Salt Stress Response Research Articles

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.

Genome-Wide Characterization of the Aquaporin Gene Family in Radish and Functional Analysis of RsPIP2-6 Involved in Salt Stress.

Aquaporins (AQPs) constitute a highly diverse family of channel proteins that transport water and neutral solutes. AQPs play crucial roles in plant development and stress responses. However, the characterization and biological functions of RsAQPs in radish (Raphanus sativus L.) remain elusive. In this study, 61 non-redundant members of AQP-encoding genes were identified from the radish genome database and located on nine chromosomes. Radish AQPs (RsAQPs) were divided into four subfamilies, including 21 plasma membrane intrinsic proteins (PIPs), 19 tonoplast intrinsic proteins (TIPs), 16 NOD-like intrinsic proteins (NIPs), and 5 small basic intrinsic proteins (SIPs), through phylogenetic analysis. All RsAQPs contained highly conserved motifs (motifs 1 and 4) and transmembrane regions, indicating the potential transmembrane transport function of RsAQPs. Tissue- and stage-specific expression patterns of AQP gene analysis based on RNA-seq data revealed that the expression levels of PIPs were generally higher than TIPs, NIPs, and SIPs in radish. In addition, quantitative real-time polymerase chain reaction (qRT-PCR) revealed that seven selected RsPIPs, according to our previous transcriptome data (e.g., RsPIP1-3, 1-6, 2-1, 2-6, 2-10, 2-13, and 2-14), exhibited significant upregulation in roots of salt-tolerant radish genotype. In particular, the transcriptional levels of RsPIP2-6 dramatically increased after 6 h of 150 mM NaCl treatment during the taproot thickening stage. Additionally, overexpression of RsPIP2-6 could enhance salt tolerance by Agrobacterium rhizogenes-mediated transgenic radish hairy roots, which exhibited the mitigatory effects of plant growth reduction, leaf relative water content (RWC) reduction and alleviation of O2– in cells, as shown by nitro blue tetrazolium (NBT) staining, under salt stress. These findings are helpful for deeply dissecting the biological function of RsAQPs on the salt stress response, facilitating practical application and genetic improvement of abiotic stress resistance in radish.

Cap-binding complex assists RNA polymerase II transcription in plant salt stress response.

Adaptive response to stress involves an extensive reprogramming of gene expression. Under stressful conditions, the induction of efficient changes in messenger RNA (mRNA) production is crucial for maximized plant survival. Transcription and pre-mRNA processing are two closely related steps in mRNA biogenesis, yet how they are controlled in plant stress response remains elusive. Here, we show that the Arabidopsis nuclear cap-binding complex (CBC) component CBP20 directly interacts with ELF7, a subunit of the transcription elongation factor RNA Pol II-associated factor 1 complex (PAF1c) to promote RNA Pol II transcription in plant response to salt stress. CBP20 and ELF7 coregulate the expression of a large number of genes including those crucial for salt tolerance. Both CBP20 and ELF7 are required for enhanced RNA Pol II elongation at salt-activated genes. Though CBP20 also regulates intron splicing, this function is largely independent of ELF7. Our study reveals the function of an RNA processing regulator CBC in assisting efficient RNA Pol II transcription and pinpoints the complex roles of CBC on mRNA production in plant salt stress resistance.

Mitogen-Activated Protein Kinase Is Involved in Salt Stress Response in Tomato (Solanum lycopersicum) Seedlings.

