Enhanced Salt Tolerance Research Articles

The synergistic effects of silicon and selenium on enhancing salt tolerance of maize plants

Silicon (Si) and selenium (Se) have been recognized as beneficial elements for plant tolerance to abiotic stresses. However, the mechanisms responsible for the alleviating effects of Si-Se interactions on salt stress are still not clear. In this study, we compared the effects of Si and Se alone and in combination on the growth, sodium (Na) accumulation, photochemical parameters, the net Na+ flux and expression of salt resistance-related genes in maize plants under salt stress. The results showed that the addition of Si and Se significantly mitigated salt toxicity, and an obvious synergistic interaction was found between them. The application of Si and Se protected the structure and function of the photosynthetic apparatus from salt stress, and no differences were found between single and combined treatments. The combination of Si and Se significantly increased the net Na+ efflux and resulted in decreased Na+ influx in the root meristematic zone. Furthermore, salt stress-responsive genes, including ZmNHX and ZmSOS2, were upregulated under the combined treatment of Si and Se. These results indicate that the synergistic effects of Si and Se against salt stress were caused by the upregulated expression of transporter genes involved in Na+ uptake, exclusion and sequestration into vacuoles in roots.

Comparative physiological and full-length transcriptome analyses reveal the molecular mechanism of melatonin-mediated salt tolerance in okra (Abelmoschus esculentus L.)

BackgroundMelatonin, a multifunctional signal molecule, has been reported to play crucial roles in growth and development and stress responses in various plant species. Okra (Abelmoschus esculentus L.) is a food crop with extremely high values of nutrition and healthcare. Recent reports have revealed the protective role of melatonin in alleviating salt stress. However, little is known about its regulatory mechanisms in response to salt stress in okra.ResultsIn this study, we explored whether exogenous melatonin pretreatment could alleviate salt stress (300 mM NaCl) of okra plants. Results showed that exogenous application of melatonin (50 μM) significantly enhanced plant tolerance to salt stress, as demonstrated by the plant resistant phenotype, as well as by the higher levels of the net photosynthetic rate, chlorophyll fluorescence and chlorophyll content in comparison with nontreated salt-stressed plants. Additionally, melatonin pretreatment remarkably decreased the levels of lipid peroxidation and H2O2 content and scavenged O2•- in melatonin-pretreated plants, which may be attributed to the higher levels of enzyme activities including POD and GR. Moreover, a combination of third- (PacBio) and second-generation (Illumina) sequencing technologies was applied to sequence full-length transcriptomes of okra. A total of 121,360 unigenes was obtained, and the size of transcript lengths ranged from 500 to 6000 bp. Illumina RNA-seq analysis showed that: Comparing with control, 1776, 1063 and 1074 differential expression genes (DEGs) were identified from the three treatments (NaCl, MT50 and MT + NaCl, respectively). These genes were enriched in more than 10 GO terms and 34 KEGG pathways. Nitrogen metabolism, sulfur metabolism, and alanine, aspartate and glutamate metabolism were significantly enriched in all three treatments. Many transcription factors including MYB, WRKY, NAC etc., were also identified as DEGs.ConclusionsOur preliminary results suggested that melatonin pretreatment enhanced salt tolerance of okra plants for the first time. These data provide the first set of full-length isoforms in okra and more comprehensive insights into the molecular mechanism of melatonin responses to salt stress.

A C-terminal fragment of Arabidopsis OXIDATIVE STRESS 2 can play a positive role in salt tolerance

The zinc finger transcription factor OXIDATIVE STRESS 2 (OXS2) was previously reported to be involved in oxidative stress tolerance and stress escape. Here we report that an Arabidopsis oxs2-1 mutant is also more sensitive to salt stress. Conversely, the overproduction of a C-terminal fragment of OXS2, the ‘AT3’ fragment, can enhance salt tolerance in Arabidopsis by upregulating the transcription of at least six salt-induced genes: COR15A, COR47, RD29B, KIN1, ACS2 and ACS6. Mutant analysis showed that the AT3-mediated salt tolerance requires MPK3, MPK6 and 14-3-3Ω. AT3 was shown to interact with MPK3 in planta, with 14-3-3Ω as a likely linker protein. AT3 can be phosphorylated by MPK3 during salt stress, upon which it relocates from the cytoplasm to the nucleus. It appears that the phosphorylation-induced nuclear localization of OXS2 contributes a positive role to the salt stress response.

