Salt Stress Response Research Articles

A cyclic nucleotide-gated channel gene HcCNGC21 positively regulates salt and drought stress responses in kenaf (Hibiscus cannabinus L.)

Cyclic Nucleotide-Gated Channels (CNGCs) serve as Ca2+ permeable cation transport pathways, which are involved in the regulation of various biological functions such as plant cell ion selective permeability, growth and development, responses to biotic and abiotic stresses. At the present study, a total of 31 CNGC genes were identified and bioinformatically analyzed in kenaf. Among these genes, HcCNGC21 characterized to localize at the plasma membrane, with the highest expression levels in leaves, followed by roots. In addition, HcCNGC21 could be significantly induced under salt or drought stress. Virus-induced gene silencing (VIGS) of HcCNGC21 in kenaf caused notable growth inhibition under salt or drought stress, characterized by reductions in plant height, stem diameter, leaf area, root length, root surface area, and root tip number. Meanwhile, the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were significantly decreased, accompanied by reduced levels of osmoregulatory substances and total chlorophyll content. However, ROS accumulation and Na+ content increased. The expression of stress-responsive genes, such as HcSOD, HcPOD, HcCAT, HcERF3, HcNAC29, HcP5CS, HcLTP, and HcNCED, was significantly downregulated in these silenced lines. However, under salt or drought stress, the physiological performance and expression of stress-related genes in transgenic Arabidopsis thaliana plants overexpressing HcCNGC21 were diametrically opposite to those of TRV2-HcCNGC21 kenaf line. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays revealed that HcCNGC21 interacts with HcAnnexin D1. These findings collectively underscore the positive role of HcCNGC21 in plant resistance to salt and drought stress.

Overexpression of stress granule protein TZF1 enhances salt stress tolerance by targeting ACA11 mRNA for degradation in Arabidopsis.

Tandem CCCH zinc finger (TZF) proteins play diverse roles in plant growth and stress response. Although as many as 11 TZF proteins have been identified in Arabidopsis, little is known about the mechanism by which TZF proteins select and regulate the target mRNAs. Here, we report that Arabidopsis TZF1 is a bona-fide stress granule protein. Ectopic expression of TZF1 (TZF1 OE), but not an mRNA binding-defective mutant (TZF1H186Y OE), enhances salt stress tolerance in Arabidopsis. RNA-seq analyses of NaCl-treated plants revealed that the down-regulated genes in TZF1 OE plants are enriched for functions in salt and oxidative stress responses. Because many of these down-regulated mRNAs contain AU- and/or U-rich elements (AREs and/or UREs) in their 3'-UTRs, we hypothesized that TZF1-ARE/URE interaction might contribute to the observed gene expression changes. Results from RNA immunoprecipitation-quantitative PCR analysis, gel-shift, and mRNA half-life assays indicate that TZF1 binds and triggers degradation of the autoinhibited Ca2+-ATPase 11 (ACA11) mRNA, which encodes a tonoplast-localized calcium pump that extrudes calcium and dampens signal transduction pathways necessary for salt stress tolerance. Furthermore, this salt stress-tolerance phenotype was recapitulated in aca11 null mutants. Collectively, our findings demonstrate that TZF1 binds and initiates degradation of specific mRNAs to enhance salt stress tolerance.

Genome-Wide Analysis of the SAUR Gene Family and Its Expression Profiles in Response to Salt Stress in Santalum album.

The SAUR (small auxin-up RNA) family constitutes a category of genes that promptly respond to the hormone auxin and play a pivotal role in diverse biological processes encompassing plant growth and the response to abiotic stress. Santalum album L., a semi-parasitic evergreen tree, is renowned for its economically valuable essential oils, positioning it among the most prized tree species. In this study, a meticulous identification and comprehensive analysis of 43 SAUR genes was conducted within S. album. Based on phylogenetic relationships, the SaSAUR genes were systematically categorized into five groups. A collinearity analysis revealed intriguing insights, disclosing 14 segmental duplications and 9 tandem duplications within the SaSAUR genes, emphasizing the pivotal role of duplication in the expansion of this gene family. Noteworthy variations in the expression levels of SaSAUR genes were observed by delving into the SaSAUR transcriptome data from various tissues, including leaves, roots, and heartwood, as well as under salt-stress conditions. Notably, SaSAUR08 and SaSAUR13 were significantly upregulated in heartwood compared with roots and leaves, while SaSAUR18 was markedly more expressed in roots compared with heartwood and leaves. Furthermore, SaSAUR27 and SaSAUR28 were found to respond closely to salt stress, hinting at their potential involvement in the salt-stress response mechanism. This research offers a comprehensive investigation of SAUR genes in S. album and establishes a foundation for future exploration of the SAUR gene family, particularly its relation to growth and salt-stress responses.

