Salt Tolerance Mechanisms of Plants

Comparison of Two Bacillus Strains Isolated from the Coastal Zone in Barley (Hordeum vulgare L.) Under Salt Stress

Salt stress is one of the most important abiotic stress factors that negatively affects sustainable crop production, agricultural productivity, and microbial life. Increasing salt stress negatively affects the growth and development of barley, posing a threat to global food security. It is now known that inoculation of plant growth-promoting rhizobacteria (PGPR) has significant potential in increasing stress tolerance and yield in agricultural products. This study focused on the effects of Bacillus cereus CUN6 and Bacillus thuringiensis SIRB2, isolated from the coastal zone and tested for their PGPR capacities, on physiological (root length, shoot length, biomass, dry weight) and biochemical (total chlorophyll, total protein, hydrogen peroxide, lipid peroxidation, peroxidase activity (POX), catalase activity (CAT)) analyses in Hordeum vulgare L. seedlings under salt stress. The results showed that the two bacterial inoculations alleviated the negative effects of salt stress by increasing the root-shoot length, biomass, dry weight, chlorophyll content, and total protein content in barley plants. However, B.thuringiensis increased growth and development especially in root length, biomass, and dry weight compared to B.cereus. On the other hand, B.cereus significantly increased root length, biomass, and chlorophyll content under salt stress; these increases were 17%, 5%, and 7%, respectively. B.thuringiensis chlorophyll content increased by 4% in 300 mM NaCl compared to the control. When compared in terms of the antioxidant defense system, B.thuringiensis inoculation was more effective on CAT activity, while B.cereus inoculation was more effective on POX activity. Under salt stress, B.cereus and B.thuringiensis inoculation significantly decreased H2O2 content in barley; these decreases were 16% and 10%, respectively. Additionally, TBARs content was significantly decreased by B.cereus and B.thuringiensis inoculation under salt stress; these decreases were determined as 8% and 9%, respectively, compared to the control. These results indicated that both bacterial inoculations can alleviate the salt tolerance of barley seedlings by regulating antioxidant metabolism. This research focused on the potential of B.cereus and B.thuringiensis as biofertilizers against salt stress in barley based on physiological and biochemical analysis.

The viscoelastic properties of Nicotiana tabacum BY-2 suspension cell lines adapted to high osmolarity

To survive and grow, plant cells must regulate the properties of their cellular microenvironment in response to ever changing external factors. How the biomechanical balance across the cell's internal structures is established and maintained during environmental variations remains a nurturing question. To provide insight into this issue we used two micro-mechanical imaging techniques, namely Brillouin light scattering and BODIPY-based molecular rotors Fluorescence Lifetime Imaging, to study Nicotiana tabacum suspension BY-2 cells long-term adapted to high concentrations of NaCl and mannitol. The molecular crowding in cytoplasm and vacuoles was examined, as well as tension in plasma membrane. To understand how sudden changes in osmolarity affect cellular mechanics, the response of the control and the already adapted cells to further short-term osmotic stimulus was also examined. The viscoelasticity of protoplasts is altered differently during adaptation processes compared to responses to sudden hyperosmolarity stress. The applied correlative approach provides evidence that adaptation to hyperosmotic stress leads to different ratios of protoplast and environmental qualities that help to maintain cell integrity. The viscoelastic properties of protoplasts are an element of plant cells long-term adaptation to high osmolarity. Moreover, such adaptation has an impact on the response to the hyperosmolarity stress.

Physiological and transcriptomic analyses revealed the alleviating effects of exogenous Ca2+ and NO compound treatment on high salt stress in Reaumuria soongorica

BACKGROUND

Soil salinization represents the most prevalent abiotic stress, severely impacting a severe impact on plant growth and crop yield. Consequently, delving into the mechanism through which exogenous substances enhance plant salt tolerance holds significant importance for the stabilization and augmentation of crop yield.

RESULT

In this study, within the context of salt stress, the seedlings of R. soongorica were subjected to exogenous Ca2+ and NO treatments. The aim was to comprehensively explore the alleviation effects of exogenous Ca2+ and NO on the high salt stress endured by R. soongorica from the perspectives of physiology and transcriptomics. The experimental results demonstrated that the combined treatment of exogenous Ca2+ and NO increased the relative water content and free water content of R. soongorica seedlings during salt stress conditions. Simultaneously, it induced a reduction in the leaf sap concentration, leaf water potential, water saturation deficit, and the ratio of bound water to free water. These modifications effectively regulated water metabolism and mitigated physiological drought induced by salt stress. In addition, the concurrent treatment of exogenous Ca2+ and NO could diminish Na+ and Cl- levels in R. soongorica seedlings under salt stress. At the same time, it was effective in elevating the contents of K+ and Ca2+, thereby facilitating the adjustment of the ion equilibrium. As a result, this treatment served to relieve the ion toxicity precipitated by salt stress, which is crucial for maintaining the physiological homeostasis and viability of the seedlings. Transcriptional analysis revealed that 65 differentially expressed genes (DEGs) were observable at three distinct stress time points in the context of high salt stress. Additionally, 154 DEGs were detected at three stress time points during the combined treatment. KEGG enrichment analysis revealed that phenylpropanoids biosynthesis, plant hormone signal transduction, MAPK signalling pathway, brassinosteroid biosynthesis and zeatin biosynthesis were significantly enriched under high salt stress and exogenous Ca2+ and NO compound treatment. Furthermore, WGCNA uncovered that multiple genes, including ADK, SBT, F-box protein, MYB, ZIP, PAL, METTL, and LRR, were implicated in the adaptive and mitigating mechanisms associated with the combined treatment of exogenous Ca2+ and NO in modulating high salt stress within R. soongorica seedlings.

CONCLUSION

The outcomes of this study are highly conducive to disclosing the mechanism through which the combined treatment of exogenous Ca2+ and NO ameliorates the salt tolerance of R. soongorica from both physiological and transcriptional aspects. It also paves a solid theoretical groundwork for the employment of biotechnology in the breeding of R. soongorica, thereby offering valuable insights and a scientific basis for further research and practical applications in enhancing the plant's ability to withstand salt stress and for the development of more salt-tolerant varieties of R. soongorica.

GHCYP706A7 governs anthocyanin biosynthesis to mitigate ROS under alkali stress in cotton

KEY MESSAGE

Flavonoid 3'-hydroxylase synthesis gene-GHCYP706A7, enhanced cotton resistance to alkali stress by scavenging ROS to regulate anthocyanin synthesis. Anthocyanins are a class of flavonoids that play a significant role in mediating plant responses to adverse environmental conditions. Flavonoid 3'-hydroxylase (F3'H), a member of the cytochrome P-450 (CYP) family, is a pivotal enzyme involved in the biosynthesis of anthocyanins. The present study identified 398 CYPs in the Gossypium hirsutum genome, of which GHCYP706A7 was responsible for F3'H synthesis and its ability to respond to alkaline stress. GHCYP706A7 suppression through virus-induced gene silencing (VIGS) diminished tolerance to alkali stress in cotton, evidenced by significantly reduced anthocyanin synthesis, markedly decreased antioxidant capacity, notable increases in reactive oxygen species, severe cellular damage, and observably decreased stomatal opening. The cumulative effects of these physiological disruptions ultimately manifest in cotton wilting and fresh weight decline. These findings lay a foundation for further investigations into the role of CYPs in regulating anthocyanin synthesis and responding to alkali stress.

Strigolactones, ROS and ABA Regulate Systemic Salt-Tolerance Priming Signals Between Dodder-Connected Tobacco Plants

The parasitic plants dodders (Cuscuta spp., Convolvulaceae) can often simultaneously parasitize two or more neighbouring hosts, forming dodder-connected plant clusters. In a dodder-connected plant cluster, salt-induced systemic priming signals are transferred from the salt-stressed host (signal donor, SD) to the other host (signal receiver, SR) through dodder and prime the SR plants for enhanced salt tolerance, but what signalling pathways regulate the dodder-mediated interplant priming signals remain unclear. In this study, using genetic analyses, we show that in dodder-connected tobacco (Nicotiana tabacum) clusters, the strigolactone (SL), reactive oxygen species (ROS) and abscisic acid (ABA) pathway in the SD plants negatively control the salt stress-induced systemic signals from SD to SR plants. Transcriptome data suggested that the salt-induced systemic signals regulated by SLs in the SD plants may also affect the ABA and ROS signalling pathway in the SR plants. Quantification of the ABA and H2O2 contents in the SD plants suggested that the SL and ROS signalling likely converge on the ABA pathway to regulate the priming signals. This study reveals the important regulatory roles of phytohormones and ROS in dodder-mediated interplant communications and provides new insight into systemic signalling during salt stress adaptation in individual plants.