Involvement of ethylene receptors in the salt tolerance response of Cucurbita pepo

Abiotic stresses have a negative effect on crop production, affecting both vegetative and reproductive development. Ethylene plays a relevant role in plant response to environmental stresses, but the specific contribution of ethylene biosynthesis and signalling components in the salt stress response differs between Arabidopsis and rice, the two most studied model plants. In this paper, we study the effect of three gain-of-function mutations affecting the ethylene receptors CpETR1B, CpETR1A, and CpETR2B of Cucurbita pepo on salt stress response during germination, seedling establishment, and subsequent vegetative growth of plants. The mutations all reduced ethylene sensitivity, but enhanced salt tolerance, during both germination and vegetative growth, demonstrating that the three ethylene receptors play a positive role in salt tolerance. Under salt stress, etr1b, etr1a, and etr2b germinate earlier than WT, and the root and shoot growth rates of both seedlings and plants were less affected in mutant than in WT. The enhanced salt tolerance response of the etr2b plants was associated with a reduced accumulation of Na+ in shoots and leaves, as well as with a higher accumulation of compatible solutes, including proline and total carbohydrates, and antioxidant compounds, such as anthocyanin. Many membrane monovalent cation transporters, including Na+/H+ and K+/H+ exchangers (NHXs), K+ efflux antiporters (KEAs), high-affinity K+ transporters (HKTs), and K+ uptake transporters (KUPs) were also highly upregulated by salt in etr2b in comparison with WT. In aggregate, these data indicate that the enhanced salt tolerance of the mutant is led by the induction of genes that exclude Na+ in photosynthetic organs, while maintaining K+/Na+ homoeostasis and osmotic adjustment. If the salt response of etr mutants occurs via the ethylene signalling pathway, our data show that ethylene is a negative regulator of salt tolerance during germination and vegetative growth. Nevertheless, the higher upregulation of genes involved in Ca2+ signalling (CpCRCK2A and CpCRCK2B) and ABA biosynthesis (CpNCED3A and CpNCED3B) in etr2b leaves under salt stress likely indicates that the function of ethylene receptors in salt stress response in C. pepo can be mediated by Ca2+ and ABA signalling pathways.

CRISPR-Cas technology based genome editing for modification of salinity stress tolerance responses in rice (Oryza sativa L.).

Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein (Cas) technology is an effective tool for site-specific genome editing, used to precisely induce mutagenesis in different plant species including rice. Salinity is one of the most stressful environmental constraints affecting agricultural productivity worldwide. As plant adaptation to salinity stress is under polygenic control therefore, 51 rice genes have been identified that play crucial role in response to salinity. This review offers an exclusive overview of genes identified in rice genome for salinity stress tolerance. This will provide an idea to produce rice varieties with enhanced salt tolerance using the potentially efficient CRISPR-Cas technology. Several undesirable off-target effects of CRISPR-Cas technology and their possible solutions have also been highlighted.

Salicylic acid improves tolerance against salt stress through boosting antioxidant defense system in black bean.

