Identification of SmNAC28 Transcription Factor and Its Mechanism of Regulating Salt Tolerance in Eggplant via S-Palmitoylation.

Raising crops for dry and saline lands: Challenges and the way forward.

A meeting on the molecular basis of ionic homeostasis and salt tolerance in plants took place in Madrid, Spain, October 22–24, 2001. This meeting was organized by Eduardo Blumwald (Davis, CA) and Alonso Rodriguez‐Navarro (Madrid, Spain) at the Centre for International Meetings on Biology (‘Instituto Juan March de Estudios e Investigaciones’). ![][1] Ionic homeostasis is a fundamental cellular phenomenon. All living cells maintain an intracellular ionic composition compatible with their constituent molecules, and this requires the regulation of multiple membrane transporters and signal transduction pathways. Other biophysical parameters such as turgor and electrical potential are also part of this essential regulation. How ionic homeostasis is achieved, however, is not completely understood. Although most transporters have already been identified, their physiological function is only starting to be demonstrated and the receptors and most components of the regulatory pathways that effect ionic homeostasis remain unknown. In the case of plants, this problem is related to mineral nutrition and salinity tolerance, both of which have great relevance for agriculture. In fact, as demonstrated by this meeting, salinity stress has been one of the keys to opening the black box of ionic homeostasis in general. Another has been the novel molecular genetics of the plant Arabidopsis thaliana . Of course, other approaches have also contributed to our present understanding of ion homeostasis in plants and were represented at the meeting. For further details, see Blumwald (2000), Hasegawa et al . (2000), Bohnert et al . (2001), Serrano and Rodriguez‐Navarro (2001) and Zhu (2001). ### Some physiology of salt tolerance Salt stress is an important threat to the future of agriculture in many productive areas of the planet. In countries such as Australia and Pakistan, salinity is already a national concern, as it was in the past in ancient Mesopotamia. Areas of California and the Mediterranean region are also threatened. … [1]: /embed/graphic-1.gif

The salt and ABA inducible transcription factor gene, SlAITR3, negatively regulates tomato salt tolerance.

This manuscript reports the identification and characterization of five transcription factors binding to the promoter of OsNHX1 in a salt stress tolerant rice genotype (Hasawi). Although NHX1 encoding genes are known to be highly regulated at the transcription level by different abiotic stresses, namely salt and drought stress, until now only onetranscription factor (TF) binding to its promoter has been reported. In order to unveil the TFs regulating NHX1 gene expression, which is known to be highly induced under salt stress, we have used a Y1H system to screen a salt induced rice cDNA expression library from Hasawi. This approach allowed us to identify five TFs belonging to three distinct TF families: one TCP (OsPCF2), one CPP (OsCPP5) and three NIN-like (OsNIN-like2, OsNIN-like3 and OsNIN-like4) binding to the OsNHX1 gene promoter. We have also shown that these TFs act either as transcriptional activators (OsPCF2, OsNIN-like4) or repressors (OsCPP5, OsNIN-like2) and their encoding genes are differentially regulated by salt and PEG-induced drought stress in two rice genotypes, Nipponbare (salt-sensitive) and Hasawi (salt-tolerant). The transactivation activity of OsNIN-like3 was not possible to determine. Increased soil salinity has a direct impact on the reduction of plant growth and crop yield and it is therefore fundamental to understand the molecular mechanisms underlying gene expression regulation under adverse environmental conditions. OsNHX1 is the most abundant K+-Na+/H+ antiporter localized in the tonoplast and its gene expression is induced by salt, drought and ABA. To investigate how OsNHX1 is transcriptionally regulated in response to salt stress in a salt-tolerant rice genotype (Hasawi), a salt-stress-induced cDNA expression library was constructed and subsequently screened using the yeast one-hybrid system and the OsNHX1 promoter as bait. Five transcription factors (TFs) belonging to three distinct TF families: one TCP (OsPCF2), one CPP (OsCPP5) and three NIN-like (OsNIN-like2, OsNIN-like3 and OsNIN-like4) were identified as binding to OsNHX1 promoter. Transactivation activity assays performed in Arabidopsis and rice protoplasts showed that OsPCF2 and OsNIN-like4 are activators of the OsNHX1 gene expression, while OsCPP5 and OsNIN-like2 act as repressors. The transactivation activity of OsNIN-like3 needs to be further investigated. Gene expression studies showed that OsNHX1 transcript level is highly induced by salt and PEG-induced drought stress in both shoots and roots in both Nipponbare and Hasawi rice genotypes. Nevertheless, OsNHX1 seems to play a particular role in shoots in response to drought. Most of the TFs binding to OsNHX1 promoter showed a modest transcriptional regulation under stress conditions, however, in response to most of the conditions studied, the OsPCF2 was induced earlier than OsNHX1, indicating that OsPCF2 may activate OsNHX1 gene expression. In addition, although the OsNHX1 response to salt and PEG-induced drought stress in either shoots or roots was quite similar in both rice genotypes, the expression of OsPCF2 in roots under salt stress and the OsNIN-like4 in roots subjected to PEG was mainly up-regulated in Hasawi, indicating that these TFs may be associated with the salt and drought stress tolerance observed for this genotype.

