthologous SlRLK genes paired with those in A. thaliana. The results of the present study may help to elucidate the role of the CHX, SOS, and RLK genes in salt stress in S. lycopersicum.

Elemental cryo-imaging reveals SOS1-dependent vacuolar sodium accumulation

Increasing soil salinity causes significant crop losses globally; therefore, understanding plant responses to salt (sodium) stress is of high importance. Plants avoid sodium toxicity through subcellular compartmentation by intricate processes involving a high level of elemental interdependence. Current technologies to visualize sodium, in particular, together with other elements, are either indirect or lack in resolution. Here we used the newly developed cryo nanoscale secondary ion mass spectrometry ion microprobe1, which allows high-resolution elemental imaging of cryo-preserved samples and reveals the subcellular distributions of key macronutrients and micronutrients in root meristem cells of Arabidopsis and rice. We found an unexpected, concentration-dependent change in sodium distribution, switching from sodium accumulation in the cell walls at low external sodium concentrations to vacuolar accumulation at stressful concentrations. We conclude that, in root meristems, a key function of the NHX family sodium/proton antiporter SALT OVERLY SENSITIVE 1 (also known as Na+/H+ exchanger 7; SOS1/NHX7) is to sequester sodium into vacuoles, rather than extrusion of sodium into the extracellular space. This is corroborated by the use of new genomic, complementing fluorescently tagged SOS1 variants. We show that, in addition to the plasma membrane, SOS1 strongly accumulates at late endosome/prevacuoles as well as vacuoles, supporting a role of SOS1 in vacuolar sodium sequestration.

TaWRKY55-TaPLATZ2 module negatively regulate saline-alkali stress tolerance in wheat

Saline-alkaline soils are a major environmental problem that limit plant growth and crop productivity. Plasma membrane H+-ATPases and the salt overly sensitive (SOS) signaling pathway play important roles in plant responses to saline-alkali stress. However, little is known about the functional genes and mechanisms regulating the transcription of H+-ATPases and SOS pathway genes under saline-alkali stress. In the present study, we identified that the plant AT-rich sequence and zinc-binding (TaPLATZ2) transcription factor are involved in wheat response to saline-alkali stress by directly suppressing the expression of TaHA2/TaSOS3. The knockdown of TaPLATZ2 enhances salt and alkali stress tolerance, while overexpression of TaPLATZ2 leads to salt and alkali stress sensitivity in wheat. In addition, TaWRKY55 directly upregulated the expression of TaPLATZ2 during saline-alkali stress. Through knockdown and overexpression of TaWRKY55 in wheat, TaWRKY55 was shown to negatively modulate salt and alkali stress tolerance. Genetic analyses confirmed that TaPLATZ2 functions downstream of TaWRKY55 in response to salt and alkaline stresses. These findings provide a TaWRKY55-TaPLATZ2-TaHA2/TaSOS3 regulatory module that regulates wheat responses to saline-alkali stress.

Na + -driven pH regulation by Na+/H+ antiporters promotes photosynthetic efficiency in cyanobacteria

Photosynthetic organisms have developed mechanisms to regulate light reactions in response to varying light conditions. Photosynthetic electron transport leads to the formation of a ΔpH across the thylakoid membrane (TM), which is crucial for regulating electron transport. However, other pH modulators remain to be identified, particularly in cyanobacteria. In this study, we evaluated the potential involvement of six Na+/H+ antiporters (NhaS1 to NhaS6) in control of pH in the cyanobacterium Synechocystis sp. PCC 6803. Synechocystis showed a strong requirement for Na+ at high light intensities, with ΔnhaS1 and ΔnhaS2 strains unable to grow under high-light conditions. We analyzed Na+ efflux-driven H + -uptake activities of NhaS1 to NhaS6 in inverted membranes of Escherichia coli. Biological fractionation and immunoelectron microscopy revealed that NhaS1 localizes to both the plasma and TMs, while NhaS2 localizes to the plasma membrane (PM). Measurement of photosynthesis activity indicated that NhaS2 promotes ATP production and electron transport from PQ to P700. Measurements of pH outside of the cells and in the cytoplasm suggested that both NhaS1 and NhaS2 are involved in PM-mediated light-dependent H+ uptake and cytoplasmic acidification. NhaS1 and NhaS2 were also found to prevent photoinhibition under high-light treatment. These results indicate that H+ transport mediated by NhaS1 and NhaS2 plays a role in regulating intracellular pH and maintaining photosynthetic electron transport.

SORTING NEXIN1 facilitates SALT OVERLY SENSITIVE1 protein accumulation to enhance salt tolerance in Arabidopsis

The plasma membrane (PM)-localized Na+/H+ antiporter Salt Overly Sensitive1 (SOS1) is essential for plant salt tolerance through facilitating Na+ efflux; however, how SOS1 localization and protein accumulation is regulated in plants remains elusive. Here, we report that Sorting Nexin 1 (SNX1) is required for plant salt-stress tolerance through affecting endosomal trafficking of SOS1 in Arabidopsis (Arabidopsis thaliana). Disruption of SNX1 caused salt hypersensitivity with increased Na+ accumulation and decreased Na+ efflux in Arabidopsis when challenged with high salinity stress. SNX1 co-localized and interacted with SOS1 in endosomes, promoting its PM localization and protein stability in plants under saline conditions. SOS1 overexpression promoted salt tolerance in the wild-type, whereas such effect was greatly compromised in the snx1-2 mutant. Pharmaceutical results showed that SOS1 recycling from the cytosol to the PM was largely blocked while its vacuolar degradation was accelerated in the snx1-2 mutant. Furthermore, salt-induced SOS1 phosphorylation enhanced its interaction and co-localization with SNX1, which is required for SOS1 PM localization in plants. Our study elucidates that SNX1 facilitates SOS1 PM localization and protein accumulation through endosomal trafficking, thereby enhancing salt tolerance in plants.

Comparative Transcriptome Analysis Reveals Mechanisms of Differential Salinity Tolerance Between Suaeda glauca and Suaeda salsa

BACKGROUND

Suaeda glauca and Suaeda salsa have obvious morphological features and strongly tolerate saline-alkali environments. However, the mechanisms that lead to the differences in saline-alkali tolerance between them remain unclear.

METHODS

In this study, we employed comparative transcriptome analysis to investigate S. glauca and S. salsa under saline-alkali stress.