ZmHAK17 encodes a Na+-selective transporter that promotes maize seed germination under salt conditions

Elevated sodium ion (Na+) in saline farmlands adversely affect crops, notably by inhibiting seed germination. Given the importance of High-Affinity K+ Transporter (HAK) family Na+ transporters in plant salt tolerance and ZmHAK4 role in maize salt tolerance, our study focuses on characterizing HAK transporters related to ZmHAK4 in maize’s salt stress response. We found that ZmHAK17 is vital for promoting seed germination under saline conditions. Expressed mainly in the germinating embryo’s radicle, ZmHAK17, encodes a Na+ transporter located in the plasma membrane. Increased ZmHAK17 transcript levels under salt stress facilitate Na+ efflux from the radicle, preventing Na+ accumulation in the embryo and reducing salt stress effects on germination. Mutants lacking ZmHAK17 exhibit salt-sensitive germination. This study highlights ZmHAK17 as a key transporter enhancing maize germination in saline conditions, deepening our understanding of HAK family Na+ transporters’ role in salt tolerance and offering a new target gene for salt-tolerant maize breeding.

The overexpression of OsMed 37_6, a mediator complex subunit enhances salt stress tolerance in rice

Mediator, a multisubunit co-activator complex, regulates transcription in eukaryotes and is involved in diverse processes in rice through its different subunits. Here, we have explored salt stress response of one of the rice Mediator subunit gene OsMED37_6. To unravel the possible mechanism of OsMed37_6 gene function, a detailed bioinformatics analysis was also followed. It was found that the gene has functional domains like Hsp70 (heat hock protein). Several salt tolerance up regulatory transcription factors are also predicted to be interacting with OsMed37_6 protein. To validate these understanding on the roles of OsMED37_6 in rice, we generated overexpression lines with OsMed37_6: pCAMBIA231: LBA4404 gene construct. It was observed that the overexpression enhances salt stress tolerance in transgenic lines. Therefore, it is a possibility that the mediator protein imparts salt tolerance by interacting with salt tolerance related transcription factors.

GROWTH REGULATING FACTOR 7-mediated arbutin metabolism enhances rice salt tolerance.

Salt stress is an environmental factor that limits plant growth and crop production. With the rapid expansion of salinized arable land worldwide, investigating the molecular mechanisms underlying the salt stress response in plants is urgently needed. Here, we report that GROWTH REGULATING FACTOR 7 (OsGRF7) promotes salt tolerance by regulating arbutin (hydroquinone-β-D-glucopyranoside) metabolism in rice (Oryza sativa). Overexpression of OsGRF7 increased arbutin content, and exogenous arbutin application rescued the salt-sensitive phenotype of OsGRF7 knockdown and knockout plants. OsGRF7 directly promoted the expression of the arbutin biosynthesis genes URIDINE DIPHOSPHATE GLYCOSYLTRANSFERASE 1 (OsUGT1) and OsUGT5, and knockout of OsUGT1 or OsUGT5 reduced rice arbutin content, salt tolerance, and grain size. Furthermore, OsGRF7 degradation through its interaction with F-BOX AND OTHER DOMAINS CONTAINING PROTEIN 13 reduced rice salinity tolerance and grain size. These findings highlight an underexplored role of OsGRF7 in modulating rice arbutin metabolism, salt stress response, and grain size, as well as its broad potential use in rice breeding.

In vivo proteolytic profiling of the type I and type II metacaspases in Chlamydomonas reinhardtii exposed to salt stress.

