Enhanced Salt Tolerance Research Articles

Exogenous melatonin enhances cell wall response to salt stress in common bean (Phaseolus vulgaris) and the development of the associated predictive molecular markers.

Common bean (Phaseolus vulgaris) is an important food crop; however, its production is affected by salt stress. Salt stress can inhibit seed germination, promote senescence, and modify cell wall biosynthesis, assembly, and architecture. Melatonin, an indole heterocycle, has been demonstrated to greatly impact cell wall structure, composition, and regulation in plants under stress. However, the molecular basis for such assumptions is still unclear. In this study, a common bean variety, "Naihua" was treated with water (W), 70 mmol/L NaCl solution (S), and 100 μmol/L melatonin supplemented with salt solution (M+S) to determine the response of common bean to exogenous melatonin and explore regulatory mechanism of melatonin against salt stress. The results showed that exogenous melatonin treatment alleviated salt stress-induced growth inhibition of the common bean by increasing the length, surface area, volume, and diameter of common bean sprouts. Moreover, RNA sequencing (RNA-seq) and real-time quantitative PCR (qRT-PCR) indicated that the cell wall regulation pathway was involved in the salt stress tolerance of the common bean enhanced by melatonin. Screening of 120 germplasm resources revealed that melatonin treatment improved the salt tolerance of more than 65% of the common bean germplasm materials. Melatonin also up-regulated cell wall pathway genes by at least 46%. Furthermore, we analyzed the response of the common bean germplasm materials to melatonin treatment under salt stress using the key genes associated with the synthesis of the common bean cell wall as the molecular markers. The results showed that two pairs of markers were significantly associated with melatonin, and these could be used as candidate markers to predict whether common bean respond to exogenous melatonin and then enhance salt tolerance at the sprouting stage. This study shows that cell wall can respond to exogenous melatonin and enhance the salt tolerance of common bean. The makers identified in this study can be used to select common bean varieties that can respond to melatonin under stress. Overall, the study found that cell wall could response melatonin and enhance the salt tolerance and developed the makers for predicting varieties fit for melatonin under stress in common bean, which may be applied in the selection or development of common bean varieties with abiotic stress tolerance.

Binding of the transcription factor MYC2-like to the ABRE of the OsCYP2 promoter enhances salt tolerance in Oryza sativa.

Cyclophilins, a type of peptidyl-prolyl cis-trans isomerase, function as important molecular chaperones in a series of biological processes. However, the expression pattern and signal transduction pathway of cyclophilins are still unclear. Here, we showed that the promoter of OsCYP2 could function as a tissue-specific promoter by GUS staining. Moreover, we found that the promoter sequence contained not only core elements but also inducible elements. Then, the ABA-responsive element was used for cDNA library screening, and the transcription factor MYC2-like was identified by a yeast one-hybrid assay and confirmed through an electrophoretic mobility shift assay. Furthermore, the relative expression showed that MYC2-like was induced by abscisic acid. In addition, MYC2-like overexpression enhanced salt tolerance in transformants and partially restored the cyp2-RNAi line. In summary, we explored a novel transcriptional signal mediated by MYC2-like, a potential regulator of salt stress-related physiological processes in rice.

Transcriptome Analysis Reveals Genes and Pathways Associated with Salt Tolerance during Seed Germination in Suaeda liaotungensis.

Seed germination is susceptible to external environmental factors, especially salt stress. Suaeda liaotungensis is a halophyte with strong salt tolerance, and the germination rate of brown seeds under 1000 mM NaCl treatment still reached 28.9%. To explore the mechanism of salt stress response during brown seed germination in Suaeda liaotungensis, we conducted transcriptomic analysis on the dry seeds (SlD), germinated seeds under the control condition (SlG_C), and salt treatment (SlG_N). Transcriptome analysis revealed that 13314 and 755 differentially expressed genes (DEGs) from SlD vs. SlG_C and SlG_C vs. SlG_N were detected, respectively. Most DEGs were enriched in pathways related to transcription regulation and hormone signal transduction, ROS metabolism, cell wall organization or biogenesis, and carbohydrate metabolic process in two contrasting groups. Compared with the control condition, POD and CAT activity, H2O2, soluble sugar, and proline contents were increased during germinated seeds under salt stress. Furthermore, functional analysis demonstrated that overexpression of SlNAC2 significantly enhanced salt tolerance during the germination stage in Arabidopsis. These results not only revealed the tolerant mechanism of brown seed germination in response to salinity stress but also promoted the exploration and application of salt-tolerant gene resources of Suaeda liaotungensis.