RESULTS

Our sequencing efforts resulted in the identification of 99,868 unigenes. We obtained 12,021 and 6227 differentially expressed genes (DEGs) from the S. glauca and S. salsa under salt stress compared with plants in the control. Notably, 1189 and 1864 were specifically upregulated DEGs in the roots and leaves of S. salsa under saline-alkali conditions, respectively. These genes were enriched in pathways such as "Plant hormone signal transduction", "Carbon metabolism" and "Starch and sucrose metabolism". Further analysis of stress-related pathways and gene expression levels revealed that key genes involved in abscisic acid (ABA) and jasmonic acid (JA) biosynthesis, ABA signal transduction, and their downstream transcription factors were upregulated in the roots of S. salsa under saline-alkali conditions. Additionally, 24 DEGs associated with stress response were identified in the roots and leaves of both species. The expression levels of these pathways and related genes were higher in S. salsa than in S. glauca, suggesting that S. salsa enhances its saline-alkali tolerance by elevating the expression of these genes.

CONCLUSIONS

This study provides a new research perspective for revealing the differences in saline-alkali tolerance mechanisms between S. glauca and S. salsa, bringing forth important candidate genes for studying their saline-alkali tolerance.

Identification of dehydrin family genes in three Medicago species and insights into their tolerant mechanism to salt stress

KEY MESSAGE

All ten dehydrin genes from three Medicago species are responsive to different kinds of abiotic stress, and CAS31 confers transgenic plants salt tolerance by down-regulating HKT1 expression. Dehydrins are protective proteins playing crucial roles in the tolerance of plants to abiotic stresses. However, a full-scale and systemic analysis of total dehydrin genes in Medicago at the genome level is still lacking. In this study, we identified ten dehydrin genes from three Medicago species (M. truncatula, M. ruthenica, and M. sativa), categorizing the coding proteins into four types. Genome collinearity analysis among the three Medicago species revealed six orthologous gene pairs. Promoter regions of dehydrin genes contained various phytohormone- and stress-related cis-elements, and transcriptome analysis showed up-regulation of all ten dehydrin genes under different stress conditions. Transformation of dehydrin gene CAS31 increased the tolerance of transgenic seedlings compared with wild-type seedlings under salt stress. Our study demonstrated that transgenic seedlings maintained the more chlorophyll, accumulated more proline and less hydrogen peroxide and malondialdehyde than wild-type seedlings under salt stress. Further study revealed that CAS31 reduced Na+ accumulation by down-regulating HKT1 expression under salt stress. These findings enhance our understanding of the dehydrin gene family in three Medicago species and provide insights into their mechanisms of tolerance.

The MdCo gene encodes a putative 2OG-Fe (II) oxygenase that positively regulates salt tolerance in transgenic tomato and apple

Salinity stress is a significant environmental factor that impacts the growth, development, quality, and yield of crops. The 2OG-Fe (II) oxygenase family of enzyme proteins plays crucial roles in plant growth and stress responses. Previously, we identified and characterized MdCo, which encodes a putative 2OG-Fe (II) oxygenase, a key gene for controlling the columnar growth habit of apples. In this study, we explored the role of MdCo in salt stress tolerance. Expression analysis suggested that MdCo exhibits high expression in roots and is significantly induced by NaCl stress. Ectopic expression of MdCo exhibited enhanced salt stress tolerance in transgenic tomatoes, and these plants were characterized by better growth performance, and higher chlorophyll content, but lower electrolyte leakage and malondialdehyde (MDA), and less hydrogen peroxide (H2O2) and superoxide radicals (O2-) under salt stress. Overexpression of MdCo can effectively scavenge reactive oxygen species (ROS) by enhancing the activities of antioxidant enzymes and up-regulating the expression of stress-associated genes under salt stress, thereby enhancing salt tolerance in apple calli. Collectively, these findings provide new insights into the function of MdCo in salt stress tolerance as well as future potential application for apple breeding aimed at improving salt stress tolerance.

Enhancing Crop Resilience: The Role of Plant Genetics, Transcription Factors, and Next-Generation Sequencing in Addressing Salt Stress

Salt stress is a major abiotic stressor that limits plant growth, development, and agricultural productivity, especially in regions with high soil salinity. With the increasing salinization of soils due to climate change, developing salt-tolerant crops has become essential for ensuring food security. This review consolidates recent advances in plant genetics, transcription factors (TFs), and next-generation sequencing (NGS) technologies that are pivotal for enhancing salt stress tolerance in crops. It highlights critical genes involved in ion homeostasis, osmotic adjustment, and stress signaling pathways, which contribute to plant resilience under saline conditions. Additionally, specific TF families, such as DREB, NAC (NAM, ATAF, and CUC), and WRKY, are explored for their roles in activating salt-responsive gene networks. By leveraging NGS technologies-including genome-wide association studies (GWASs) and RNA sequencing (RNA-seq)-this review provides insights into the complex genetic basis of salt tolerance, identifying novel genes and regulatory networks that underpin adaptive responses. Emphasizing the integration of genetic tools, TF research, and NGS, this review presents a comprehensive framework for accelerating the development of salt-tolerant crops, contributing to sustainable agriculture in saline-prone areas.

The dual role of methylglyoxal in plant stress response and regulation of DJ-1 protein

Methylglyoxal (MG) is a highly reactive metabolic intermediate that plays important roles in plant salt stress response. This review explores the sources of MG in plants, how salt stress promotes MG production, and the dual role of MG under salt stress conditions. Both the positive role of low concentrations of MG as a signalling molecule and the toxic effects of high concentrations of MG in plant response to salt stress are discussed. The MG detoxification pathways, especially the glyoxalase system, are described in detail. Special attention is given to the novel role of the DJ-1 protein in the glyoxalase system as glyoxalase III to remove MG, and as a deglycase to decrease glycation damage caused by MG on DNA, proteins, and other biomolecules. This review aims to provide readers with comprehensive perspectives on the functions of MG in plant salt stress response, the roles of the DJ-1 protein in MG detoxification and repair of glycation-damaged molecules, as well as the broader functional implications of MG in plant salt stress tolerance. New perspectives on maintaining plant genome stability, breeding for salt-tolerant crop varieties, and improving crop quality are discussed.