To evaluate the effect of salicylic acid (SA) on seed germination of black bean plant under saline conditions, seeds were primed with salicylic acid (0, 2, 10, and 20 mM) and germinated under salt stress (0, 50, and 100 mM NaCl). The measured parameters included the percentage and rate of seed germination, seedling length and dry weight, malondialdehyde and hydrogen peroxide levels, and activity of catalase, ascorbate peroxidase and guaiacol peroxidase in the seedlings. Results showed the values of germination indices decreased with increasing the level of salt stress. However, SA priming (10 mM) alleviated the harmful effects of salt stress in black bean. SA increased seed germination percentage by 72% and 45% at 50 and 100 mM NaCl respectively, compared to the control condition. Germination rate augmented by 33% (at 50 mM NaCl) and 60% (at 100 mM NaCl) by SA priming compared to the seeds exposed to salt stress alone. Seedlings dry weight (+ 51% at 50 mM and + 34% at 100 mM) and length (+ 57% at 50 mM and + 29% at 100 mM NaCl) were significantly higher by priming with 10 mM salicylic acid, compared to exclusively salt stress-treated seeds. SA priming increased antioxidant enzymes activities and decreased the levels of lipid peroxidation and hydrogen peroxide in salt stressed black bean seedlings. In conclusion, salicylic acid priming (particularly at 10 mM) enhances salt tolerance in black bean via lessening of oxidative stress.

Functional Characterization of a Sugar Beet BvbHLH93 Transcription Factor in Salt Stress Tolerance.

The basic/helix–loop–helix (bHLH) transcription factor (TF) plays an important role for plant growth, development, and stress responses. Previously, proteomics of NaCl treated sugar beet leaves revealed that a bHLH TF, BvbHLH93, was significantly increased under salt stress. The BvbHLH93 protein localized in the nucleus and exhibited activation activity. The expression of BvbHLH93 was significantly up-regulated in roots and leaves by salt stress, and the highest expression level in roots and leaves was 24 and 48 h after salt stress, respectively. Furthermore, constitutive expression of BvbHLH93 conferred enhanced salt tolerance in Arabidopsis, as indicated by longer roots and higher content of chlorophyll than wild type. Additionally, the ectopic expression lines accumulated less Na+ and MDA, but more K+ than the WT. Overexpression of the BvBHLH93 enhanced the activities of antioxidant enzymes by positively regulating the expression of antioxidant genes SOD and POD. Compared to WT, the overexpression plants also had low expression levels of RbohD and RbohF, which are involved in reactive oxygen species (ROS) production. These results suggest that BvbHLH93 plays a key role in enhancing salt stress tolerance by enhancing antioxidant enzymes and decreasing ROS generation.

ThNAC12 from Tamarix hispida directly regulates ThPIP2;5 to enhance salt tolerance by modulating reactive oxygen species

NAC (NAM, ATAF1/2 and CUC2) transcription factors play critical roles in plant development and abiotic stress responses, and aquaporins have diverse functions in environmental stress responses. In this study, we described the salt-induced transcriptional responses of ThNAC12 and ThPIP2;5 in Tamarix hispida, and their regulatory mechanisms in response to salt stress. Using yeast one-hybrid (Y1H), chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays, we identified that ThNAC12 directly binds to the NAC recognition sequence (NACRS) of the ThPIP2;5 promoter and then activates the ThPIP2;5 expression. Subcellular localization and transcriptional activation assays demonstrated that ThNAC12 was a nuclear protein with a C-terminal transactivation domain. Compared with the corresponding control plants, transgenic plants overexpressing ThNAC12 exhibited enhanced salt tolerance and displayed increased reactive oxygen species (ROS) scavenging capability and antioxidant enzyme activity levels under salt stress. All results suggested that overexpression of ThNAC12 in plants enhanced salt tolerance through modulation of ROS scavenging via direct regulation of ThPIP2;5 expression in T. hispida.

Melatonin promotes seed germination under salt stress by regulating ABA and GA3 in cotton (Gossypium hirsutum L.)

