Comprehensive genome-wide identification of Snf2 gene family and their expression profile under salt stress in six Brassica species of U's triangle model.

MAIN CONCLUSION: We comprehensively identified and analyzed the Snf2 gene family. Some Snf2 genes were involved in responding to salt stress based on the RNA-seq and qRT-PCR analysis. Sucrose nonfermenting 2 (Snf2) proteins are core components of chromatin remodeling complexes that not only alter DNA accessibility using the energy of ATP hydrolysis, but also play a critical regulatory role in growth, development, and stress response in eukaryotes. However, the comparative study of Snf2 gene family in the six Brassica species in U's triangle model remains unclear. Here, a total of 405 Snf2 genes were identified, comprising 53, 50, and 46 in the diploid progenitors: Brassica rapa (AA, 2n = 20), Brassica nigra (BB, 2n = 16), and Brassica oleracea (CC, 2n = 18), and 93, 91, and 72 in the allotetraploid: Brassica juncea (AABB, 2n = 36), Brassica napus (AACC, 2n = 38), and Brassica carinata (BBCC, 2n = 34), respectively. These genes were classified into six clades and further divided into 18 subfamilies based on their conserved motifs and domains. Intriguingly, these genes showed highly conserved chromosomal distributions and gene structures, indicating that few dynamic changes occurred during the polyploidization. The duplication modes of the six Brassica species were diverse, and the expansion of most Snf2 in Brassica occurred primarily through dispersed duplication (DSD) events. Additionally, the majority of Snf2 genes were under purifying selection during polyploidization, and some Snf2 genes were associated with various abiotic stresses. Both RNA-seq and qRT-PCR analysis showed that the expression of BnaSnf2 genes was significantly induced under salt stress, implying their involvement in salt tolerance response in Brassica species. The results provide a comprehensive understanding of the Snf2 genes in U's triangle model species, which will facilitate further functional analysis of the Snf2 genes in Brassica plants.

Genome-Wide Analysis of BBX Gene Family in Three Medicago Species Provides Insights into Expression Patterns under Hormonal and Salt Stresses.

BBX protein is a class of zinc finger transcription factors that have B-box domains at the N-terminus, and some of these proteins contain a CCT domain at the C-terminus. It plays an important role in plant growth, development, and metabolism. However, the expression pattern of BBX genes in alfalfa under hormonal and salt stresses is still unclear. In this study, we identified a total of 125 BBX gene family members by the available Medicago reference genome in diploid alfalfa (Medicago sativa spp. Caerulea), a model plant (M. truncatula), and tetraploid alfalfa (M. sativa), and divided these members into five subfamilies. We found that the conserved motifs of BBXs of the same subfamily reveal similarities. We analyzed the collinearity relationship and duplication mode of these BBX genes and found that the expression pattern of BBX genes is specific in different tissues. Analysis of the available transcriptome data suggests that some members of the BBX gene family are involved in multiple abiotic stress responses, and the highly expressed genes are often clustered together. Furthermore, we identified different expression patterns of some BBX genes under salt, ethylene, salt and ethylene, salicylic acid, and salt and salicylic acid treatments, verified by qRT-PCR, and analyzed the subcellular localization of MsBBX2, MsBBX17, and MsBBX32 using transient expression in tobacco. The results showed that BBX genes were localized in the nucleus. This study systematically analyzed the BBX gene family in Medicago plants, which provides a basis for the study of BBX gene family tolerance to abiotic stresses.

The m6A reader ECT8 is an abiotic stress sensor that accelerates mRNA decay in Arabidopsis.