Ongoing soil salinization has emerged as a major adverse environmental stress that globally threatens crop growth and productivity (Munns et al., 2020). As one of the most important cereal crops, rice (Oryza sativa L.) is a glycophyte and hence often severely affected by salinity stress (Negrão et al., 2011). Developing salt tolerant rice cultivars by exploiting more genetic salt tolerant resources will greatly contribute to global food security. Presence–absence variations (PAVs), referring to the presence or absence of gene variability in diverse rice accessions, are an important source of genetic diversity and have been revealed to play key roles in the determination of plant evolution and agronomical traits (Della Coletta et al., 2021; Wang et al., 2023). However, it remains unclear how they modulate stress response, especially salt stress. Currently, with the availability of rice pan-genomic data, PAVs can be systematically identified and described, enabling in-depth exploration of their roles in rice genetic diversity and salt stress response. The expression of genes can be altered by nearby PAV due to their interruptions in gene or regulatory elements (Scott et al., 2021). Several eQTLs associated with salt tolerance have been identified using a set of SNPs generated from the super pan-genome of rice (Wei et al., 2024). Additionally, PAVs known as hidden variants have the ability to reveal new eQTLs that cannot be detected by SNPs (Shang et al., 2022). To discover PAVs affecting gene expression under normal and salt stress conditions, we identified PAV associated with gene expression levels (PAV-expression quantitative loci, PAV-eQTLs) among the Global MiniCore Rice Collection of 202 accessions that have been published previously (Shang et al., 2022; Wei et al., 2024). We defined the PAV located in the c. 2 kb as cis-eQTL and identified 2427 and 2898 cis-PAV-eGenes under normal and salt stress conditions, respectively. Based on occurrence in different conditions, 1692 belonged to static PAV-eGenes and 1206 eGenes pertained dynamic PAV-eGene only under salt stress environment (Fig. 1a, upper panel). Given the crucial role of transcription factors (TFs) involved in salt stress response, we focused on 22 members that overlapped with differentially expressed genes (DEGs) and dynamic PAV-eGenes under the salt stress condition and TF dataset, of which these data were sourced from PlantTFDB (Fig. 1a, lower panel; Supporting Information Table S1). Through examination of a Manhattan plot of PAV-eQTL c. 22 members, we found that 12 members have significant and unique association peaks (Fig. S1). The person correction of 22 genes between the Fragments per Kilobase of transcript per Million mapped reads (FPKM) and survival rate under salt stress condition was further analyzed, and the result indicated that 12 members showed a significant correlation between the expression levels and the survival rate (Figs 1b, S2). Next, we found that seven candidate genes can simultaneously meet both of the above conditions (Fig. S3). Finally, we further analyzed the significant positions where PAVs fall and combined with the gene function, focusing on OsMADS56 (also named as GL10) that regulated heading date and grain size (Figs 1c, S3; Table S1). Among these significant PAVs of OsMADS56, we found that one PAV (Chr10_20,863489) resulted in the complete absence of both the ATG and first exon (Fig. 1d). Based on sequence variations of this PAVs across 202 rice accessions, they were classified into two haplotypes (Hap1 and Hap2) of OsMADS56 (Fig. 1d). The Hap1 containing 1.0 Kb PAV was detected in six salt-tolerant cultivars (Fig. S4). Furthermore, these accessions containing Hap1 had much higher survival rate and lower dead leaf rate than those with Hap2 after NaCl treatment (Fig. 1e, left and middle panel). Additionally, the FPKM values of Hap1 were significantly higher than Hap2 (Fig. 1e, right panel), indicating that this PAV disrupted the expression of OsMADS56 to cause more sensitivity to salt tolerance. To further reveal the genetic effect of this natural variation in OsMADS56 on salt tolerance, we obtained the near isogenic lines (NILs) of OsMADS56, NIL-GL10 and NIL-gl10, corresponding to Hap1 and Hap2, respectively (Zhan et al., 2022), and found that the survival rate of NIL-GL10 was obviously higher than that of NIL-gl10 under salt stress (Fig. 1f). Collectively, these results support the notion that OsMADS56 is likely to be crucial for salt tolerance in rice. We found that OsMADS56 was significantly induced when exposed to 150 mM NaCl and reached the peak at 6 h (Fig. S5a). Subsequently, the pOsMADS56::GUS transgenic seedlings were used to further verify the response to salt stress. In accordance with the quantitative real-time polymerase chain reaction assays, the expression of OsMADS56 was enhanced after exposed to NaCl treatment for 1 h, peaked at 6 h, and then decreased (Fig. S5b). To confirm the