Plant Growth–Promoting Rhizobacteria Enhance Salt Tolerance in Oat by Upregulating the Antioxidant System and Promoting Root Growth

Plant Growth–Promoting Rhizobacteria Enhance Salt Tolerance in Oat by Upregulating the Antioxidant System and Promoting Root Growth

Nitrate-responsive OsMADS27 promotes salt tolerance in rice

Salt stress is a major constraint on plant growth and yield. Nitrogen (N) fertilizers are known to alleviate salt stress. However, the underlying molecular mechanisms remain unclear. Here, we show that nitrate-dependent salt tolerance is mediated by OsMADS27 in rice. The expression of OsMADS27 is specifically induced by nitrate. The salt-inducible expression of OsMADS27 is also nitrate dependent. OsMADS27 knockout mutants are more sensitive to salt stress than the wild type, whereas OsMADS27 overexpression lines are more tolerant. Transcriptomic analyses revealed that OsMADS27 upregulates the expression of a number of known stress-responsive genes as well as those involved in ion homeostasis and antioxidation. We demonstrate that OsMADS27 directly binds to the promoters of OsHKT1.1 and OsSPL7 to regulate their expression. Notably, OsMADS27-mediated salt tolerance is nitrate dependent and positively correlated with nitrate concentration. Our results reveal the role of nitrate-responsive OsMADS27 and its downstream target genes in salt tolerance, providing a molecular mechanism for the enhancement of salt tolerance by nitrogen fertilizers in rice. OsMADS27 overexpression increased grain yield under salt stress in the presence of sufficient nitrate, suggesting that OsMADS27 is a promising candidate for the improvement of salt tolerance in rice.

Biochar-based nutritional nanocomposites: a superior treatment for alleviating salt toxicity and improving physiological performance of dill (Anethum graveolens).

Biochar-supported metal oxide nanocomposites as functional materials could help to improve the production and stress tolerance of plants by enhancing the physicochemical properties of biochar. This experiment was carried out to assess the effects of unmodified biochar (30gkg-1 soil) and biochar-based nanocomposites (BNCs) of iron (30g BNC-FeOkg-1 soil), zinc (30g BNC-ZnO kg-1 soil), and a combined form (15g BNC-FeO + 15g BNC-ZnOkg-1 soil) on dill (Anethum graveolens L.) plants under various salinity levels (non-saline, 6 and 12dSm-1). The biochar-related treatments reduced sodium content of the plants, leading to a decline in osmolytes, antioxidant enzymes activities, reactive oxygen species (ROS), lipid peroxidation, NADP reduction, abscisic acid, jasmonic acid, and salicylic acid in dill leaf tissues. The combined form of BNCs reduced sodium content of leaf tissue by about 22% and 26% under 6 and 12dSm-1 salinities, respectively. In contrast, addition of biochar, particularly biochar-based nanocomposites to the saline soil, enhanced potassium, iron, and zinc contents of leaf tissue, photosynthetic pigments, leaf water content, oxygen evolution rate, hill reaction and ATPase activities, endogenous indole-3-acetic acid, plant organs biomass, and consequently essential oil yield of plant organs. The combined form of BNCs in comparison with unmodified biochar improved vegetative, inflorescence, and seed biomass under 12dSm-1 salinity by about 33%, 25%, and 6%, respectively. These findings revealed that BNCs with novel structure can potentially enhance salt tolerance, plant biomass, and essential oil yield of different organs in salt-stressed dill plants through decreasing leaf sodium content and ROS generation and increasing nutrient availability, water status, and photosynthetic pigments.

OsABT Is Involved in Abscisic Acid Signaling Pathway and Salt Tolerance of Roots at the Rice Seedling Stage.

