Project description:Stomatal regulation is crucial to reduce water consumption under drought conditions. Extracellular ATP (eATP) serves as a signaling agent in stomatal regulation; however, it is less known whether the eATP mediation of stomatal aperture is linked to apyrases (APYs), the principal enzymes that control the concentration of eATP. To clarify the role of APYs in stomatal control, PeAPY1 and PeAPY2 were isolated from Populus euphratica and transferred into Arabidopsis. Compared with the wild-type Arabidopsis and loss-of-function mutants (Atapy1 and Atapy2), PeAPY1- and PeAPY2-transgenic plants decreased stomatal aperture under mannitol treatment (200 mM, 2 h) and reduced water loss during air exposure (90 min). The role of apyrase in stomatal regulation resulted from its control in eATP-regulated stomatal movements and increased stomatal sensitivity to ABA. The bi-phasic dose-responses to applied nucleotides, i.e., the low ATP (0.3-1.0 mM)-promoted opening and high ATP (>2.0 mM)-promoted closure, were both restricted by P. euphratica apyrases. It is noteworthy that eATP at a low concentration (0.3 mM) counteracted ABA action in the regulation of stomatal aperture, while overexpression of PeAPY1 or PeAPY2 effectively diminished eATP promotion in opening, and consequently enhanced ABA action in closure. We postulate a speculative model of apyrase signaling in eATP- and ABA-regulated stomatal movements under drought.
Project description:High NaCl (200 mM) increases the transcription of phospholipase Dδ (PLDδ) in roots and leaves of the salt-resistant woody species Populus euphratica. We isolated a 1138 bp promoter fragment upstream of the translation initiation codon of PePLDδ. A promoter-reporter construct, PePLDδ-pro::GUS, was introduced into Arabidopsis plants (Arabidopsis thaliana) to demonstrate the NaCl-induced PePLDδ promoter activity in root and leaf tissues. Mass spectrometry analysis of DNA pull-down-enriched proteins in P. euphratica revealed that PeGLABRA3, a basic helix-loop-helix transcription factor, was the target transcription factor for binding the promoter region of PePLDδ. The PeGLABRA3 binding to PePLDδ-pro was further verified by virus-induced gene silencing, luciferase reporter assay (LRA), yeast one-hybrid assay, and electrophoretic mobility shift assay (EMSA). In addition, the PeGLABRA3 gene was cloned and overexpressed in Arabidopsis to determine the function of PeGLABRA3 in salt tolerance. PeGLABRA3-overexpressed Arabidopsis lines (OE1 and OE2) had a greater capacity to scavenge reactive oxygen species (ROS) and to extrude Na+ under salinity stress. Furthermore, the EMSA and LRA results confirmed that PeGLABRA3 interacted with the promoter of AtPLDδ in transgenic plants. The upregulated AtPLDδ in PeGLABRA3-transgenic lines resulted in an increase in phosphatidic acid species under no-salt and saline conditions. We conclude that PeGLABRA3 activated AtPLDδ transcription under salt stress by binding to the AtPLDδ promoter region, conferring Na+ and ROS homeostasis control via signaling pathways mediated by PLDδ and phosphatidic acid.
Project description:Plasma membrane proton pumps play a crucial role in maintaining ionic homeostasis in salt-resistant Populus euphratica under saline conditions. High levels of NaCl (200 mM) induced PeHA1 expression in P. euphratica roots and leaves. We isolated a 2022 bp promoter fragment upstream of the translational start of PeHA1 from P. euphratica. The promoter-reporter construct PeHA1-pro::GUS was transferred to tobacco plants, demonstrating that β-glucuronidase activities increased in root, leaf, and stem tissues under salt stress. DNA affinity purification sequencing revealed that PeWRKY1 protein targeted the PeHA1 gene. We assessed the salt-induced transcriptional response of PeWRKY1 and its interaction with PeHA1 in P. euphratica. PeWRKY1 binding to the PeHA1 W-box in the promoter region was verified by a yeast one-hybrid assay, EMSA, luciferase reporter assay, and virus-induced gene silencing. Transgenic tobacco plants overexpressing PeWRKY1 had improved expression of NtHA4, which has a cis-acting W-box in the regulatory region, and improved H+ pumping activity in both in vivo and in vitro assays. We conclude that salt stress up-regulated PeHA1 transcription due to the binding of PeWRKY1 to the W-box in the promoter region of PeHA1. Thus, we conclude that enhanced H+ pumping activity enabled salt-stressed plants to retain Na+ homeostasis.