function of OsMADS56 in salt stress, the loss-of-function osmads56 mutants mediated by CRISPR/Cas9 system and OsMADS56 overexpressing transgenic plants driven by the Ubiquitin promoter were obtained. We selected two T1 homozygous frame-shift osmads56 mutants (Cas9-72 and Cas9-73) and two independent overexpression lines with elevated OsMADS56 expression (OE-2 and OE-6) in XS134 background, as well as one T1 homozygous frame-shift mutant (Cas9-6) in ZH11 to further investigate their responses to 150 mM NaCl (Fig. S6). Compared with the wild-type (WT), OsMADS56 overexpressing lines exhibited several specific advantages under NaCl treatment, including higher seed germination rates during the germination stage (Figs 1g, S7), lesser inhibition effects on shoot length, root length, and fresh weight in the post-germination stage (Fig. S8), as well as higher survival rates at the four-leaf stage (Fig. 1h), suggesting that overexpression of OsMADS56 caused hyposensitivity to salt stress in rice. Nevertheless, osmads56 mutants from XS134 and ZH11 both exhibited much more severe salt stress-sensitive characteristics than their corresponding WT (Figs 1g,h, S7–S9). Furthermore, our RNA-seq data showed that the transcriptions of positively regulated genes for salt tolerance, such as SKC1 and OsSIK2, were drastically enhanced in overexpression lines under salt stress, compared with WT, which were notably reduced in the osmads56 mutants (Fig. S10). Together, these data indicated that OsMADS56 plays a positive regulatory role in rice salt tolerance. Emerging evidence suggests that salt stress-induced osmotic stress causes increased reactive oxygen species (ROS) generation, which in turn creates oxidative stress that results in physiological damage to plant cells (Castro et al., 2021). To detect the ROS accumulation, we compared 3,3′-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) staining in osmads56 variants, OsMADS56 overexpression lines, and WT leaves. Without NaCl treatment, there was no noticeable difference between above plants. However, after being exposed to 150 mM NaCl treatment, the DAB and NBT staining results showed that more ROS accumulated in the osmads56 mutants, but less in the OsMADS56 overexpression lines, than in their corresponding WT (Fig. 1i). Since the ROS accumulation is related to the activity of ROS-scavenging enzymes, we then measured the antioxidant enzyme activities, such as catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD). As expected, all of the mentioned enzyme activities were increased under osmotic stress treatment; however, the enzyme activities of osmads56 mutants were clearly lower than those of WT, whereas the enzyme activities were evidently higher in the OsMADS56 OE plants than in the WT (Fig. 1i). Consequently, we speculated that the OsMADS56 gene could improve the salt stress tolerance through enhancing the activity of certain ROS-scavenging enzymes in rice. To investigate the genetic interactions between OsMADS56 and other salt tolerance genes, all 202 accessions from the pan-genomic population were classified by functional nucleotide polymorphisms (FNPs) of GS3, SKC1, STG5, and MKK10.2. Coincidentally, in the presence of OsMADS56, significant differences were observed in salt tolerance between the groups containing GS3/SKC1 and gs3/skc1, implying that OsMADS56 had an additive effect on salt tolerance for these genes (Fig. 1j). A similar additive effect of OsMADS56 also occurred on the STG5 and MKK10.2 genes in terms of salt tolerance (Fig. S11). These results indicate that different combinations of OsMADS56 and these genes' FNPs have significant effects on salt tolerance, suggesting their potential synergistic regulation of salt tolerance. In conclusion, we innovatively determined the effects of PAVs on salt stress response in rice and successfully identified a novel salt tolerance gene OsMADS56, suggesting that super pan-genome and transcriptomics technologies rendered an effective way to identify functional PAV-eQTLs in salinity tolerance. OsMADS56 overexpression lines reduced the accumulation of ROS by up-regulating ROS-scavenging enzyme activities, thereby enhancing the salt stress tolerance in rice. Our findings also provide insights into an alternative multi-gene aggregation strategy for salt tolerance, implying that OsMADS56 might be a promising genetic resource for developing salt tolerance rice cultivars. These discoveries are expected to contribute to rice production in the face of the continuous threat of salt stress. More critically, previous studies have revealed that OsMADS56 also contributes to grain size, thermotolerance, and photoperiodic flowering in rice (Ryu et al., 2009; Zhan et al., 2022; He et al., 2024). Thus, OsMADS56 provides a promising target for increasing productivity, stress tolerance, and adaptability of rice globally. The rice cultivar Xiushui134 (Oryza sativa L. ssp. Japonica) was used as WT for physiological experiments