Metacaspases are cysteine proteases present in plants, fungi and protists. While the association of metacaspases with cell death is studied in a range of organisms, their native substrates are largely unknown. Here, we explored the in vivo proteolytic landscape of the two metacaspases, CrMCA-I and CrMCA-II, present in the green freshwater alga Chlamydomonas reinhardtii, using mass spectrometry-based degradomics approach, during control conditions and salt stress. Comparison between the cleavage events of CrMCA-I and CrMCA-II in metacaspase mutants revealed unique cleavage preferences and substrate specificity. Degradome analysis demonstrated the relevance of the predicted metacaspase substrates to the physiology of C. reinhardtii cells and its adaptation during salt stress. Functional enrichment analysis indicated an involvement of CrMCA-I in the catabolism of carboxylic acids, while CrMCA-II plays an important role in photosynthesis and translation. Altogether, our findings suggest distinct cellular functions of the two metacaspases in C. reinhardtii during salt stress response.

Functional identification of DNA demethylase gene CaROS1 in pepper (Capsicum annuum L.) involved in salt stress.

Pepper, which is a widely cultivated important vegetable, is sensitive to salt stress, and the continuous intensification of soil salinization has affected pepper production worldwide. However, genes confer to salt tolerance are rarely been cloned in pepper. Since the REPRESSOR OF SILENCING 1 (ROS1) is a DNA demethylase that plays a crucial regulatory role in plants in response to various abiotic stresses, including salt stress. We cloned a ROS1 gene in pepper, named CaROS1 (LOC107843637). Bioinformatic analysis showed that the CaROS1 protein contains the HhH-GPD glycosylase and RRM_DME domains. qRT-PCR analyses showed that the CaROS1 was highly expressed in young and mature fruits of pepper and rapidly induced by salt stress. Functional characterization of the CaROS1 was performed by gene silencing in pepper and overexpressing in tobacco, revealed that the CaROS1 positively regulates salt tolerance ability. More detailly, CaROS1-silenced pepper were more sensitive to salt stress, and their ROS levels, relative conductivity, and malondialdehyde content were significantly higher in leaves than those of the control plants. Besides, CaROS1-overexpressing tobacco plants were more tolerant to salt stress, with a higher relative water content, total chlorophyll content, and antioxidant enzyme activity in leaves compared to those of WT plants during salt stress. These results revealed the CaROS1 dose play a role in salt stress response, providing the theoretical basis for salt tolerance genetic engineering breeding in pepper.

The fungus Acremonium alternatum enhances salt stress tolerance by regulating host redox homeostasis and phytohormone signaling.

While endophytic fungi offer promising avenues for bolstering plant resilience against abiotic stressors, the molecular mechanisms behind this biofortification remain largely unknown. This study employed a multifaceted approach, combining plant physiology, proteomic, metabolomic, and targeted hormonal analyses to illuminate the early response of Brassica napus to Acremonium alternatum during the nascent stages of their interaction. Notably, under optimal growth conditions, the initial reaction to fungus was relatively subtle, with no visible alterations in plant phenotype and only minor impacts on the proteome and metabolome. Interestingly, the identified proteins associated with the Acremonium response included TUDOR 1, Annexin D4, and a plastidic K+ efflux antiporter, hinting at potential processes that could counter abiotic stressors, particularly salt stress. Subsequent experiments validated this hypothesis, showcasing significantly enhanced growth in Acremonium-inoculated plants under salt stress. Molecular analyses revealed a profound impact on the plant's proteome, with over 50% of salt stress response proteins remaining unaffected in inoculated plants. Acremonium modulated ribosomal proteins, increased abundance of photosynthetic proteins, enhanced ROS metabolism, accumulation of V-ATPase, altered abundances of various metabolic enzymes, and possibly promoted abscisic acid signaling. Subsequent analyses validated the accumulation of this hormone and its enhanced signaling. Collectively, these findings indicate that Acremonium promotes salt tolerance by orchestrating abscisic acid signaling, priming the plant's antioxidant system, as evidenced by the accumulation of ROS-scavenging metabolites and alterations in ROS metabolism, leading to lowered ROS levels and enhanced photosynthesis. Additionally, it modulates ion sequestration through V-ATPase accumulation, potentially contributing to the observed decrease in chloride content.