Project description:BackgroundTo investigate the salt tolerance of Populus talassica × Populus euphratica, morphological and physiological parameters were measured on the second day after the 15th, 30th and 45th days of NaCl treatment, revealing significant effects of NaCl on growth. To further elucidate the mechanisms underlying salt tolerance, transcriptomic and metabolomic analysis were conducted under different NaCl treatments.ResultsThe results of morphological and physiological indexes showed that under low salt treatment, P. talassica × P. euphratica was able to coordinate the growth of aboveground and belowground parts. Under high salt concentration, the growth and water balance of P. talassica × P. euphratica were markedly inhibited. The most significant differences between treatments were observed on the second day after the 45th day of NaCl treatment. Transcriptomic analysis showed that the pathways of gene enrichment in the roots and stems of P. talassica × P. euphratica were different in the salt resistance response. And it involves several core pathways such as plant hormone signal transduction, phenylpropanoid biosynthesis, MAPK signaling pathway-plant, plant- pathogen interaction, carbon metabolism, biosynthesis of amino acids, and several key Transcription factors (TFs) such as AP2/ERF, NAC, WRKY and bZIP. Metabolomic analysis revealed that KEGG pathway enrichment analysis showed unique metabolic pathways were enriched in P. talassica × P. euphratica under both 200 mM and 400 mM NaCl treatments. Additionally, while there were some differences in the metabolic pathways enriched in the roots and stems, both tissues commonly enriched pathways related to the biosynthesis of secondary metabolites, biosynthesis of cofactors, biosynthesis of amino acids, flavonoid biosynthesis, and ABC transporters. Association analysis further indicated that biosynthesis of amino acids and plant hormone signal transduction pathway play key roles in the response of P. talassica × P. euphratica to salt stress. The interactions between the differentially expressed genes (DEGs) and several differentially accumulated metabolites (DAMs), especially the strong association between LOC105124002 and Jasmonoyl-L-Isoleucine (pme2074), were again revealed by the interactions analysis.ConclusionsIn this study, we resolved the changes of metabolic pathways in roots and stems of P. talassica × P. euphratica under different NaCl treatments and explored the associations between characteristic DEGs and DAMs, which provided insights into the mechanisms of P. talassica × P. euphratica in response to salt stress.
Project description:Salinization is one of the major factors that threaten the existence of plants worldwide. Populus euphratica has been deemed to be a promising candidate for stress response research because of its high capacity to tolerate extreme salt stress. We carried out a genome-wide transcriptome analysis to identify the differentially expressed genes (DEGs) response to salt shock and elucidate the early salt tolerance mechanisms in P. euphratica. Both hierarchical clustering and DEG analysis demonstrated a predominant variation from time-course rather than NaCl intensity within 24 hours salt shock. Among the identified 1,678 salt-responsive DEGs, 74.1% (1,244) have not been reported before. We further created an integrated regulatory gene network of the salt response in P. euphratica by combining DEGs, transcription factors (TFs), Helitrons, miRNAs and their targets. The prominent pathways in this network are plant hormone transduction, starch and sucrose metabolism, RNA transport, protein processing in endoplasmic reticulum, etc. In addition, the network indicates calcium-related genes play key roles in P. euphratica response to salt shock. These results illustrated an overview of the systematic molecular response in P. euphratica under different intensities of salt shock and revealed the complex regulatory mechanism.