and genetic transformation. The knockout mutants of OsMADS56 were generated by CRISPR/Cas9 system, and OsMADS56 overexpressing lines were driven by Ubiquitin promoter. The osmads56 mutant in Zhonghua11 (ZH11) background was purchased from the WIMI Biotechnology Co., Ltd (Changzhou, China) (Lu et al., 2017). Plants were grown in the growth chamber or glasshouse with a 14 h : 10 h, 30°C : 25°C, light : dark cycle (300 μmol photons m−2 s−1). Relative humidity was controlled at 60% humidity. The RNA-seq data and the DEGs dataset were collected from our previous studies (Shang et al., 2022; Wei et al., 2024). The method of eQTL analysis was conducted in the same way as described in Wei et al. (2024). For PAV-eGene, eQTL with lead SNP located within 2 kb upstream and downstream of the gene were classified as cis, while the others were considered as trans. To analyze seed germination under salt treatment, roughly 90 seeds of osmads56 mutants, OsMADS56 overexpressing lines, and corresponding WT (three replicates per genotype) were randomly placed in ½-strength Murashige & Skoog medium (½ MS medium) supplemented with 150 mM NaCl. Seeds were considered to have germinated when the radicle or germ reaches a length of c. 1 mm. The germination rates were recorded daily. For phenotype analysis at post-germination, the uniformly germinated seeds were grown on ½ MS medium containing 150 mM NaCl at 28°C. Then, the shoot length, root length, and fresh weight were measured to assess the salt inhibition. For salinity stress testing, 15-d-old seedlings grown in ½ MS medium were treated with 150 mM NaCl solution for 3–5 d. After 7-d recovery, seedlings were photographed and the survival rate was determined. Seeds and seedlings grown in ½ MS medium were used as the control. For salt stress response by quantitative real-time polymerase chain reaction, the WT (XS134) was exposed to 150 mM NaCl, and the samples were, collected at different time points. Nitroblue tetrazolium staining and 3,3′-diaminobenzidine staining were used for detecting O2− and H2O2, respectively, as described previously (Zhang et al., 2014). The activities of CAT, APX, and SOD were determined as reported previously (Foyer & Noctor, 2005). To analyze the promoter activity of OsMADS56, a 3.5-kb region upstream of the translation start codon of OsMADS56 was cloned into pCXGUS-P vector (Chen et al., 2009) to create pOsMADS56::GUS construct. Then, the resulting construct was transformed into rice calli of XS134 by an Agrobacterium tumefaciens-mediated method (Hiei et al., 1994). Rice samples were incubated in GUS staining solution at 37°C in the dark for 12 h, and chlorophyll was removed using 75% ethanol. Sixteen-day-old seedlings were treated with 150 mM NaCl for 6 h, while seedlings without NaCl treatment were considered as a control. Whole plants were then sampled for RNA sequencing. TRIzol (Life technologies, Carlsbad, CA, USA) was used for extracting total RNA. For transcriptome analysis, cDNA libraries were constructed according to standard Illumina protocols and sequenced using the Illumina HiSeq 4000 system. Differentially expressed genes were defined as those with a twofold expression difference and a P-value < 0.05. The extracted RNA was reverse transcribed with First Strand cDNA Synthesis Kit (Thermo, Waltham, MA, USA). Quantitative real-time polymerase chain reaction was performed with the SYBR Premix Ex Taq (Takara, Otsu, Shiga, Japan) following the operation manual, and the rice OsActin1 gene was used as endogenous control. Data from three biological replicates and three technical repetitions were collected. A list of primers is shown in Table S2. We thank Prof. Shaokui Wang (South China Agricultural University, Guangdong) for kindly providing the near isogenic lines NIL-GL10 and NIL-gl10. This work was supported by grants from STI2030-Major Projects (2023ZD04076), The National Natural Science Foundation of China (32188102, 32301882), Innovation Program of Chinese Academy of Agricultural Sciences, Youth Innovation of Chinese Academy of Agricultural Sciences (Y2023QC36), and the Special Project for Public Welfare Research Institute of Fujian Province (2021R1027005). None declared. LS, QQ and YZ designed the research. YC, YL, YZ, HW, YP, HH, HQ and XC performed the experiments. LY, ZZ, XZ, TW, WH, XL, CS, QY and XY analysed the data. LS, LC, YL and FW revised the manuscript. All authors reviewed and approved the final manuscript. YC, YL, HW and YP contributed equally to this work. All study data are included in the article and Supporting Information. The DEGs dataset from this article can be found in the PlantTFDB (https://planttfdb.gao-lab.org/). RNA-seq raw data have been deposited in the NCBI SRA database with bioproject no. PRJNA1009219. Fig. S1 Manhattan plot of presence–absence variation-eQTL c. 22 candidate genes under salt stress condition. Fig. S2 Scatter plot of pearson's correction coefficient of 21 candidate genes between