N 6-methyladenosine (m6A) is the most abundant mRNA modification and plays diverse roles in eukaryotes, including plants. It regulates various processes, including plant growth, development, and responses to external or internal stress responses. However, the mechanisms underlying how m6A is related to environmental stresses in both mammals and plants remain elusive. Here, we identified EVOLUTIONARILY CONSERVED C-TERMINAL REGION 8 (ECT8) as an m6A reader protein and showed that its m6A-binding capability is required for salt stress responses in Arabidopsis (Arabidopsis thaliana). ECT8 accelerates the degradation of its target transcripts through direct interaction with the decapping protein DECAPPING 5 within processing bodies. We observed a significant increase in the ECT8 expression level under various environmental stresses. Using salt stress as a representative stressor, we found that the transcript and protein levels of ECT8 rise in response to salt stress. The increased abundance of ECT8 protein results in the enhanced binding capability to m6A-modified mRNAs, thereby accelerating their degradation, especially those of negative regulators of salt stress responses. Our results demonstrated that ECT8 acts as an abiotic stress sensor, facilitating mRNA decay, which is vital for maintaining transcriptome homeostasis and enhancing stress tolerance in plants. Our findings not only advance the understanding of epitranscriptomic gene regulation but also offer potential applications for breeding more resilient crops in the face of rapidly changing environmental conditions.

Artificially designed synthetic promoter for a high level of salt induction using a cis-engineering approach.

This work aimed to design a synthetic salt-inducible promoter using a cis-engineering approach. The designed promoter (PS) comprises a minimal promoter sequence for basal-level expression and upstream cis-regulatory elements (CREs) from promoters of salinity-stress-induced genes. The copy number, spacer lengths, and locations of CREs were manually determined based on their occurrence within native promoters. The initial activity profile of the synthesized PS promoter in transiently transformed N. tabacum leaves shows a seven-fold, five-fold, and four-fold increase in reporter GUS activity under salt, drought, and abscisic acid stress, respectively, at the 24-h interval, compared to the constitutive CaMV35S promoter. Analysis of gus expression in stable Arabidopsis transformants showed that the PS promoter induces over a two-fold increase in expression under drought or abscisic acid stress and a five-fold increase under salt stress at 24- and 48-h intervals, compared to the CaMV35S promoter. The promoter PS exhibits higher and more sustained activity under salt, drought, and abscisic acid stress compared to the constitutive CaMV35S.

Oil Palm AP2 Subfamily Gene EgAP2.25 Improves Salt Stress Tolerance in Transgenic Tobacco Plants.

AP2/ERF transcription factor genes play an important role in regulating the responses of plants to various abiotic stresses, such as cold, drought, high salinity, and high temperature. However, less is known about the function of oil palm AP2/ERF genes. We previously obtained 172 AP2/ERF genes of oil palm and found that the expression of EgAP2.25 was significantly up-regulated under salinity, cold, or drought stress conditions. In the present study, the sequence characterization and expression analysis for EgAP2.25 were conducted, showing that it was transiently over-expressed in Nicotiana tabacum L. The results indicated that transgenic tobacco plants over-expressing EgAP2.25 could have a stronger tolerance to salinity stress than wild-type tobacco plants. Compared with wild-type plants, the over-expression lines showed a significantly higher germination rate, better plant growth, and less chlorophyll damage. In addition, the improved salinity tolerance of EgAP2.25 transgenic plants was mainly attributed to higher antioxidant enzyme activities, increased proline and soluble sugar content, reduced H2O2 production, and lower MDA accumulation. Furthermore, several stress-related marker genes, including NtSOD, NtPOD, NtCAT, NtERD10B, NtDREB2B, NtERD10C, and NtP5CS, were significantly up-regulated in EgAP2.25 transgenic tobacco plants subjected to salinity stress. Overall, over-expression of the EgAP2.25 gene significantly enhanced salinity stress tolerance in transgenic tobacco plants. This study lays a foundation for further exploration of the regulatory mechanism of the EgAP2.25 gene in conferring salinity tolerance in oil palm.

A Sweet Potato MYB Transcription Factor IbMYB330 Enhances Tolerance to Drought and Salt Stress in Transgenic Tobacco.