GhADT5 enhances alkali stress tolerance in cotton by regulating phenylalanine-derived flavonoid biosynthesis and antioxidant defense

Phenylalanine (Phe), an aromatic amino acid, is a key precursor of flavonoids, which are crucial for plant growth and development. Arogenate dehydratase (ADT) catalyzes the final step in Phe biosynthesis. This study identified eleven ADT genes in G. hirsutum, twelve in G. barbadense, six in G. arboreum, and six in G. raimondii. Among them, GhADT5 exhibited the highest upregulation under alkali stress. Silencing GhADT5 using virus-induced gene silencing (VIGS) reduced cotton tolerance to alkali stress. GhADT5 silencing also led to decreased plant phenylalanine content, total flavonoid content, and activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). These reductions caused intracellular accumulation of Malondialdehyde (MDA) and reactive oxygen species (ROS). This oxidative damage ultimately reduced tolerance to alkali stress. In addition, silenced plants displayed reduced stomatal aperture, cellular deformation, and irregular intercellular breaks in the leaf epidermis. In summary, these findings suggest that GhADT5 may enhance resistance to alkali stress by regulating enzymatic and non-enzymatic antioxidant systems. This study highlights the role of GhADT5 under alkali stress and provides novel insights for breeding cotton varieties with improved stress tolerance.

Polyploidization leads to salt stress resilience via ethylene signaling in citrus plants

Polyploidization is a common occurrence in the evolutionary history of flowering plants, significantly contributing to their adaptability and diversity. However, the molecular mechanisms behind these adaptive advantages are not well understood. Through comprehensive phenotyping of diploid and tetraploid clones from Citrus and Poncirus genera, we discovered that genome doubling significantly enhances salt stress resilience. Epigenetic and transcriptomic analyses revealed that increased ethylene production in the roots of tetraploid plants was associated with hypomethylation and enhanced chromatin accessibility of the ACO1 gene. This increased ethylene production activates the transcription of reactive oxygen species scavenging genes and stress-related hormone biosynthesis genes. Consequently, tetraploid plants exhibited superior root functionality under salt stress, maintaining improved cytosolic K+/Na+ homeostasis. To genetically validate the link between salt stress resilience and ACO1 expression, we generated overexpression and knockout lines, confirming the central role of ACO1 expression regulation following genome doubling in salt stress resilience. Our work elucidates the molecular mechanisms underlying the role of genome doubling in stress resilience. We also highlight the importance of chromatin dynamics in fine-tuning ethylene gene expression and activating salt stress resilience pathways, offering valuable insights into plant adaptation and crop genome evolution.

Identification of Ethylene Response Factors in Wheat Reveals That TaERF16-B Contributes to Salt Tolerance

Soil salinization is a major abiotic stressor that significantly reduces wheat yield. Identifying novel salt-tolerance genes and integrating them into wheat breeding programs can enhance wheat productivity in saline soils. Ethylene response factor (ERF) plays an important role in plant response to salt stress, and thus far, four wheat ERF genes have been identified to be involved in salt stress response. To systematically identify salt tolerance-related ERF genes in wheat, in this study, 213 ERF sequences were isolated from the whole genome of common wheat and classified into 54 members based on subgenome homology, named TaERF1 to TaERF54. Transcriptome sequencing results showed different expression patterns of TaERF members in leaves after 1, 6, 24, and 48 h of NaCl treatment. Based on association analysis, nine TaERF genes were correlated with the leaf salt injury index. Among them, five SNPs of TaERF16-B formed two haplotypes: Hap1 and Hap2. RT-qPCR results showed that the expression level of TaERF16-B was significantly higher in Hap2-typed germplasms than that in Hap1-typed germplasms after 1 and 6 h of NaCl treatment. A Kompetitive Allele-Specific PCR marker K52 was developed for genotyping TaERF16-B haplotypes, which further confirmed the significant correlation between TaERF16-B and salt tolerance-related phenotypes in mapping population and wheat germplasms. This study provides new genes and molecular markers for improving salt tolerance in wheat.

Arabidopsis thaliana Plants' Overexpression of the MYB Transcription Factor VhMYB60 in the Face of Stress Hazards Enhances Salt and Cold Tolerance

'Beta' (Vitisriparia × V. labrusca) is a vine fruit tree of the genus Vitis which is a cross between American and riparian grapes. In the current situation of grape production in northern regions, cold, drought, and salinity are important bottlenecks restricting its development, while some grape rootstocks with excellent traits show the disadvantage of poor resilience. 'Beta' (Vitis riparia × V. labrusca), one of the most extensively utilized rootstocks in viticulture, has demonstrated remarkable resilience to adverse conditions. However, the mechanisms by which 'Beta' rootstocks resist abiotic stresses are unknown and need to be further investigated. In this study, we successfully isolated and cloned a novel MYB transcription factor, VhMYB60, from the 'Beta' grapevine. This factor spans 972 base pairs and encodes a protein comprising 323 amino acids. Subcellular localization studies revealed that VhMYB60 is predominantly expressed within the nucleus. Furthermore, tissue-specific expression analysis demonstrated that VhMYB60 is more abundantly expressed in the mature leaves and roots of the grape plant. Further studies showed that salt and cold stress notably increased VhMYB60 gene expression in both mature leaves and grape roots. Compared with the control, Arabidopsis thaliana (Arabidopsis) plants molecularly modified to overexpress VhMYB60 exhibited enhanced salt and cold resistance and improved survival rates. Moreover, notable changes were detected in chlorophyll, malondialdehyde (MDA), proline, peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) levels. Concurrently, the expression levels of structural genes that are positively correlated with resistance to adversity stress were markedly elevated in Arabidopsis plants that overexpress VhMYB60. Consequently, VhMYB60 may serve as a pivotal transcription factor in the regulation of 'Beta' resistance.

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.

High concentration of phosphate treatment increased the tolerance of Robinia pseudoacacia roots to salt stress

KEY MESSAGE

High P increased the tolerance of R. pseudoacacia roots to salt stress. Salt is an important abiotic factor that restricts plant growth and development in soil. An appropriate concentration of P can increase plant tolerance to salt stress. We investigated the physiological and transcriptional regulatory effects of high P (HP) or low P (LP) on the response of R. pseudoacacia roots to salt stress. A pot experiment was carried out to grow R. pseudoacacia seedlings in vermiculite media supplemented with 0 mM, 150 mM or 300 mM NaCl under HP or LP conditions. The root dry weight and concentrations of free proline, P, ions, and phytohormones were measured, and the transcription of the genes was analyzed under NaCl stress under HP or LP conditions. The results revealed that R. pseudoacacia responds to NaCl stress by regulating the absorption and utilization of P and the levels of free proline, phytohormones and Na+, K+, Ca2+, and Mg2+ as well as changing the expression levels of key genes. Compared with those under the LP condition, the roots of the R. pseudoacacia under the HP condition presented greater P concentrations, lower JA concentrations, and more stable K+ levels when subjected to NaCl stress, which increased their tolerance to NaCl stress. Moreover, genes involved in the cell wall, root growth, root architecture regulation, biomass accumulation, stress response, osmotic regulation and ion balance maintenance were upregulated under NaCl stress under HP conditions. In addition, NaCl stress impairs N metabolism under LP conditions. Our findings provide new insights into the response of woody plants to salt stress under different P conditions and contribute to the development of scientific afforestation in saline-alkali areas.

Abscisic acid signaling gates salt-induced responses of plant roots

Soil salinity presents a dual challenge for plants, involving both osmotic and ionic stress. In response, plants deploy distinct yet interconnected mechanisms to cope with these facets of salinity stress. In this investigation, we observed a substantial overlap in the salt (NaCl)-induced transcriptional responses of Arabidopsis roots with those triggered by osmotic stress or the plant stress hormone abscisic acid (ABA), as anticipated. Notably, a specific cluster of genes responded uniquely to sodium (Na+) ions and are not regulated by the known monovalent cation sensing mechanism MOCA1. Surprisingly, expression of sodium-induced genes exhibited a negative correlation with the ABA response and preceded the activation of genes induced by the osmotic stress component of salt. Elevated exogenous ABA levels resulted in the complete abolition of sodium-induced responses. Consistently, the ABA insensitive snrk2.2/2.3 double mutant displayed prolonged sodium-induced gene expression, coupled with increased root cell damage and root swelling under high salinity conditions. Moreover, ABA biosynthesis and signaling mutants were unable to redirect root growth to avoid high sodium concentrations and had increased sodium accumulation in the shoot. In summary, our findings unveil an unexpected and pivotal role for ABA signaling in mitigating cellular damage induced by salinity stress and modulating sodium-induced responses in plant roots.

Stress sensing and response through biomolecular condensates in plants

Plants have developed intricate mechanisms for rapid and efficient stress perception and adaptation in response to environmental stressors. Recent research highlights the emerging role of biomolecular condensates in modulating plant stress perception and response. These condensates function through numerous mechanisms to regulate cellular processes such as transcription, translation, RNA metabolism, and signaling pathways under stress conditions. In this review, we provide an overview of current knowledge on stress-responsive biomolecular condensates in plants, including well-defined condensates such as stress granules, processing bodies, and the nucleolus, as well as more recently discovered plant-specific condensates. By briefly referring to findings from yeast and animal studies, we discuss mechanisms by which plant condensates perceive stress signals and elicit cellular responses. Finally, we provide insights for future investigations on stress-responsive condensates in plants. Understanding how condensates act as stress sensors and regulators will pave the way for potential applications in improving plant resilience through targeted genetic or biotechnological interventions.