the Fragments per Kilobase of transcript per Million mapped reads and salt stress condition and survival rate. Fig. S3 Identification of candidate genes. Fig. S4 Structure and 1-kb presence–absence variations of OsMADS56 in several major salt-tolerant varieties. Fig. S5 OsMADS56 was responsive to NaCl. Fig. S6 Development of osmads56 mutants through CRISPR/Cas9-mediated two different target sites and the acquisition of OsMADS56 overexpression lines. Fig. S7 Phenotypes and germination rate of the wild-type, overexpressing transgenic plants (OE-2), and knockout plants (Cas9-72) for OsMADS56 under ½ MS and 150 mM NaCl treatment. Fig. S8 Statistical analysis of shoot length, primary root length, and fresh weight of the OsMADS56 overexpression lines and osmads56 mutants after salt stress treatment. Fig. S9 Response and the corresponding survival rate of the osmads56 mutants in ZH11 background to 5-d NaCl treatment followed by a 7-d recovery. Fig. S10 Changes in levels of salt-responsive genes in OsMADS56 overexpression lines, osmads56 mutants, and wild-type plants under salt treatment. Fig. S11 Relationship between OsMADS56 and salt tolerance genes (STG5 and MKK10.2). Table S1 List of 22 candidate genes that overlapped with differentially expressed genes and dynamic presence–absence variation-eGenes under salt stress condition and transcription factor database. Table S2 Primers used in this study. Please note: Wiley is not responsible for the content or functionality of any Supporting Information supplied by the authors. Any queries (other than missing material) should be directed to the New Phytologist Central Office. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Simple SummaryThis review focuses on plant growth and development harmed by abiotic stress, primarily salt stress. Salt stress raises the intracellular osmotic pressure, leading to hazardous sodium buildup. Plants react to salt stress signals by regulating ion homeostasis, activating the osmotic stress pathway, modulating plant hormone signaling, and altering cytoskeleton dynamics and cell wall composition. Understanding the processes underlying these physiological and biochemical responses to salt stress could lead to more effective agricultural crop yield measures. In this review, researchers outline recent advances in plant salt stress control. The study of plant salt tolerance processes is essential, both theoretically and practically, to improve agricultural output, produce novel salt-tolerant cultivars, and make full use of saline soil. Based on past research, this paper discusses the adverse effects of salt stress on plants, including photosynthesis suppression, ion homeostasis disturbance, and membrane peroxidation. The authors have also covered the physiological mechanisms of salt tolerance, such as the scavenging of reactive oxygen species and osmotic adjustment. This study further identifies specific salt stress-responsive mechanisms linked to physiological systems. Based on previous studies, this article reviews the current methodologies and techniques for improving plant salt tolerance. Overall, it is hoped that the above-mentioned points will impart helpful background information for future agricultural and crop plant production.Salinity is significant abiotic stress that affects the majority of agricultural, irrigated, and cultivated land. It is an issue of global importance, causing many socio-economic problems. Salt stress mainly occurs due to two factors: (1) soil type and (2) irrigation water. It is a major environmental constraint, limiting crop growth, plant productivity, and agricultural yield. Soil salinity is a major problem that considerably distorts ecological habitats in arid and semi-arid regions. Excess salts in the soil affect plant nutrient uptake and osmotic balance, leading to osmotic and ionic stress. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, the production of enzymes, compatible solutes, metabolites, and molecular or genetic networks. Different plant species have different salt overly sensitive pathways and high-affinity K+ channel transporters that maintain ion homeostasis. However, little progress has been made in developing salt-tolerant crop varieties using different breeding approaches. This review highlights the interlinking of plant morpho-physiological, molecular, biochemical, and genetic approaches to produce salt-tolerant plant species. Most of the research emphasizes the significance of plant growth-promoting rhizobacteria in protecting plants from biotic and abiotic stressors. Plant growth, survival, and yield can be stabilized by utilizing this knowledge using different breeding and agronomical techniques. This information marks existing research areas and future gaps that require more attention to reveal new salt tolerance determinants in plants—in the future, creating genetically modified plants could help increase crop growth and the toleration of saline environments.