CwJAZ4/9 negatively regulates jasmonate-mediated biosynthesis of terpenoids through interacting with CwMYC2 and confers salt tolerance in Curcuma wenyujin.

Plant JASMONATE ZIM-DOMAIN (JAZ) genes play crucial roles in regulating the biosynthesis of specialized metabolites and stressful responses. However, understanding of JAZs controlling these biological processes lags due to numerous JAZ copies. Here, we found that two leaf-specific CwJAZ4/9 genes from Curcuma wenyujin are strongly induced by methyl-jasmonate (MeJA) and negatively correlated with terpenoid biosynthesis. Yeast two-hybrid, luciferase complementation imaging and in vitro pull-down assays confirmed that CwJAZ4/9 proteins interact with CwMYC2 to form the CwJAZ4/9-CwMYC2 regulatory cascade. Furthermore, transgenic hairy roots showed that CwJAZ4/9 acts as repressors of MeJA-induced terpenoid biosynthesis by inhibiting the terpenoid pathway and jasmonate response, thus reducing terpenoid accumulation. In addition, we revealed that CwJAZ4/9 decreases salt sensitivity and sustains the growth of hairy roots under salt stress by suppressing the salt-mediated jasmonate responses. Transcriptome analysis for MeJA-mediated transgenic hairy root lines further confirmed that CwJAZ4/9 negatively regulates the terpenoid pathway genes and massively alters the expression of genes related to salt stress signaling and responses, and crosstalks of multiple phytohormones. Altogether, our results establish a genetic framework to understand how CwJAZ4/9 inhibits terpenoid biosynthesis and confers salt tolerance, which provides a potential strategy for producing high-value pharmaceutical terpenoids and improving resistantC. wenyujin varieties by a genetic approach.

Overexpression of the WRKY transcription factor gene NtWRKY65 enhances salt tolerance in tobacco (Nicotiana tabacum)

BackgroundSalt stress severely inhibits plant growth, and the WRKY family transcription factors play important roles in salt stress resistance. In this study, we aimed to characterize the role of tobacco (Nicotiana tabacum) NtWRKY65 transcription factor gene in salinity tolerance.ResultsThis study characterized the role of tobacco (Nicotiana tabacum) NtWRKY65 transcription factor gene in salinity tolerance using four NtWRKY65 overexpression lines. NtWRKY65 is localized to the nucleus, has transactivation activity, and is upregulated by NaCl treatment. Salinity treatment resulted in the overexpressing transgenic tobacco lines generating significantly longer roots, with larger leaf area, higher fresh weight, and greater chlorophyll content than those of wild type (WT) plants. Moreover, the overexpressing lines showed elevated antioxidant enzyme activity, reduced malondialdehyde content, and leaf electrolyte leakage. In addition, the Na+ content significantly decreased, and the K+/Na+ ratio was increased in the NtWRKY65 overexpression lines compared to those in the WT. These results suggest that NtWRKY65 overexpression enhances salinity tolerance in transgenic plants. RNA-Seq analysis of the NtWRKY65 overexpressing and WT plants revealed that NtWRKY65 might regulate the expression of genes involved in the salt stress response, including cell wall component metabolism, osmotic stress response, cellular oxidant detoxification, protein phosphorylation, and the auxin signaling pathway. These results were consistent with the morphological and physiological data. These findings indicate that NtWRKY65 overexpression confers enhanced salinity tolerance.ConclusionsOur results indicated that NtWRKY65 is a critical regulator of salinity tolerance in tobacco plants.

Identification and function analysis of PP2C gene family shows that BnaA2.PP2C73 negatively regulates drought and salt stress responses in Brassica napus L.