Proteomic Analysis to Understand the Promotive Effect of Ethanol on Soybean Growth Under Salt Stress

Finding solutions to mitigate the impact of salinity on crops is important for global food security because soil salinity significantly reduces plant growth and grain yield. Ethanol may play an important role in mitigating the negative salt-induced effects on crops. Soybean root growth was significantly reduced under salt stress; however, it was restored and comparable to control values by ethanol application even under stress. To study the positive mechanism of ethanol on soybean growth, a proteomic approach was carried out. The categories with the greatest changes in protein numbers were protein metabolism, transport, and cell organization in biological processes, nucleus and cytosol in cellular components, and nucleic acid binding activity in molecular functions. Proteomic data were confirmed using immunoblot analysis. Reactive oxygen species enzymes increased under salt stress; among them, mitochondrial ascorbate peroxidase was further accumulated by ethanol application. Among the cell wall and membrane-associated proteins, xyloglucan xyloglucosyl transferase and H+-ATPase increased and decreased, respectively, under salt stress; however, they were restored to control levels by ethanol application. These results suggest that soybeans were adversely affected by salt stress and recovered with ethanol application via the regulation of cell wall and membrane functions through the detoxification of reactive oxygen species.

Novel NhaC Na+/H+ antiporter in cyanobacteria contributes to key molecular processes for salt tolerance

Genome mining has revealed the halotolerant cyanobacterium Halothece sp. PCC7418 harbors considerable enrichment in the ion transport gene family for putative Na+/H+ antiporters. Here, we compared transcriptomic profiles of these encoding genes under various abiotic stresses and discovered that Halothece NhaC (hnhaC) was one of 24 genes drastically upregulated under salt stress. Critical roles of HnhaC in salt-stress protection and response were identified by a complementation assay using the salt-sensitive mutant Escherichia coli strain TO114. Expression of HnhaC rendered this mutant more tolerant to high concentrations of NaCl and LiCl. Antiporter activity assays showed that HnhaC protein predominantly exhibited Na+/H+ and Li+/H+ antiporter activities under neutral or alkaline pH conditions. Furthermore, expression of HnhaC conferred adaptive benefits onto E. coli by enabling a conditional filamentation phenotype. Dissecting the molecular mechanism of this phenotype revealed that differentially expressed genes were associated with clusters of SOS-cell division inhibitor, SOS response repair, and Z-associated proteins. Together, these results strongly indicate that HnhaC is an Na+/H+ antiporter that contributes to salt tolerance. The ubiquitous existence of several Na+/H+ antiporters represents a complex molecular system in halotolerant cyanobacteria, which can be deployed differently in response to growth and to environmental stresses.

Analysis of Ion Transport Properties of Glycine max HKT Transporters and Identifying a Regulation of GmHKT1;1 by the Non-Functional GmHKT1;4

High-affinity potassium transporters (HKTs) play an important role in plants responding to salt stress, but the transport properties of the soybean HKT transporters at the molecular level are still unclear. Here, using Xenopus oocyte as a heterologous expression system and two-electrode voltage-clamp technique, we identified four HKT transporters, GmHKT1;1, GmHKT1;2, GmHKT1;3 and GmHKT1;4, all of which belong to type I subfamily, but have distinct ion transport properties. While GmHKT1;1, GmHKT1;2 and GmHKT1;3 function as Na+ transporters, GmHKT1;1 is less selective against K+ than the two other transporters. Astonishingly, GmHKT1;4, which lacks transmembrane segments and has no ion permeability, is significantly expressed, and its gene expression pattern is different from the other three GmHKTs under salt stress. Interestingly, GmHKT1;4 reduced the Na+/K+ currents mediated by GmHKT1;1. Further study showed that the transport ability of GmHKT1;1 regulated by GmHKT1;4 was related to the structural differences in the first intracellular domain and the fourth repeat domain. Overall, we have identified one unique GmHKT member, GmHKT1;4, which modulates the Na+ and K+ transport ability of GmHKT1;1 via direct interaction. Thus, we have revealed a new type of HKT interaction model for altering their ion transport properties.

Rice OsCIPK17-OsCBL2/3 module enhances shoot Na+ exclusion and plant salt tolerance in transgenic Arabidopsis

Soil salinity is detrimental to plant growth and remains a major threat to crop productivity of the world. Plants employ various physiological and molecular mechanisms to maintain growth under salt stress. Identification of genes and genetic loci underlying plant salt tolerance holds the key to breeding salt tolerant crops. CIPK-CBL pathways regulate adaptive responses of plants (especially ion transport) to abiotic stresses via fine-tuned Ca2+ signal transduction. In this study, we showed that over-expression of OsCIPK17 in Arabidopsis enhanced primary root elongation under salt stress, which is in a Ca2+ dependent manner. Further investigation revealed that, under salt stress, OsCIPK17 transcript level was significantly induced and its protein moved from the cytosol to the tonoplast. Using both Y2H and BiFC, tonoplast-localised OsCBL2 and OsCBL3 were shown to interact with OsCIPK17. Interestingly, over-expressing salt-induced OsCBL2 or OsCBL3 in Arabidopsis led to enhanced primary root elongation under salt stress. In this process, OsCIPK17 was shown recruited to the tonoplast (similar to the effect of salt stress). Furthermore, transgenic Arabidopsis lines individually over-expressing OsCIPK17, OsCBL2 and OsCBL3 all demonstrated larger biomass and less Na + accumulation in the shoot under salt stress. All data combined suggest that OsCIPK17- OsCBL2/3 module is a major component of shoot Na+ exclusion and therefore plant salt tolerance, which is through enhanced Na + compartmentation into the vacuole in the root. OsCIPK17 and OsCBL2/3 are therefore potential genetic targets that can be used for delivering salt tolerant rice cultivars.

Polyamines and hydrogen peroxide: Allies in plant resilience against abiotic stress

The increasing prevalence and severity of abiotic stresses on plants due to climate change is among the crucial issues of decreased crop productivity worldwide. These stresses affect crop productivity and pose a challenge to food security. Polyamines (Pas) and hydrogen peroxide (H₂O₂) could play a vital role to minimize the impact of several abiotic stresses on the plants. Pas are small molecules that regulate various physiological and developmental processes in plants and confer stress tolerance and protection against dehydration and cellular damage. Pas also interact with plant growth regulators and participate in various signaling routes that can mediate stress response. H₂O₂ on the other hand, acts as a signaling agent and plays a pivotal part in controlling crop growth and productivity. It can trigger oxidative damage at high levels but acts as a stress transducer and regulator at low concentrations. H₂O₂ is involved in stress defense mechanisms and the activation of genes involved in conferring tolerance. Therefore, the main focus of this paper is to explore roles of Pas and H₂O₂ in plant responses to various abiotic stress, highlighting their involvement in stress retaliation and signaling routes. Emphasis has been placed on understanding how Pas and H₂O₂ function and interact with other signaling molecules. Also, interaction of Pas and H₂O₂ with calcium ions, abscisic acid and nitrogen has been discussed, along with activation of MAPK cascade. This additive understanding could contribute to adopt strategies to improve crop productivity and enhance plant resilience to environmental challenges.