Transcription factor OsMYB2 triggers amino acid transporter OsANT1 expression to regulate rice growth and salt tolerance

Amino acid transporters (AATs) play important roles in plant growth and stress tolerance; however, whether the abscisic acid signaling pathway regulates their transcription in rice (Oryza sativa) under salt stress remains unclear. In this study, we report that the transcription factor OsMYB2 (MYB transcription factor 2) of the abscisic acid signaling pathway mediates the expression of the gene encoding the AAT aromatic and neutral AAT 1 (OsANT1), which positively regulates growth and salt tolerance in rice. OsANT1 was mainly expressed in the leaf blade and panicle under normal conditions and transports leucine, phenylalanine, tyrosine, and proline (Pro), positively regulating tillering and yield in rice. Nevertheless, salt stress induced the accumulation of abscisic acid and strongly increased the expression level of OsANT1 in the root, resulting in enhanced salt tolerance of rice seedlings, as evidenced by higher Pro concentration and antioxidant-like enzyme activities and lower malondialdehyde and hydrogen peroxide concentrations. Moreover, we showed that OsMYB2 interacts with the promoter of OsANT1 and promotes its expression. Overexpression of OsMYB2 also improved tillering, yield, and salt tolerance in rice. In conclusion, our results suggest that the transcription factor OsMYB2 triggers OsANT1 expression and regulates growth and salt tolerance in rice, providing insights into the role of the abscisic acid signaling pathway in the regulatory mechanism of AATs in response to salt stress.

A plant endophytic bacterium Burkholderia seminalis strain 869T2 increases plant growth under salt stress by affecting several phytohormone response pathways

BACKGROUND

Due to global warming and gradual climate change, plants are subjected to a wide range of environmental stresses, adversely affecting plant growth and production worldwide. Plants have developed various mechanisms to overpower these abiotic stresses, including salt stress, drought, and high light intensity. Apart from their own defense strategies, plants can get help from the beneficial endophytic bacteria inside host plants and assist them in enduring severe growth conditions. A previously isolated plant endophytic bacteria, Burkholderia seminalis 869T2, from vetiver grass can produce auxin, synthesize siderophore, and solubilize phosphate. The B. seminalis 869T2 can colonize inside host plants and increase the growth of bananas, Arabidopsis, and several leafy vegetables.

RESULTS

We further demonstrated that different growth parameters of Arabidopsis and pak choi plants were significantly increased after inoculating the B. seminalis 869T2 under normal, salt, and drought stress conditions compared to the mock-inoculated plants. Both transcriptome analysis and quantitative real-time PCR results showed that expression levels of genes related to phytohormone signal transduction pathways, including auxin, gibberellin, cytokinin, and abscisic acid were altered in Arabidopsis plants after inoculated with the strain 869T2 under salt stress, in comparison to the mock-inoculated control with salt treatments. Furthermore, the accumulation levels of hydrogen peroxide (H2O2), electrolyte leakage (EL), and malondialdehyde (MDA) were lower in the 869T2-inoculated Arabidopsis and pak choi plants than in control plants under salt and drought stresses.

CONCLUSIONS

The plant endophytic bacterium strain B. seminalis 869T2 may affect various phytohormone responses and reduce oxidative stress damage to increase salt and drought stress tolerances of host plants.

Redefining the role of sodium exclusion within salt tolerance

Salt contamination of soils and irrigation water is a significant environmental concern for crop production. Leaf sodium (Na+) exclusion is commonly proposed to be a key subtrait of salt tolerance for many crop plants. High-Affinity Potassium (K+) Transporter 1 (HKT1) proteins have previously been identified as major controllers of leaf Na+ exclusion across diverse species. However, leaf Na+ exclusion does not always correlate with salt tolerance. We discuss literature which shows leaf Na+ accumulation can, in some circumstances, be tolerated without a detrimental effect on yield when HKT1 still functions to exclude Na+ from reproductive tissues. We conclude that, by having an ultimate role in the protection of reproductive performance, HKT1s' role in adaptation to salinity warrants redefinition.

Tissue-Specific Regulation of Vesicular Trafficking Mediated by Rab-GEF Complex MON1/CCZ1 From Solanum chilense Increases Salt Stress Tolerance in Arabidopsis thaliana

Salt stress constrains the development and growth of plants. To tolerate it, mechanisms of endocytosis and vacuolar compartmentalization of Na+ are induced. In this work, the genes that encode a putative activator of vesicular trafficking called MON1/CCZ1 from Solanum chilense, SchMON1 and SchCCZ1, were co-expressed in roots of Arabidopsis thaliana to determine whether the increase in prevacuolar vesicular trafficking also increases the Na+ compartmentalization capacity and tolerance. Initially, we demonstrated that both SchMON1 and SchCCZ1 genes rescued the dwarf phenotype of both A. thaliana mon1-1 and ccz1a/b mutants associated with the loss of function, and both proteins colocalized with their functional targets, RabF and RabG, in endosomes. Transgenic A. thaliana plants co-expressing these genes improved salt stress tolerance compared to wild type plants, with SchMON1 contributing the most. At the sub-cellular level, co-expression of SchMON1/SchCCZ1 reduced ROS levels and increased endocytic activity, and number of acidic structures associated with autophagosomes. Notably, greater Na+ accumulation in vacuoles of cortex and endodermis was evidenced in the SchMON1 genotype. Molecular analysis of gene expression in each genotype supported these results. Altogether, our analysis shows that root activation of prevacuolar vesicular trafficking mediated by MON1/CCZ1 emerges as a promising physiological molecular mechanism to increase tolerance to salt stress in crops of economic interest.

Comparative transcriptome and metabolome analysis reveals the differential response to salinity stress of two genotypes brewing sorghum

Salinity tolerance in brewing sorghum is a very important trait, especially in areas that are affected by soil salinity. In order to elucidate the mechanism underlying salt tolerance, we conducted a comparative analysis of the transcriptome and metabolome in two distinct sweet sorghum genotypes, namely the salt-tolerant line NY1298 and the salt-sensitive line MY1176, following exposure to salt treatment. Our initial findings indicate the presence of genotype-specific responses in brewing sorghum under salt stress conditions. Notably, there were variations in the expression of genes and metabolites among different genotypes in response to high-salt stress. Specifically, certain transcription factors belonging to the WRKY, MYB, and NAC families were identified as being involved in the response to increased external salinity. WGCNA analysis identified stage-specific gene expression for different salinity gradients in each cultivar, and explored the gene function by KEGG enrichment analysis. Combined analysis of DEGs and DEMs in hormone synthesis found AUX/IAA, SAUR, CRE1, A-ARR, PP2C, SNRK2 genes, and 3-indoleacetic acid and jasmonic acid were evidently differential expression among different salt concentrations. Taken together, our study carried out a comprehensive overview of two genotypes of brewing sorghum gene and metabolite expression differences in response to salt stress, and expanded the understanding of responsive mechanism of brewing sorghum to salt stress.

Correlation analysis of transcriptome and metabolomics and functional study of Galactinol synthase gene (VcGolS3) of blueberry under salt stress

Soil salinity poses a significant environmental challenge for the growth and development of blueberries. However, the specific mechanisms by which blueberries respond to salt stress are still not fully understood. Here, we employed a comprehensive approach integrating physiological, metabolomic, and transcriptomic analyses to identify key metabolic pathways in blueberries under salt stress. Our findings indicate that blueberries primarily adapt to salt stress by modulating pathways associated with carbohydrate metabolism, organic acid metabolism, amino acid metabolism, and various organic compounds. Key metabolites involved in this response include sucrose, propionic acid, and palmitic acid. A total of 241 transcription factors were differentially expressed, with significant involvement from families such as AP2, Dof, GATA, WRKY, and TCP. Notably, the galactose metabolism pathway was associated with 5 DAMs and 24 DEGs, while the starch and sucrose metabolism pathway contained 5 DAMs and 23 DEGs, highlighting their crucial roles in mitigating salt stress. Overexpression of VcGolS3 in transgenic Arabidopsis conferred tolerance to salt and drought stresses, primarily evidenced by a significant increase in GolS enzyme activity and reduced ROS accumulation. This study provides valuable insights into the molecular mechanisms underlying the blueberry response to salt stress and lays the groundwork for breeding salt- and drought-tolerant blueberry varieties.

