Salt Stress In Arabidopsis Research Articles

AtC3H3, an Arabidopsis Non-TZF Gene, Enhances Salt Tolerance by Increasing the Expression of Both ABA-Dependent and -Independent Stress-Responsive Genes.

Salinity causes widespread crop loss and prompts plants to adapt through changes in gene expression. In this study, we aimed to investigate the function of the non-tandem CCCH zinc-finger (non-TZF) protein gene AtC3H3 in response to salt stress in Arabidopsis. AtC3H3, a gene from the non-TZF gene family known for its RNA-binding and RNase activities, was up-regulated under osmotic stress, such as high salt and drought. When overexpressed in Arabidopsis, AtC3H3 improved tolerance to salt stress, but not drought stress. The expression of well-known abscisic acid (ABA)-dependent salt stress-responsive genes, namely Responsive to Desiccation 29B (RD29B), RD22, and Responsive to ABA 18 (RAB18), and representative ABA-independent salt stress-responsive genes, namely Dehydration-Responsive Element Binding protein 2A (DREB2A) and DREB2B, was significantly higher in AtC3H3-overexpressing transgenic plants (AtC3H3 OXs) than in wild-type plants (WT) under NaCl treatment, indicating its significance in both ABA-dependent and -independent signal transduction pathways. mRNA-sequencing (mRNA-Seq) analysis using NaCl-treated WT and AtC3H3 OXs revealed no potential target mRNAs for the RNase function of AtC3H3, suggesting that the potential targets of AtC3H3 might be noncoding RNAs and not mRNAs. Through this study, we conclusively demonstrated that AtC3H3 plays a crucial role in salt stress tolerance by influencing the expression of salt stress-responsive genes. These findings offer new insights into plant stress response mechanisms and suggest potential strategies for improving crop resilience to salinity stress.

Genome-wide analysis of the MYB gene family and functional analysis of BhMYB79 in wax gourd

Wax gourd (Benincasa hispida) is an important cucurbit crop with economic and medicinal value. The myeloblastosis (MYB) gene family is one of the largest gene families in plants and regulates various biological processes, whereas the MYB gene family has not been systematically studied in wax gourd. In this study, we performed genome-wide identification of the MYB gene family in wax gourd and analyzed their phylogenetic relationship, MYB DNA-binding domain (MYB DBD), gene structure, protein motif, synteny, duplication mode and expression pattern. As a result, a total of 215 BhMYB genes (BhMYBs) were identified, belonging to four subfamilies: 1R-, 2R-, 3R- and 4R-MYB subfamilies. Genes of 1R-MYB subfamily and 2R-MYB subfamily were subdivided into different subgroups respectively. The analysis of MYB DBD, gene structure and protein motif showed that the most genes in the same subgroup have similar characteristics and the 2R-MYB genes were more conserved than the 1R-MYB genes. Interestingly, the long terminal retrotransposons (LTR-RTs) were found in the long introns of several BhMYBs. The results of synteny analysis showed that there were more syntenic gene pairs between wax gourd and other cucurbit crops, while the least number of syntenic gene pairs existed between wax gourd and rice. Gene duplication was the main reason for the expansion of the MYB gene family in wax gourd, with the transposed duplication (TRD) mode contributing more. All duplication BhMYB genes were under purifying selection pressure. Further expression analysis showed that many BhMYBs exhibited obvious tissue-specific expression and several BhMYBs were significantly induced by one or more abiotic stresses. BhMYB79 was particularly expressed in roots and significantly induced by salt, drought, cold and heat stresses, overexpression of which led to reduced tolerance to salt stress in Arabidopsis. In conclusion, our results provide a systematic analysis of wax gourd MYB gene family and facilitate the biological role study of BhMYB79 during wax gourd salt stress response process.

FERONIA regulates salt tolerance in Arabidopsis by controlling photorespiratory flux.