Salt stress impairs plant growth and development, thereby causing low yield and inferior quality of crops. In this study, tomato (Solanum lycopersicum L. ‘Micro-Tom’) seedlings treated with different concentrations of sodium chloride (NaCl) were investigated in terms of decreased plant height, stem diameter, dry weight, fresh weight, leaves relative water content and root activity. To reveal the response mechanism of tomato seedlings to salt stress, the transcriptome of tomato leaves was conducted. A total of 6589 differentially expressed genes (DEGs) were identified and classified into different metabolic pathways, especially photosynthesis, carbon metabolism, biosynthesis of amino acids and mitogen-activated protein kinase (MAPK) signaling pathway. Of these, approximately 42 DEGs were enriched in the MAPK signaling pathway, most of which mainly included plant hormone, hydrogen peroxide (H2O2), wounding and pathogen infection signaling pathways. To further explore the roles of MAPK under salt stress, MAPK phosphorylation inhibitor SB203580 (SB) was applied. We found that SB further decreased endogenous jasmonic acid, abscisic acid and ethylene levels under salt stress condition. Additionally, in comparison with NaCl treatment alone, SB + NaCl treatment reduced the content of O2− and H2O2 and the activities of antioxidant enzyme and downregulated the expression levels of genes related to pathogen infection. Together, the results revealed that MAPK might be involved in the salinity response of tomato seedlings by regulating hormone balance, ROS metabolism, antioxidant capacity and plant immunity.

Integrated Full-Length Transcriptome and MicroRNA Sequencing Approaches Provide Insights Into Salt Tolerance in Mangrove (Sonneratia apetala Buch.-Ham.).

MicroRNAs (miRNAs) are small RNA molecules that serve as key players in plant stress responses. Although stress-regulated miRNAs have been explored in various plants, they are not well studied in mangroves. Herein, we combined PacBio isoform sequencing (Iso-Seq) with BGISEQ short-read RNA-seq to probe the role of miRNAs in the salt stress response of the mangrove plant, Sonneratia apetala Buch.-Ham. A total of 1,702,463 circular consensus sequencing reads were generated that produced 295,501 nonredundant full-length transcripts from the leaves of a 1-year-old S. apetala. After sequencing nine small RNA libraries constructed from control and 1- and 28-day 300 mM NaCl treatments, we identified 143 miRNAs (114 known and 29 novel) from a total of >261 million short reads. With the criteria of |log2FC| ≥ 1 and q-value < 0.05, 42 and 70 miRNAs were differentially accumulated after 1- and 28-day salt treatments, respectively. These differential accumulated miRNAs potentially targeted salt-responsive genes encoding transcription factors, ion homeostasis, osmotic protection, and detoxificant-related proteins, reminiscent of their responsibility for salinity adaptation in S. apetala. Particularly, 62 miRNAs were Sonneratia specific under salt stress, of which 34 were co-expressed with their 131 predicted targets, thus producing 140 miRNA–target interactions. Of these, 82 miRNA-target pairs exhibited negative correlations. Eighteen miRNA targets were categorized for the ‘environmental information processing’ during KEGG analysis and were related to plant hormone signal transduction (ko04075), MAPK signaling pathway–plant (ko04016), and ABC transporters (ko02010). These results underscored miRNAs as possible contributors to mangrove success in severe environments and offer insights into an miRNA-mediated regulatory mechanism of salt response in S. apetala.

Integration of eQTL Analysis and GWAS Highlights Regulation Networks in Cotton under Stress Condition.

The genus Gossypium is one of the most economically important crops in the world. Here, we used RNA-seq to quantify gene expression in a collection of G. arboreum seedlings and performed eGWAS on 28,382 expressed genes. We identified a total of 30,089 eQTLs in 10,485 genes, of which >90% were trans-regulate target genes. Using luciferase assays, we confirmed that different cis-eQTL haplotypes could affect promoter activity. We found ~6600 genes associated with ~1300 eQTL hotspots. Moreover, hotspot 309 regulates the expression of 325 genes with roles in stem length, fresh weight, seed germination rate, and genes related to cell wall biosynthesis and salt stress. Transcriptome-wide association study (TWAS) identified 19 candidate genes associated with the cotton growth and salt stress response. The variation in gene expression across the population played an essential role in population differentiation. Only a small number of the differentially expressed genes between South China, the Yangtze River region, and the Yellow River region sites were located in different chromosomal regions. The eQTLs found across the duplicated gene pairs showed conservative cis- or trans- regulation and that the expression levels of gene pairs were correlated. This study provides new insights into the evolution of gene expression regulation in cotton, and identifies eQTLs in stress-related genes for use in breeding improved cotton varieties.