Salt stress is a major environmental factor affecting plant growth and crop production worldwide, and the transcription factors (TFs) play crucial roles in plant response to salt stress. Identifying genes related to salt-tolerance contributes to salt-tolerant crop breeding. A comparative transcriptome analysis was carried out to investigate global gene expression of the entire TFs in two maize varieties with different salt-tolerant ability. Fifty-five TF families including 1283 TF genes were identified. Among them, 314 TF genes were differentially expressed in the two maize varieties under salt stress. 177 TF genes were detected with significantly higher expression levels in salt-tolerance variety compared with the salt-sensitive one. The differential expression of a set of TF families clearly demonstrated their important roles in salt tolerance. Further phylogenetic analysis and gene expression analysis of heat shock factors (HSFs) revealed that majority of these TFs were induced by salt stress, but different classes/subclasses had different response to salt stress. HSF class-B genes were detected with significantly higher expression levels in salt-tolerance variety compared with the salt-sensitive one under salt stress, which may result in different plants salt-tolerance ability. These results contribute to a better understanding of the complex mechanism of TFs in response to salt stress in maize and provide new sight for further research to perform systematic analysis of the TF families and to reveal their potential functions in the salt-tolerance for plants.

Genome-wide identification of R2R3-MYB transcription factors in Betula platyphylla and functional analysis of BpMYB95 in salt tolerance

Trehalose (Tre), which was an osmoprotective or stabilizing molecule, played a protective role against different abiotic stresses in plants and showed remarkable perspectives in salt stress. In this study, the potential role of Tre in improving the resistance to salt stress in tomato plants was investigated. Tomato plants (Micro Tom) were treated with Hoagland nutrient solution (CK), 10 mM Tre (T), 150 mM sodium chloride (NaCl, S), and 10 mM Tre+150 mM NaCl (S+T) for 5 days. Our results showed that foliar application of Tre alleviated the inhibition of tomato plant growth under salt stress. In addition, salt stress decreased the values of net photosynthetic rate (Pn, 85.99%), stomata conductance (gs, 57.3%), and transpiration rate (Tr, 47.97%), but increased that of intercellular carbon dioxide concentration (Ci, 26.25%). However, exogenous application of Tre significantly increased photosynthetic efficiency, increased the activity of Calvin cycle enzymes [ribulose diphosphate carboxylase/oxygenase (Rubisco), fructose-1,6-bisphosphate aldolase (FBA), fructose-1, 6-bisphosphatase (FBPase), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and transketolase (TK)], up-regulated the expression of genes encoding enzymes, induced stomatal opening, and alleviated salt-induced damage to the chloroplast membrane and structure. In the saline environment, photosynthetic electron transport was restricted, resulting the J-I-P phase to decrease. At the same time, the absorption, capture, and transport energies per excited cross-section and per active reaction center decreased, and the dissipation energy increased. Conversely, Tre reversed these values and enhanced the photosystem response to salt stress by protecting the photosynthetic electron transport system. In addition, foliage application with Tre significantly increased the potassium to sodium transport selectivity ratio (SK–Na) by 16.08%, and increased the levels of other ions to varying degrees. Principal component analysis (PCA) analysis showed that exogenous Tre could change the distribution of elements in different organs and affect the expressions of SlSOS1, SlNHX, SlHKT1.1, SlVHA, and SlHA-A at the transcriptional level under salt stress, thereby maintaining ion homeostasis. This study demonstrated that Tre was involved in the process of mitigating salt stress toxicity in tomato plants and provided specific insights into the effectiveness of Tre in mediating salt tolerance.