MYB transcription factors (TFs) play vital roles in plant growth, development, and response to adversity. Although the MYB gene family has been studied in many plant species, there is still little known about the function of R2R3 MYB TFs in sweet potato in response to abiotic stresses. In this study, an R2R3 MYB gene, IbMYB330 was isolated from sweet potato (Ipomoea batatas). IbMYB330 was ectopically expressed in tobacco and the functional characterization was performed by overexpression in transgenic plants. The IbMYB330 protein has a 268 amino acid sequence and contains two highly conserved MYB domains. The molecular weight and isoelectric point of IbMYB330 are 29.24 kD and 9.12, respectively. The expression of IbMYB330 in sweet potato is tissue-specific, and levels in the root were significantly higher than that in the leaf and stem. It showed that the expression of IbMYB330 was strongly induced by PEG-6000, NaCl, and H2O2. Ectopic expression of IbMYB330 led to increased transcript levels of stress-related genes such as SOD, POD, APX, and P5CS. Moreover, compared to the wild-type (WT), transgenic tobacco overexpression of IbMYB330 enhanced the tolerance to drought and salt stress treatment as CAT activity, POD activity, proline content, and protein content in transgenic tobacco had increased, while MDA content had decreased. Taken together, our study demonstrated that IbMYB330 plays a role in enhancing the resistance of sweet potato to stresses. These findings lay the groundwork for future research on the R2R3-MYB genes of sweet potato and indicates that IbMYB330 may be a candidate gene for improving abiotic stress tolerance in crops.

Overexpression of sweetpotato glutamylcysteine synthetase (IbGCS) in Arabidopsis confers tolerance to drought and salt stresses.

Various environmental stresses induce the production of reactive oxygen species (ROS), which have deleterious effects on plant cells. Glutathione (GSH) is an antioxidant used to counteract reactive oxygen species. Glutathione is produced by glutamylcysteine synthetase (GCS) and glutathione synthetase (GS). However, evidence for the GCS gene in sweetpotato remains scarce. In this study, the full-length cDNA sequence of IbGCS isolated from sweetpotato cultivar Xu18 was 1566 bp in length, which encodes 521 amino acids. The qRT-PCR analysis revealed a significantly higher expression of the IbGCS in sweetpotato flowers, and the gene was induced by salinity, abscisic acid (ABA), drought, extreme temperature and heavy metal stresses. The seed germination rate, root elongation and fresh weight were promoted in T3 Arabidopsis IbGCS-overexpressing lines (OEs) in contrast to wild type (WT) plants under mannitol and salt stresses. In addition, the soil drought and salt stress experiment results indicated that IbGCS overexpression in Arabidopsis reduced the malondialdehyde (MDA) content, enhanced the levels of GCS activity, GSH and AsA content, and antioxidant enzyme activity. In summary, overexpressing IbGCS in Arabidopsis showed improved salt and drought tolerance.

Unraveling a Small Secreted Peptide SUBPEP3 That Positively Regulates Salt-Stress Tolerance in Pyrus betulifolia.

Small secreted peptides (SSPs) play important roles in regulating plants' growth and development in response to external stimulus, but the genes and functions of SSPs in many species are still unknown. Therefore, it is particularly significant to characterize and annotate SSP genes in plant genomes. As a widely used stock of pears, Pyrus betulifolia has strong resistance to biotic and abiotic stresses. In this study, we analyzed the SSPs genes in the genome of P. betulifolia according to their characteristics and homology. A total of 1195 SSP genes were identified, and most of them are signaling molecules. Among these, we identified a new SSP, subtilase peptide 3 (SUBPEP3), which derived from the PA region of preSUBPEP3, increasing the expression level under salt stress. Both adding synthetic peptide SUBPEP3 to the culture medium of pears and the overexpression of SUBPEP3 in tobacco can improve the salt tolerance of plants. In summary, we annotated the SSP genes in the P. betulifolia genome and identified a small secreted peptide SUBPEP3 that regulates the salt tolerance of P. betulifolia, which provides an important theoretical basis for further revealing the function of SSPs.