Photorespiration is an energetically costly metabolic pathway in plants that responds to environmental stresses. The molecular basis of the regulation of the photorespiratory cycle under stress conditions remains unclear. Here, we discovered that FERONIA (FER) regulates photorespiratory flow under salt stress in Arabidopsis (Arabidopsis thaliana). FER mutation results in hypersensitivity to salt stress, but disruption of ferredoxin-dependent glutamate synthase 1 (GLU1), an enzyme that participates in the photorespiratory pathway by producing glutamate, greatly suppresses fer-4 hypersensitivity to salt stress primarily due to reduced glycine yield. In contrast, disrupting mitochondrial serine hydroxymethyltransferase1 (SHM1), which is supposed to increase glycine levels by hampering the conversion of glycine to serine in the photorespiratory cycle, aggravates fer-4 hypersensitivity to salt stress. Biochemical data show that FER interacts with and phosphorylates SHM1, and this phosphorylation modulates SHM1 stability. Additionally, the production of proline and its intermediate △1-pyrroline-5-carboxylate (P5C), which are both synthesized from glutamate, also contributes to fer-4 hypersensitivity to salt stress. In conclusion, this study elucidates the functional mechanism of FER in regulating salt tolerance by modulating photorespiratory flux, which greatly broadens our understanding of how plants adapt to high salinity.

Understanding Ameliorating Effects of Boron on Adaptation to Salt Stress in Arabidopsis.

When faced with salinity stress, plants typically exhibit a slowdown in their growth patterns. Boron (B) is an essential micronutrient for plants that are known to play a critical role in controlling cell wall properties. In this study, we used the model plant Arabidopsis thaliana Col-0 and relevant mutants to explore how the difference in B availability may modulate plant responses to salt stress. There was a visible root growth suppression of Col-0 with the increased salt levels in the absence of B while this growth reduction was remarkably alleviated by B supply. Pharmacological experiments revealed that orthovanadate (a known blocker of H+-ATPase) inhibited root growth at no B condition, but had no effect in the presence of 30 μM B. Salinity stress resulted in a massive K+ loss from mature zones of A. thaliana roots; this efflux was attenuated in the presence of B. Supplemental B also increased the magnitude of net H+ pumping by plant roots. Boron availability was also essential for root halotropism. Interestingly, the aha2Δ57 mutant with active H+-ATPase protein exhibited the same halotropism response as Col-0 while the aha2-4 mutant had a stronger halotropism response (larger bending angle) compared with that of Col-0. Overall, the ameliorative effect of B on the A. thaliana growth under salt stress is based on the H+-ATPase stimulation and a subsequent K+ retention, involving auxin- and ROS-pathways.

SOS2-AFP2 module regulates seed germination by inducing ABI5 degradation in response to salt stress in Arabidopsis

Soil salinity pose a significant challenge to global agriculture, threatening crop yields and food security. Understanding the salt tolerance mechanisms of plants is crucial for improving their survival under salt stress. AFP2, a negative regulator of ABA signaling, has been shown to play a crucial role in salt stress tolerance during seed germination. Mutations in AFP2 gene lead to increased sensitivity to salt stress. However, the underline mechanisms by which AFP2 regulates seed germination under salt stress remain elusive. In this study, we identified a protein interaction between AFP2 and SOS2, a Ser/Thr protein kinase known to play a critical role in salt stress response. Using a combination of genetic, biochemical, and physiological approaches, we investigated the role of the SOS2-AFP2 module in regulating seed germination under salt stress. Our findings reveal that SOS2 physically interacts with AFP2 and stabilizes it, leading to the degradation of the ABI5 protein, a negative transcription factor in seed germination under salt stress. This study sheds light on previously unknown connections within salt stress and ABA signaling, paving the way for novel strategies to enhance plant resilience against environmental challenges.

Brassinosteroids biosynthetic gene MdBR6OX2 regulates salt stress tolerance in both apple and Arabidopsis