Climate change is dramatically increasing the overall area of saline soils around the world, which is increasing by approximately two million hectares each year. Soil salinity decreases crop yields and, thereby, makes farming less profitable, potentially causing increased poverty and hunger in many areas. A solution to this problem is increasing the salt tolerance of crop plants. Transcription factors (TFs) within crop plants represent a key to understanding salt tolerance, as these proteins play important roles in the regulation of functional genes linked to salt stress. The basic leucine zipper (bZIP) TF has a well-documented role in the regulation of salt tolerance. To better understand how bZIP TFs are linked to salt tolerance, we performed a genome-wide analysis in wheat using the Chinese spring wheat genome, which has been assembled by the International Wheat Genome Sequencing Consortium. We identified 89 additional bZIP gene sequences, which brings the total of bZIP gene sequences in wheat to 237. The majority of these 237 sequences included a single bZIP protein domain; however, different combinations of five other domains also exist. The bZIP proteins are divided into ten subfamily groups. Using an in silico analysis, we identified five bZIP genes (ABF2, ABF4, ABI5, EMBP1, and VIP1) that were involved in regulating salt stress. By scrutinizing the binding properties to the 2000 bp upstream region, we identified putative functional genes under the regulation of these TFs. Expression analyses of plant tissue that had been treated with or without 100 mM NaCl revealed variable patterns between the TFs and functional genes. For example, an increased expression of ABF4 was correlated with an increased expression of the corresponding functional genes in both root and shoot tissues, whereas VIP1 downregulation in root tissues strongly decreased the expression of two functional genes. Identifying strategies to sustain the expression of the functional genes described in this study could enhance wheat's salt tolerance.

BackgroundSalt stress significantly influences plant growth and reduces crop yield. It is highly anticipated to develop salt-tolerant crops with salt tolerance genes and transgenic technology. Hence, it is critical to identify salt tolerance genes that can be used to improve crop salt tolerance.ResultsWe report that the transcription elongation factor suppressor of Ty 4-2 (SPT4-2) is a positive modulator of salt tolerance in Arabidopsis thaliana. AtSPT4-2 expression is induced by salt stress. Knockout mutants of AtSPT4-2 display a salt-sensitive phenotype, whereas AtSPT4-2 overexpression lines exhibit enhanced salt tolerance. Comparative transcriptomic analyses revealed that AtSPT4-2 may orchestrate the expression of genes associated with salt tolerance, including stress-responsive markers, protein kinases and phosphatases, salt-responsive transcription factors and those maintaining ion homeostasis, suggesting that AtSPT4-2 improves salt tolerance mainly by maintaining ion homeostasis and enhancing stress tolerance.ConclusionsAtSPT4-2 positively modulates salt tolerance by maintaining ion homeostasis and regulating stress-responsive genes and serves as a candidate for the improvement of crop salt tolerance.

The WRKY transcription factor family is one of the largest groups of transcription factor in plants, playing important roles in growth, development, and biotic and abiotic stress responses. Many WRKY genes have been cloned from a variety of plant species and their functions have been analyzed. However, the studies on WRKY transcription factors in tree species under abiotic stress are still not well characterized. To understand the effects of the WRKY gene in response to abiotic stress, mRNA abundances of 102 WRKY genes in Populus simonii × P. nigra were identified by RNA sequencing under normal and salt stress conditions. The expression of 23 WRKY genes varied remarkably, in a tissue-specific manner, under salt stress. Since the WRKY56 was one of the genes significantly induced by NaCl treatment, its cDNA fragment containing an open reading frame from P. simonii × P. nigra was then cloned and transferred into Arabidopsis using the floral dip method. Under salt stress, the transgenic Arabidopsis over-expressed the WRKY56 gene, showing an increase in fresh weight, germination rate, proline content, and peroxidase and superoxide dismutase activity, when compared with the wild type. In contrast, transgenic Arabidopsis displayed a decrease in malondialdehyde content under salt stress. Overall, these results indicated that the WRKY56 gene played an important role in regulating salt tolerance in transgenic Arabidopsis.