Physiological and Transcriptome Analysis on Diploid and Polyploid Populus ussuriensis Kom. under Salt Stress.

Populus ussuriensis Kom. is a valuable forest regeneration tree species in the eastern mountainous region of Northeast China. It is known that diploid P. ussuriensis (CK) performed barely satisfactorily under salt stress, but the salt stress tolerance of polyploid (i.e., triploid (T12) and tetraploid (F20)) P. ussuriensis is still unknown. In order to compare the salt stress tolerance and salt stress response mechanism between diploid and polyploid P. ussuriensis, phenotypic observation, biological and biochemistry index detections, and transcriptome sequencing (RNA-seq) were performed on CK, T12, and F20. Phenotypic observation and leaf salt injury index analysis indicated CK suffered more severe salt injury than T12 and F20. SOD and POD activity detections indicated the salt stress response capacity of T12 was stronger than that of CK and F20. MDA content, proline content and relative electric conductivity detections indicated CK suffered the most severe cell-membrane damage, and T12 exhibited the strongest osmoprotective capacity under salt stress. Transcriptome analysis indicated the DEGs of CK, T12, and F20 under salt stress were different in category and change trend, and there were abundant WRKY, NAM, MYB and AP2/ERF genes among the DEGs in CK, T12, and F20 under salt stress. GO term enrichment indicated the basic growth progresses of CK, and F20 was obviously influenced, while T12 immediately launched more salt stress response processes in 36 h after salt stress. KEGG enrichment indicated the DEGs of CK mainly involved in plant–pathogen interaction, ribosome biogenesis in eukaryotes, protein processing in endoplasmic reticulum, degradation of aromatic compounds, plant hormone signal transduction, photosynthesis, and carbon metabolism pathways. The DEGs of T12 were mainly involved in plant–pathogen interaction, cysteine and methionine metabolism, phagosomes, biosynthesis of amino acids, phenylalanine, tyrosine and tryptophan biosynthesis, plant hormone signal transduction, and starch and sucrose metabolism pathways. The DEGs of F20 were mainly involved in plant hormone signal transduction, plant–pathogen interaction, zeatin biosynthesis, and glutathione metabolism pathways. In conclusion, triploid exhibited stronger salt stress tolerance than tetraploid and diploid P. ussuriensis (i.e., T12 > F20 > CK). The differences between the DEGs of CK, T12, and F20 probably are the key clues for discovering the salt stress response signal transduction network in P. Ussuriensis.

Genome-Wide Analysis of CqCrRLK1L and CqRALF Gene Families in Chenopodium quinoa and Their Roles in Salt Stress Response.

Chenopodium quinoa is a halophyte with exceptional nutritional qualities, and therefore it is potentially an ideal crop to grow in saline soils, not only addressing the problem of land salinization, but also providing nutrient food for the health of humans. Currently, the molecular mechanisms underlying salt tolerance in quinoa are still largely unknown. In Arabidopsis thaliana, Catharanthus roseus receptor-like kinase (CrRLK1Ls) FERONIA (FER) and its ligands rapid alkalinization factors (RALFs) have been reported that participate in the regulation of salt tolerance. Here, we performed a genome-wide analysis and identified 26 CqCrRLK1L and 18 CqRALF family genes in quinoa genome. Transcriptomic profiling of the leaf, root, stamen, and pistil tissues of quinoa reveals that different CqCrRLK1L and CqRALF genes exhibit tissue-specific expression patterns, which is consistent with that observed in other plant species. RNA-seq data show that three CqCrRLK1L genes are highly up-regulated after salt treatment, suggesting that some CqCrRLK1L family genes are transcriptionally responsive to salt stress in quinoa. Biochemical study indicates that CqRALF15, a paralog of Arabidopsis RALF22, is physically associated with CrRLK1L proteins CqFER and AtFER. CqRALF15 and AtRALF22 are functionally conserved in inducing the internalization of AtFER and in triggering root growth inhibition in both quinoa and Arabidopsis. Moreover, overexpression of CqRALF15 in Arabidopsis results in enhanced leaf bleaching under salt stress, indicating that CqRALF15 is involved in salt stress response. Together, our study characterizes CqCrRLK1L and CqRALF family genes in quinoa at genomic, transcriptional, and protein levels, and provides evidence to support their roles in salt stress response.