Poplar glutathione S-transferase PtrGSTF8 contributes to reactive oxygen species scavenging and salt tolerance.

Glutathione S-transferases (GSTs) constitute a protein superfamily encoded by a large gene family and play a crucial role in plant growth and development. However, their precise functions in wood plant responses to abiotic stress are not fully understood. In this study, we isolated a Phi class glutathione S-transferase-encoding gene, PtrGSTF8, from poplar (Populus alba × P. glandulosa), which is significantly up-regulated under salt stress. Moreover, compared with wild-type (WT) plants, transgenic tobacco plants exhibited significant salt stress tolerance. Under salt stress, PtrGSTF8-overexpressing tobacco plants showed a significant increase in plant height and root length, and less accumulation of reactive oxygen species. In addition, these transgenic tobacco plants exhibited higher superoxide dismutase, peroxidase, and catalase activities and reduced malondialdehyde content compared with WT plants. Quantitative real-time PCR experiments showed that the overexpression of PtrGSTF8 increased the expression of numerous genes related to salt stress. Furthermore, PtrMYB108, a MYB transcription factor involved in salt resistance in poplar, was found to directly activate the promoter of PtrGSTF8, as demonstrated by yeast one-hybrid assays and luciferase complementation assays. Taken together, these findings suggest that poplar PtrGSTF8 contributes to enhanced salt tolerance and confers multiple growth advantages when overexpressed in tobacco.

The Characterization of G-Quadruplexes in Tobacco Genome and Their Function under Abiotic Stress.

Tobacco is an ideal model plant in scientific research. G-quadruplex is a guanine-rich DNA structure, which regulates transcription and translation. In this study, the prevalence and potential function of G-quadruplexes in tobacco were systematically analyzed. In tobacco genomes, there were 2,924,271,002 G-quadruplexes in the nuclear genome, 430,597 in the mitochondrial genome, and 155,943 in the chloroplast genome. The density of the G-quadruplex in the organelle genome was higher than that in the nuclear genome. G-quadruplexes were abundant in the transcription regulatory region of the genome, and a difference in G-quadruplex density in two DNA strands was also observed. The promoter of 60.4% genes contained at least one G-quadruplex. Compared with up-regulated differentially expressed genes (DEGs), the G-quadruplex density in down-regulated DEGs was generally higher under drought stress and salt stress. The G-quadruplex formed by simple sequence repeat (SSR) and its flanking sequence in the promoter region of the NtBBX (Nitab4.5_0002943g0010) gene might enhance the drought tolerance of tobacco. This study lays a solid foundation for further research on G-quadruplex function in tobacco and other plants.

Unraveling wheat's response to salt stress during early growth stages through transcriptomic analysis and co-expression network profiling.

BACKGROUND: Soil salinization is one of the vital factors threatening the world's food security. To reveal the biological mechanism of response to salt stress in wheat, this study was conducted to resolve the transcription level difference to salt stress between CM6005 (salt-tolerant) and KN9204 (salt-sensitive) at the germination and seedling stage. RESULTS: To investigate the molecular mechanism underlying salt tolerance in wheat, we conducted comprehensive transcriptome analyses at the seedling and germination stages. Two wheat cultivars, CM6005 (salt-tolerant) and KN9204 (salt-sensitive) were subjected to salt treatment, resulting in a total of 24 transcriptomes. Through expression-network analysis, we identified 17 modules, 16 and 13 of which highly correlate with salt tolerance-related phenotypes in the germination and seedling stages, respectively. Moreover, we identified candidate Hub genes associated with specific modules and explored their regulatory relationships using co-expression data. Enrichment analysis revealed specific enrichment of gibberellin-related terms and pathways in CM6005, highlighting the potential importance of gibberellin regulation in enhancing salt tolerance. In contrast, KN9204 exhibited specific enrichment in glutathione-related terms and activities, suggesting the involvement of glutathione-mediated antioxidant mechanisms in conferring resistance to salt stress. Additionally, glucose transport was found to be a fundamental mechanism for salt tolerance during wheat seedling and germination stages, indicating its potential universality in wheat. Wheat plants improve their resilience and productivity by utilizing adaptive mechanisms like adjusting osmotic balance, bolstering antioxidant defenses, accumulating compatible solutes, altering root morphology, and regulating hormones, enabling them to better withstand extended periods of salt stress. CONCLUSION: Through utilizing transcriptome-level analysis employing WGCNA, we have revealed a potential regulatory mechanism that governs the response to salt stress and recovery in wheat cultivars. Furthermore, we have identified key candidate central genes that play a crucial role in this mechanism. These central genes are likely to be vital components within the gene expression network associated with salt tolerance. The findings of this study strongly support the molecular breeding of salt-tolerant wheat, particularly by utilizing the genetic advancements based on CM6005 and KN9204.