SOS2-AFP2 module regulates seed germination by inducing ABI5 degradation in response to salt stress in Arabidopsis

Soil salinity pose a significant challenge to global agriculture, threatening crop yields and food security. Understanding the salt tolerance mechanisms of plants is crucial for improving their survival under salt stress. AFP2, a negative regulator of ABA signaling, has been shown to play a crucial role in salt stress tolerance during seed germination. Mutations in AFP2 gene lead to increased sensitivity to salt stress. However, the underline mechanisms by which AFP2 regulates seed germination under salt stress remain elusive. In this study, we identified a protein interaction between AFP2 and SOS2, a Ser/Thr protein kinase known to play a critical role in salt stress response. Using a combination of genetic, biochemical, and physiological approaches, we investigated the role of the SOS2-AFP2 module in regulating seed germination under salt stress. Our findings reveal that SOS2 physically interacts with AFP2 and stabilizes it, leading to the degradation of the ABI5 protein, a negative transcription factor in seed germination under salt stress. This study sheds light on previously unknown connections within salt stress and ABA signaling, paving the way for novel strategies to enhance plant resilience against environmental challenges.

Kinetochore and ionomic adaptation to whole-genome duplication in Cochlearia shows evolutionary convergence in three autopolyploids

Whole-genome duplication (WGD) occurs in all kingdoms and impacts speciation, domestication, and cancer outcome. However, doubled DNA management can be challenging for nascent polyploids. The study of within-species polyploidy (autopolyploidy) permits focus on this DNA management aspect, decoupling it from the confounding effects of hybridization (in allopolyploid hybrids). How is autopolyploidy tolerated, and how do young polyploids stabilize? Here, we introduce a powerful model to address this: the genus Cochlearia, which has experienced many polyploidization events. We assess meiosis and other polyploid-relevant phenotypes, generate a chromosome-scale genome, and sequence 113 individuals from 33 ploidy-contrasting populations. We detect an obvious autopolyploidy-associated selection signal at kinetochore components and ion transporters. Modeling the selected alleles, we detail evidence of the kinetochore complex mediating adaptation to polyploidy. We compare candidates in independent autopolyploids across three genera separated by 40 million years, highlighting a common function at the process and gene levels, indicating evolutionary flexibility in response to polyploidy.

SOS1 gene family in mangrove (Kandelia obovata): Genome-wide identification, characterization, and expression analyses under salt and copper stress

BACKGROUND

Salt Overly Sensitive 1 (SOS1), a plasma membrane Na+/H+ exchanger, is essential for plant salt tolerance. Salt damage is a significant abiotic stress that impacts plant species globally. All living organisms require copper (Cu), a necessary micronutrient and a protein cofactor for many biological and physiological processes. High Cu concentrations, however, may result in pollution that inhibits the growth and development of plants. The function and production of mangrove ecosystems are significantly impacted by rising salinity and copper contamination.

RESULTS

A genome-wide analysis and bioinformatics techniques were used in this study to identify 20 SOS1 genes in the genome of Kandelia obovata. Most of the SOS1 genes were found on the plasma membrane and dispersed over 11 of the 18 chromosomes. Based on phylogenetic analysis, KoSOS1s can be categorized into four groups, similar to Solanum tuberosum. Kandelia obovata's SOS1 gene family expanded due to tandem and segmental duplication. These SOS1 homologs shared similar protein structures, according to the results of the conserved motif analysis. The coding regions of 20 KoSOS1 genes consist of amino acids ranging from 466 to 1221, while the exons include amino acids ranging from 3 to 23. In addition, we found that the 2.0 kb upstream promoter region of the KoSOS1s gene contains several cis-elements associated with phytohormones and stress responses. According to the expression experiments, seven randomly chosen genes experienced up- and down-regulation of their expression levels in response to copper (CuCl2) and salt stressors.

CONCLUSIONS

For the first time, this work systematically identified SOS1 genes in Kandelia obovata. Our investigations also encompassed physicochemical properties, evolution, and expression patterns, thereby furnishing a theoretical framework for subsequent research endeavours aimed at functionally characterizing the Kandelia obovata SOS1 genes throughout the life cycle of plants.

Understanding Ameliorating Effects of Boron on Adaptation to Salt Stress in Arabidopsis

When faced with salinity stress, plants typically exhibit a slowdown in their growth patterns. Boron (B) is an essential micronutrient for plants that are known to play a critical role in controlling cell wall properties. In this study, we used the model plant Arabidopsis thaliana Col-0 and relevant mutants to explore how the difference in B availability may modulate plant responses to salt stress. There was a visible root growth suppression of Col-0 with the increased salt levels in the absence of B while this growth reduction was remarkably alleviated by B supply. Pharmacological experiments revealed that orthovanadate (a known blocker of H+-ATPase) inhibited root growth at no B condition, but had no effect in the presence of 30 μM B. Salinity stress resulted in a massive K+ loss from mature zones of A. thaliana roots; this efflux was attenuated in the presence of B. Supplemental B also increased the magnitude of net H+ pumping by plant roots. Boron availability was also essential for root halotropism. Interestingly, the aha2Δ57 mutant with active H+-ATPase protein exhibited the same halotropism response as Col-0 while the aha2-4 mutant had a stronger halotropism response (larger bending angle) compared with that of Col-0. Overall, the ameliorative effect of B on the A. thaliana growth under salt stress is based on the H+-ATPase stimulation and a subsequent K+ retention, involving auxin- and ROS-pathways.