Salt stress is a critical limiting factor for fruit yield and quality of apples. Brassinosteroids (BRs) play an important role in response to abiotic stresses. In the present study, application of 2,4- Epicastasterone on seedlings of Malus ‘M9T337’ and Malus domestica ‘Gala3’ alleviated the physiological effects, such as growth inhibition and leaf yellowing, induced by salt stress. Further analysis revealed that treatment with NaCl induced expression of genes involved in BR biosynthesis in ‘M9T337’ and ‘Gala3’. Among which, the expression of BR biosynthetic gene MdBR6OX2 showed a three-fold upregulation upon salt treatment, suggesting its potential role in response to salt stress in apple. MdBR6OX2, belonging to the CYP450 family, contains a signal peptide region and a P450 domain. Expression patterns analysis showed that the expression of MdBR6OX2 can be significantly induced by different abiotic stresses. Overexpressing MdBR6OX2 enhanced the tolerance of apple callis to salt stress, and the contents of endogenous BR-related compounds, such as Typhastero (TY), Castasterone (CS) and Brassinolide (BL) were significantly increased in transgenic calli compared with that of wild-type. Extopic expression of MdBR6OX2 enhanced tolerance to salt stress in Arabidopsis. Genes associated with salt stress were significantly up-regulated, and the contents of BR-related compounds were significantly elevated under salt stress. Our data revealed that BR-biosynthetic gene MdBR6OX2 positively regulates salt stress tolerance in both apple calli and Arabidopsis.

A root cap-localized NAC transcription factor controls root halotropic response to salt stress in Arabidopsis

Plants are capable of altering root growth direction to curtail exposure to a saline environment (termed halotropism). The root cap that surrounds root tip meristematic stem cells plays crucial roles in perceiving and responding to environmental stimuli. However, how the root cap mediates root halotropism remains undetermined. Here, we identified a root cap-localized NAC transcription factor, SOMBRERO (SMB), that is required for root halotropism. Its effect on root halotropism is attributable to the establishment of asymmetric auxin distribution in the lateral root cap (LRC) rather than to the alteration of cellular sodium equilibrium or amyloplast statoliths. Furthermore, SMB is essential for basal expression of the auxin influx carrier gene AUX1 in LRC and for auxin redistribution in a spatiotemporally-regulated manner, thereby leading to directional bending of roots away from higher salinity. Our findings uncover an SMB-AUX1-auxin module linking the role of the root cap to the activation of root halotropism.

The maize ATP-binding cassette (ABC) transporter ZmMRPA6 confers cold and salt stress tolerance in plants.

ZmMRPA6 was cloned and characterized as the first ATP-binding cassette (ABC) transporter in maize to be proven to participate in cold and salt tolerance. Homologous genes AtABCC4 and AtABCC14 of ZmMRPA6 also responded to salt stress. ATP-binding cassette (ABC) proteins are major transmembrane transporters that play significant roles in plant development against various abiotic stresses. However, available information regarding stress-related ABC genes in maize is minimal. In this study, a maize ABC transporter gene, ZmMRPA6, was identified through genome-wide association analysis (GWAS) for cold tolerance in maize seeds germination and functionally characterized. During germination and seedling stages, the zmmrpa6 mutant exhibited enhanced resistance to cold or salt stress. Mutated of ZmMRPA6 did not affect the expression of downstream response genes related cold or salt response at the transcriptional level. Mass spectrometry analysis revealed that most of the differential proteins between zmmrpa6 and wild-type plants were involved in response to stress process including oxidative reduction, hydrolase activity, small molecule metabolism, and photosynthesis process. Meanwhile, the plants which lack the ZmMRPA6 homologous genes AtABCC4 or AtABCC14 were sensitive to salt stress in Arabidopsis. These results indicated that ZmMRPA6 and its homologous genes play a conserved role in cold and salt stress, and functional differentiation occurs in monocotyledonous and dicotyledonous plants. In summary, these findings dramatically improved our understanding of the function of ABC transporters resistance to abiotic stresses in plants.

Persulfidation maintains cytosolic G6PDs activity through changing tetrameric structure and competing cysteine sulfur oxidation under salt stress in Arabidopsis and tomato.