Although previous studies have found that melatonin can promote seed germination, the phytohormone regulation mechanism by which exogenous melatonin mediates salt tolerance during cotton seed germination is still largely unknown. The effects of melatonin on germination traits and physiological parameters of GXM9 cotton seeds (Gossypium hirsutum L.) under three salt stress treatments (CK, germination of seeds pretreated with water alone; S, germination of seeds pretreated in 150 mM NaCl under salt stress; SM, germination of seeds pretreated in 20 μM melatonin under 150 mM NaCl solution) in the laboratory was investigated. The results showed that salt stress (150 mM) inhibited cotton seed germination and endogenous melatonin accumulation, and pretreatment with 20 μM exogenous melatonin enhanced the cotton germination rate and hypocotyl length as well as the content of endogenous melatonin during seed germination. This suggests that exogenous melatonin promotes seed germination from a morphological perspective. The contents of starch, α-amylase (EC3.3.1.1), β-galactosidase (EC3.2.1.23), abscisic acid (ABA), and gibberellin (GA) were determined simultaneously. The results showed that the α-amylase and β-galactosidase contents in the cotton seeds decreased by 56.97% and 20.18%, respectively, under salt stress compared with the control, while the starch content increased by 11.53% compared with the control at day 7. The ABA content increased by 25.18% and GA content decreased by 27.99% under salt stress compared with the control at 24 h. When exogenous melatonin was applied to the cotton seeds, the content of α-amylase and β-galactosidase increased by 121.77% and 32.76%, respectively, whereas the starch contents decreased by 13.55% compared with the S treatment at day 7. Similarly, the ABA content increased by 12.20% and the GA content increased by 4.77% at 24 h. To elucidate the molecular mechanism by which melatonin promotes seed germination under salt stress, the effects of ABA- and GA-related genes on plant hormone signal transduction were analyzed by quantitative real-time PCR and RNA sequencing. The results indicated that melatonin regulated the expression of ABA and GA genes in the plant signal transduction pathway, induced embryo root development and seed germination, and alleviated dormancy. The expression of the ABA signaling gene GhABF2 was up-regulated and GhDPBF2 was down-regulated, and the expression of GA signaling genes (e.g., GhGID1C and GhGID1B) was up-regulated by melatonin. In conclusion, melatonin enhances salt tolerance in cotton seeds by regulating ABA and GA and by mediating the expression of hormone-related genes in plant hormone signal transduction. This should help us to explore the regulatory mechanisms of cotton resistance and provide a foundation for the cultivation of new varieties.

Chitosan nanoparticles effectively combat salinity stress by enhancing antioxidant activity and alkaloid biosynthesis in Catharanthus roseus (L.) G. Don

Chitosan nanoparticles (CSNPs) are non-toxic and biodegradable stimulants of growth and secondary metabolite production, which offer new routes to combat plant stress. Salinity is a common and significant abiotic stress that adversely affects plant growth and development. The possible benefits of CSNPs in salt stress mitigation have not yet been reported in Catharanthus roseus, an important source of anticancer alkaloids. Plants were exposed to 150 mM NaCl as a salt stress treatment, while CSNPs were applied as a foliar spray at 1% concentration. Plant growth was considerably impaired under salt stress conditions; however, CSNPs treatment significantly reversed this effect. Specifically, CSNPs retarded chlorophyll reduction and induced activities of catalase, ascorbate peroxidase, and glutathione reductase. Thus, CSNPs alleviated the oxidative stress, indicated by lower levels of malondialdehyde and H2O2, thereby enabling membrane function retention and enhancing salt tolerance. Higher alkaloid accumulation was observed in salt-stressed plants following CSNP spraying than in controls. Interestingly, the expression levels of mitogen-activated protein kinases (MAPK3), geissoschizine synthase (GS), and octadecanoid-derivative responsive AP2-domain (ORCA3) genes were significantly elevated in salt-stressed plants sprayed with CSNPs. Overall, CSNP treatment overcame the deleterious effects of salinity in C. roseus by activating the antioxidant defense system, which helps to scavenge reactive oxygen species, and inducing expression of MAPK3, GS, and ORCA3 genes, thus, leading to higher alkaloid accumulation and better protection against salinity stress.