Application of Synthetic Microbial Communities of Kalidium schrenkianum in Enhancing Wheat Salt Stress Tolerance

Soil salinization poses a significant challenge to global agriculture, particularly in arid and semi-arid regions like Xinjiang. Kalidium schrenkianum, a halophytic plant adapted to saline-alkaline conditions, harbors endophytic microorganisms with potential plant growth-promoting properties. In this study, 177 endophytic bacterial strains were isolated from K. schrenkianum, and 11 key strains were identified through functional screening based on salt tolerance, nutrient solubilization, and growth-promoting traits. Synthetic microbial communities (SMCs) were then constructed using these strains and optimized to enhance wheat growth under salt stress. The SMCs significantly improved seed germination, root length, and seedling vigor in both spring and winter wheat in hydroponic and pot experiments. Furthermore, the SMCs enhanced the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and levels of malondialdehyde (MDA) and proline (PRO). They also reduced oxidative stress and improved chlorophyll content in wheat seedlings. These results demonstrate the potential of microbial consortia derived from extreme environments as eco-friendly biofertilizers for improving crop performance in saline soils, offering a sustainable alternative to chemical fertilizers and contributing to agricultural resilience and productivity.

Arbuscular mycorrhizal fungi and salinity stress mitigation in plants

In recent decades, climate change has caused a decrease in rainfall, increasing sea levels, temperatures rising, and as a result, an expansion in salt marshes across the globe. An increase in water and soil salinity has led to a decline in the cultivated areas in different areas, and consequently, a substantial decrease in crop production. Therefore, it has forced scientists to find cheap, effective and environmentally friendly methods to minimize salinity's impact on crops. One of the best strategies is to use beneficial soil microbes, including arbuscular mycorrhizal fungi, in order to increase plant tolerance to salt. The findings of this review showed that salinity can severely impact the morphological, physiological, and biochemical structures of plants, lowering their productivity. Although plants have natural capabilities to deal with salinity, these capacities are limited depending on plant type, and variety, as well as salinity levels, and other environmental factors. Furthermore, result of the present review indicates that arbuscular mycorrhizal fungi have a significant effect on increasing plant resistance in saline soils by improving the soil structure, as well as stimulating various plant factors including photosynthesis, antioxidant defense system, secondary metabolites, absorption of water and nutrients.

Application of Trichoderma harzianum enhances salt tolerance and yield of Indian mustard through increasing antioxidant enzyme activity

Growth and yield reduction of crops due to salt stress have become a serious issue worldwide. Trichoderma is very well known as a plant growth-promoting fungi under abiotic stress conditions. Therefore, this study was designed to investigate the effect of Trichoderma harzianum on the growth, yield, nutrient uptake, and antioxidant activity of three Indian mustard genotypes under saline condition (EC 9.28 dS m-1). A two-factorial (Trichoderma and Indian mustard genotypes) pot experiment was conducted following a completely randomized design (CRD) with four replicates. Trichoderma was applied to soil as compost and suspension. The BD-7104 genotype showed better performance than Tori-7 under saline conditions. Compared to control, application of T. harzianum showed better performance in enhancing growth and yield of all the genotypes by increasing plants' tolerance to salt stress. Again, Trichoderma application increased the chlorophyll, proline, and oil content of Indian mustard. The generation of antioxidant enzymes viz., SOD, CAT, APX, and POD was significantly increased and, synthesis of H2O2 and MDA was decreased to a variable degree under different Trichoderma treatments. On average, application of Trichoderma as compost enhanced seed yield by 23 % than control. The better growth and yield in Trichoderma treated plants were the results of better uptake and assimilation of N, P, S, Ca, Mg, and K and reduced uptake of Na with a lower Na/K. Overall, BD-7104 genotype can be grown in soil treated with Trichoderma as compost at a rate of TdC12.5 for obtaining better yield and nutritional quality under salinity stress condition.

Ion homeostasis and coordinated salt tolerance mechanisms in a barley (Hordeum vulgare L.)doubled haploid line

Salinization poses a significant challenge in agriculture. Identifying salt-tolerant plant germplasm resources and understanding their mechanisms of salt tolerance are crucial for breeding new salt-tolerant plant varieties. However, one of the primary obstacles to achieving this goal in crops is the physiological complexity of the salt-tolerance trait. In a previous study, we developed a salt-tolerant barley doubled haploid (DH) line, designated as DH20, through mutagenesis combined with microspore culture, establishing it as an idea model for elucidating the mechanisms of salt tolerance. In this study, ion homeostasis, key osmotic agents, antioxidant enzyme activities and gene expression were compared between Hua30 (the original material used as a control) and DH20. The results indicated that under salt treatment, DH20 exhibited significantly higher shoot fresh and dry weight, relative plant height, shoot K+/Na+ ratio, improved stomatal guard cell function, and better retention of chloroplast ultrastructure compared to Hua30. Notably, the K+ efflux in DH20 was significantly lower while the Na+ and H+ efflux was significantly higher than those in Hua30 under salt stress in mesophyll cells. Furthermore, the activities of ascorbate peroxidase, superoxide dismutase, and peroxidase, along with the levels of proline, betaine, malondialdehyde, and soluble protein, were correlated with ion efflux and played a vital role in the response of DH20 to salt stress. Compared to Hua30, the relative expression levels of the HvSOS1, HvSOS2, HvSOS3, HvHKT1;3, HvNHX1, HvNHX2, and HvNHX3 genes, which showed a strong correlation with Na+, K+, and H+ efflux, exhibited significant differences at 24 h under salt stress in DH20. These findings suggest that ion homeostasis, key osmolytes, antioxidant enzyme activities, and associated gene expression are coordinated in the salt tolerance of DH20, with K+ retention and Na+ and H+ efflux serving as important mechanisms for coping with salt stress. These findings present new opportunities for enhancing salinity tolerance, not only in barley but in other cereals as well, including wheat and rice, by integrating this trait with other traditional mechanisms. Furthermore, MIFE measurements of NaCl-induced ion fluxes from leaf mesophyll provide plant breeders with an efficient method to screen germplasm for salinity stress tolerance in barley and potentially other crops. Clinical trial number: Not applicable.

Pan-genome analyses of 11 Fraxinus species provide insights into salt adaptation in ash trees

Ash trees (Fraxinus) exhibit rich genetic diversity and wide adaptation to various ecological environments, and several species are highly salt tolerant. Dissecting the genomic basis of salt adaptation in Fraxinus is vital for its resistance breeding. Here, we present 11 high-quality chromosome-level genome assemblies for Fraxinus species, which reveal two unequal subgenome compositions and two recent whole-genome triplication events in their evolutionary history. A Fraxinus pan-genome was constructed on the basis of structural variations and revealed that presence-absence variations (PAVs) of transmembrane transport genes have likely contributed to salt adaptation in Fraxinus. Through whole-genome resequencing of an F1 population from an interspecies cross of F. velutina 'Lula 3' (salt tolerant) with F. pennsylvanica 'Lula 5' (salt sensitive), we mapped salt-tolerance PAV-based quantitative trait loci (QTLs) and pinpointed two PAV-QTLs and candidate genes associated with Fraxinus salt tolerance. Mechanistically, FvbHLH85 enhances salt tolerance by mediating reactive oxygen species and Na+/K+ homeostasis, whereas FvSWEET5 enhances salt tolerance by mediating osmotic homeostasis. Collectively, these findings provide valuable genomic resources for Fraxinus salt-resistance breeding and the research community.

The dual-action evolutionarily conserved NatB catalytic subunit NAA20 regulates poplar root development in response to salt and osmotic stresses

In Populus simonii, the N-terminal acetyltransferase subunit gene PsiNAA20 was induced by salt stress and osmotic stress and regulates root development. The spatiotemporal specificity of PsiNAA20-interacting gene expression and translation efficiency suggested dual functions in poplar root development under salt stress and osmotic stress.

Trade-Off Between Enzymatic Antioxidant Defense and Accumulation of Organic Metabolite Affects Salt Tolerance of White Clover Associated with Redox, Water, and Metabolic Homeostases

White clover (Trifolium repens) is an excellent perennial cold-season ground-cover plant for municipal landscaping and urban greening. It is, therefore, widely distributed and utilized throughout the world. However, poor salt tolerance greatly limits its promotion and application. This study aims to investigate the difference in the mechanism of salt tolerance in relation to osmotic adjustment, enzymatic and nonenzymatic antioxidant defenses, and organic metabolites remodeling between salt-tolerant PI237292 (Trp004) and salt-sensitive Korla (KL). Results demonstrated that salt stress significantly induced chlorophyll loss, water imbalance, and accumulations of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2.-), resulting in reduced cell membrane stability in two types of white clovers. However, Trp004 maintained significantly higher leaf relative water content and chlorophyll content as well as lower osmotic potential and oxidative damage, compared with KL under salt stress. Although Trp004 exhibited significantly lower activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, monodehydroasorbate reductase, dehydroascorbate reductase, and glutathione reductase than KL in response to salt stress, significantly higher ascorbic acid (ASA), dehydroascorbic acid (DHA), glutathione (GSH), glutathione disulfide (GSSG), ASA/DHA, and GSH/GSSG were detected in Trp004. These findings indicated a trade-off relationship between antioxidant enzymes and nonenzymatic antioxidants in different white clover genotypes adapting to salt stress. In addition, Trp004 accumulated more organic acids (glycolic acid, succinic acid, fumaric acid, malic acid, linolenic acid, and cis-sinapic acid), amino acids (serine, l-allothreonine, and 4-aminobutyric acid), sugars (tagatose, fructose, glucoheptose, cellobiose, and melezitose), and other metabolites (myo-inositol, arabitol, galactinol, cellobiotol, and stigmasterol) than KL when they suffered from the same salt concentration and duration of stress. These organic metabolites helped to maintain osmotic adjustment, energy supply, reactive oxygen species homeostasis, and cellular metabolic homeostasis with regard to salt stress. Trp004 can be used as a potential resource for cultivating in salinized soils.