Rice is a staple cereal crop worldwide, and increasing its yields is vital to ensuring global food security. Salinity is a major factor that affects rice yield. Therefore, it is necessary to investigate salt tolerance mechanisms in rice. Proteins containing WD40 repeats play important roles in eukaryotic development and environmental adaptation. Here, we showed that overexpression of OsABT, a gene encoding a WD40-repeat protein, enhanced salt tolerance in rice seedlings by regulating root activity, relative conductivity, malondialdehyde and H2O2 content, and O2•− production rate. Root ion concentrations indicated that OsABT overexpression lines could maintain lower Na+ and higher K+/Na+ ratios and upregulated expression of salt-related genes OsSOS1 and OsHAK5 compared with the wild-type (WT) Nipponbare plants. Furthermore, Overexpression of OsABT decreased the abscisic acid (ABA) content, while downregulating the ABA synthesis genes OsNCED3 and OsNCED4 and upregulating the ABA catabolic gene OsABA8ox2. The yeast two-hybrid and bimolecular fluorescence complementation analyses showed that OsABT interacted with the ABA receptor proteins OsPYL4, OsPYL10, and PP2C phosphatase OsABIL2. A transcriptome analysis revealed that the differentially expressed genes between OsABT overexpression lines and WT plants were enriched in plant hormone signal transduction, including ABA signaling pathway under salt stress. Thus, OsABT can improve the salt tolerance in rice seedling roots by inhibiting reactive oxygen species accumulation, thereby regulating the intracellular Na+/K+ balance, ABA content, and ABA signaling pathway.

Enhanced salt-tolerance of Bacillus subtilis glutaminase by fusing self-assembling amphipathic peptides at its N-terminus.

Glutaminase (EC 3.5.1.2) can catalyze the deamidation of glutamine, which has been used to improve umami taste in oriental fermented foods. However, a high salt concentration is still a fundamental challenge for glutaminase application, especially in soy sauce production. To improve the salt tolerance of glutaminase, the self-assembling amphiphilic peptides EAK16 and ELK16 were fused to the N-terminus of a mutant (E3C/E55F/D213T) derived from Bacillus subtilis glutaminase, yielding the fusion enzymes EAK16-E3C/E55F/D213T and ELK16-E3C/E55F/D213T, respectively. As ELK16-E3C/E55F/D213T was expressed as insoluble active inclusion bodies, only the purified EAK16-E3C/E55F/D213T was subjected to further analyses. After the incubation with 18% (w/v) NaCl for 200 min, the residual activities of EAK16-E3C/E55F/D213T in a NaCl-free solution reached 43.6%, while E3C/E55F/D213T was completely inactivated. When the enzyme reaction was conducted in the presence of 20% NaCl, the relative activity of EAK16-E3C/E55F/D213T was 0.47-fold higher than that of E3C/E55F/D213T. As protein surface hydrophobicity and protein particle size analysis suggested, oligomerization may play an important role in the salt-tolerance enhancement of the fusions. Furthermore, EAK16-E3C/E55F/D213T achieved a 0.88-fold increase in the titer of glutamic acid in a model system of soy sauce fermentation compared to E3C/E55F/D213T. Therefore, the fusion with self-assembling amphiphilic peptides is an efficient strategy to improve the salt-tolerance of glutaminase.

Melatonin-induced physiology and transcriptome changes in banana seedlings under salt stress conditions.

Soil salinization poses a serious threat to the ecological environment and agricultural production and is one of the most common abiotic stresses in global agricultural production. As a salt-sensitive plant, the growth, development, and production of bananas (Musa acuminata L.) are restricted by salt stress. Melatonin is known to improve the resistance of plants to stress. The study analyzed the effects of 100 μM melatonin on physiological and transcriptome changes in banana varieties (AAA group cv. Cavendish) under 60 mmol/l of NaCl salt stress situation. The phenotypic results showed that the application of exogenous melatonin could maintain banana plants’ health growth and alleviate the damage caused by salt stress. The physiological data show that the application of exogenous melatonin can enhance salt tolerance of banana seedlings by increasing the content of proline content and soluble protein, slowing down the degradation of chlorophyll, reducing membrane permeability and recovery of relative water content, increasing the accumulation of MDA, and enhancing antioxidant defense activity. Transcriptome sequencing showed that melatonin-induced salt tolerance of banana seedlings involved biological processes, molecular functions, and cellular components. We also found that differentially expressed genes (DEGs) are involved in a variety of metabolic pathways, including amino sugar and nucleotide sugar metabolism, phenylalanine metabolism, cyanoamino acid metabolism, starch and sucrose metabolism, and linoleic acid metabolism. These major metabolism and biosynthesis may be involved in the potential mechanism of melatonin under salt stress. Furthermore, some members of the transcription factor family, such as MYB, NAC, bHLH, and WRKY, might contribute to melatonin alleviating salt stress tolerance of the banana plant. The result laid a basis for further clarifying the salt stress resistance mechanism of bananas mediated by exogenous melatonin and provides theoretical bases to utilize melatonin to improve banana salt tolerance in the future.