Glucose-6-phosphate dehydrogenases (G6PDs) are essential regulators of cellular redox. Hydrogen sulfide (H2 S) is a small gasotransmitter that improves plant adaptation to stress; however, its role in regulating G6PD oligomerization to resist oxidative stress remains unknown in plants. Persulfidation of cytosolic G6PDs was analyzed by mass spectrometry (MS). The structural change model of AtG6PD6 homooligomer was built by chemical cross-linking coupled with mass spectrometry (CXMS). We isolated AtG6PD6C159A and SlG6PDCC155A transgenic lines to confirm the invivo function of persulfidated sites with the g6pd5,6 background. Persulfidation occurs at Arabidopsis G6PD6 Cystine (Cys)159 and tomato G6PDC Cys155, leading to alterations of spatial distance between lysine (K)491-K475 from 42.0 Å to 10.3 Å within the G6PD tetramer. The structural alteration occurs in the structural NADP+ binding domain, which governs the stability of G6PD homooligomer. Persulfidation enhances G6PD oligomerization, thereby increasing substrate affinity. Under high salt stress, cytosolic G6PDs activity was inhibited due to oxidative modifications. Persulfidation protects these specific sites and prevents oxidative damage. In summary, H2 S-mediated persulfidation promotes cytosolic G6PD activity by altering homotetrameric structure. The cytosolic G6PD adaptive regulation with two kinds of protein modifications at the atomic and molecular levels is critical for the cellular stress response.

The salt-activated CBF1/CBF2/CBF3-GALS1 module fine-tunes galactan-induced salt hypersensitivity in Arabidopsis.

Plant growth and development are significantly hampered in saline environments, limiting agricultural productivity. Thus, it is crucial to unravel the mechanism underlying plant responses to salt stress. β-1,4-Galactan (galactan), which forms the side chains of pectic rhamnogalacturonan I, enhances plant sensitivity to high-salt stress. Galactan is synthesized by GALACTAN SYNTHASE1 (GALS1). We previously showed that NaCl relieves the direct suppression of GALS1 transcription by the transcription factors BPC1 and BPC2 to induce the excess accumulation of galactan in Arabidopsis (Arabidopsis thaliana). However, how plants adapt to this unfavorable environment remains unclear. Here, we determined that the transcription factors CBF1, CBF2, and CBF3 directly interact with the GALS1 promoter and repress its expression, leading to reduced galactan accumulation and enhanced salt tolerance. Salt stress enhances the binding of CBF1/CBF2/CBF3 to the GALS1 promoter by inducing CBF1/CBF2/CBF3 transcription and accumulation. Genetic analysis suggested that CBF1/CBF2/CBF3 function upstream of GALS1 to modulate salt-induced galactan biosynthesis and the salt response. CBF1/CBF2/CBF3 and BPC1/BPC2 function in parallel to regulate GALS1 expression, thereby modulating the salt response. Our results reveal a mechanism in which salt-activated CBF1/CBF2/CBF3 inhibit BPC1/BPC2-regulated GALS1 expression to alleviate galactan-induced salt hypersensitivity, providing an activation/deactivation fine-tune mechanism for dynamic regulation of GALS1 expression under salt stress in Arabidopsis. This article is protected by copyright. All rights reserved.

CRK41 Modulates Microtubule Depolymerization in Response to Salt Stress in Arabidopsis

The pivotal role of cysteine-rich receptor-like kinases (CRKs) in modulating growth, development, and responses to stress has been widely acknowledged in Arabidopsis. However, the function and regulation of CRK41 has remained unclear. In this study, we demonstrate that CRK41 is critical for modulating microtubule depolymerization in response to salt stress. The crk41 mutant exhibited increased tolerance, while overexpression of CRK41 led to hypersensitivity to salt. Further analysis revealed that CRK41 interacts directly with the MAP kinase3 (MPK3), but not with MPK6. Inactivation of either MPK3 or MPK6 could abrogate the salt tolerance of the crk41 mutant. Upon NaCl treatment, microtubule depolymerization was heightened in the crk41 mutant, yet alleviated in the crk41mpk3 and crk41mpk6 double mutants, indicating that CRK41 suppresses MAPK-mediated microtubule depolymerizations. Collectively, these results reveal that CRK41 plays a crucial role in regulating microtubule depolymerization triggered by salt stress through coordination with MPK3/MPK6 signalling pathways, which are key factors in maintaining microtubule stability and conferring salt stress resistance in plants.

Evolution of the WRKY66 Gene Family and Its Mutations Generated by the CRISPR/Cas9 System Increase the Sensitivity to Salt Stress in Arabidopsis.