The transcription factor MdERF023 negatively regulates salt tolerance by modulating ABA signaling and Na+/H+ transport in apple

KEY MESSAGE

MdERF023 is a transcription factor that can reduce salt tolerance by inhibiting ABA signaling and Na+/H+ homeostasis. Salt stress is one of the principal environmental stresses limiting the growth and productivity of apple (Malus × domestica). The APETALA2/ethylene response factor (AP2/ERF) family plays key roles in plant growth and various stress responses; however, the regulatory mechanism involved has not been fully elucidated. In the present study, we identified an AP2/ERF transcription factor (TF), MdERF023, which plays a negative role in apple salt tolerance. Stable overexpression of MdERF023 in apple plants and calli significantly decreased salt tolerance. Biochemical and molecular analyses revealed that MdERF023 directly binds to the promoter of MdMYB44-like, a positive modulator of ABA signaling-mediated salt tolerance, and suppresses its transcription. In addition, MdERF023 downregulated the transcription of MdSOS2 and MdAKT1, thereby reducing the Na+ expulsion, K+ absorption, and salt tolerance of apple plants. Taken together, these results suggest that MdERF023 reduces apple salt tolerance by inhibiting ABA signaling and ion transport, and that it could be used as a potential target for breeding new varieties of salt-tolerant apple plants via genetic engineering.

Transcriptome Analysis of the Regulatory Mechanisms of Holly (Ilex dabieshanensis) under Salt Stress Conditions

The holly Ilex dabieshanensis K. Yao & M. B. Deng, a tree endemic to the Dabieshan Mountains region in China, is a commonly used landscaping plant. Like other crops, its growth is affected by salt stress. The molecular mechanism underlying salt tolerance in holly is still unclear. In this study, we used NaCl treatment and RNA sequencing (RNA-seq) at different times to identify the salt stress response genes of holly. A total of 4775 differentially expressed genes (DEGs) were identified. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the DEGs obtained at different salt treatment times (3, 6, 9, 12, and 24 h), as compared to control (ck, 0 h), showed that plant hormone signal transduction and carotenoid biosynthesis were highly enriched. The mechanism by which holly responds to salt stress involves many plant hormones, among which the accumulation of abscisic acid (ABA) and its signal transduction may play an important role. In addition, ion homeostasis, osmotic metabolism, accumulation of antioxidant enzymes and nonenzymatic antioxidant compounds, and transcription factors jointly regulate the physiological balance in holly, providing important guarantees for its growth and development under conditions of salt stress. These results lay the foundation for studying the molecular mechanisms of salt tolerance in holly and for the selection of salt-tolerant varieties.

A teosinte-derived allele of ZmSC improves salt tolerance in maize

Maize, a salt-sensitive crop, frequently suffers severe yield losses due to soil salinization. Enhancing salt tolerance in maize is crucial for maintaining yield stability. To address this, we developed an introgression line (IL76) through introgressive hybridization between maize wild relatives Zea perennis, Tripsacum dactyloides, and inbred Zheng58, utilizing the tri-species hybrid MTP as a genetic bridge. Previously, genetic variation analysis identified a polymorphic marker on Zm00001eb244520 (designated as ZmSC), which encodes a vesicle-sorting protein described as a salt-tolerant protein in the NCBI database. To characterize the identified polymorphic marker, we employed gene cloning and homologous cloning techniques. Gene cloning analysis revealed a non-synonymous mutation at the 1847th base of ZmSCIL76 , where a guanine-to-cytosine substitution resulted in the mutation of serine to threonine at the 119th amino acid sequence (using ZmSCZ58 as the reference sequence). Moreover, homologous cloning demonstrated that the variation site derived from Z. perennis. Functional analyses showed that transgenic Arabidopsis lines overexpressing ZmSCZ58 exhibited significant reductions in leaf number, root length, and pod number, alongside suppression of the expression of genes in the SOS and CDPK pathways associated with Ca2+ signaling. Similarly, fission yeast strains expressing ZmSCZ58 displayed inhibited growth. In contrast, the ZmSCIL76 allele from Z. perennis alleviated these negative effects in both Arabidopsis and yeast, with the lines overexpressing ZmSCIL76 exhibiting significantly higher abscisic acid (ABA) content compared to those overexpressing ZmSCZ58 . Our findings suggest that ZmSC negatively regulates salt tolerance in maize by suppressing downstream gene expression associated with Ca2+ signaling in the CDPK and SOS pathways. The ZmSCIL76 allele from Z. perennis, however, can mitigate this negative regulatory effect. These results provide valuable insights and genetic resources for future maize salt tolerance breeding programs.

Overexpression of a plasmalemma Na+/H+ antiporter from the halophyte Nitraria sibirica enhances the salt tolerance of transgenic poplar

The plasmalemma Na+/H+ antiporter Salt Overly Sensitive 1 (SOS1) is responsible for the efflux of Na+ from the cytoplasm, an important determinant of salt resistance in plants. In this study, an ortholog of SOS1, referred to as NsSOS1, was cloned from Nitraria sibirica, a typical halophyte that grows in deserts and saline-alkaline land, and its expression and function in regulating the salt tolerance of forest trees were evaluated. The expression level of NsSOS1 was higher in leaves than in roots and stems of N. sibirica, and its expression was upregulated under salt stress. Histochemical staining showed that β-glucuronidase (GUS) driven by the NsSOS1 promoter was strongly induced by abiotic stresses and phytohormones including salt, drought, low temperature, gibberellin, and methyl jasmonate, suggesting that NsSOS1 is involved in the regulation of multiple signaling pathways. Transgenic 84 K poplar (Populus alba × P. glandulosa) overexpressing NsSOS1 showed improvements in survival rate, root biomass, plant height, relative water levels, chlorophyll and proline levels, and antioxidant enzyme activities versus non-transgenic poplar (NT) under salt stress. Transgenic poplars accumulated less Na+ and more K+ in roots, stems, and leaves, which had a lower Na+/K+ ratio compared to NT under salt stress. These results indicate that NsSOS1-mediated Na+ efflux confers salt tolerance to transgenic poplars, which show more efficient photosynthesis, better scavenging of reactive oxygen species, and improved osmotic adjustment under salt stress. Transcriptome analysis of transgenic poplars confirmed that NsSOS1 not only mediates Na+ efflux but is also involved in the regulation of multiple metabolic pathways. The results provide insight into the regulatory mechanisms of NsSOS1 and suggest that it could be used to improve the salt tolerance of forest trees.