Protein phosphatases type 2 C (PP2C) genes play a significant role in ABA signaling. Brassica napus, a pivotal industrial oilseed crop of global significance, stands at the forefront of agricultural importance. However, a comprehensive study of PP2C genes in B. napus is still missing. In this investigation, a comprehensive analysis was undertaken to identify 258 PP2C genes in B. napus, categorizing PP2C genes into 13 distinct subfamilies based on gene structural characteristics and the presence of conserved motifs. The collinearity patterns uncovered that the expansion of BnaPP2C gene family was strongly influenced by pivotal segmental duplication events with strong purifying selection. Fifty of 258 PP2C genes belonging to the subfamily E were located on 16 chromosomes. Subfamily E expansion was facilitated by segmental duplication and the promoters are rich in cis-elements. The qRT-PCR showed that subfamily E genes were transcriptionally responsive to a range of abiotic stresses, including ABA, MeJA, NaCl and drought. Additionally, the proteins encoded by selected genes from subfamily E were located in cytoplasm and BnaA2.PP2C73 negatively regulated drought and salt stress responses. These results will serve as a valuable resource for future research in understanding the fundamental characteristics and evolutionary dynamics of PP2C gene family in B. napus, providing new genetic targets to improve the abiotic stress resistance of B. napus.

Distinct growth patterns in seedling and tillering wheat plants suggests a developmentally restricted role of HYD2 in salt-stress response

Key messageMutants lacking functional HYD2 homoeologs showed improved seedling growth, but comparable or increased susceptibility to salt stress in tillering plants, suggesting a developmentally restricted role of HYD2 in salt response.Salinity stress threatens global food security by reducing the yield of staple crops such as wheat (Triticum ssp.). Understanding how wheat responds to salinity stress is crucial for developing climate resilient varieties. In this study, we examined the interplay between carotenoid metabolism and the response to salt (NaCl) stress, a specific form of salinity stress, in tetraploid wheat plants with mutations in carotenoid β-hydroxylase 1 (HYD1) and HYD2. Our investigation encompassed both the vulnerable seedling stage and the more developed tillering stage of wheat plant growth. Mutant combinations lacking functional HYD2 homoeologs, including hyd-A2 hyd-B2, hyd-A1 hyd-A2 hyd-B2, hyd-B1 hyd-A2 hyd-B2, and hyd-A1 hyd-B1 hyd-A2 hyd-B2, had longer first true leaves and slightly enhanced root growth during germination under salt stress compared to the segregate wild-type (control) plants. Interestingly, these mutant seedlings also showed decreased levels of neoxanthin and violaxanthin (xanthophylls derived from β-carotene) and an increase in β-carotene in roots. However, tillering hyd mutant and segregate wild-type plants generally did not differ in their height, tiller count, and biomass production under acute or prolonged salt stress, except for decreases in these parameters observed in the hyd-A1 hyd-B1 hyd-A2 hyd-B2 mutant that indicate its heightened susceptibility to salt stress. Taken together, these findings suggest a significant, yet developmentally restricted role of HYD2 homoeologs in salt-stress response in tetraploid wheat. They also show that hyd-A2 hyd-B2 mutant plants, previously demonstrated for possessing enriched nutritional (β-carotene) content, maintain an unimpaired ability to withstand salt stress.

Unraveling the dynamics of salt stress response in wheat cultivars: insights into growth inhibition, antioxidant enzyme activity, and AOX gene expression

Unraveling the dynamics of salt stress response in wheat cultivars: insights into growth inhibition, antioxidant enzyme activity, and AOX gene expression

Arabidopsis class II TPS controls root development and confers salt stress tolerance through enhanced hydrophobic barrier deposition.