Group Ⅲ WRKY transcription factors (TFs) play pivotal roles in responding to the diverse abiotic stress and secondary metabolism of plants. However, the evolution and function of WRKY66 remains unclear. Here, WRKY66 homologs were traced back to the origin of terrestrial plants and found to have been subjected to both motifs' gain and loss, and purifying selection. A phylogenetic analysis showed that 145 WRKY66 genes could be divided into three main clades (Clade A-C). The substitution rate tests indicated that the WRKY66 lineage was significantly different from others. A sequence analysis displayed that the WRKY66 homologs had conserved WRKY and C2HC motifs with higher proportions of crucial amino acid residues in the average abundance. The AtWRKY66 is a nuclear protein, salt- and ABA- inducible transcription activator. Simultaneously, under salt stress and ABA treatments, the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities, as well as the seed germination rates of Atwrky66-knockdown plants generated by the clustered, regularly interspaced, short palindromic repeats/CRISPR-associated 9 (CRISPR/Cas9) system, were all lower than those of wild type (WT) plants, but the relative electrolyte leakage (REL) was higher, indicating the increased sensitivities of the knockdown plants to the salt stress and ABA treatments. Moreover, RNA-seq and qRT-PCR analyses revealed that several regulatory genes in the ABA-mediated signaling pathway involved in stress response of the knockdown plants were significantly regulated, being evidenced by the more moderate expressions of the genes. Therefore, the AtWRKY66 likely acts as a positive regulator in the salt stress response, which may be involved in an ABA-mediated signaling pathway.

RAP2.6 enhanced salt stress tolerance by reducing Na+ accumulation and stabilizing the electron transport in Arabidopsis thaliana

The transcription factors of the AP2/ERF family are involved in plant growth and development and responses to biotic and abiotic stresses. Here, we found RAP2.6, a transcription factor which belongs to the ERF subfamily, was responsive to salt stress in Arabidopsis. Under salt stress conditions, rap2.6 mutant seedlings were the sensitivity deficiency to salt stress which was reflected in higher germination rate and longer root length compared to the wild type. Also, the expressions of salt-related gene including SOS1, SOS2, SOS3, NHX1, NHX3, NHX5 and HKT1 in rap2.6 mutant seedlings were lower than the wild type under salt stress. rap2.6 mutant adult lacked salt stress tolerance based on the results of the phenotype, survival rates and ion leakage. Compared to wild type, rap2.6 mutant adult accumulated more Na+ in leaves and roots while the salt-related gene expressions were lower. In addition, the photosynthetic electron transport and PSII energy distribution in rap2.6 mutant plant leaves had been more seriously affected under salt stress conditions compared to the wild type. In summary, this study identified essential roles of RAP2.6 in regulating salt stress tolerance in Arabidopsis.

A Novel R2R3-MYB Transcription Factor FtMYB22 Negatively Regulates Salt and Drought Stress through ABA-Dependent Pathway.

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is a coarse cereal with strongly abiotic resistance. The MYB family plays a regulatory role in plant growth, development, and responses to biotic and abiotic stresses. However, the characteristics and regulatory mechanisms of MYB transcription factors in Tartary buckwheat remain unclarified. Here, this study cloned the FtMYB22 gene from Tartary buckwheat, and investigated its involvement in responding to individual water deficit and salt stress in Arabidopsis. Sequence analysis highlighted that the N-termini of FtMYB22 contained two highly conserved SANT domains and one conserved domain from the SG20 subfamily. Nucleus-localized FtMYB22 did not have individual transcriptional activation activity. Water deficiency and salt stress induced the high expression of the GUS gene, which was driven by the promoter of FtMYB22. Yeast stress experiments showed that the overexpression of FtMYB22 significantly reduced the growth activity of transgenic yeast under water deficit or salt stress. Consistently, the overexpression of FtMYB22 reduced the salt and water deficit stress resistance of the transgenic plants. In addition, physiological parameters showed that transgenic plants had lower proline and antioxidant enzyme activity under stress conditions. Compared to the wild-type (WT), transgenic plants accumulated more malondialdehyde (MDA), H2O2, and O2−; they also showed higher ion permeability and water loss rates of detached leaves under stress treatments. Notably, FtMYB22 was involved in plant stress resistance through an ABA-dependent pathway. Under stress conditions, the expression of RD29A, RD29B, PP2CA, KIN1, COR15A, and other genes in response to plant stress in transgenic lines was significantly lower than that in the WT (p < 0.05). Furthermore, yeast two-hybrid assay showed that there was a significant interaction between FtMYB22 and the ABA receptor protein RCAR1/2, which functioned in the ABA signal pathway. Altogether, FtMYB22, as a negative regulator, inhibited a variety of physiological and biochemical reactions, affected gene expression and stomatal closure in transgenic plants through the ABA-dependent pathway, and reduced the tolerance of transgenic Arabidopsis to water deficiency and salt stress. Based on these fundamental verifications, further studies would shed light on the hormone signal response mechanism of FtMYB22.