SOS1 tonoplast neo-localization and the RGG protein SALTY are important in the extreme salinity tolerance of Salicornia bigelovii

The identification of genes involved in salinity tolerance has primarily focused on model plants and crops. However, plants naturally adapted to highly saline environments offer valuable insights into tolerance to extreme salinity. Salicornia plants grow in coastal salt marshes, stimulated by NaCl. To understand this tolerance, we generated genome sequences of two Salicornia species and analyzed the transcriptomic and proteomic responses of Salicornia bigelovii to NaCl. Subcellular membrane proteomes reveal that SbiSOS1, a homolog of the well-known SALT-OVERLY-SENSITIVE 1 (SOS1) protein, appears to localize to the tonoplast, consistent with subcellular localization assays in tobacco. This neo-localized protein can pump Na+ into the vacuole, preventing toxicity in the cytosol. We further identify 11 proteins of interest, of which SbiSALTY, substantially improves yeast growth on saline media. Structural characterization using NMR identified it as an intrinsically disordered protein, localizing to the endoplasmic reticulum in planta, where it can interact with ribosomes and RNA, stabilizing or protecting them during salt stress.

Molecular cloning and characterization of a salt overly sensitive3 (SOS3) gene from the halophyte Pongamia

A high concentration of sodium (Na+) is the primary stressor for plants in high salinity environments. The Salt Overly Sensitive (SOS) pathway is one of the best-studied signal transduction pathways, which confers plants the ability to export too much Na+ out of the cells or translocate the cytoplasmic Na+ into the vacuole. In this study, the Salt Overly Sensitive3 (MpSOS3) gene from Pongamia (Millettia pinnata Syn. Pongamia pinnata), a semi-mangrove, was isolated and characterized. The MpSOS3 protein has canonical EF-hand motifs conserved in other calcium-binding proteins and an N-myristoylation signature sequence. The MpSOS3 gene was significantly induced by salt stress, especially in Pongamia roots. Expression of the wild-type MpSOS3 but not the mutated nonmyristoylated MpSOS3-G2A could rescue the salt-hypersensitive phenotype of the Arabidopsis sos3-1 mutant, which suggested the N-myristoylation signature sequence of MpSOS3 was required for MpSOS3 function in plant salt tolerance. Heterologous expression of MpSOS3 in Arabidopsis accumulated less H2O2, superoxide anion radical (O2-), and malondialdehyde (MDA) than wild-type plants, which enhanced the salt tolerance of transgenic Arabidopsis plants. Under salt stress, MpSOS3 transgenic plants accumulated a lower content of Na+ and a higher content of K+ than wild-type plants, which maintained a better K+/Na+ ratio in transgenic plants. Moreover, no development and growth discrepancies were observed in the MpSOS3 heterologous overexpression plants compared to wild-type plants. Our results demonstrated that the MpSOS3 pathway confers a conservative salt-tolerant role and provided a foundation for further study of the SOS pathway in Pongamia.

The translocation of a chloride channel from the Golgi to the plasma membrane helps plants adapt to salt stress

A key mechanism employed by plants to adapt to salinity stress involves maintaining ion homeostasis via the actions of ion transporters. While the function of cation transporters in maintaining ion homeostasis in plants has been extensively studied, little is known about the roles of their anion counterparts in this process. Here, we describe a mechanism of salt adaptation in plants. We characterized the chloride channel (CLC) gene AtCLCf, whose expression is regulated by WRKY transcription factor under salt stress in Arabidopsis thaliana. Loss-of-function atclcf seedlings show increased sensitivity to salt, whereas AtCLCf overexpression confers enhanced resistance to salt stress. Salt stress induces the translocation of GFP-AtCLCf fusion protein to the plasma membrane (PM). Blocking AtCLCf translocation using the exocytosis inhibitor brefeldin-A or mutating the small GTPase gene AtRABA1b/BEX5 (RAS GENES FROM RAT BRAINA1b homolog) increases salt sensitivity in plants. Electrophysiology and liposome-based assays confirm the Cl-/H+ antiport function of AtCLCf. Therefore, we have uncovered a mechanism of plant adaptation to salt stress involving the NaCl-induced translocation of AtCLCf to the PM, thus facilitating Cl- removal at the roots, and increasing the plant's salinity tolerance.

NADPH oxidase-dependent H2O2 production mediates salicylic acid-induced salt tolerance in mangrove plant Kandelia obovata by regulating Na+/K+ and redox homeostasis

Salicylic acid (SA) is known to enhance salt tolerance in plants. However, the mechanism of SA-mediated response to high salinity in halophyte remains unclear. Using electrophysiological and molecular biological methods, we investigated the role of SA in response to high salinity in mangrove species, Kandelia obovata, a typical halophyte. Exposure of K. obovata roots to high salinity resulted in a rapid increase in endogenous SA produced by phenylalanine ammonia lyase pathway. The application of exogenous SA improved the salt tolerance of K. obovata, which depended on the NADPH oxidase-mediated H2O2. Exogenous SA and H2O2 increased Na+ efflux and reduced K+ loss by regulating the transcription levels of Na+ and K+ transport-related genes, thus reducing the Na+/K+ ratio in the salt-treated K. obovata roots. In addition, exogenous SA-enhanced antioxidant enzyme activity and its transcripts, and the expressions of four genes related to AsA-GSH cycle as well, then alleviated oxidative damages in the salt-treated K. obovata roots. However, the above effects of SA could be reversed by diphenyleneiodonium chloride (the NADPH oxidase inhibitor) and paclobutrazol (a SA biosynthesis inhibitor). Collectively, our results demonstrated that SA-induced salt tolerance of K. obovata depends on NADPH oxidase-generated H2O2 that affects Na+/K+ and redox homeostasis in response to high salinity.

Populus euphratica PeNADP-ME interacts with PePLDδ to mediate sodium and ROS homeostasis under salinity stress

Populus euphratica phospholipase Dδ (PePLDδ) is transcriptionally regulated and mediates reactive oxygen species (ROS) and ion homeostasis under saline conditions. The purpose of this study is to explore the post-transcriptional regulation of PePLDδ in response to salt environment. P. euphratica PePLDδ was shown to interact with the NADP-dependent malic enzyme (NADP-ME) by screening the yeast two-hybrid libraries. The transcription level of PeNADP-ME increased upon salt exposure to NaCl (200 mM) in leaves and roots of P. euphratica. PeNADP-ME had a similar subcellular location with PePLDδ in the cytoplasm, and the interaction between PeNADP-ME and PePLDδ was further verified by GST pull-down and yeast two-hybrid. To clarify whether PeNADP-ME interacts with PePLDδ to enhance salt tolerance, PePLDδ and PeNADP-ME were overexpressed singly or doubly in Arabidopsis thaliana. Dual overexpression of PeNADP-ME and PePLDδ resulted in an even more pronounced improvement in salt tolerance compared with single transformants overexpressing PeNADP-ME or PePLDδ alone. Greater Na+ limitation and Na+ efflux in roots were observed in doubly overexpressed plants compared with singly overexpressed plants with PeNADP-ME or PePLDδ. Furthermore, NaCl stimulation of SOD, APX, and POD activity and transcription were more remarkable in the doubly overexpressed plants. It is noteworthy that the enzymic activity of NADP-ME and PLD, and total phosphatidic acid (PA) concentrations were significantly higher in the double-overexpressed plants than in the single transformants. We conclude that PeNADP-ME interacts with PePLDδ in Arabidopsis to promote PLD-derived PA signaling, conferring Na+ extrusion and ROS scavenging under salt stress.