Zinc oxide nanoparticles foliar use and arbuscular mycorrhiza inoculation retrieved salinity tolerance in Dracocephalum moldavica L. by modulating growth responses and essential oil constituents

The production of medicinal plants under stressful environments offers an alternative to meet the requirements of sustainable agriculture. The action of mycorrhizal fungus; Funneliformis mosseae and zinc in stimulating growth and stress tolerance in medicinal plants is an intriguing area of research. The current study evaluated the combined use of nano-zinc and mycorrhizal fungus on the physiochemical responses of Dracocephalum moldavica under salinity stress. The study employed a factorial based on a completely randomized design with three replications. The treatments were different levels of salinity (0, 50, and 100 mM NaCl), two levels of mycorrhiza application (0 and 5 g kg- 1 of soil), and two levels of foliar spraying of nano zinc oxide (0 and 1000 ppm). Salinity decreased the photosynthetic pigments content, SPAD value, and chlorophyll fluorescence data (Fm, Fv, Fv/Fm). Plant dry weight, Na+ content, and essential oil content were significantly higher at 50 mM salinity + co-application of mycorrhiza and nano zinc oxide. Electrolyte leakage increased under salt stress, while mycorrhizal inoculation compensated for the trait. The main essential oil constituents were geranyl acetate, nerol, geranial, geraniol, viridiflorol, hexadecane, humulene, and germacrene D. Energy metabolism demonstrates the effectiveness of treatment combinations in promoting the biosynthesis and accumulation of essential oil components. The overall results with more comprehensive field-based studies would be advisable for the extension section to utilize marginal salty lands for the reliable production of a valuable medicinal plant.

ABA-activated low-nanomolar Ca2+-CPK signalling controls root cap cycle plasticity and stress adaptation

Abscisic acid (ABA) regulates plant stress adaptation, growth and reproduction. Despite extensive ABA-Ca2+ signalling links, imaging ABA-induced increases in Ca2+ concentration has been challenging, except in guard cells. Here we visualize ABA-triggered [Ca2+] dynamics in diverse organs and cell types of Arabidopsis thaliana using a genetically encoded Ca2+ ratiometric sensor with a low-nanomolar Ca2+-binding affinity and a large dynamic range. The subcellular-targeted Ca2+ ratiometric sensor reveals time-resolved and unique spatiotemporal Ca2+ signatures from the initial plasma-membrane nanodomain, to cytosol, to nuclear oscillation. Via receptors and sucrose-non-fermenting1-related protein kinases (SnRK2.2/2.3/2.6), ABA activates low-nanomolar Ca2+ transient and Ca2+-sensor protein kinase (CPK10/30/32) signalling in the root cap cycle from stem cells to cell detachment. Surprisingly, unlike the prevailing NaCl-stimulated micromolar Ca2+ spike, salt stress induces a low-nanomolar Ca2+ transient through ABA signalling, repressing key transcription factors that dictate cell fate and enzymes that are crucial to root cap maturation and slough. Our findings uncover ABA-Ca2+-CPK signalling that modulates root cap cycle plasticity in adaptation to adverse environments.

Revisiting the role of light signaling in plant responses to salt stress

As one of the grave environmental hazards, soil salinization seriously limits crop productivity, growth, and development. When plants are exposed to salt stress, they suffer a sequence of damage mainly caused by osmotic stress, ion toxicity, and subsequently oxidative stress. As sessile organisms, plants have developed many physiological and biochemical strategies to mitigate the impact of salt stress. These strategies include altering root development direction, shortening the life cycle, accelerating dormancy, closing stomata to reduce transpiration, and decreasing biomass. Apart from being a prime energy source, light is an environmental signal that profoundly influences plant growth and development and also participates in plants' response to salt stress. This review summarizes the regulatory network of salt tolerance by light signals in plants, which is vital to further understanding plants' adaptation to high salinity. In addition, the review highlights potential future uses of genetic engineering and light supplement technology by light-emitting diode (LED) to improve crop growth in saline-alkali environments in order to make full use of the vast saline land.

MsMYB206-MsMYB450-MsHY5 complex regulates alfalfa tolerance to salt stress via regulating flavonoid biosynthesis during the day and night cycles

Flavonoids are the major secondary metabolites participating in many biological processes of plants. Although flavonoid biosynthesis has been extensively studied, its regulatory mechanisms during the day and night cycles remain poorly understood. In this study, three proteins, MsMYB206, MsMYB450, and MsHY5, were found to interact with each other, in which MsMYB206 directly transactivated two flavonoid biosynthetic genes, MsFLS and MsF3'H. The expression patterns of MsMYB206, MsMYB450, MsFLS, and MsF3'H were fully consistent at regular intervals across day/night cycles that were higher at night than in the daytime. On the contrary, both gene expression levels and protein contents of MsHY5 increased in the daytime but decreased at night, and the lower expression of MsHY5 at night led to strengthened interaction between MsMYB206 and MsMYB450. The MsMYB206-overexpression plants were more salt-tolerant and their flavonoid contents were higher than the WT during the day/night cycles. This study revealed one mechanism interpreting the fluctuating flavonoid contents during day/night cycles regulated by the MsMYB206/MsMYB450/MsHY5-MsFLS/MsF3'H module that also contributed to salt tolerance in alfalfa.

Characterization of the wall-associated kinase (WAK) gene family in Gossypium barbadense reveals the positive role of GbWAK5 in salt tolerance

KEY MESSAGE

We characterized the WAK gene family in Gossypium barbadense and revealed the potential function of GbWAK5 in regulating salt tolerance by modulating ion homeostasis. Soil salinization is one of the main factors restricting cotton production. Although the role of the wall-associated kinases (WAKs) in plants has been extensively studied, its response to salt stress in sea-island cotton (Gossypium barbadense L.) has not been reported. Here, we conducted a whole-genome analysis of the WAK gene family in G. barbadense, identifying a total of 70 GbWAK genes, which were classified into five clades. Segmental and tandem duplication events have contributed to the expansion of the GbWAK gene family. A large number of cis-acting elements were predicted in the GbWAK promoter region. Through RNA sequencing, 37 GbWAKs that potentially play a role in cotton's response to salt stress were screened out, among which 10 genes with sustained up-regulated expression were confirmed by quantitative real-time PCR (qRT-PCR). GbWAK5, a member of Clade II, was significantly up-regulated following NaCl treatment and exhibited a typical WAK structure. Subcellular localization indicated that GbWAK5 is localized on the plasma membrane. Virus-induced gene silencing (VIGS) experiments revealed that the knockdown of GbWAK5 resulted in more severe dehydration and wilting in plants compared to the control under NaCl treatment. RNA-seq analysis revealed that several ion transport-related genes were down-regulated in TRV:GbWAK5 plants under salt stress, while TRV:GbWAK5 plants accumulated more Na+ and exhibited a higher Na+/K+ ratio compared to TRV:00 plants. These results offer a comprehensive analysis of the G. barbadense WAK gene family for the first time, and conclude that GbWAK5 is a promising gene for improving cotton's resistance to salt stress.

The GRAS transcription factor OsGRAS2 negatively impacts salt tolerance in rice

KEY MESSAGE

Transcription factor OsGRAS2 regulates salt stress tolerance and yield in rice. Plant-specific GRAS transcription factors are involved in many different aspects of plant growth and development, as well as in biotic and abiotic stress responses, although whether and how they participate in salt stress tolerance in rice (Oryza sativa) remains unclear. A screen of a previously generated set of activation-tagged lines revealed that Activation Tagging Line 63 (AC63) displayed a salt stress-sensitive phenotype. Subsequent thermal asymmetric interlace polymerase chain reaction (TAIL-PCR) showed that AC63 was due to overexpression of OsGRAS2. Ectopic overexpression of OsGRAS2 caused increased salt stress sensitivity, while osgras2 loss-of-function lines displayed salt stress-resistant phenotypes. Further, we observed that OsGRAS2 impacts Na+ and K+ ion homeostasis in the shoots. Mutation of OsGRAS2 increased salt tolerance without yield penalty. Phylogenetic tree analysis indicated that OsGRAS2 belonged to the LISCL subfamily of GRAS transcription factors and had high amino acid similarity to OsGRAS23. Both OsGRAS2 and OsGRAS23 underwent homomeric and heteromeric interactions, indicating that they formed homo- and hetero-dimers. Moreover, OsGRAS2 and OsGRAS23 showed transcriptional activation activity that was mostly governed by motif1, which was located at the N-terminal region. Further, we found OsGRAS2 binds to the OsWRKY53 promoter to increase its expression, thereby negatively impacting the OsHKT1;5 expression. This study demonstrates a novel insight into how LISCL subfamily GRAS transcription factors impact salt stress tolerance in rice.