LocusDivergence analysis of GWAS candidates identified for root:shoot ratio changes under salt stress in Arabidopsis

LocusDivergence analysis of GWAS candidates identified for root:shoot ratio changes under salt stress in Arabidopsis

A Ca2+-sensor switch for tolerance to elevated salt stress in Arabidopsis.

Excessive Na+ in soils inhibits plant growth. Here, we report that Na+ stress triggers primary calcium signals specifically in a cell group within the root differentiation zone, thus forming a "sodium-sensing niche" in Arabidopsis. The amplitude of this primary calcium signal and the speed of the resulting Ca2+ wave dose-dependently increase with rising Na+ concentrations, thus providing quantitative information about the stress intensity encountered. We also delineate a Ca2+-sensing mechanism that measures the stress intensity in order to mount appropriate salt detoxification responses. This is mediated by a Ca2+-sensor-switch mechanism, in which the sensors SOS3/CBL4 and CBL8 are activated by distinct Ca2+-signal amplitudes. Although the SOS3/CBL4-SOS2/CIPK24-SOS1 axis confers basal salt tolerance, the CBL8-SOS2/CIPK24-SOS1 module becomes additionally activated only in response to severe salt stress. Thus, Ca2+-mediated translation of Na+ stress intensity into SOS1 Na+/H+ antiporter activity facilitates fine tuning of the sodium extrusion capacity for optimized salt-stress tolerance.

Heterologous expression of ZmNF-YA12 confers tolerance to drought and salt stress in Arabidopsis

Drought and salinity are serious environmental factors limiting the growth and productivity of plants worldwide. Therefore, it is necessary to develop ways to improve drought and salinity stress tolerance in plants. In this study, a drought-responsive nuclear factor Y subunit A gene, ZmNF-YA12, was cloned from maize. qPCR revealed ZmNF-YA12 transcript in all vegetative and reproductive tissues, with higher levels in young roots. Expression analyses of maize revealed that ZmNF-YA12 was induced by abscisic acid (ABA), jasmonic acid (JA), and abiotic stresses, including dehydration, high salinity, cold, and polyethylene glycol (PEG) treatment. The heterologous expression of ZmNF-YA12 in Arabidopsis plants resulted in increased root length and better plant growth than in wild-type (WT) plants under conditions of mannitol, salt, and JA stress on 1/2 MS medium. Transgenic Arabidopsis showed improved tolerance to drought and salt stresses in soil, and higher proline content and lower malondialdehyde (MDA) content than WT controls. The transgenic plants also maintained higher peroxidase (POD) activities than WT plants under conditions of NaCl stress. A yeast two-hybrid experiment demonstrated that ZmNF-YA12 interacted with ZmNF-YC1 and ZmNF-YC15. Moreover, the transcript levels of stress-responsive genes (RD29A, RD29B, RAB18, and RD22) were markedly increased in transgenic lines under conditions of drought and salt stress. These observations suggested that the ZmNF-YA12 gene may confers drought and salt stress tolerance by regulating stress-related genes or interacting with ZmNF-YC1 and ZmNF-YC15, and has potential applications in molecular breeding with maintenance of production under conditions of stress.