Project description:Populus euphratica is mainly distributed in desert environments with dry and hot climate in summer and cold in winter. Compared with other poplars, P. euphratica is more resistant to salt stress. It is critical to investigate the transcriptome and molecular basis of salt tolerance in order to uncover stress-related genes. In this study, salt-tolerant treatment of P. euphratica resulted in an increase in osmo-regulatory substances and recovery of antioxidant enzymes. To improve the mining efficiency of candidate genes, the analysis combining both the transcriptome WGCNA and the former GWAS results was selected, and a range of key regulatory factors with salt resistance were found. The PeERF1 gene was highly connected in the turquoise modules with significant differences in salt stress traits, and the expression levels were significantly different in each treatment. For further functional verification of PeERF1, we obtained stable overexpression and dominant suppression transgenic lines by transforming into Populus alba × Populusglandulosa. The growth and physiological characteristics of the PeERF1 overexpressed plants were better than that of the wild type under salt stress. Transcriptome analysis of leaves of transgenic lines and WT revealed that highly enriched GO terms in DEGs were associated with stress responses, including abiotic stimuli responses, chemical responses, and oxidative stress responses. The result is helpful for in-depth analysis of the salt tolerance mechanism of poplar. This work provides important genes for poplar breeding with salt tolerance.
Project description:Glutathione S-transferases (GSTs) play a crucial role in responding to abiotic stress and are an important target for research on plant stress tolerance mechanisms. Populus euphratica is a promising candidate species for investigating the abiotic tolerance mechanisms in woody plants. In our previous study, PeGSTU58 was identified as being associated with seed salinity tolerance. In the present study, PeGSTU58 was cloned from P. euphratica and functionally characterized. PeGSTU58 encodes a Tau class GST and is located in both the cytoplasm and nucleus. Transgenic Arabidopsis overexpressing PeGSTU58 displayed enhanced tolerance to salt and drought stress. Under salt and drought stress, the transgenic plants exhibited significantly higher activities of antioxidant enzymes, including SOD, POD, CAT, and GST, compared to the wild-type (WT) plants. Additionally, the expression levels of several stress-responsive genes, including DREB2A, COR47, RD22, CYP8D11, and SOD1 were upregulated in PeGSTU58 overexpression lines compared to those in WT Arabidopsis under salt and drought stress conditions. Furthermore, yeast one-hybrid assays and luciferase analysis showed that PebHLH35 can directly bind to the promoter region of PeGSTU58 and activate its expression. These results indicated that PeGSTU58 was involved in salt and drought stress tolerances by maintaining ROS homeostasis, and its expression was positively regulated by PebHLH35.
Project description:Phospholipase Dα (PLDα), which produces signaling molecules phosphatidic acid (PA), has been shown to play a critical role in plants adapting to salt environments. However, it is unclear whether phospholipase Dδ (PLDδ) can mediate the salt response in higher plants. PePLDδ was isolated from salt-resistant Populus euphratica and transferred to Arabidopsis thaliana to testify the salt tolerance of transgenic plants. The NaCl treatment (130 mM) reduced the root growth and whole-plant fresh weight of wild-type (WT) A. thaliana, vector controls (VC) and PePLDδ-overexpressed lines, although a less pronounced effect was observed in transgenic plants. Under salt treatment, PePLDδ-transgenic Arabidopsis exhibited lower electrolyte leakage, malondialdehyde content and H2O2 levels than WT and VC, resulting from the activated antioxidant enzymes and upregulated transcripts of genes encoding superoxide dismutase, ascorbic acid peroxidase and peroxidase. In addition, PePLDδ-overexpressed plants increased the transcription of genes encoding the plasma membrane Na+/H+ antiporter (AtSOS1) and H+-ATPase (AtAHA2), which enabled transgenic plants to proceed with Na+ extrusion and reduce K+ loss under salinity. The capacity to regulate reactive oxygen species (ROS) and K+/Na+ homeostasis was associated with the abundance of specific PA species in plants overexpressing PePLDδ. PePLDδ-transgenic plants retained a typically higher abundance of PA species, 34:2 (16:0-18:2), 34:3 (16:0-18:3), 36:4 (18:2-18:2), 36:5 (18:2-18:3) and 36:6 (18:3-18:3), under control and saline conditions. It is noteworthy that PA species 34:2 (16:0-18:2), 34:3 (16:0-18:3), 36:4 (18:2-18:2) and 36:5 (18:2-18:3) markedly increased in response to NaCl in transgenic plants. In conclusion, we suppose that PePLDδ-derived PA enhanced the salinity tolerance by regulating ROS and K+/Na+ homeostasis in Arabidopsis.