Effects of K+ and Ca2+ supplement during fertigation on leaf gas exchange and salt tolerance of cotton at full and deficit irrigation regimes

Modulation of K+ and Ca2+ levels could enhance salt tolerance in crops, yet the underlying mechanisms remain largely elusive. The objective of this study was to investigate the effects of K+ and Ca2+ supplement during fertigation on leaf gas exchange in cotton plants subjected to salt stress and deficit irrigation regime. The leaf gas exchange parameters, leaf nitrogen concentration, chlorophyll content, plant water status, abscisic acid concentration in leaf ([ABA]leaf), K+ and Na+ concentration in leaf, as well as water use efficiency were evaluated. The results showed that: stomatal conductance (gs), transpiration rate (Tr) and net photosynthetic rate (An) were significantly decreased by 150 mM NaCl stress, whereas K+Ca treatment significantly alleviated the negative impact of salt under full irrigation. The relative water content and leaf water potential (Ψ1) was significantly decreased by salt stress. At full irrigation, K+Ca treatment further decreased Ψ1 in the salt-stressed plants than the non-K+Ca treatment. K+ and Ca2+ addition had a more positive effect on gs and Tr than on An, resulting in significantly lowered intrinsic and instantaneous water use efficiencies in salt-stressed plants at full irrigation. K and K+Ca treatments significantly increased the content of K+ and the ratio of K+/Na+ in leaf under salt stress and deficit irrigation. Salinity induced-reduction in gs was associated with high [ABA]leaf and a lower Ψ1, whereas, the alleviation of gs and An in the salt-stressed plants at full irrigation upon K+ and Ca2+ addition could be attributed to osmoregulation and increased concentration of K+ and the ratio of K+/Na+ in leaf. In conclusion, at full irrigation, K+Ca treatment notably alleviated the salinity-induced depression in gs and An, ameliorating plants performance under salt stress condition. These results provide useful information for better irrigation and fertilization management in a future water-limited and salinity-affected soil environment.

Ectopic expression of a wheat superoxide dismutase gene TaSOD5 enhances salt and oxidative stress tolerance in Arabidopsis

Superoxide dismutase (SOD) is a crucial reactive oxygen species (ROS) scavenger, which converts superoxide radical to H2O2, so it is thought to enhance abiotic stress tolerance by reducing ROS and thus avoiding oxidative damage. In this study, we isolated a salt- and oxidative stress-responsive copper-zinc (Cu/Zn) SOD encoding gene TaSOD5 from wheat. The ectopic overexpression of TaSOD5 in Arabidopsis thaliana increased total SOD and Cu/Zn SOD activities and enhanced tolerance to salt stress. Arabidopsis ectopically expressing TaSOD5 possessed a superior resistance to oxidative stress stimulated by exogenous H2O2. Ectopic overexpression of TaSOD5 elevated the activities of both ROS scavengers and an O2.- producer - NADPH oxidase. These findings show that Cu/Zn SOD enhanced salt tolerance via regulating the machinery of redox homeostasis rather than improving SOD activity alone.

Overexpression of isochorismate synthase enhances salt tolerance in barley

Isochorismate synthase (ICS) is a key enzyme for the synthesis of salicylic acid (SA) in plants. SA plays an important role in the response of plants to abiotic stress. In this study, transgenic barley was constructed to evaluate the function of ICS under salt stress. ICSOE lines showed obvious salt stress tolerance, this results from the increased outward Na+ flux and inward K+ flux in roots, thereby maintaining a lower cytosolic Na+/K+ ratio under salt stress. Overexprssion of ICS also improved Na+ sequestration in shoots under salt stress. In addition, ICSOE lines displayed less accumulation of reactive oxygen species and oxidative damage, accompanied by higher activity of antioxidant enzymes. The improved Na+/K+ ratio, Na+ sequestration, and antioxidative competence play an important role in the enhanced salt tolerance of ICSOE lines. These findings help to elucidate the abiotic stress resistance of the ICS pathway in barley.