The transcription factor ThDOF8 binds to a novel cis-element and mediates molecular responses to salt stress in Tamarix hispida.

Salt stress is a common abiotic factor that restricts plant growth and development. As a halophyte, Tamarix hispida is a good model plant for exploring salt-tolerance genes and regulatory mechanisms. DNA-binding with one finger (DOF) is an important transcription factor (TF) that influences and controls various signaling substances involved in diverse biological processes related to plant growth and development, but the regulatory mechanisms of DOF TFs in response to salt stress are largely unknown in T. hispida. In the present study, a newly identified Dof gene, ThDOF8, was cloned from T. hispida, and its expression was found to be induced by salt stress. Transient overexpression of ThDOF8 enhanced T. hispida salt tolerance by enhancing proline levels, and increasing the activities of the antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD). These results were also verified in stably transformed Arabidopsis. Results from TF-centered yeast one-hybrid (Y1H) assays and EMSAs showed that ThDOF8 binds to a newly identified cis-element (TGCG). Expression profiling by gene chip analysis identified four potential direct targets of ThDOF8, namely the cysteine-rich receptor-like kinases genes, CRK10 and CRK26, and two glutamate decarboxylase genes, GAD41, and GAD42, and these were further verified by ChIP-quantitative-PCR, EMSAs, Y1H assays, and ß-glucuronidase enzyme activity assays. ThDOF8 can bind to the TGCG element in the promoter regions of its target genes, and transient overexpression of ThCRK10 also enhanced T. hispida salt tolerance. On the basis of our results, we propose a new regulatory mechanism model, in which ThDOF8 binds to the TGCG cis-element in the promoter of the target gene CRK10 to regulate its expression and improve salt tolerance in T. hispida. This study provides a basis for furthering our understanding the role of DOF TFs and identifying other downstream candidate genes that have the potential for improving plant salt tolerance via molecular breeding.

N6-methyladenosine mRNA methylation positively regulated the response of poplar to salt stress.

As the most abundant form of methylation modification in messenger RNA (mRNA), the distribution of N6-methyladenosine (m6A) has been preliminarily revealed in herbaceous plants under salt stress, but its function and mechanism in woody plants were still unknown. Here, we showed that global m6A levels increased during poplar response to salt stress. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) revealed that m6A significantly enriched in the coding sequence region and 3'-untranslated regions in poplar, by recognising the conserved motifs, AGACU, GGACA and UGUAG. A large number of differential m6A transcripts have been identified, and some have been proved involving in salt response and plant growth and development. Further combined analysis of MeRIP-seq and RNA-seq revealed that the m6A hypermethylated and enrich in the CDS region preferred to positively regulate expression abundance. Writer inhibitor, 3-deazaneplanocin A treatment increased the sensitivity of poplar to salt stress by reducing mRNA stability to regulate the expression of salt-responsive transcripts PagMYB48, PagGT2, PagNAC2, PagGPX8 and PagARF2. Furthermore, we verified that the methyltransferase PagFIP37 plays a positively role in the response of poplar to salt stress, overexpressed lines have stronger salt tolerance, while RNAi lines were more sensitive to salt, which relied on regulating mRNA stability in an m6A manner of salt-responsive transcripts PagMYB48, PagGT2, PagNAC2, PagGPX8 and PagARF2. Collectively, these results revealed the regulatory role of m6A methylation in poplar response to salt stress, and revealed the importance and mechanism of m6A methylation in the response of woody plants to salt stress for the first time.