Project description:The transcription of glycine-rich RNA-binding protein 2 (PeGRP2) transiently increased in the roots and shoots of Populus euphratica (a salt-resistant poplar) upon initial salt exposure and tended to decrease after long-term NaCl stress (100 mM, 12 days). PeGRP2 overexpression in the hybrid Populus tremula × P. alba '717-1B4' (P. × canescens) increased its salt sensitivity, which was reflected in the plant's growth and photosynthesis. PeGRP2 contains a conserved RNA recognition motif domain at the N-terminus, and RNA affinity purification (RAP) sequencing was developed to enrich the target mRNAs that physically interacted with PeGRP2 in P. × canescens. RAP sequencing combined with RT-qPCR revealed that NaCl decreased the transcripts of PeGRP2-interacting mRNAs encoding photosynthetic proteins, antioxidative enzymes, ATPases, and Na+/H+ antiporters in this transgenic poplar. Specifically, PeGRP2 negatively affected the stability of the target mRNAs encoding the photosynthetic proteins PETC and RBCMT; antioxidant enzymes SOD[Mn], CDSP32, and CYB1-2; ATPases AHA11, ACA8, and ACA9; and the Na+/H+ antiporter NHA1. This resulted in (i) a greater reduction in Fv/Fm, YII, ETR, and Pn; (ii) less pronounced activation of antioxidative enzymes; and (iii) a reduced ability to maintain Na+ homeostasis in the transgenic poplars during long-term salt stress, leading to their lowered ability to tolerate salinity stress.
Project description:Sodium chloride (NaCl) induced expression of a jacalin-related mannose-binding lectin (JRL) gene in leaves, roots, and callus cultures of Populus euphratica (salt-resistant poplar). To explore the mechanism of the PeJRL in salinity tolerance, the full length of PeJRL was cloned from P. euphratica and was transformed into Arabidopsis. PeJRL was localized to the cytoplasm in mesophyll cells. Overexpression of PeJRL in Arabidopsis significantly improved the salt tolerance of transgenic plants, in terms of seed germination, root growth, and electrolyte leakage during seedling establishment. Under NaCl stress, transgenic plants retained K⁺ and limited the accumulation of Na⁺. PeJRL-transgenic lines increased Na⁺ extrusion, which was associated with the upward regulation of SOS1, AHA1, and AHA2 genes encoding plasma membrane Na⁺/proton (H⁺) antiporter and H⁺-pumps. The activated H⁺-ATPases in PeJRL-overexpressed plants restricted the channel-mediated loss of K⁺ that was activated by NaCl-induced depolarization. Under salt stress, PeJRL⁻transgenic Arabidopsis maintained reactive oxygen species (ROS) homeostasis by activating the antioxidant enzymes and reducing the production of O₂- through downregulation of NADPH oxidases. Of note, the PeJRL-transgenic Arabidopsis repressed abscisic acid (ABA) biosynthesis, thus reducing the ABA-elicited ROS production and the oxidative damage during the period of salt stress. A schematic model was proposed to show the mediation of PeJRL on ABA response, and ionic and ROS homeostasis under NaCl stress.