The mechanism of conferring salt tolerance by AtTPS9 involves enhanced deposition of suberin lamellae in the Arabidopsis root endodermis, resulting in reduction of Na+ transported to the leaves. Members of the class I trehalose-6-phosphate synthase (TPS) enzymes are known to play an important role in plant growth and development in Arabidopsis. However, class II TPSs and their functions in salinity stress tolerance are not well studied. We characterized the function of a class II TPS gene, AtTPS9, to understand its role in salt stress response and root development in Arabidopsis. The attps9 mutant exhibited significant reduction of soluble sugar levels in the leaves and formation of suberin lamellae (SL) in the endodermis of roots compared to the wild type (WT). The reduction in SL deposition (hydrophobic barriers) leads to increased apoplastic xylem loading, resulting in enhanced Na+ content in the plants, which explains salt sensitivity of the mutant plants. Conversely, AtTPS9 overexpression lines exhibited increased SL deposition in the root endodermis along with increased salt tolerance, showing that regulation of SL deposition is one of the mechanisms of action of AtTPS9 in conferring salt tolerance to Arabidopsis plants. Our data showed that besides salt tolerance, AtTPS9 also regulates seed germination and root development. qRT-PCR analyses showed significant downregulation of selected SNF1-RELATED PROTEIN KINASE2 genes (SnRK2s) and ABA-responsive genes in the mutant, suggesting that AtTPS9 may regulate the ABA-signaling intermediates as part of the mechanism conferring salinity tolerance.

Pps1, phosphatidylserine synthase, regulates the salt stress response in Schizosaccharomyces pombe.

Phosphatidylserine (PS) is important for maintaining growth, cytoskeleton, and various functions in yeast; however, its role in stress responses is poorly understood. In Schizosaccharomyces pombe, the PS synthase deletion (pps1∆) mutant shows defects in growth, morphology, cytokinesis, actin cytoskeleton, and cell wall integrity, and these phenotypes are rescued by ethanolamine supplementation. Here, we evaluated the role of Pps1 in the salt stress response in S. pombe. We found that pps1∆ cells are sensitive to salt stresses such as KCl and CaCl2 even in the presence of ethanolamine. Loss of the functional cAMP-dependent protein kinase (git3∆ or pka1∆) or phospholipase B Plb1 (plb1∆) enhanced the salt stress-sensitive phenotype in pps1∆ cells. Green fluorescent protein (GFP)-Pps1 was localized at the plasma membrane and endoplasmic reticulum regardless of the stress conditions. In pka1∆ cells, GFP-Pps1 was accumulated around the nucleus under the KCl stress. Pka1 was localized in the nucleus and the cytoplasm under normal conditions and transferred from the nucleus to the cytoplasm under salt-stress conditions. Pka1 translocated from the nucleus to the cytoplasm during CaCl2 stress in the wild-type cells, while it remained localized in the nucleus in pps1∆ cells. Expression and phosphorylation of Pka1-GFP were not changed in pps1∆ cells. Our results demonstrate that Pps1 plays an important role in the salt stress response in S. pombe.

Halophytes and heavy metals: A multi-omics approach to understand the role of gene and genome duplication in the abiotic stress tolerance of Cakile maritima.

The origin of diversity is a fundamental biological question. Gene duplications are one mechanism that provides raw material for the emergence of novel traits, but evolutionary outcomes depend on which genes are retained and how they become functionalized. Yet, following different duplication types (polyploidy and tandem duplication), the events driving gene retention and functionalization remain poorly understood. Here we used Cakile maritima, a species that is tolerant to salt and heavy metals and shares an ancient whole-genome triplication with closely related salt-sensitive mustard crops (Brassica), as a model to explore the evolution of abiotic stress tolerance following polyploidy. Using a combination of ionomics, free amino acid profiling, and comparative genomics, we characterize aspects of salt stress response in C. maritima and identify retained duplicate genes that have likely enabled adaptation to salt and mild levels of cadmium. Cakile maritima is tolerant to both cadmium and salt treatments through uptake of cadmium in the roots. Proline constitutes greater than 30% of the free amino acid pool in C. maritima and likely contributes to abiotic stress tolerance. We find duplicated gene families are enriched in metabolic and transport processes and identify key transport genes that may be involved in C. maritima abiotic stress tolerance. These findings identify pathways and genes that could be used to enhance plant resilience and provide a putative understanding of the roles of duplication types and retention on the evolution of abiotic stress response.

Identification, Classification, and Transcriptional Analysis of Rab GTPase Genes from Tomato (Solanum lycopersicum) Reveals Salt Stress Response Genes.