Integrated Analysis of Metatranscriptome and Amplicon Sequencing to Reveal Distinctive Rhizospheric Microorganisms of Salt-Tolerant Rice

Salt stress poses a significant constraint on rice production, so further exploration is imperative to elucidate the intricate molecular mechanisms governing salt tolerance in rice. By manipulating the rhizosphere microbial communities or targeting specific microbial functions, it is possible to enhance salt tolerance in crops, improving crop yields and food security in saline environments. In this study, we conducted rice rhizospheric microbial amplicon sequencing and metatranscriptome analysis, revealing substantial microbiomic differences between the salt-tolerant rice cultivar TLJIAN and the salt-sensitive HUAJING. Fungal taxa including Hormiactis, Emericellopsis, Ceriosporopsis, Dirkmeia, and Moesziomyces predominated in the rhizosphere of salt-tolerant rice, while bacterial genera such as Desulfoprunum and Hydrogenophaga exhibited notable differences. Metatranscriptomic analysis identified 7192 differentially expressed genes (DEGs) in the two rice varieties, with 3934 genes being upregulated and 3258 genes being downregulated. Enrichment analyses in KEGG and GO pathways highlighted the majority of DEGs were associated with the "two-component system", "sulfur metabolism", and "microbial metabolism in diverse environments". The interaction network of DEGs and microbial taxa revealed upregulation of transporters, transcriptional factors, and chaperones, such as ABC transporters and chaperonin GroEL, in the rhizosphere microbiomes of salt-tolerant varieties. Our multi-omics network analysis unveiled that fungi like Ceriosporopsis and Dirkmeria, along with bacteria such as Desulfoprunum, Rippkaea, and Bellilinea, showed a positive correlation with flavonoid synthesis in salt-tolerant rice. This study provides an in-depth exploration of the distinctive microbial communities associated with the rhizosphere of salt-tolerant rice varieties, shedding light on the complex interactions between these microbial consortia and their host plants under stress conditions.

Physiological, Photosynthetic Characteristic and Transcriptome Analysis of PsnWRKY70 Transgenic Populus simonii × Populus nigra Under Salt Stress

The PsnWRKY70 transcription factor (TF) was reported to play an important role in the salt stress response mechanism of Populus simonii × Populus nigra in our previous research, and we also produced several PsnWRKY70 overexpression (OEXs) and RNAi suppression (REXs) P. simonii × P. nigra lines. In order to further compare the photosynthetic and physiological characteristics of NT (non-transgenic line) and transgenic lines under salt stress, the dynamic phenotypic change, Na+ and K+ content in leaf and root tissues, superoxide dismutase (SOD) and peroxidase (POD) activity, malondialdehyde (MDA) content, chlorophyll content (Chl), photosynthesis parameters (net photosynthetic rate, Pn; stomatal conductance, Gs; intercellular CO2 concentration, Ci; transpiration rate, Tr), chlorophyll fluorescence parameters (electron transport rate, ETR; maximum photochemical efficiency of photosystem II (PSII), Fv/Fm; actual efficiency of PSII, ΦPSII; photochemical quenching coefficient, qP; non-photochemical quenching, NPQ; the photosynthetic light-response curves of ΦPSII and ETR) and RNA-seq of NT, OEX and REX lines were detected and analyzed. The phenotypic observation, MDA content and Chl detection results indicate that the stress damage of REXs was less severe than that of NT and OEX lines under salt stress. Photosynthesis parameter (Pn, Gs, Tr and Ci) and chlorophyll fluorescence parameter (ETR, Fv/Fm, ΦPSII qP and NPQ) detection results indicate that the REX lines exhibited much better photosynthetic adaptability than NT and OEX lines during salt stress. The photosynthetic light-response curves of ΦPSII and ETR of NT, OEX and REX lines indicate that REXs exhibited better ability to activate the photosynthetic protection mechanism and adapt to a certain degree of strong light than NT and OEX lines under salt stress. RNA-seq analysis indicates that the DEGs between OEX1 vs. NT and REX1 vs. NT in different tissues (apical bud and fifth functional leaf) were all different in category and change trend. The expression of PsnWRKY70 was significantly up-regulated in both the apical bud and fifth functional leaf of OEX1, and showed no significant change (namely maintained low expression level) in both the apical bud and fifth functional leaf of REX1, thus indicating the negative regulation role of PsnWRKY70 in P. simonii × P. nigra under salt stress. Additionally, there were a lot of stress response-related TF genes (such as bHLH, WRKY, MYB, NAM and AP2/EREBP) and photosynthesis-related genes among all the DEGs. In REX1, the expression of three Photosystem I P700 chlorophyll a apoprotein A1 genes (Potri.003G065200, Potri.013G141800 and Potri.019G028100) and a Photosystem II protein D1 gene (Potri.013G138300) were significantly up-regulated after 6 days of salt stress. In OEX1, the Heterodimeric geranylgeranyl pyrophosphate synthase small subunit gene (Potri.015G043400) and Phospho-2-dehydro-3-deoxyheptonate aldolase 1 gene (Potri.007G095700) were significantly down-regulated after 6 days of salt stress. These photosynthesis-related genes are probably regulated by PsnWRKY70 TF in response to salt stress. In conclusion, the REX lines suffered less severe salt damage and exhibited better photosynthetic adaptability than NT and OEXs under salt stress. The differences among the DEGs between OEX1 vs. NT and REX1 vs. NT in apical bud and fifth functional leaf, and the significantly differentially expressed photosynthesis-related genes are probably the key clues for discovering the photosynthesis adaptability mechanism of PsnWRKY70 transgenic P. simonii × P. nigra under salt stress.

CALMODULIN-BINDING RECEPTOR-LIKE CYTOPLASMIC KINASE 3 regulates salt tolerance through CATALASE 2 in Arabidopsis

Soil salinization threatens global crop production. Here, we report that a receptor-like cytoplasmic kinase, CALMODULIN-BINDING RECEPTOR-LIKE CYTOPLASMIC KINASE 3 (CRCK3), plays an essential role in plant salt tolerance via CATALASE 2 (CAT2), a hydrogen peroxide (H2O2)-scavenging enzyme in Arabidopsis (Arabidopsis thaliana). CRCK3 was induced by salt stress, and its knockout mutant displayed a salt-sensitive phenotype compared with wild-type plants. CRCK3 was activated by salt stress in a calcium-dependent manner, and its kinase activity was required for plant salt tolerance. CRCK3 physically interacted with CAT2, and CRCK3-mediated salt tolerance depended on CAT2. Salt treatment significantly induced CAT2 phosphorylation via the action of CRCK3, and this phosphorylation was required for CAT2-mediated H2O2 scavenging to reduce reactive oxygen species (ROS) content and oxidative damage in plants under saline conditions. CRCK3 phosphorylated CAT2 at the Thr209 residue, resulting in elevated catalase activity to reduce ROS accumulation under saline conditions. Therefore, the CRCK3-CAT2 module mediates plant salt tolerance by maintaining redox homeostasis. This study expands our knowledge of how plants respond to salt stress.

Rooting for survival: how plants tackle a challenging environment through a diversity of root forms and functions

The current climate crisis has global impacts and will affect the physiology of plants across every continent. Ensuring resilience of our agricultural and natural ecosystems to the environmental stresses imposed by climate change will require molecular insight into the adaptations employed by a diverse array of plants. However, most current studies continue to focus on a limited set of model species or crops. Root systems are particularly understudied even though their functions in water and nutrient uptake are likely pivotal for plant stress resilience and sustainable agriculture. In this review, we highlight anatomical adaptations in roots that enable plant survival in different ecological niches. We then present the current state of knowledge for the molecular underpinnings of these adaptations. Finally, we identify areas where future research using a biodiversity approach can fill knowledge gaps necessary for the development of climate-resilient crops of the future.

Integrated metabolomic and transcriptomic analysis reveals the role of root phenylpropanoid biosynthesis pathway in the salt tolerance of perennial ryegrass

Perennial ryegrass (Lolium perenne) is a widely cultivated forage and turf grass species. Salt stress can severely damage the growth of grass plants. The genome-wide molecular mechanisms of salt tolerance have not been well understood in perennial grass species. In this study, the salt sensitive genotype P1 (PI265351, Chile) and the salt tolerant genotype P2 (PI368892, Algeria) of perennial ryegrass were subjected to 200 mM NaCl, and transcriptomics and metabolomics analyses were performed. A total of 5,728 differentially expressed genes (DEGs) were identified through pairwise comparisons. Antioxidant enzyme encoding genes (LpSOD1, LpCAT1), ion channel gene LpCaC1 and transcription factors (LpERFs, LpHSF1 and LpMYB1) were significantly upregulated in P2, suggesting their involvement in regulating expression of salt-responsive genes for salt tolerance. Functional analysis of DEGs revealed that biosynthesis of secondary metabolites, carbohydrate metabolism and signal transduction were the main pathways in response to salt stress. Weighted gene co-expression network analysis (WGCNA) based on RNA-Seq data showed that membrane transport and ABC transporters were significantly correlated with salt tolerance-related traits. The combined transcriptomics and metabolomics analysis demonstrated that the phenylpropanoid biosynthesis pathway was a major secondary metabolic pathway in the salt response of perennial ryegrass. Especially, the tolerant genotype P2 had greater amounts of upregulated phenylpropanoids, flavonoids and anthocyanins and higher expressions of relevant genes in the pathway than the sensitive genotype P1, indicating a role of phenylpropanoid biosynthesis for perennial ryegrass to adapt to salt stress. The results provided insights into the molecular mechanisms of perennial ryegrass adaptation to salinity and laid a base for genetic improvement of salt tolerance in perennial grass species.