Salt stress is a common abiotic stress that limits the growth, development and yield of maize (Zea mays L.). To better understand the response of maize to salt stress and the mechanism by which exogenous glycine betaine (GB) alleviates the damaging effects of salt stress, the morphology, physiological and biochemical indexes, and root transcriptome expression profiles of seedlings of salt-sensitive inbred line P138 and salt-tolerant inbred line 8723 were compared under salt stress and GB-alleviated salt stress conditions. The results showed that under salt stress the growth of P138 was significantly inhibited and the vivo ion balance was disrupted, whereas 8723 could prevent salt injury by maintaining a high ratio of K+ to Na+. The addition of a suitable concentration of GB could effectively alleviate the damage caused by salt stress, and the mitigating effect on salt-sensitive inbred line P138 was more obvious than that on 8723. Transcriptome analysis revealed that 219 differentially expressed genes (DEGs) were up-regulated and 153 DEGs were down-regulated in both P138 and 8723 under NaCl treatment, and that 487 DEGs were up-regulated and 942 DEGs were down-regulated in both P138 and 8723 under salt plus exogenous GB treatment. In 8723 the response to salt stress is mainly achieved through stabilizing ion homeostasis, strong signal transduction activation, increasing reactive oxygen scavenging. GB alleviates salt stress in maize mainly by inducing gene expression changes to enhance the ion balance, secondary metabolic level, reactive oxygen scavenging mechanism, signal transduction activation. In addition, the transcription factors involved in the regulation of salt stress response and exogenous GB mitigation mainly belong to the MYB, MYB-related, AP2-EREBP, bHLH, and NAC families. We verified 10 selected up-regulated DEGs by quantitative real-time polymerase chain reaction (qRT-PCR), and the expression results were basically consistent with the transcriptome expression profiles. Our results from this study may provide the theoretical basis for determining maize salt tolerance mechanisms and the mechanism by which GB regulates salt tolerance.

As one of the most severe environmental stresses, salt stress can cause a series of changes in plants. In salt tolerant plant Zoysia macrostachya, germination, physiology, and genetic variation under salinity have been studied previously, and the morphology and distribution of salt glands have been clarified. However, no study has investigated the transcriptome of such species under salt stress. In the present study, we compared transcriptome of Z. macrostachya under normal conditions and salt stress (300 mmol/L NaCl, 24 h) aimed to identify transcriptome responses and molecular mechanisms under salt stress in Z. macrostachya. A total of 8703 differently expressed genes (DEGs) were identified, including 4903 up-regulated and 3800 down-regulated ones. Moreover, a series of molecular processes were identified by Gene Ontology (GO) analysis, and these processes were suggested to be closely related to salt tolerance in Z. macrostachya. The identified DEGs concentrated on regulating plant growth via plant hormone signal transduction, maintaining ion homeostasis via salt secretion and osmoregulatory substance accumulation and preventing oxidative damage via increasing the activity of ROS (reactive oxygen species) scavenging system. These changes may be the most important responses of Z. macrostachya under salt stress. Some key genes related to salt stress were identified meanwhile. Collectively, our findings provided valuable insights into the molecular mechanisms and genetic underpinnings of salt tolerance in Z. macrostachya.

Maize (Zea mays L.) is a major food and feed crop and an important raw material for energy, chemicals, and livestock. The NF-Y family of transcription factors in maize plays a crucial role in the regulation of plant development and response to environmental stress. In this study, we successfully cloned and characterized the maize NF-Y transcription factor gene ZmNF-YB10. We used bioinformatics, quantitative fluorescence PCR, and other techniques to analyze the basic properties of the gene, its tissue expression specificity, and its role in response to drought, salt, and other stresses. The results indicated that the gene was 1209 base pairs (bp) in length, with a coding sequence (CDS) region of 618 bp, encoding a polypeptide composed of 205 amino acid residues. This polypeptide has a theoretical isoelectric point of 5.85 and features a conserved structural domain unique to the NF-Y family. Quantitative fluorescence PCR results demonstrated that the ZmNF-YB10 gene was differentially upregulated under drought and salt stress treatments but exhibited a negatively regulated expression pattern under alkali and cold stress treatments. Transgenic Arabidopsis thaliana subjected to drought and salt stress in soil showed greener leaves than wild-type A. thaliana. In addition, the overexpression lines showed reduced levels of hydrogen peroxide (H2O2), superoxide (O2-), and malondialdehyde (MDA) and increased activities of peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD). Western blot analysis revealed a distinct band at 21.8 kDa. Salt and drought tolerance analyses conducted in E. coli BL21 indicated a positive regulation. In yeast cells, ZmNF-YB10 exhibited a biological function that enhances salt and drought tolerance. Protein interactions were observed among the ZmNF-YB10, ZmNF-YC2, and ZmNF-YC4 genes. It is hypothesized that the ZmNF-YB10, ZmNF-YC2, and ZmNF-YC4 genes may play a role in the response to abiotic stresses, such as drought and salt tolerance, in maize.