Salinity in plants generates an osmotic and ionic imbalance inside cells that compromises the viability of the plant. Rab GTPases, the largest family within the small GTPase superfamily, play pivotal roles as regulators of vesicular trafficking in plants, including the economically important and globally cultivated tomato (Solanum lycopersicum). Despite their significance, the specific involvement of these small GTPases in tomato vesicular trafficking and their role under saline stress remains poorly understood. In this work, we identified and classified 54 genes encoding Rab GTPases in cultivated tomato, elucidating their genomic distribution and structural characteristics. We conducted an analysis of duplication events within the S. lycopersicum genome, as well as an examination of gene structure and conserved motifs. In addition, we investigated the transcriptional profiles for these Rab GTPases in various tissues of cultivated and wild tomato species using microarray-based analysis. The results showed predominantly low expression in most of the genes in both leaves and vegetative meristem, contrasting with notably high expression levels observed in seedling roots. Also, a greater increase in gene expression in shoots from salt-tolerant wild tomato species was observed under normal conditions when comparing Solanum habrochaites, Solanum pennellii, and Solanum pimpinellifolium with S. lycopersicum. Furthermore, an expression analysis of Rab GTPases from Solanum chilense in leaves and roots under salt stress treatment were also carried out for their characterization. These findings revealed that specific Rab GTPases from the endocytic pathway and the trans-Golgi network (TGN) showed higher induction in plants exposed to saline stress conditions. Likewise, disparities in gene expression were observed both among members of the same Rab GTPase subfamily and between different subfamilies. Overall, this work emphasizes the high degree of conservation of Rab GTPases, their high functional diversification in higher plants, and the essential role in mediating salt stress tolerance and suggests their potential for further exploration of vesicular trafficking mechanisms in response to abiotic stress conditions.

Transcriptome and metabolome analysis reveals the salt stress-response mechanism in desert isolated Chlorella sp. DT025

Understanding salt stress-response mechanisms is beneficial for biodiesel production using microalgae. Herein, using physiological and multi-omics analyses, we revealed substance changes and the salt-stress response of Chlorella sp. DT025, isolated from a desert salt marsh. Using 15–30 g/L NaCl, high biomass (4.1–2.6 g/L) and high lipid content (45–65 %) were obtained. Under salt stress, the levels of chlorophyll synthesis-, photosynthesis-, Calvin cycle-, and starch synthesis-related differentially expressed genes (DEGs) were downregulated, while the contents of chlorophyll, most amino acids and nucleotides were decreased. Moreover, the levels of TCA cycle-, fatty acid (FA) synthesis and degradation-, glycerophospholipid metabolism-, nitrogen metabolism-, proline synthesis-, and antioxidant metabolism-related DEGs were upregulated, increasing FAs (major 16- and 18- carbon FAs), phosphatidylglycerol, lysophosphatidylglycerol, digalactosyldiacylglycerol, proline, catalase, and superoxide. These results reveal the molecular basis of salt tolerance in DT025 and suggest that it exhibits active metabolism using lipids as substances for energy storage and release under salt stress.

The GARP family transcription factor MtHHO3 negatively regulates salt tolerance in Medicago truncatula

High salinity is one of the detrimental environmental factors restricting plant growth and crop production throughout the world. This study demonstrated that the GARP family transcription factor MtHHO3 is involved in response to salt stress and abscisic acid (ABA) signaling in Medicago truncatula. The transcription of MtHHO3 was repressed by salt, osmotic stress, and ABA treatment. The seed germination assay showed that, overexpression of MtHHO3 in Arabidopsis thaliana caused hypersensitivity to salt and osmotic stress, but increased resistance to ABA inhibition. Overexpression of MtHHO3 in M. truncatula resulted in decreased tolerance of salinity, while loss-of-function mutants mthho3-1 and mthho3-2 were more resistant to salt stress compared with wild-type plants. qRT-PCR analyses showed that MtHHO3 downregulated the expression of genes in stress and ABA responsive pathways. We further demonstrated that MtHHO3 repressed the transcription of the pathogenesis-related gene MtPR2 by binding to its promoter. Overall, these results indicate that MtHHO3 negatively regulates salt stress response in plants and deepen our understanding of the role of the GARP subfamily transcription factors in modulating salt stress and ABA signaling.