Melatonin Mediates the Regulation of Morphological and Anatomical Traits in Carex leucochlora under Continuous Salt Stress

Soil salinity is one of the most critical factors limiting plant growth and development. Carex leucochlora is an important turfgrass species with a wide distribution in northern China that is highly sensitive to salt stress, which impairs its development. Recently, melatonin has emerged as a nontoxic biomolecule that regulates growth and enhances salt tolerance in plants. In this study, the mechanism of melatonin’s regulation of plant growth and anatomical characteristics in C. leucochlora seedlings under continuous salt stress was explored. Our results indicated that salt stress strongly suppressed plant growth and leaf cell activity, inhibited root morphology and root activity, and negatively affected leaf and root anatomic structures in the seedlings. Conversely, melatonin (150 μmol L−1) pretreatment improved the detrimental effect of salt stress by restoring the morphology of the leaf, alleviating damage to the cell membrane, improving root activity, and altering the root architecture and plant growth attributes. Moreover, after 12 days of salt stress, anatomical observations of the leaf showed that the thickness of the leaf blade, vascular bundle area of the leaf main vein, vesicular cell area, thickness of the upper epidermis, and thickness of the lower epidermis were increased by 30.55, 15.63, 12.60, 16.76 and 27.53%, respectively, with melatonin under salinity. Melatonin treatment also showed an increase of 5.91, 7.59, 15.57, and 20.51% in epidermal thickness, vascular cylinder diameter, xylem vessel diameter, and pith cell diameter, respectively, compared with salt stress after 12 days. These results suggest that melatonin alleviated salt stress through augmenting seedling growth, leaf cell activity, and root characteristics, maintained the stability of anatomic traits to maintain chloroplast cell homeostasis, and also protected the vascular tissues to promote the radial transport of water and ions in the C. leucochlora seedlings. These modifications induced by the exogenous application of melatonin may help C. leucochlora to acclimate successfully to saline soils.

A novel Ca2+ sensor switch for elevated salt tolerance in plants

Calcium signaling is vital for sensing and alleviating salt stress in plants. In this issue of Developmental Cell, Steinhorst etal. show that salt stress quantitatively translates into an increasing Ca2+ signaling output that activates the CBL8-CIPK24-SOS1 module, which, functioning with CBL4-CIPK24-SOS1, confers enhanced salt tolerance under severe salinity stress.

The combination of RNA-seq transcriptomics and data-independent acquisition proteomics reveals the mechanisms underlying enhanced salt tolerance by the ZmPDI gene in Zoysia matrella [L.] Merr.

Zoysia matrella [L.] Merr. is one of the three most economically important Zoysia species due to its strong salt tolerance and wide application. However, the molecular mechanisms regulating salt tolerance in Z. matrella remain unknown. The protein disulfide isomerase ZmPDI of Z. matrella was obtained by salt stress screening with yeast cells, and its expression was significantly upregulated after salt stress. Based on the obtained ZmPDI overexpression transgenic Z. matrella plants, we carried out salt tolerance identification and found that ZmPDI can significantly enhance the salt tolerance of Z. matrella. Root samples of OX-ZmPDI transgenic and wild-type plants were collected at 0 and 24 h after salt treatments for RNA-seq and data-independent acquisition (DIA) proteome sequencing. Combined analysis of the transcriptome and proteome revealed that ZmPDI may enhance the salt tolerance of Z. matrella by regulating TUBB2, PXG4, PLDα2, PFK4, and 4CL1. This research presents the molecular regulatory mechanism of the ZmPDI gene in Z. matrella for resistance to salt stress and facilitates the use of molecular breeding to improve the salt tolerance of grasses.