Exogenous zinc application mitigates negative effects of salinity on barley (Hordeum vulgare) growth by improving root ionic homeostasis

Detrimental effects of salinity could be mitigated by exogenous zinc (Zn) application; however, the mechanisms underlying this amelioration are poorly understood. This study demonstrated the interaction between Zn and salinity by measuring plant biomass, photosynthetic performance, ion concentrations, ROS accumulation, antioxidant activity and electrophysiological parameters in barley (Hordeum vulgare L.). Salinity stress (200mM NaCl for 3weeks) resulted in a massive reduction in plant biomass; however, both fresh and dry weight of shoots were increased by ~30% with adequate Zn supply. Zinc supplementation also maintained K+ and Na+ homeostasis and prevented H2 O2 toxicity under salinity stress. Furthermore, exposure to 10mM H2 O2 resulted in massive K+ efflux from root epidermal cells in both the elongation and mature root zones, and pre-treating roots with Zn reduced ROS-induced K+ efflux from the roots by 3-4-fold. Similar results were observed for Ca2+ . The observed effects may be causally related to more efficient regulation of cation-permeable non-selective channels involved in the transport and sequestration of Na+ , K+ and Ca2+ in various cellular compartments and tissues. This study provides valuable insights into Zn protective functions in plants and encourages the use of Zn fertilisers in barley crops grown on salt-affected soils.

Understanding the role of boron in plant adaptation to soil salinity

Soil salinity is a major environmental constraint affecting the sustainability and profitability of agricultural production systems. Salinity stress tolerance has been present in wild crop relatives but then lost, or significantly weakened, during their domestication. Given the genetic and physiological complexity of salinity tolerance traits, agronomical solutions may be a suitable alternative to crop breeding for improved salinity stress tolerance. One of them is optimizing fertilization practices to assist plants in dealing with elevated salt levels in the soil. In this review, we analyse the causal relationship between the availability of boron (an essential metalloid micronutrient) and plant's adaptive responses to salinity stress at the whole-plant, cellular, and molecular levels, and a possibility of using boron for salt stress mitigation. The topics covered include the impact of salinity and the role of boron in cell wall remodelling, plasma membrane integrity, hormonal signalling, and operation of various membrane transporters mediating plant ionic and water homeostasis. Of specific interest is the role of boron in the regulation of H+-ATPase activity whose operation is essential for the control of a broad range of voltage-gated ion channels. The complex relationship between boron availability and expression patterns and the operation of aquaporins is also discussed.

The signalling pathways, calcineurin B-like protein 5 (CBL5)-CBL-interacting protein kinase 8 (CIPK8)/CIPK24-salt overly sensitive 1 (SOS1), transduce salt signals in seed germination in Arabidopsis

For plant growth under salt stress, sensing and transducing salt signals are central to cellular Na+ homoeostasis. The calcineurin B-like protein (CBL)-CBL-interacting protein kinase (CIPK) complexes play critical roles in transducing salt signals in plants. Here, we show that CBL5, an ortholog of CBL4 and CBL10 in Arabidopsis, interacts with and recruits CIPK8/CIPK24 to the plasma membrane. Yeast cells coexpressing CBL5, CIPK8/CIPK24 and SOS1 demonstrated lesser Na+ accumulation and a better growth phenotype than the untransformed or SOS1 transgenic yeast cells under salinity. Overexpression of CBL5 improved the growth of the cipk8 or cipk24 single mutant but not the cipk8 cipk24 double mutant under salt stress, suggesting that CIPK8 and CIPK24 were the downstream targets of CBL5. Interestingly, seed germination in cbl5 was severely inhibited by NaCl, which was recovered by the overexpression of CBL5. Furthermore, CBL5 was mainly expressed in the cotyledons and hypocotyls, which are essential to seed germination. Na+ efflux activity in the hypocotyls of cbl5 was reduced relative to the wild-type under salt stress, enhancing Na+ accumulation. These findings indicate that CBL5 functions in seed germination and protects seeds and germinating seedlings from salt stress through the CBL5-CIPK8/CIPK24-SOS1 pathways.

Creating Climate-Resilient Crops by Increasing Drought, Heat, and Salt Tolerance

Over the years, the changes in the agriculture industry have been inevitable, considering the need to feed the growing population. As the world population continues to grow, food security has become challenged. Resources such as arable land and freshwater have become scarce due to quick urbanization in developing countries and anthropologic activities; expanding agricultural production areas is not an option. Environmental and climatic factors such as drought, heat, and salt stresses pose serious threats to food production worldwide. Therefore, the need to utilize the remaining arable land and water effectively and efficiently and to maximize the yield to support the increasing food demand has become crucial. It is essential to develop climate-resilient crops that will outperform traditional crops under any abiotic stress conditions such as heat, drought, and salt, as well as these stresses in any combinations. This review provides a glimpse of how plant breeding in agriculture has evolved to overcome the harsh environmental conditions and what the future would be like.

Proteomic profiling of Arabidopsis G-protein β subunit AGB1 mutant under salt stress

Salt stress is a limiting environmental factor that inhibits plant growth in most ecological environments. The functioning of G-proteins and activated downstream signaling during salt stress is well established and different G-protein subunits and a few downstream effectors have been identified. Arabidopsis G-protein β-subunit (AGB1) regulates the movement of Na+ from roots to shoots along with a significant role in controlling Na+ fluxes in roots, however, the molecular mechanism of AGB1 mediated salt stress regulation is not well understood. Here, we report the comparative proteome profiles of Arabidopsis AGB1 null mutant agb1-2 to investigate how the absence of AGB1 modulates the protein repertoire in response to salt stress. High-resolution two-dimensional gel electrophoresis (2-DE) showed 27 protein spots that were differentially modulated between the control and NaCl treated agb1-2 seedlings of which seven were identified by mass spectrometry. Functional annotation and interactome analysis indicated that the salt-responsive proteins were majorly associated with cellulose synthesis, structural maintenance of chromosomes, DNA replication/repair, organellar RNA editing and indole glucosinolate biosynthesis. Further exploration of the functioning of these proteins could serve as a potential stepping stone for dissection of molecular mechanism of AGB1 functions during salt stress and in long run could be extrapolated to crop plants for salinity stress management.