Comparative Analysis of Salt Responsive MicroRNAs in Two Sweetpotato [Ipomoea batatas (L.) Lam.] Cultivars With Different Salt Stress Resistance.

Sweetpotato [Ipomoea batatas (L.) Lam.] is an important food, vegetable and economic crop, but its productivity is remarkably affected by soil salinity. MiRNAs are a class of endogenous non-coding small RNAs that play an important role in plant resistance to salt stress. However, the function of miRNAs still remains largely unknown in sweetpotato under salt stress. Previously, we identified salt-responsive miRNAs in one salt-sensitive sweetpotato cultivar “Xushu 32.” In this study, we identified miRNAs in another salt-tolerant cultivar “Xushu 22” by high-throughput deep sequencing and compared the salt-responsive miRNAs between these two cultivars with different salt sensitivity. We identified 687 miRNAs in “Xushu 22,” including 514 known miRNAs and 173 novel miRNAs. Among the 759 miRNAs from the two cultivars, 72 and 109 miRNAs were specifically expressed in “Xushu 32” and “Xushu 22,” respectively, and 578 miRNAs were co-expressed. The comparison of “Xushu 32” and “Xushu 22” genotypes showed a total of 235 miRNAs with obvious differential expression and 177 salt-responsive miRNAs that were obviously differently expressed between “Xushu 32” and “Xushu 22” under salt stress. The target genes of the miRNAs were predicted and identified using the Target Finder tool and degradome sequencing. The results showed that most of the targets were transcription factors and proteins related to metabolism and stress response. Gene Ontology analysis revealed that these target genes are involved in key pathways related to salt stress response and secondary redox metabolism. The comparative analysis of salt-responsive miRNAs in sweetpotato cultivars with different salt sensitivity is helpful for understanding the regulatory pattern of miRNA in different sweetpotato genotypes and improving the agronomic traits of sweetpotato by miRNA manipulation in the future.

PtoNF-YC9-SRMT-PtoRD26 module regulates the high saline tolerance of a triploid poplar

BackgroundSensing and responding to stresses determine the tolerance of plants to adverse environments. The triploid Chinese white poplar is widely cultivated in North China because of its adaptation to a wide range of habitats including highly saline ones. However, its triploid genome complicates any detailed investigation of the molecular mechanisms underlying its adaptations.ResultsWe report a haplotype-resolved genome of this triploid poplar and characterize, using reverse genetics and biochemical approaches, a MYB gene, SALT RESPONSIVE MYB TRANSCRIPTION FACTOR (SRMT), which combines NUCLEAR FACTOR Y SUBUNIT C 9 (PtoNF-YC9) and RESPONSIVE TO DESICCATION 26 (PtoRD26), to regulate an ABA-dependent salt-stress response signaling. We reveal that the salt-inducible PtoRD26 is dependent on ABA signaling. We demonstrate that ABA or salt drives PtoNF-YC9 shuttling into the nucleus where it interacts with SRMT, resulting in the rapid expression of PtoRD26 which in turn directly regulates SRMT. This positive feedback loop of SRMT-PtoRD26 can rapidly amplify salt-stress signaling. Interference with either component of this regulatory module reduces the salt tolerance of this triploid poplar.ConclusionOur findings reveal a novel ABA-dependent salt-responsive mechanism, which is mediated by the PtoNF-YC9-SRMT-PtoRD26 module that confers salt tolerance to this triploid poplar. These genes may therefore also serve as potential and important modification targets in breeding programs.