Co-overexpression of AVP1, PP2A-C5, and AtCLCc in Arabidopsis thaliana greatly increases tolerance to salt and drought stresses

Abiotic stresses such as salinity and drought impose a severe constraint on global food production, posing a serious challenge in agriculture. Stacking beneficial genes in transgenic crops will likely improve crop yield under abiotic stress conditions. Previous studies showed that individually overexpressing the Arabidopsis vacuolar H + -pyrophosphatase gene AVP1 , the protein phosphatase 2 A catalytic subunit gene PP2A-C5, and the chloride channel protein gene AtCLCc contributed to enhanced salt tolerance and overexpression of AVP1 alone could also improve drought tolerance. We hypothesized that co-overexpressing AVP1 , PP2A-C5, and AtCLCc, would combine the benefits of these three genes, leading to a further increase in salt tolerance in transgenic plants due to the potential synergism of these genes. Indeed, co-overexpression of these three genes in Arabidopsis significantly improved salt and drought tolerance under single as well as under combined salt and drought stresses. The AVP1 / PP2A-C5/AtCLCc co-overexpressing plants displayed robust growth and produced greater amount of biomass as well as viable seeds than wild-type and single gene overexpression plants under saline and drought conditions. This study demonstrates that successful co-overexpression of several well-chosen genes is an effective strategy to achieve greater abiotic stress tolerance and could potentially lead to higher crop yield in regions of the world with saline soil and low precipitation. • Co-overexpression of genes that function synergistically in plant cells could greatly increase salt tolerance in transgenic plants. • This research provides an effective strategy to achieve greater abiotic stress tolerance in plants. • This approach could potentially lead to higher crop yield in semiarid and arid regions of the world

Involvement of Auxin-Mediated CqEXPA50 Contributes to Salt Tolerance in Quinoa (Chenopodium quinoa) by Interaction with Auxin Pathway Genes.

Soil salinization is a global problem that limits crop yields and threatens agricultural development. Auxin-induced expansins contribute to plant salt tolerance through cell wall loosening. However, how auxins and expansins contribute to the adaptation of the halophyte quinoa (Chenopodium quinoa) to salt stress has not yet been reported. Here, auxin was found to contribute to the salt tolerance of quinoa by promoting the accumulation of photosynthetic pigments under salt stress, maintaining enzymatic and nonenzymatic antioxidant systems and scavenging excess reactive oxygen species (ROS). The Chenopodium quinoa expansin (Cqexpansin) family and the auxin pathway gene family (Chenopodium quinoa auxin response factor (CqARF), Chenopodium quinoa auxin/indoleacetic acid (CqAux/IAA), Chenopodium quinoa Gretchen Hagen 3 (CqGH3) and Chenopodium quinoa small auxin upregulated RNA (CqSAUR)) were identified from the quinoa genome. Combined expression profiling identified Chenopodium quinoa α-expansin 50 (CqEXPA50) as being involved in auxin-mediated salt tolerance. CqEXPA50 enhanced salt tolerance in quinoa seedlings was revealed by transient overexpression and physiological and biochemical analyses. Furthermore, the auxin pathway and salt stress-related genes regulated by CqEXPA50 were identified. The interaction of CqEXPA50 with these proteins was demonstrated by bimolecular fluorescence complementation (BIFC). The proteins that interact with CqEXPA50 were also found to improve salt tolerance. In conclusion, this study identified some genes potentially involved in the salt tolerance regulatory network of quinoa, providing new insights into salt tolerance.

Jasmonic acid pretreatment improves salt tolerance of wheat by regulating hormones biosynthesis and antioxidant capacity

Salt stress is a severe environmental factor that detrimentally affects wheat growth and production worldwide. Previous studies illustrate that exogenous jasmonic acid (JA) significantly improved salt tolerance in plants. However, little is known about the underlying molecular mechanisms of JA induced physiochemical changes in wheat seedlings under salt stress conditions. In this study, biophysiochemical and transcriptome analysis was conducted to explore the mechanisms of exogenous JA induced salt tolerance in wheat. Exogenous JA increased salt tolerance of wheat seedlings by alleviating membrane lipid oxidation, improving root morphology, enhancing the contents of ABA, JA and SA and increasing relative water content. In the RNA-seq profiles, we identified a total of 54,263 unigenes and 1,407 unigenes showed differentially expressed patterns in JA pretreated wheat seedlings exposed to salt stress comparing to those with salt stress alone. Subsequently, gene ontology (GO) and KEGG pathway enrichment analysis characterized that DEGs involved in linoleic acid metabolism and plant hormone signal transduction pathways were up-regulated predominantly in JA pretreated wheat seedlings exposed to salt stress. We noticed that genes that involved in antioxidative defense system and that encoding transcription factors were mainly up- or down-regulated. Moreover, SOD, POD, CAT and APX activities were increased in JA pretreated wheat seedlings exposed to salt stress, which is in accordance with the transcript profiles of the relevant genes. Taken together, our results demonstrate that the genes and enzymes involved in physiological and biochemical processes of antioxidant system, plant hormones and transcriptional regulation contributed to JA-mediated enhancement of salt tolerance in wheat. These findings will facilitate the elucidation of the potential molecular mechanisms associated with JA-dependent amelioration of salt stress in wheat and lay theoretical foundations for future studies concerning the improvement of plant tolerance to abiotic environmental stresses.