Restructuring the Cellular Responses: Connecting Microbial Intervention With Ecological Fitness and Adaptiveness to the Maize (Zea mays L.) Grown in Saline-Sodic Soil.

Salt stress hampers plant growth and development. It is now becoming one of the most important threats to agricultural productivity. Rhizosphere microorganisms play key roles in modulating cellular responses and enable plant tolerant to salt stress, but the detailed mechanisms of how this occurs need in-depth investigation. The present study elucidated that the microbe-mediated restructuring of the cellular responses leads to ecological fitness and adaptiveness to the maize (Zea mays L.) grown in saline–sodic soil. In the present study, effects of seed biopriming with B. safensis MF-01, B. altitudinis MF-15, and B. velezensis MF-08 singly and in consortium on different growth parameters were recorded. Soil biochemical and enzymatic analyses were performed. The activity and gene expression of High-Affinity K+ Transporter (ZmHKT-1), Sodium/Hydrogen exchanger 1 (zmNHX1), and antioxidant enzymes (ZmAPX1.2, ZmBADH-1, ZmCAT, ZmMPK5, ZmMPK7, and ZmCPK11) were studied. The expression of genes related to lateral root development (ZmHO-1, ZmGSL-1, and ZmGSL-3) and root architecture were also carried out. Seeds bioprimed with consortium of all three strains have been shown to confer increased seed germination (23.34–26.31%) and vigor indices (vigor index I: 38.71–53.68% and vigor index II: 74.11–82.43%) as compared to untreated control plant grown in saline–sodic soil at 30 days of sowing. Results indicated that plants treated with consortium of three strains induced early production of adventitious roots (tips: 4889.29, forks: 7951.57, and crossings: 2296.45) in maize compared to plants primed with single strains and untreated control (tips: 2019.25, forks: 3021.45, and crossings: 388.36), which was further confirmed by assessing the transcript level of ZmHO-1 (7.20 folds), ZmGSL-1 (4.50 folds), and ZmGSL-3 (12.00 folds) genes using the qPCR approach. The uptake and translocation of Na+, K+, and Ca2+ significantly varied in the plants treated with bioagents alone or in consortium. qRT-PCR analysis also revealed that the ZmHKT-1 and zmNHX1 expression levels varied significantly in the maize root upon inoculation and showed a 6- to 11-fold increase in the plants bioprimed with all the three strains in combination. Further, the activity and gene expression levels of antioxidant enzymes were significantly higher in the leaves of maize subjected seed biopriming with bioagents individually or in combination (3.50- to 12.00-fold). Our research indicated that ZmHKT-1 and zmNHX1 expression could effectively enhance salt tolerance by maintaining an optimal Na+/K+ balance and increasing the antioxidant activity that keeps reactive oxygen species at a low accumulation level. Interestingly, up-regulation of ZmHKT-1, NHX1, ZmHO-1, ZmGSL-1, and ZmGSL-3 and genes encoding antioxidants regulates the cellular responses that could effectively enhance the adaptiveness and ultimately leads to better plant growth and grain production in the maize crop grown in saline–sodic soil.

Generation of new salt-tolerant wheat lines and transcriptomic exploration of the responsive genes to ethylene and salt stress

Wheat (Triticum aestivum L.) is one of the most important staple crops. Most of wheat varieties are sensitive to salt stress, which is a major limitation for wheat production. To develop salt-tolerant wheat varieties for sustainable grain production, we used ethylmethylsulfonate to mutagenize over 90,000 seeds of the wheat cultivar Luyuan502. A total of 2000 salt-tolerant lines were identified after screening the plants in a salinized field. We further analyzed ethylene sensitivity, salt related physiological changes, and preliminary crop yield of the selected plants. We found 11 salt-tolerant lines exhibiting ethylene insensitivity and high grain production. Transcriptome analysis revealed 3278 differently expressed genes (DEGs) in the selected mutants, including the ones encoding CABs, PERs/PODs, BGLUs, CYP707s, and ZEPs. Most of DEGs may be involved in photosynthesis, biosynthesis of secondary metabolites, cyanoamino acid metabolism, carotenoid biosynthesis, thiamine metabolism, and cutin, suberine and wax biosynthesis pathways. In addition, 9 novel ETHYLENE RESPONSE FACTORs (ERFs) were identified and analyzed in the mutants. These ERFs may play critical roles in ethylene response and salt tolerance. The mutant lines with decreased ethylene sensitivity exhibited enhanced salt tolerance, suggesting that ethylene sensitivity was closely related with salt tolerance.