OsMPK4 promotes phosphorylation and degradation of IPA1 in response to salt stress to confer salt tolerance in rice

Salt stress adversely affects plant growth, development, and crop yield. Rice (Oryza sativa L.) is one of the most salt-sensitive cereal crops, especially at the early seedling stage. Mitogen-activated protein kinase (MAPK/MPK) cascades have been shown to play critical roles in salt response in Arabidopsis. However, the roles of the MPK cascade signaling in rice salt response and substrates of OsMPK remain largely unknown. Here, we report that the salt-induced OsMPK4-Ideal Plant Architecture 1 (IPA1) signaling pathway regulates the salt tolerance in rice. Under salt stress, OsMPK4 could interact with IPA1 and phosphorylate IPA1 at Thr180, leading to degradation of IPA1. Genetic evidence shows that IPA1 is a negative regulator of salt tolerance in rice, whereas OsMPK4 promotes salt response in an IPA1-dependent manner. Taken together, our results uncover an OsMPK4-IPA1 signal cascade that modulates the salt stress response in rice and sheds new light on the breeding of salt-tolerant rice varieties.

Transcriptome-wide characterization, evolutionary analysis, and expression pattern analysis of the NF-Y transcription factor gene family and salt stress response in Panax ginseng

Jilin ginseng (Panax ginseng C. A. Meyer) has a long history of medicinal use worldwide. The quality of ginseng is governed by a variety of internal and external factors. Nuclear factor Y (NF-Y), an important transcription factor in eukaryotes, plays a crucial role in the plant response to abiotic stresses by binding to a specific promoter, the CCAAT box. However, the NF-Y gene family has not been reported in Panax ginseng. In this study, 115 PgNF-Y transcripts with 40 gene IDs were identified from the Jilin ginseng transcriptome database. These genes were classified into the PgNF-YA (13), PgNF-YB (14), and PgNF-YC (13) subgroups according to their subunit types, and their nucleotide sequence lengths, structural domain information, and amino acid sequence lengths were analyzed. The phylogenetic analysis showed that the 79 PgNF-Y transcripts with complete ORFs were divided into three subfamilies, NF-YA, NF-YB, and NF-YC. PgNF-Y was annotated to eight subclasses under three major functions (BP, MF, and CC) by GO annotation, indicating that these transcripts perform different functions in ginseng growth and development. Expression pattern analysis of the roots of 42 farm cultivars, 14 different tissues of 4-year-old ginseng plants, and the roots of 4 different-ages of ginseng plants showed that PgNF-Y gene expression differed across lineages and had spatiotemporal specificity. Coexpression network analysis showed that PgNF-Ys acted synergistically with each other in Jilin ginseng. In addition, the analysis of the response of PgNF-YB09, PgNF-YC02, and PgNF-YC07-04 genes to salt stress treatment was investigated by fluorescence quantitative PCR. The expression of these genes increased after salt stress treatment, indicating that they may be involved in the regulation of the response to salt stresses in ginseng. These results provide important functional genetic resources for the improvement and gene breeding of ginseng in the future.Conclusions: This study fills a knowledge gap regarding the NF-Y gene family in ginseng, provides systematic theoretical support for subsequent research on PgNF-Y genes, and provides data resources for resistance to salt stress in ginseng.

OsPP65 Negatively Regulates Osmotic and Salt Stress Responses Through Regulating Phytohormone and Raffinose Family Oligosaccharide Metabolic Pathways in Rice