Characterization of the PaHAK Gene and Its Expression During the In Vitro Seed Germination of Two Botanical Avocado Varieties Under Saline Stress

Soil salinity is one of the main challenges that modern agriculture faces. Avocado, which is classified as a glycophyte, is very sensitive to salt stress. There are botanical varieties of avocado that differ in their salt tolerance. This study investigated how salt stress affects the in vitro germination of two avocado botanical varieties americana (West Indian breed) and drymifolia (Mexican native) with different salt tolerances. This study also assessed the potential role of the avocado PaHAK2 high-affinity K+ transporter HAK/KUP/KT in response to saline stress during germination. Salinity (60 mM NaCl) delayed the germination speed of the drymifolia variety relative to the americana variety. A computational 3D inference protein model of the PaHAK2 protein showed 10 highly conserved transmembrane domains. During the imbibition period, there was a differential increase in the expression of the PaHAK2 gene at 60 mM NaCl in both varieties, which suggests the presence of osmotic adjustment and regulation. The enhanced expression of PaHAK2 in the americana variety suggests an adaptive advantage to salinity. We conclude that PaHAK2 participates in the response of avocado to salt stress during seed germination.

Integrated Transcriptomic, Proteomic, and Metabolomic Analyses Revealed Molecular Mechanism for Salt Resistance in Soybean (Glycine max L.) Seedlings

Salt stress poses a significant challenge to plant growth and restricts agricultural development. To delve into the intricate mechanisms involved in soybean's response to salt stress and find targets to improve the salt resistance of soybean, this study integrated transcriptomic, proteomic, and metabolomic analyses to explore the regulatory networks involved in soybean salt tolerance. Transcriptomic analysis revealed significant changes in transcription factors, hormone-related groups, and calcium ion signaling. Notably, the biosynthetic pathways of cutin, suberine, and wax biosynthesis play an important role in this process. Proteomic results indicated salt-induced DNA methylation and the enrichment of phosphopyruvate hydrase post-salt stress, as well as its interaction with enzymes from various metabolic pathways. Metabolomic data unveiled the synthesis of various metabolites, including lipids and flavonoids, in soybean following salt stress. Furthermore, the integrated multiomics results highlighted the activation of multiple metabolic pathways in soybean in response to salt stress, with six pathways standing out prominently: stilbenoid, diarylheptanoid, and gingerol biosynthesis; carotenoid biosynthesis; carbon fixation in photosynthetic organisms; alanine, aspartate, and glutamate metabolism; thiamine metabolism; and pyruvate metabolism. These findings not only offer valuable insights into leveraging multiomics profiling techniques for uncovering salt tolerance mechanisms but also identify candidate genes for soybean improvement.

SlNAC12, a novel NAC-type transcription factor, confers salt stress tolerance in tomato

KEY MESSAGE

SlNAC12 enhances salt stress tolerance of transgenic tomato by regulating ion homeostasis, antioxidant activity and flavonoids biosynthesis Soil salinization is a major environmental factor that adversely affects plant growth and development. NAC (NAM, ATAF1/2, and CUC2) is a large family of plant-specific transcription factors that play crucial roles in stress response. Here, we investigated the role of a novel NAC transcription factor, SlNAC12, in conferring salt stress tolerance in tomato (Solanum lycopersicum). Subcellular localization and yeast assays studies revealed that SlNAC12 is localized in the nucleus with weak transcriptional activity. SlNAC12 transcript was induced by salt stress in the leaves and roots of tomato seedlings. Overexpression of SlNAC12 in tomato led to significantly reduced plant height and root length. Transgenic tomato lines overexpressing of SlNAC12 (OE#1 and OE#3) exhibited enhanced tolerance to salinity, as evidenced by reduced the inhibitory effect of growth parameters under salt stress compared to wild type (WT). Overexpression of SlNAC12 in tomato affected Na+ and K+ homeostasis, leading to reduced Na+/K+ ratio, enhanced activity of antioxidant enzymes and decreased reactive oxygen species (ROS) accumulation under salt stress. Furthermore, the transcript levels of several genes involved in flavonoids metabolism and the levels of flavonoids accumulation were increased in SlNAC12-overexpressing tomato lines. Collectively, this study suggests that SlNAC12 transcription factor enhances salt stress tolerance in tomato is correlated with ion homeostasis, antioxidant enzyme systems, and flavonoids accumulation.

Improving grain yield and salt tolerance by optimizing plant height with beneficial haplotypes in rice (Oryza sativa)

INTRODUCTION

Rice (Oryza sativa L.), a staple food for billions worldwide, is challenged by salt stress. Owing to the limited understanding of the physiological and genetic basis of rice salt tolerance, few genes have been identified as valuable in rice breeding, causing a major bottleneck in the development of high-yield, salt-tolerant rice varieties.

OBJECTIVE

This study aims to identify salt tolerance genes/quantitative trait loci (QTLs) with breeding potential in rice.

METHODS

Field trials were conducted with 166 Chinese rice cultivars from saline-affected regions and 412 global rice accessions to assess salt tolerance. Genome-wide association study (GWAS) was performed to identify key loci related to high yield and salt tolerance. Additionally, the impact of introducing beneficial haplotypes on grain yield and salt tolerance was assessed.

RESULTS

The optimal rice plant height of 100-120 cm was crucial for sustaining high yield under both normal and salt stress conditions. GWAS revealed 6 novel QTLs/genes associated with rice plant growth and grain yield across various environments, distinct from previously recognized salt stress-related genes. Notably, the gene PHS10.1, encoding a serine/threonine protein kinase, may regulate carbon metabolism, starch and sucrose metabolism, influencing plant growth and grain yield. Certain haplotypes of the genes regulating plant height and grain yield, including SD1, Ghd7.1, GH3.5, and PHS10.1, were selected in traditional breeding. Moreover, optimizing plant height through the introgression of beneficial alleles of these genes increased grain yield in recipient lines under both normal and saline conditions.

CONCLUSION

We propose that utilizing beneficial haplotypes to optimize plant height can effectively balance the growth-stress trade-offs in rice plants. This represents a promising breeding strategy for the development of crop varieties that are both high-yielding and salt-tolerant.

SaTDT enhanced plant tolerance to NaCl stress by modulating the levels of malic acid and citric acid in cells

The issue of soil salinization is a global concern that significantly impairs crop productivity, quality, and distribution. Tonoplast Dicarboxylate Transporter (TDT) is a pivotal malic acid transporter localized on the vacuolar membrane, involving in maintaining intracellular pH homeostasis in plants. However, the molecular mechanisms and regulatory pathways underlying plant salt tolerance through TDT remain elusive. In this study, we cloned a gene encoding vacuolar membrane dicarboxylic acid transporter designated as SaTDT from the halophyte Spartina alterniflora. Subsequently, its role in regulating salt stress was investigated. The heterologous expression of SaTDT in Arabidopsis thaliana was observed to enhance the transgenic plants' tolerance to salt stress and alleviate the growth damage caused by this stress. The overexpression of SaTDT can simultaneously enhance plant photosynthetic efficiency by regulating the cellular contents of malic acid and citric acid, or by increasing the activity of MDH and PEPC enzymes. It also regulates and balances energy utilization during carbon assimilation under salt-stressed conditions, thereby establishing an energetic foundation for enhancing plant tolerance to stress. SaTDT also has the capacity to enhance the plant cells' ability in regulating antioxidant enzyme activity or osmotic accumulation, thereby playing a crucial role in maintaining intracellular redox homeostasis. In conclusion, our findings establish a foundation basis for elucidating the regulatory role of the SaTDT gene in S.alterniflora's adaptation to high-salinity habitats.