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The cover image is based on the Original Research TaPUB15, a U-Box E3 ubiquitin ligase gene from wheat, enhances salt tolerance in rice by Qiaoru Li et al., https://doi.org/10.1002/fes3.250.

Natural variation in the promoter of GsERD15B affects salt tolerance in soybean.

SummarySalt stress has detrimental effects on crop growth and yield, and the area of salt‐affected land is increasing. Soybean is a major source of vegetable protein, oil and feed, but considered as a salt‐sensitive crop. Cultivated soybean (Glycine max) is domesticated from wild soybean (G. soja) but lost considerable amount of genetic diversity during the artificial selection. Therefore, it is important to exploit the gene pool of wild soybean. In this study, we identified 34 salt‐tolerant accessions from wild soybean germplasm and found that a 7‐bp insertion/deletion (InDel) in the promoter of GsERD15B (early responsive to dehydration 15B) significantly affects the salt tolerance of soybean. GsERD15B encodes a protein with transcriptional activation function and contains a PAM2 domain to mediate its interaction with poly(A)‐binding (PAB) proteins. The 7‐bp deletion in GsERD15B promoter enhanced the salt tolerance of soybean, with increased up‐regulation of GsERD15B, two GmPAB genes, the known stress‐related genes including GmABI1, GmABI2, GmbZIP1, GmP5CS, GmCAT4, GmPIP1:6, GmMYB84 and GmSOS1 in response to salt stress. We propose that natural variation in GsERD15B promoter affects soybean salt tolerance, and overexpression of GsERD15B enhanced salt tolerance probably by increasing the expression levels of genes related to ABA‐signalling, proline content, catalase peroxidase, dehydration response and cation transport.

Integrated Analysis of the Transcriptome and Metabolome Revealed the Molecular Mechanisms Underlying the Enhanced Salt Tolerance of Rice Due to the Application of Exogenous Melatonin.

High salinity is one of the major abiotic stresses limiting rice production. Melatonin has been implicated in the salt tolerance of rice. However, the molecular basis of melatonin-mediated salt tolerance in rice remains unclear. In the present study, we performed an integrated transcriptome and metabolome profiling of rice seedlings treated with salt, melatonin, or salt + melatonin. The application of exogenous melatonin increased the salt tolerance of rice plants by decreasing the sodium content to maintain Na+/K+ homeostasis, alleviating membrane lipid oxidation, and enhancing chlorophyll contention. A comparative transcriptome analysis revealed that complex molecular pathways contribute to melatonin-mediated salt tolerance. More specifically, the AP2/EREBP–HB–WRKY transcriptional cascade and phytohormone (e.g., auxin and abscisic acid) signaling pathways were activated by an exogenous melatonin treatment. On the basis of metabolome profiles, 64 metabolites, such as amino acids, organic acids, nucleotides, and secondary metabolites, were identified with increased abundances only in plants treated with salt + melatonin. Several of these metabolites including endogenous melatonin and its intermediates (5-hydroxy-L-tryptophan, N1-acetyl-N2-formyl-5-methoxykynuramine), gallic acid, diosmetin, and cyanidin 3-O-galactoside had antioxidant functions, suggesting melatonin activates multiple antioxidant pathways to alleviate the detrimental effects of salt stress. Combined transcriptome and metabolome analyses revealed a few gene–metabolite networks related to various pathways, including linoleic acid metabolism and amino acid metabolism that are important for melatonin-mediated salt tolerance. The data presented herein may be useful for further elucidating the multiple regulatory roles of melatonin in plant responses to abiotic stresses.