Iodine Enhances the Nutritional Value but Not the Tolerance of Lettuce to NaCl

Positive stress or essential and nonessential elements can improve nutritive values (biofortification) of edible plants. In the present study, we evaluate (i) the effect of moderate salinity on lettuce biofortification, evaluated as nutritional bioactive compound accumulation, and (ii) the role of iodine in enhancing salt tolerance by increasing photorespiration and the content of antioxidants in lettuce. Physiological (gas exchange and chlorophyll fluorescence emission) and biochemical (photosynthetic pigment and bioactive compound) analyses were performed on lettuce plants grown under moderate salinity (50 mM NaCl alone or 50 mM NaCl in combination with iodine, KIO3). Our results show that NaCl + iodine treatment improves the nutritional value of lettuce in terms of bioactive compounds acting as antioxidants. More specifically, iodine enhances the accumulation of photosynthetic pigments and polyphenols, such as anthocyanins, under salt but does not improve the salt tolerance. Our findings indicate that iodine application under moderate salinity could be a valid strategy in plant biofortification by improving nutritional bioactive compound accumulation, thus exercising functional effects on human health.

N7 -SSPP fusion gene improves salt stress tolerance in transgenic Arabidopsis and soybean through ROS scavenging.

Considerable signal crosstalk exists in the regulatory network of senescence and stress response. Numerous senescence-associated genes are also involved in plant stress tolerance. However, the underlying mechanisms and application potential of these genes in stress-tolerant crop breeding remain poorly explored. We found that overexpression of SENESCENCE-SUPPRESSED PROTEIN PHOSPHATASE (SSPP), a negative regulator of leaf senescence, significantly improved plant salt tolerance by increasing reactive oxygen species (ROS) scavenging in both Arabidopsis and soybean. However, overexpression of SSPP severely suppressed normal plant growth, limiting its direct use in agriculture. We previously revealed that the N-terminal 1-14 residues of ACS7 (termed 'N7 ') negatively regulated its protein stability through the ubiquitin/proteasome pathway, and the N7 -mediated protein degradation was suppressed by environmental and senescence signals. To avoid the adverse effects of SSPP, the N7 element was fused to the N-terminus of SSPP. We demonstrated that N7 -SSPP fusion gene effectively rescued SSPP-induced growth suppression but maintained enhanced salt tolerance in Arabidopsis and soybean. Particularly, N7 -SSPP enhanced tolerance to long-term salt stress and increased seed yield in soybean. These results suggest that N7 -SSPP overcomes the disadvantages of SSPP on plant growth inhibition and effectively improves salt tolerance through enhanced ROS scavenging, providing an effective strategy of using posttranslational regulatory element for salt-tolerant crop breeding.

Auxin response factor gene MdARF2 is involved in ABA signaling and salt stress response in apple

Auxin response factors (ARFs) play key roles throughout the whole process of plant growth and development, and mediate auxin response gene transcription by directly binding with auxin response elements (AuxREs). However, their functions in abiotic stresses are largely limited, especially in apples. Here, the auxin response factor gene MdARF2 (HF41569) was cloned from apple cultivar ‘Royal Gala’ (Malus×domestica Borkh.). Phylogenetic analysis showed that ARF2 proteins are highly conserved among different species and MdARF2 is the closest relative to PpARF2 of Prunus persica, but they differ at the DNA level. MdARF2 contains three typical conserved domains including the B3 DNA-binding domain, Auxin_resp domain and AUX_IAA domain. The subcellular localization demonstrated that MdARF2 is localized in the nucleus. The three-dimensional structure prediction of the proteins showed that MdARF2 is highly similar with AtARF2, and they contain helices, folds, and random coils. The promoter of MdARF2 contains cis-acting elements which respond to various stresses, as well as environmental and hormonal signals. Expression analysis showed that MdARF2 is widely expressed in all tissues of apple, with the highest expression of MdARF2 in root. Functional analysis with a series of MdARF2 transgenic apple calli indicated that MdARF2 can reduce the sensitivity to ABA signaling and enhance salt tolerance in apple. In summary, the results of this research provide a new basis for studying the regulation of abiotic stresses by ARFs.