Quantitative N-glycoproteomics characterization of differential N-glycosylation in Sorghum bicolor under salinity stress

Salt stress is one of the significant environmental stresses that severely affect plant growth and development. Here, we report quantitative N-glycoproteomics characterization of differential N-glycosylation in Sorghum bicolor under low, median and high salinity stress. 21,621 intact N-glycopeptides coming from the combination of 127 N-glycan structures on 6574 N-glycosites from 5321 proteins were identified; differential N-glycosylation was observed for 682 N-glycoproteins which are mainly involved in the pathways of biosynthesis of secondary metabolites, biosynthesis of amino acids and several metabolic pathways. 41 N-glycan structures modifying on 338 N-glycopeptides from 122 glycoproteins were co-quantified and deregulated under at least one salt stress, including enzymes of energy production and carbohydrate metabolisms, cell wall organization related proteins, glycosyltransferases and so on. Intriguingly, with increasing salt concentration, there was an increase in the percentage of complex N-glycans on the altered N-glycopeptides. Furthermore, the observation of glycoproteins with distinct salt sensitivity is noteworthy, particularly the upregulated hyposensitive glycoproteins that predominantly undergo complex N-glycan modification. This is the first N-glycoproteome description of salt stress response at the intact N-glycopeptide level in sorghum and a further validation of data reported here would likely provide deeper insights into the stress physiology of this important crop plant.

The evolutive role of shoot apical meristems in the adaptation of angiosperms to life at sea and the jump to potential environmental biotechnology applications

Seagrasses have adapted to a submerged lifestyle in seawater through a complex set of evolutionary processes. However, they show sensitivity to increases in natural salinity levels such as those commonly found in discharges of desalination plants, which have exponentially grown due to water scarcity in highly populated temperate areas, such as the Mediterranean basin. This study assessed the effects of brine-derived hypersalinity on the Mediterranean seagrass Posidonia oceanica, focusing on the metabolic responses of shoot apical meristems (SAMs). Although most physiological and genetic studies have used leaves, SAMs are more directly correlated with plant survival and might be more responsive to salinity stress. The experiments were: a controlled mesocosm of more than six practical salinity units (psu) over natural levels using either artificial salts or desalination brine and field transplantation experiments comparing two sites following the dilution plume of the brine (+5 and + 2 psu) with control. Hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS), and ascorbate were measured to determine oxidative stress and damage, as well as relative expression of genes related to osmotic regulation and oxidative responses. Overall, relative expression of genes related to osmotic regulation (SOS1, SOS3, AKT 2/3) and oxidative stress (STRK1, CAT, MnSOD, FeSOD, APX, GR) was higher in SAMs at higher brine exposures, indicating a more active metabolic response in this organ. Similarly, reactive oxygen species (ROS) production and lipid peroxidation were higher closer to brine discharge and total ascorbate lower, indicating a correlative response with stressor intensity. These findings confirm that SAMs play an essential role in P. oceanica hypersalinity responses and its adaptation to life in the marine environment. Finally, the use of P. oceanica SAMs in this study is highly recommended for an early detection of threats caused by desalination brines that may cause physiological damage and meadow regression.

Characterization of tae-miR156(s) and their response to abiotic stress in wheat (Triticum aestivum L.)

The microRNA156 (miR156) has been widely studied in plants, however, the characterization of the miR156 family of genes in wheat and their expression patterns under abiotic stress are not completely clear. In this study, a total of 20 miR156 family members, referred to as tae-miR156a to tae-miR156t, were identified in wheat with their loci mapped to various chromosomes. These members were divided into five subgroups: miR156a/b/c/d/e/f, miR156g/h/i, miR156j/k, miR156l/m/n/o/p/q, and miR156r/s/t. They were highly conserved during evolution. The prediction of cis-elements in the tae-MIR156(s) promoter region revealed that the tae-MIR156(s) had diverse cis-acting elements; of these, 15 tae-MIR156(s) and 6 tae-MIR156(s) were found to be drought-responsive elements and cold-responsive elements, respectively. And the prediction target genes of tae-miR156(s) are mainly SPL transcription factor genes. Expression analysis based on quantitative real-time polymerase chain reaction (qRT‒PCR) showed that miR156(s) have different expression levels in the various wheat tissues, and the subgroups' response to abiotic stress varied. Among them, miR156g/h/i were strongly induced in the root of cold and heat stress, and miR156a/b/c/d/e/f were significantly increased in roots after drought stress, whereas miR156r/s/t were highly inhibited in leaves and roots after salt stress. These findings imply that tae-miR156(s) are involved in stress response in wheat, and they provide new fundamental knowledge for further analysis of the function of miR156 and its regulatory mechanism in response to abiotic stress.

The varying responses of leaves and roots and the link between sugar metabolic genes and the SWEET family in Dendrobium officinale under salt stress

BACKGROUND

Dendrobium officinale Kimura et Migo is a perennial epiphytic herb in traditional Chinese medicine, showing remarkable resistance to salt stress. Water-soluble sugars serve as important osmoprotectants and play crucial roles in plant stress responses. Previous studies have primarily focused on sugar metabolism in individual tissues under stress, resulting in a limited understanding of the regulatory differences between tissues and the relationship between sugar metabolism and transport.

RESULTS

A variety of salt-responsive genes were identified through transcriptome analysis of D. officinale. GO and KEGG enrichment analyses revealed functional differences among the differentially expressed genes (DEGs) between leaves and roots. Expression analysis indicated that sugar metabolic genes and D. officinale Sugars Will Eventually be Exported Transporters (DoSWEETs) displayed distinct expression patterns in leaves and roots under salt stress. Most sugar metabolic genes were up-regulated in the leaves and down-regulated in the roots in response to salt, while DoSWEETs predominantly responded in the roots. Specifically, DoSWEET2a, 6a, 12a, 14, and 16 were confirmed via RT-qPCR. Additionally, positive correlations were observed between certain genes (scrK, INV, SUS) and DoSWEETs, with INV (LOC110096666) showing a strong positive correlation with all detected DoSWEETs in both leaves and roots.

CONCLUSIONS

Our findings not only illustrated the distinct responses of leaves and roots to salt stress, but also highlighted the relationship between sugar metabolic genes and DoSWEETs in adapting to such stress. This enhances our understanding of the differential responses of plant tissues to salt stress and identified candidate genes for salt-resistance breeding in D. officinale.

Filling the gaps on root hair development under salt stress and phosphate starvation using current evidence coupled with a meta-analysis approach

Population expansion is a global issue, especially for food production. Meanwhile, global climate change is damaging our soils, making it difficult for crops to thrive and lowering both production and quality. Poor nutrition and salinity stress affect plant growth and development. Although the impact of individual plant stresses has been studied for decades, the real stress scenario is more complex due to the exposure to multiple stresses at the same time. Here we investigate using existing evidence and a meta-analysis approach to determine molecular linkages between 2 contemporaneous abiotic stimuli, phosphate (Pi) deficiency and salinity, on a single plant cell model, the root hairs (RHs), which is the first plant cell exposed to them. Understanding how these 2 stresses work molecularly in RHs may help us build super-adaptable crops and sustainable agriculture in the face of global climate change.

OsAAH confers salt tolerance in rice seedlings

Soil salinization is becoming a great threat that reduces crop productivity worldwide. In this study, we found that rice allantoate amidohydrolase (OsAAH) expression was significantly upregulated by salt stress, and its overexpression conferred salt tolerance at the seedling stage. Compared to wild type (WT), the contents of ureides (allantoin and allantoate) were significantly increased in Osaah mutants and reduced in OsAAH overexpression lines both before and after salt treatments. Exogenous allantoin significantly promoted salt tolerance in OsAAH overexpression, but not in Osaah mutants. Subcellular localization showed that OsAAH was also localized to the peroxisomes in addition to the previously reported endoplasmic reticulum (ER). The differential expression of peroxisome-related genes was identified between Osaah mutants and WT. Furthermore, the contents of H2O2 and malondialdehyde (MDA) were significantly accumulated in Osaah mutants and reduced in OsAAH overexpression lines. The activities of antioxidant enzymes were significantly reduced in Osaah mutants and enhanced in OsAAH overexpression under NaCl treatment. The transcription factor OsABI5 could directly bind to OsAAH promoter and activate OsAAH expression. Our findings reveal that OsAAH could be induced by salt stress through the activation of OsABI5 and then confer salt tolerance by enhancing the scavenging capacity of reactive oxygen species (ROS), which contributes to rice breeding in salt tolerance.

Chloride accumulation in inland rivers of China and its toxic impact on cotton

The escalation of major ion concentrations in freshwater and soil poses diverse effects on ecosystems and the environment. Excessive ions can exhibit toxicity to aquatic organisms and terrestrial plants. Currently, research on ion toxicity primarily focuses on cation toxicity. Notably, there is a noticeable research gap in understanding the impact of chloride ion (Cl-) on plant growth and development, as well as on the defense mechanisms against Cl- toxicity. In the present study, sampling was conducted on major rivers in China to measure Cl- concentrations. The results revealed that certain rivers exhibited excessive levels of Cl-, emphasizing the critical need to address Cl- toxicity issues. Subsequently, when salt-tolerant cotton seedlings were subjected to various chloride treatments, it was observed that excessive Cl- severely hindered plant growth and development. A combined analysis of transcriptomic and metabolomic data shed light on significantly enriched pathways related to galactose metabolism, arginine and proline metabolism, carotenoid metabolism, and alpha-linolenic acid metabolism under chloride stress. In summary, this research provides a scientific foundation and references for environmental management and water resource protection and offers novel insights for mitigating the adverse impacts of Cl-, thereby contributing to the preservation of ecosystem health.