Multicolor Fluorescence Imaging for the Early Detection of Salt Stress in Arabidopsis

Salt stress is one of the abiotic factors that causes adverse effects in plants and there is an urgent need to detect salt stress in plants as early as possible. Multicolor fluorescence imaging, as a powerful tool in plant phenotyping, can provide information about primary and secondary metabolism in plants to detect the responses of the plants exposed to stress in the early stage. The purpose of this study was to evaluate the potential of multicolor fluorescence imaging’s application in the early detection of salt stress in plants. In this study, the measurements were conducted on Arabidopsis and the multicolor fluorescence images were acquired at 440, 520, 690, and 740 nm with a self-developed imaging system consisting of a UV light-emitting diode (LED) panel for an excitation at 365 nm, a charge coupled device (CCD) camera, interference filters, and a computer. We developed a classification method using the imaging analysis of multicolor fluorescence based on principal component analysis (PCA) and a support vector machine (SVM). The results showed that the four principal fluorescence feature combinations were the ideal indicators as the inputs of the SVM model, and the classification accuracies of the control and salt-stress treatment at 5 days and 9 days were 92.65% and 98.53%, respectively. The results indicated that multicolor fluorescence imaging combined with PCA and SVM could act as a tool for early detection in salt-stressed plants.

Ectopic Expression of a Salt-Inducible Gene, LcSAIN3, from Sheepgrass Improves Seed Germination and Seedling Growth under Salt Stress in Arabidopsis.

Sheepgrass is a perennial native grass species in China, and it can tolerate high levels of salt stress with an aggressive and vigorous rhizome system. Many salt-stress-responsive genes have been identified in sheepgrass. In this study, we report the cloning and characterization of a novel salt-induced gene, LcSAIN3 (Leymus chinensis salt-induced 3), from sheepgrass. Expression analysis confirmed that LcSAIN3 was induced by PEG, ABA, and salt treatments, and the expression of LcSAIN3 was significantly increased in salt-tolerant germplasms under salt treatment. Subcellular localization analysis indicated that the GFP-LcSAIN3 protein was mainly localized in the chloroplasts. The heterologous expression of LcSAIN3 in Arabidopsis increased the seed germination rate of transgenic plants under salt, ABA, and mannitol treatments. The seedling survival rate, plant height, and fresh weight of the transgenic plants were higher than those of WT plants under salt stress. The overexpression of LcSAIN3 caused a relatively high accumulation of free proline, enhanced SOD activity, and led to the upregulation of several stress-responsive genes such as AtRD26, AtRD29B, AtSOS1, and AtP5CS1. These results suggest that LcSAIN3 could be a potential target for molecular breeding to improve plants’ salt tolerance.

Ethylene signaling in salt-stressed Arabidopsis thaliana ein2-1 and ctr1-1 mutants – A dissection of molecular mechanisms involved in acclimation

To pinpoint ethylene-mediated molecular mechanisms involved in the adaptive response to salt stress we conducted a comparative study of Arabidopsis thaliana wild type (Col-0), ethylene insensitive (ein2-1), and constitutive signaling (ctr1-1) mutant plants. Reduced germination and survival rates were observed in ein2-1 plants at increasing NaCl concentrations. By contrast, ctr1-1 mutation conferred salt stress tolerance during early vegetative development, corroborating earlier studies. Аll genotypes experienced strong stress as evidenced by the accumulation of reactive oxygen species (ROS) and increased membrane lipid peroxidation. However, the isoenzyme profiles of ROS scavenging enzymes demonstrated a higher peroxidase (POX) activity in ctr1-1 individuals under control and salt stress conditions. A markedly elevated free L-Proline (L-Pro) content was detected in the ethylene constitutive mutant. This coincided with the increased levels of Delta-1-Pyrroline-5-Carboxylate Synthase (P5CS) which is the rate-limiting enzyme from the proline biosynthetic pathway. A stabilized upregulation of a stress-induced P5CS1 splice variant was observed in the ctr1-1 background, which was not documented in the ethylene insensitive mutant ein2-1. Transcript profiling of the major SALT OVERLY SENSITIVE (SOS) pathway players (SOS1, SOS2, and SOS3) revealed altered gene expression in the organs of the ethylene signaling mutants. Overall suppressed SOS expression was observed in the ein2-1 mutants while only the SOS transcript profiles in the ctr1-1 roots were similar to the wild type. Altogether, we provide experimental evidence for ethylene-mediated molecular mechanisms implicated in the acclimation response to salt stress in Arabidopsis, which operate mainly through the regulation of free proline accumulation and enhanced ROS scavenging.