Scrutinizes the Sustainable Role of Halophilic Microbial Strains on Oxygen-Evolving Complex, Specific Energy Fluxes, Energy Flow and Nitrogen Assimilation of Sunflower Cultivars in a Suboptimal Environment.

Environmental extremes such as hypersaline conditions are significant threats to agricultural productivity. The sustainable use of halophilic microbial strains was evaluated in plant in a salt stress environment. Oxygen-evolving complex (OEC), energy compartmentalization, harvesting efficiencies (LHE), specific energy fluxes (SEF), and nitrogen assimilation of oilseed crops (Sunflower cultivars) in a suboptimal environment was examined. Plants were grown in a plastic pot (15 ×18 cm2) containing sterilized (autoclaved at 120°C for 1 h) soil. Twenty-five ml suspension (107 CFU/ml) each of Bacillus cereus strain KUB-15 and KUB-27 (accession number NR 074540.1) and Bacillus licheniformis strain AAB9 (accession number MW362506), were applied via drenching method. Month-old plants were subjected to salt stress via gradual increment method. The energy compartmentalization of microbial inoculated plants exposed to salt stress revealed higher photosystem II (PSII) activity at the donor side, lesser photo-inhibition, and increased performance of oxygen-evolving complex compared to control. High potassium (K+) and low sodium (Na+) ions in treated leaves with the activated barricade of the antioxidant system stimulated by Bacillus strains favored enhanced photochemical efficiency, smooth electron transport, and lesser energy dissipation in the stressed plants. Moreover, the results reveal the increased activity of nitrite reductase (NiR) and nitrate reductase (NR) by microbial inoculation that elevated the nitrogen availability in the salt-stressed plant. The current research concludes that the application of bio-inoculants that reside in the hyper-saline environment offers substantial potential to enhance salt tolerance in sunflowers by modulating their water uptake, chlorophyll, nitrogen metabolism, and better photochemical yield.

SbWRKY55 regulates sorghum response to saline environment by its dual role in abscisic acid signaling.

SbWRKY55 functions as a key component of the ABA-mediated signaling pathway; transgenic sorghum regulates plant responses to saline environments and will help save arable land and ensure food security. Salt tolerance in plants is triggered by various environmental stress factors and endogenous hormonal signals. Numerous studies have shown that WRKY transcription factors are involved in regulating plant salt tolerance. However, the underlying mechanism for WRKY transcription factors regulated salt stress response and signal transduction pathways remains largely unknown. In this study, the SbWRKY55 transcription factor was found to be the key component for reduced levels of salt and abscisic acid in SbWRKY55 overexpression significantly reduced salt tolerance in sorghum and Arabidopsis. Mutation of the homologous gene AtWRKY55 in A. thaliana significantly enhanced salt tolerance, and SbWRKY55 supplementation in the mutants restored salt tolerance. In the transgenic sorghum with SbWRKY55 overexpression, the expression levels of genes involved in the abscisic acid (ABA) pathway were altered, and the endogenous ABA content decreased. Yeast one-hybrid assays and dual-luciferase reporter assay showed that SbWRKY55 binds directly to the promoter of SbBGLU22 and inhibits its expression level. In addition, both in vivo and in vitro biochemical analyses showed that SbWRKY55 interacts with the FYVE zinc finger protein SbFYVE1, blocking the ABA signaling pathway. This could be an important feedback regulatory pathway to balance the SbWRKY55-mediated salt stress response. In summary, the results of this study provide convincing evidence that SbWRKY55 functions as a key component in the ABA-mediated signaling pathway, highlighting the dual role of SbWRKY55 in ABA signaling. This study also showed that SbWRKY55 could negatively regulate salt tolerance in sorghum.