Moving forward to understand the alteration of physiological mechanism by seed priming with different halo-agents under salt stress

Soil salinity hampers the survival and productivity of crops. To minimize salt-associated damages in plant, better salt management practices in agriculture have become a prerequisite. Seed priming with different halo-agents is a technique, which improves the primed plant's endurance to tackle sodium. Salt tolerance is achieved in tolerant plants through fundamental physiological mechanisms- ion-exclusion and tissue tolerance, and salt-tolerant plants may (Na+ accumulators) or may not (Na+ excluders) allow sodium movement to leaves. While Na+ excluders depend on ion exclusion in roots, Na+ accumulators are proficient Na+ managers that can compartmentalize Na+ in leaves and use them beneficially as inexpensive osmoticum. Salt-sensitive plants are Na+ accumulators, but their inherent tissue tolerance ability and ion-exclusion process are insufficient for tolerance. Seed priming with different halo-agents aids in 'rewiring' of the salt tolerance mechanisms of plants. The resetting of the salt tolerance mechanism is not universal for every halo-agent and might vary with halo-agents. Here, we review the physiological mechanisms that different halo-agents target to confer enhanced salt tolerance in primed plants. Calcium and potassium-specific halo-agents trigger Na+ exclusion in roots, thus ensuring a low amount of Na+ in leaves. In contrast, Na+-specific priming agents favour processes for Na+ inclusion in leaves, improve plant tissue tolerance or vacuolar sequestration, and provide the greatest benefit to salt-sensitive and sodium accumulating plants. Overall, this review will help to understand the underlying mechanism behind plant's inherent nature towards salt management and its amelioration with different halo-agents, which helps to optimize crop stress performance.

A B-box transcription factor OsBBX17 regulates saline-alkaline tolerance through the MAPK cascade pathway in rice

Rice OsBBX17 encodes a B-box zinc finger transcription factor in which the N-terminal B-box structural domain interacts with OsMPK1. In addition, it directly binds to the G-box of OsHAK2 and OsHAK7 promoters and represses their transcription. Under saline-alkaline conditions, the expression of OsBBX17 was inhibited. Meanwhile, activation of the OsMPK1-mediated mitogen-activated protein kinase cascade pathway caused OsMPK1 to interact with OsBBX17 and phosphorylate OsBBX17 at the Thr-95 site. It reduced OsBBX17 DNA-binding activity and enhanced saline-alkaline tolerance by deregulating transcriptional repression of OsHAK2 and OsHAK7. Genetic assays showed that the osbbx17-KO had an excellent saline-alkaline tolerance, whereas the opposite was in OsBBX17-OE. In addition, overexpression of OsMPK1 significantly improved saline-alkaline tolerance, but knockout of OsMPK1 caused an increased sensitivity. Further overexpression of OsBBX17 in the osmpk1-KO caused extreme saline-alkaline sensitivity, even a quick death. OsBBX17 was validated in saline-alkaline tolerance from two independent aspects, transcriptional level and post-translational protein modification, unveiling a mechanistic framework by which OsMPK1-mediated phosphorylation of OsBBX17 regulates the transcription of OsHAK2 and OsHAK7 to enhance the Na+ /K+ homeostasis, which partially explains light on the molecular mechanisms of rice responds to saline-alkaline stress via B-box transcription factors for the genetic engineering of saline-alkaline tolerant crops.

Integrative multi-omics analyses of date palm (Phoenix dactylifera) roots and leaves reveal how the halophyte land plant copes with sea water

Date palm (Phoenix dactylifera L.) is able to grow and complete its life cycle while being rooted in highly saline soils. Which of the many well-known salt-tolerance strategies are combined to fine-tune this remarkable resilience is unknown. The precise location, whether in the shoot or the root, where these strategies are employed remains uncertain, leaving us unaware of how the various known salt-tolerance mechanisms are integrated to fine-tune this remarkable resilience. To address this shortcoming, we exposed date palm to a salt stress dose equivalent to seawater for up to 4 weeks and applied integrative multi-omics analyses followed by targeted metabolomics, hormone, and ion analyses. Integration of proteomic into transcriptomic data allowed a view beyond simple correlation, revealing a remarkably high degree of convergence between gene expression and protein abundance. This sheds a clear light on the acclimatization mechanisms employed, which depend on reprogramming of protein biosynthesis. For growth in highly saline habitats, date palm effectively combines various salt-tolerance mechanisms found in both halophytes and glycophytes: "avoidance" by efficient sodium and chloride exclusion at the roots, and "acclimation" by osmotic adjustment, reactive oxygen species scavenging in leaves, and remodeling of the ribosome-associated proteome in salt-exposed root cells. Combined efficiently as in P. dactylifera L., these sets of mechanisms seem to explain the palm's excellent salt stress tolerance.

Designing salt stress-resilient crops: Current progress and future challenges

Excess soil salinity affects large regions of land and is a major hindrance to crop production worldwide. Therefore, understanding the molecular mechanisms of plant salt tolerance has scientific importance and practical significance. In recent decades, studies have characterized hundreds of genes associated with plant responses to salt stress in different plant species. These studies have substantially advanced our molecular and genetic understanding of salt tolerance in plants and have introduced an era of molecular design breeding of salt-tolerant crops. This review summarizes our current knowledge of plant salt tolerance, emphasizing advances in elucidating the molecular mechanisms of osmotic stress tolerance, salt-ion transport and compartmentalization, oxidative stress tolerance, alkaline stress tolerance, and the trade-off between growth and salt tolerance. We also examine recent advances in understanding natural variation in the salt tolerance of crops and discuss possible strategies and challenges for designing salt stress-resilient crops. We focus on the model plant Arabidopsis (Arabidopsis thaliana) and the four most-studied crops: rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), and soybean (Glycine max).