Although type 2C protein phosphatases (PP2Cs) have been demonstrated to play important roles in regulating plant development and various stress responses, their specific roles in rice abiotic stress tolerance are still largely unknown. In this study, the functions of OsPP65 in rice osmotic and salt stress tolerance were investigated. Here, we report that OsPP65 is responsive to multiple stresses and is remarkably induced by osmotic and salt stress treatments. OsPP65 was highly expressed in rice seedlings and leaves and localized in the nucleus and cytoplasm. OsPP65 knockout rice plants showed enhanced tolerance to osmotic and salt stresses. Significantly higher induction of genes involved in jasmonic acid (JA) and abscisic acid (ABA) biosynthesis or signaling, as well as higher contents of endogenous JA and ABA, were observed in the OsPP65 knockout plants compared with the wild-type plants after osmotic stress treatment. Further analysis indicated that JA and ABA function independently in osmotic stress tolerance conferred by loss of OsPP65. Moreover, metabolomics analysis revealed higher endogenous levels of galactose and galactinol but a lower content of raffinose in the OsPP65 knockout plants than in the wild-type plants after osmotic stress treatment. These results together suggest that OsPP65 negatively regulates osmotic and salt stress tolerance through regulation of the JA and ABA signaling pathways and modulation of the raffinose family oligosaccharide metabolism pathway in rice. OsPP65 is a promising target for improvement of rice stress tolerance using gene editing.

De novo transcriptome sequencing of Capsicum frutescens. L and comprehensive analysis of salt stress alleviating mechanism by Bacillus atrophaeus WU-9.

Salt stress, as one of the most severe environmental stresses, can cause a series of changes in plants. However, the explanation of plant salt stress alleviating mechanism of plant growth-promoting rhizobacteria (PGPR) was hindered by the limited availability of transcriptomic information for salt stress-treated plants grown in a microorganism-controlled environment. Our previous reports have selected Bacillus atrophaeus WU-9 as PGPR significantly alleviating pepper (Capsicum frutescens. L) salt stress. In this work, the RNA-seq analysis of salt stress-treated and untreated plants, grown with and without WU-9 in a microorganism-controlled environment, was used to reveal the plant salt stress alleviating mechanisms of WU-9. Twelve sequencing libraries, prepared by treating with WU-9 and salt (150 mM NaCl for 36 h), were constructed by RNA-Seq technique. Non-inoculated seedlings mainly respond to salt stress through regulation of signal transduction, such as ethylene-activated signaling pathway, signaling and cell communication, etc. And ethylene signal participated in salt stress response in pepper through regulating defense responses, fruit ripening and senescence. WU-9 inoculation under salt stress mainly improves salt tolerance and plant growth by regulating salt stress-responding ethylene and auxin signal transduction, utilization of proline, photosynthesis, antioxidant enzyme activities and cell enlargement. Furthermore, 86 differentially expressed genes and 20 transcription factors were identified as associated with salt stress response and tolerance. Thus, this innovative transcriptomic study identified the salt stress response and alleviation in C. frutescens. L with PGPR inoculation. This result provided novel insights into the salinity alleviation in pepper regulated by PGPR.

Differential role of Capsicum annuum FANTASTIC FOUR-like gene CaFAF1 on drought and salt stress responses

As sessile organisms, plants are potentially susceptible to diverse environmental stresses, including drought, salt, and extreme temperatures. To adapt and survive under these adverse conditions, plants have evolved sophisticated defense mechanisms. Here, we isolated the FANTASTIC FOUR-like gene CaFAF1 ( Capsicum annuum Fantastic Four 1 ) from pepper and functionally characterized this gene with respect to its responses to drought and salt stresses. We found that CaFAF1 expression was relatively abundant in all examined pepper tissues and was significantly induced by drought and salt stress. Compared with control plants, CaFAF1 -silenced pepper plants exhibited enhanced drought tolerance, accompanied by a high expression of stress-related genes and enhanced abscisic acid-mediated stomatal closure. In contrast, CaFAF1 -silenced pepper plants were sensitive to salt stress, with high electrolyte leakage and lipid peroxidation. CaFAF1 overexpression in Arabidopsis resulted in a phenotype that is the opposite of that after CaFAF1 silencing in pepper. A cell-free degradation assay using leaf crude extracts from drought- or salt-stressed pepper plants revealed that CaFAF1 degradation was promoted by drought and delayed by salt stress. Thus, we suggest that CaFAF1 plays negative and positive roles in response to drought and salt stresses, respectively, possibly via modulation of its protein stability. • We found four FANTASTIC FOUR (FAF) domain-containing genes CaFAFs in pepper genome. • CaFAF1 shows the highest induction in response to high salinity. • CaFAF1 negatively regulates drought tolerance via ABA-mediated stomatal movement. • CaFAF1 positively regulates high slat tolerance via modulation of its protein stability.