Autophagy receptor OsNBR1 modulates salt stress tolerance in rice.

KEY MESSAGE: Autophagy receptor OsNBR1 modulates salt stress tolerance by affecting ROS accumulation in rice. The NBR1 (next to BRCA1 gene 1), as important selective receptors, whose functions have been reported in animals and plants. Although the function of NBR1 responses to abiotic stress has mostly been investigated in Arabidopsis thaliana, the role of NBR1 under salt stress conditions remains unclear in rice (Oryza sativa). In this study, by screening the previously generated activation-tagged line, we identified a mutant, activation tagging 10 (AC10), which exhibited salt stress-sensitive phenotypes. TAIL-PCR (thermal asymmetric interlaced PCR) showed that the AC10 line carried a loss-of-function mutation in the OsNBR1 gene. OsNBR1 was found to be a positive regulator of salt stress tolerance and was localized in aggregates. A loss-of-function mutation in OsNBR1 increased salt stress sensitivity, whereas overexpression of OsNBR1 enhanced salt stress resistance. The osnbr1 mutants showed higher ROS (reactive oxygen species) production, whereas the OsNBR1 overexpression (OsNBR1OE) lines showed lower ROS production, than Kitaake plants under normal and salt stress conditions. Furthermore, RNA-seq analysis revealed that expression of OsRBOH9 (respiratory burst oxidase homologue) was increased in osnbr1 mutants, resulting in increased ROS accumulation in osnbr1 mutants. Together our results established that OsNBR1 responds to salt stress by influencing accumulation of ROS rather than by regulating transport of Na+ and K+ in rice.

Identification of the MYB gene family in Sorghum bicolor and functional analysis of SbMYBAS1 in response to salt stress.

Salt stress adversely affects plant growth and development. It is necessary to understand the underlying salt response mechanism to improve salt tolerance in plants. MYB transcription factors can regulate plant responses to salt stress. However, only a few studies have explored the role of MYB TFs in Sorghum bicolor (L.) Moench. So we decided to make a systematic analysis and research on the sorghum MYB family. A total of 210 MYB genes in sorghum were identified in this study. Furthermore, 210 MYB genes were distributed across ten chromosomes, named SbMYB1-SbMYB210. To study the phylogeny of the identified TFs, 210 MYB genes were divided into six subfamilies. We further demonstrated that SbMYB genes have evolved under strong purifying selection. SbMYBAS1 (SbMYB119) was chosen as the study object, which the expression decreased under salt stress conditions. Further study of the SbMYBAS1 showed that SbMYBAS1 is located in the nucleus. Under salt stress conditions, Arabidopsis plants overexpressed SbMYBAS1 showed significantly lower dry/fresh weight and chlorophyll content but significantly higher membrane permeability, MDA content, and Na+/K+ ratio than the wild-type Arabidopsis plants. Yeast two-hybrid screening result showed that SbMYBAS1 might interact with proteins encoded by SORBI_302G184600, SORBI_3009G247900 and SORBI_3004G59600. Results also showed that SbMYBAS1 could regulate the expression of AtGSTU17, AtGSTU16, AtP5CS2, AtUGT88A1, AtUGT85A2, AtOPR2 and AtPCR2 under salt stress conditions. This work laid a foundation for the study of the response mechanism of sorghum MYB gene family to salt stress.

Response of salt stress resistance in highland barley (Hordeum vulgare L. var. nudum) through phenylpropane metabolic pathway.