Importin-β From the Recretohalophyte Limonium bicolor Enhances Salt Tolerance in Arabidopsis thaliana by Reducing Root Hair Development and Abscisic Acid Sensitivity.

AimsTo elucidate the genetics underlying salt tolerance in recretohalophytes and assess its relevance to non-halophytes, we cloned the Limonium bicolor homolog of Arabidopsis thaliana (Arabidopsis) SUPER SENSITIVE TO ABA AND DROUGHT2 (AtSAD2) and named it LbSAD2, an importin-β gene associated with trichome initiation and reduced abscisic acid (ABA) sensitivity, and then we assessed the heterologously expressed LbSAD2 in Arabidopsis.MethodsWe examined LbSAD2 expression and assessed the effect of heterologous LbSAD2 expression in Arabidopsis on root hair/trichome induction; the expression levels of possible related genes in trichome/root hair development; some physiological parameters involved in salt tolerance including germination rate, root length, and contents of Na+, proline, and malondialdehyde; and the response of ABA at the germination stage.ResultsThe LbSAD2 gene is highly expressed in the salt gland development stage and salt treatment, especially located in the salt gland by in situ hybridization, and the LbSAD2 protein contains some special domains compared with AtSAD2, which may suggest the involvement of LbSAD2 in salt tolerance. Compared with the SAD2/GL1 mutant CS65878, which lacks trichomes, CS65878-35S:LbSAD2 had higher trichome abundance but lower root hair abundance. Under 100 mM NaCl treatment, CS65878-35S:LbSAD2 showed enhanced germination and root lengths; improved physiological parameters, including high proline and low contents of Na+ and malondialdehyde; higher expression of the salt-tolerance genes Δ1-PYRROLINE-5-CARBOXYLATE SYNTHETASE 1 (P5CS1) and GST CLASS TAU 5 (GSTU5); reduced ABA sensitivity; and increased expression of the ABA signaling genes RESPONSIVE TO ABA 18 (RAB18) and SNF1-RELATED PROTEIN KINASE 2 (SRK2E), but not of the ABA biosynthesis gene 9-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3).ConclusionLbSAD2 enhances salt tolerance in Arabidopsis by specifically reducing root hair development, Na+ accumulation, and ABA sensitivity.

Soil microbiome-mediated salinity tolerance in poplar plantlets is source-dependent

Soil salinization is a global environmental problem and one of the most common land degradation processes. To effectively utilize saline lands, it is crucial to improve plant growth and stress tolerance, particularly through the microbiome intervention strategy. However, less is known about the interactions of microbes with trees than those with crops or herbaceous plants. Here, we examined how natural soil microbes affected the performance of salt-sensitive Populus deltoides × P. euramericana ’Nanlin895’ (NL895) under salt stress. Gnotobiotic NL895 plantlets were inoculated with soil microbiome extracted from no-salt (NS; soluble salt: 0.71 g/kg), low-salt (LS; 5.14 g/kg), and high-salt (HS; 23.07 g/kg) lands, and then exposed to salt treatments. Compared to control, 33.8%, 18.0%, and 29.9% of the aboveground biomass was increased by NS, LS, and HS inoculation, respectively. The salt injury index was lower in LS and HS than in NS treatments. Rhizosphere microbial communities of all treatments were taxonomically and functionally different across multiple stages, while the variation extent was larger in bacterial than in fungal communities. FUNGuild and PICRUSt2 analysis demonstrated the changes of fungal trophic modes and bacterial metabolic pathways, respectively. In summary, our findings revealed the stronger potential of NS than LS and HS inoculants in growth promotion, while weaker strength than LS and HS inoculants in enhancing salt tolerance of NL895 plantlets. This source-dependent effect should be considered in future microbiome engineering, aiming at harnessing soil microbes to create predictable plant phenotypes.