PACLOBUTRAZOL DEPENDENT SALT TOLERANCE IS RELATED TO CLC1 AND NHX1 GENE EXPRESSION IN SOYBEAN PLANTS

Paclobutrazol (PBZ) enhances plant resistance to salt stress in two ways: directly, by straight clearance of reactive oxygen species; and indirectly by enhancing antioxidant enzyme activity, photosynthetic efficiency, and metabolite content, and by regulating transcription factors associated with stress. However, the regulatory effects of PBZ under salt stress in soybean are still not well explained and need further investigation. With this aim, the combination effect of salinity (250 mM NaCl) and three different doses of PBZ (5, 10 and 20 ppm) on physiological, biochemical and molecular traits of soybean (Glycine max L.) leaves were studied in soil experiments. Furthermore, physiological parameters (relative growth rate, relative water content), chlorophyll, malondialdehyde (MDA), hydrogen peroxide (H2O2) content and as well as enzymatic antioxidants (SOD, POX, APX, CAT and GST), ion content (Na, Cl) and soybean Na+/H+ antiporter GmNHX1 and chloride channel GmCLC1 gene expressions were investigated. The results showed that PBZ caused a reduction in salt-induced damages and an increase in biomass yield, water status, and chlorophyll. Moreover, PBZ regulated enzymatic antioxidants and alleviated the oxidative damages under salinity. In this study, for a first time it was determined that PBZ increased both GmNHX1 (ABA dependent or independent) and GmCLC1 (ABA independent) gene expressions and reduced Na and Cl concentrations in soybean under salinity. In conclusion, PBZ plays a role as a regulator and stimulant in salt stress response by mostly regulating ion balance in soybean leaves.

Parental legacy versus regulatory innovation in salt stress responsiveness of allopolyploid cotton (Gossypium) species.

SUMMARYPolyploidy provides an opportunity for evolutionary innovation and species diversification, especially under stressful conditions. In allopolyploids, the conditional dynamics of homoeologous gene expression can be either inherited from ancestral states pre‐existing in the parental diploids or novel upon polyploidization, the latter potentially permitting a wider range of phenotypic responses to stresses. To gain insight into regulatory mechanisms underlying the diversity of salt resistance in Gossypium species, we compared global transcriptomic responses to modest salinity stress in two allotetraploid (AD‐genome) cotton species, Gossypium hirsutum and G. mustelinum, relative to their model diploid progenitors (A‐genome and D‐genome). Multivariate and pairwise analyses of salt‐responsive changes revealed a profound alteration of gene expression for about one third of the transcriptome. Transcriptional responses and associated functional implications of salt acclimation varied across species, as did species‐specific coexpression modules among species and ploidy levels. Salt responsiveness in both allopolyploids was strongly biased toward the D‐genome progenitor. A much lower level of transgressive downregulation was observed in the more salt‐tolerant G. mustelinum than in the less tolerant G. hirsutum. By disentangling inherited effects from evolved responses, we show that expression biases that are not conditional upon salt stress approximately equally reflect parental legacy and regulatory novelty upon allopolyploidization, whereas stress‐responsive biases are predominantly novel, or evolved, in allopolyploids. Overall, our work suggests that allopolyploid cottons acquired a wide range of stress response flexibility relative to their diploid ancestors, most likely mediated by complex suites of duplicated genes and regulatory factors.

Genome-Wide Identification of NRT Gene Family and Expression Analysis of Nitrate Transporters in Response to Salt Stress in Poncirus trifoliata.