Highland barley (Hordeum vulgare L. var. nudum) is a grain crop that grows on the plateau under poor and high salt conditions. Therefore, to cultivate high-quality highland barley varieties, it is necessary to study the molecular mechanism of strong resistance in highland barley, which has not been clearly explained. In this study, a high concentration of NaCl (240 mmol/L), simulating the unfavorable environment, was used to spray the treated highland barley seeds. Transcriptomic analysis revealed that the expression of more than 8,000 genes in highland barley seed cells was significantly altered, suggesting that the metabolic landscape of the cells was deeply changed under salt stress. Through the KEGG analysis, the phenylpropane metabolic pathway was significantly up-regulated under salt stress, resulting in the accumulation of polyphenols, flavonoids, and lignin, the metabolites for improving the stress resistance of highland barley seed cells, being increased 2.71, 1.22, and 1.17 times, respectively. This study discovered that the phenylpropane metabolic pathway was a significant step forward in understanding the stress resistance of highland barley, and provided new insights into the roles of molecular mechanisms in plant defense.

Combined transcriptomic and metabolomic analysis of alginate oligosaccharides alleviating salt stress in rice seedlings.

BACKGROUND: Salt stress is one of the key factors limiting rice production. Alginate oligosaccharides (AOS) enhance plant stress resistance. However, the molecular mechanism underlying salt tolerance in rice induced by AOS remains unclear. FL478, which is a salt-tolerant indica recombinant inbred line and IR29, a salt-sensitive rice cultivar, were used to comprehensively analyze the effects of AOS sprayed on leaves in terms of transcriptomic and metabolite profiles of rice seedlings under salt stress. RESULTS: In this experiment, exogenous application of AOS increased SOD, CAT and APX activities, as well as GSH and ASA levels to reduce the damage to leaf membrane, increased rice stem diameter, the number of root tips, aboveground and subterranean biomass, and improved rice salt tolerance. Comparative transcriptomic analyses showed that the regulation of AOS combined with salt treatment induced the differential expression of 305 and 1030 genes in FL478 and IR29. The expressed genes enriched in KEGG pathway analysis were associated with antioxidant levels, photosynthesis, cell wall synthesis, and signal transduction. The genes associated with light-trapping proteins and RLCK receptor cytoplasmic kinases, including CBA, LHCB, and Lhcp genes, were fregulated in response to salt stress. Treatment with AOS combined with salt induced the differential expression of 22 and 50 metabolites in FL478 and IR29. These metabolites were mainly related to the metabolism of amino and nucleotide sugars, tryptophan, histidine, and ß -alanine. The abundance of metabolites associated with antioxidant activity, such as 6-hydroxymelatonin, wedelolactone and L-histidine increased significantly. Combined transcriptomic and metabolomic analyses revealed that dehydroascorbic acid in the glutathione and ascorbic acid cycles plays a vital role in salt tolerance mediated by AOS. CONCLUSION: AOS activate signal transduction, regulate photosynthesis, cell wall formation, and multiple antioxidant pathways in response to salt stress. This study provides a molecular basis for the alleviation of salt stress-induced damage by AOS in rice.

Intraspecific divergence in essential oil content, composition and genes expression patterns of monoterpene synthesis in Origanum vulgare subsp. vulgare and subsp. gracile under salinity stress.