The uptake and transportation of nitrate play a crucial role in plant growth and development. These processes mostly depend on nitrate transporters (NRT), which guarantee the supplement of nutrition in the plant. In this study, genes encoding NRT with Major Facilitator Superfamily (MFS) domain were identified in trifoliate orange (Poncirus trifoliata (L.) Raf.). Totally, 56 NRT1s, 6 NRT2s, and 2 NAR2s were explored. The bioinformation analysis, including protein characteristics, conserved domain, motif, phylogenetic relationship, cis-acting element, and synteny correlation, indicated the evolutionary conservation and functional diversity of NRT genes. Additionally, expression profiles of PtrNRTs in different tissues demonstrated that NRT genes possessed spatio-temporal expression specificity. Further, the salt condition was certified to induce the expression of some NRT members, like PtrNPF2.1, PtrNPF7.4, and PtrNAR2.1, proposing the potential role of these NRTs in salt stress response. The identification of NRT genes and the expression pattern analysis in various tissues and salt stress lay a foundation for future research between nitrogen transport and salt resistance in P. trifoliata.

Identification and Characterization of Abiotic Stress-Responsive NF-YB Family Genes in Medicago.

Nuclear factor YB (NF-YB) are plant-specific transcription factors that play a critical regulatory role in plant growth and development as well as in plant resistance against various stresses. In this study, a total of 49 NF-YB genes were identified from the genomes of Medicago truncatula and Medicago sativa. Multiple sequence alignment analysis showed that all of these NF-YB members contain DNA binding domain, NF-YA interaction domain and NF-YC interaction domain. Phylogenetic analysis suggested that these NF-YB proteins could be classified into five distinct clusters. We also analyzed the exon–intron organizations and conserved motifs of these NF-YB genes and their deduced proteins. We also found many stress-related cis-acting elements in their promoter region. In addition, analyses on genechip for M. truncatula and transcriptome data for M. sativa indicated that these NF-YB genes exhibited a distinct expression pattern in various tissues; many of these could be induced by drought and/or salt treatments. In particular, RT-qPCR analysis revealed that the expression levels of gene pairs MsNF-YB27/MtNF-YB15 and MsNF-YB28/MtNF-YB16 were significantly up-regulated under NaCl and mannitol treatments, indicating that they are most likely involved in salt and drought stress response. Taken together, our study on NF-YB family genes in Medicago is valuable for their functional characterization, as well as for the application of NF-YB genes in genetic breeding for high-yield and high-resistance alfalfa.

Effect of salinity stress on phytochemical characteristics of Centella asiatica

Salinity is one of the predominant abiotic stresses which affects plant growth by inducing excessive production of reactive oxygen species (ROS) that leads to oxidative damage of plant cells. Plants alleviate salinity stress by regulating intracellular concentrations of various phytochemicals like phenol, tannin, antioxidants, etc. The present work aimed to study the impact of salt stress on the production of various phytochemicals like phenol, tannin, flavonoids, antioxidants, total protein content, etc. The Salt stress response of the test plant Centella asiatica was studied by irrigating variant concentrations (50mM, 100mm, 150mm, 200mM, 250mm) of salt (NaCl). The phytochemical activity of the plants grown under salinity stress was estimated by using an appropriate biochemical assay. Comparative analysis of the photochemical activity of the test plants in comparison with the control revealed that various phytochemicals were increased in response to salt stress. Salt stress increased the levels of antioxidants from 10.79 to 14.31 μg/ml), phenol from 30.8 to 43.3 in μg/ml, flavonoids (from 490 to 683.33 in μg/ml), tannin from 55.5 to 64.5 in μg/ml, and proteins from 5720 to 6080 in μg/ml in the C. asiatica plants. To sum up, salt stress elicited phytochemical accumulation in the C. asiatica plant, thereby improving the plant's growth by enhancing its resistance to salt stress. This finding may play an important role in the sustainable cultivation of commercially important crops like C. asiatica.