BACKGROUND: Oregano (Origanum vulgare L.), one of the important medicinal plants in the world, has valuable pharmacological compounds with antimicrobial, antiviral, antioxidant, anti-inflammatory, antispasmodic, antiurolithic, antiproliferative and neuroprotective activities. Phenolic monoterpenes such as thymol and carvacrol with many medical importance are found in Oregano essential oil. The biosynthesis of these compounds is carried out through the methyl erythritol-4 phosphate (MEP) pathway. Environmental stresses such as salinity might improve the secondary metabolites in medicinal plants. The influence of salinity stress (0 (control), 25, 50 and 100 mM NaCl) on the essential oil content, composition and expression of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), γ-terpinene synthase (Ovtps2) and cytochrome P450 monooxygenases (CYP71D180) genes involved in thymol and carvacrol biosynthesis, was investigated in two oregano subspecies (vulgare and gracile). RESULTS: Essential oil content was increased at low NaCl concentration (25 mM) compared with non-stress conditions, whereas it was decreased as salinity stress intensified (50 and 100 mM). Essential oil content was significantly higher in subsp. gracile than subsp. vulgare. The highest (0.20 mL pot-1) and lowest (0.06 mL pot-1) amount of essential oil yield was obtained in subsp. gracile at 25 and 100 mM NaCl, respectively. The content of carvacrol, as the main component of essential oil, decreased with increasing salinity level in subsp. gracile, but increased in subsp. vulgare. The highest expression of DXR, Ovtps2 and CYP71D180 genes was observed at 50 mM NaCl in subsp. vulgare. While, in subsp. gracile, the expression of the mentioned genes decreased with increasing salinity levels. A positive correlation was obtained between the expression of DXR, Ovtps2 and CYP71D180 genes with carvacrol content in both subspecies. On the other hand, a negative correlation was found between the expression of CYP71D180 and carvacrol content in subsp. gracile. CONCLUSIONS: The findings of this study demonstrated that both oregano subspecies can tolerate NaCl salinity up to 50 mM without significant reduction in essential oil yield. Also, moderate salinity stress (50 mM NaCl) in subsp. vulgare might increase the carvacrol content partly via increment the expression levels of DXR, Ovtps2 and CYP71D180 genes.

Overexpression of a Fragaria vesca 1R-MYB Transcription Factor Gene (FvMYB114) Increases Salt and Cold Tolerance in Arabidopsis thaliana.

The MYB (v-MYB avian myeloblastosis viral oncogene homolog) transcription factor (TF) family has numerous members with complex and diverse functions, which play an indispensable role in regulating the response of plants to stress. In this study, a new 1R-MYB TF gene was obtained from Fragaria vesca (a diploid strawberry) by cloning technology and given a new name, FvMYB114. According to the subcellular localization results, FvMYB114 protein was a nuclear localization protein. Overexpression of FvMYB114 greatly enhanced the adaptability and tolerance of Arabidopsis thaliana to salt and low temperature. Under salt and cold stress, the transgenic plants had greater proline and chlorophyll contents and higher activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) than the wild-type (WT) and unloaded-line (UL) A. thaliana. However, malondialdehyde (MDA) was higher in the WT and UL lines. These results suggested that FvMYB114 may be involved in regulating the response of A. thaliana to salt stress and cold stress. FvMYB114 can also promote the expression of genes, such as the genes AtSOS1/3, AtNHX1 and AtLEA3 related to salt stress and the genes AtCCA1, AtCOR4 and AtCBF1/3 related to cold stress, further improving the tolerance of transgenic plants to salt and cold stress.

Genome-wide identification, evolution and expression analysis of NAC gene family under salt stress in wild emmer wheat (Triticum dicoccoides. L).

The NAC transcription factor (TF) family is one of the largest plant-specific gene families, playing the vital roles in plant growth and development as well as stress response. Although it has been extensively characterized in many plants, the significance of NAC family in wild emmer wheat is not well understood up to now. Here, a total of 200 NAC transcription factors were identified in wild emmer (TdNACs) through a genome-search method, which were classified into 12 subfamilies based on phylogenetic relationship. And the members in the subfamily shared similar exon-intron structure and conversed domain organization. Collinearity analysis revealed that segmental duplication and polyploidization contributed mainly to the expansion of TdNACs. Furthermore, the genetic variations of TdNACs were investigated using the re-sequencing data and genetic bottleneck has occurred on NAC genes when wild emmer domesticated to cultivated emmer wheat. Finally, the expression patterns of these TdNACs were investigated using RNA-seq data of the salt-tolerant genotype under salt stress to obtain salt-responsive TdNACs, and 10 out of which were further validated using QPCR analysis. This study provided the targets for further functional study of TdNAC genes, and also contributed to mine novel genes for improving the salt tolerance in wheat and other crops.