Concentration-dependent alterations in gene expression induced by cadmium in Solanum lycopersicum

Spraying Zinc Sulfate to Reveal the Mechanism through the Glutathione Metabolic Pathway Regulates the Cadmium Tolerance of Seashore Paspalum (Paspalum vaginatum Swartz)

Cadmium (Cd) is considered to be one of the most toxic metals, causing serious harm to plants' growth and humans' health. Therefore, it is necessary to study simple, practical, and environmentally friendly methods to reduce its toxicity. Until now, people have applied zinc sulfate to improve the Cd tolerance of plants. However, related studies have mainly focused on physiological and biochemical aspects, with a lack of in-depth molecular mechanism research. In this study, we sprayed high (40 mM) and low (2.5 mM) concentrations of zinc sulfate on seashore paspalum (Paspalum vaginatum Swartz) plants under 0.5 mM Cd stress. Transcriptome sequencing and physiological indicators were used to reveal the mechanism of Cd tolerance. Compared with the control treatment, we found that zinc sulfate decreased the content of Cd2+ by 57.03-73.39%, and that the transfer coefficient of Cd decreased by 58.91-75.25% in different parts of plants. In addition, our results indicate that the antioxidant capacity of plants was improved, with marked increases in the glutathione content and the activity levels of glutathione reductase (GR), glutathione S-transferase (GST), and other enzymes. Transcriptome sequencing showed that the differentially expressed genes in both the 0.5 Zn and 40 Zn treatments were mainly genes encoding GST. This study suggests that genes encoding GST in the glutathione pathway may play an important role in regulating the Cd tolerance of seashore paspalum. Furthermore, the present study provides a theoretical reference for the regulation mechanism caused by zinc sulfate spraying to improve plants' Cd tolerance.

A critical review on plant annexin: Structure, function, and mechanism

Plant annexins are evolutionary conserved protein family widely exist in almost all plant species, characterized by a shorter N-terminal region and four conservative annexin repeats. Plant annexins have Ca²⁺ channel-regulating activity and peroxidase as well as ATPase/GTPase activities, which give annexins functional specificity. They are widely involved in regulating diverse aspects of biochemical and cellular processes, plant growth and development, and responses to biotic and abiotic environmental stresses. Though many studies have reviewed the function of annexins, great progress have been made in the study of plant annexins recently. In this review, we outline the current understanding of basic properties of plant annexins and summarize the emerging advances in understanding the functional roles of annexins in plants and highlight the regulation mechanisms of annexin protein in response to stress especially to salt and cold stress. The interesting questions related to plant annexin that remain to be further elucidated are also discussed.

A meta-analysis of transcriptomic profiles reveals molecular pathways response to cadmium stress of Gramineae

As a non-essential heavy metal, cadmium (Cd) is toxic to plants. In the last 15 years, over 70 transcriptome studies have been published to decipher the molecular response mechanism against Cd stress in different plants. To extract generalization results from transcriptomic data across different plants and obtain some hub genes that respond to Cd stress, we carried out a meta-analysis of 32 published datasets. Cluster analysis revealed that plant species played a more decisive role than the media used and exposure time in the transcriptome patterns of plant roots response to Cd. The datasets from a Gramineae-like (GL) group were closer in clustering. 838 DEGs were commonly Cd-regulated in at least nine of 18 GL datasets. Gene ontology and KEGG pathway analyses revealed that oxidative stress-related terms and lignin synthesis-related terms were significantly enriched. Mapman analysis revealed that these common DEGs were mainly involved in regulation, cellular response, secondary metabolism, transport, cell wall and lipid metabolism. In Oryza sativa, 15 DEGs were up-regulated in at least four of five HM (As, Cr, Cd, Hg and Pb) groups, such as Os10g0517500 (methionine gamma-lyase) and Os01g0159800 (bHLH107). Moreover, our datasets can be used to retrieve log2FC value of specific genes across 29 studies (48 datasets), which provides data reference for the subsequent selection of HM-related genes. Our results provide the basis for further understanding of Cd tolerance mechanisms in plants.

The Recovery of Soybean Plants after Short-Term Cadmium Stress

BACKGROUND

Cadmium is a non-essential heavy metal, which is toxic even in relatively low concentrations. Although the mechanisms of Cd toxicity are well documented, there is limited information concerning the recovery of plants after exposure to this metal.

METHODS

The present study describes the recovery of soybean plants treated for 48 h with Cd at two concentrations: 10 and 25 mg/L. In the frame of the study the growth, cell viability, level of membrane damage makers, mineral content, photosynthesis parameters, and global methylation level have been assessed directly after Cd treatment and/or after 7 days of growth in optimal conditions.

RESULTS

The results show that exposure to Cd leads to the development of toxicity symptoms such as growth inhibition, increased cell mortality, and membrane damage. After a recovery period of 7 days, the exposed plants showed no differences in relation to the control in all analyzed parameters, with an exception of a slight reduction in root length and changed content of potassium, magnesium, and manganese.

CONCLUSIONS

The results indicate that soybean plants are able to efficiently recover even after relatively severe Cd stress. On the other hand, previous exposure to Cd stress modulated their mineral uptake.

Insights about the toxicity of tannery effluent on chicken (Gallus gallus domesticus) embryos

Although tannery effluent (TE) toxicity has already been demonstrated in different vertebrate models, our knowledge about their effects on birds remains significantly incipient. Thus, the aim of the current study was to evaluate the impact of ephemeral exposure of Gallus gallus domesticus eggs to environmental predictive TE dilutions (1.4% and 6.5%). Eggs at E6 developmental stage were opened in order to assess embryos' external morphology and genotoxic biomarkers. Based on our data, embryos exposed in ovo to TE recorded higher mortality rate, lower biomass and different morphological abnormalities such as optic vesicle depigmentation, pericardial and encephalic edemas, as well as body rotation error. Embryos exposed to TE showed lower crown-rump length head and anterior-posterior length, as well as reduced beak size. Embryos exposed to the highest TE dilution (6.5%) also showed greater lower/upper limb development, larger optic vesicle area and smaller crystalline lens area than the other groups. On the other hand, differences in mitotic index were not observed between groups; however, total erythrocyte chromosomal abnormalities, mainly in metaphase and anaphase, were higher in embryos exposed to TE. These phases presented chromosome fragments formed from typical chromosome breakage, laggard chromosome and chromosome bridge. Higher Cr, Mn and Zn concentrations in embryos exposed to TE strongly suggest that the observed abnormalities were directly associated with the absorption of chemical constituents. The present study is pioneer in investigating the morphotoxic and genotoxic potential of TE (a complex mixture of various xenobiotics) in bird embryos in order to better understand the eco (toxicological) magnitude of this pollutant in aquatic ecosystems.

Cynara cardunculus L. as a Multipurpose Crop for Plant Secondary Metabolites Production in Marginal Stressed Lands

Cardoon (Cynara cardunculus L.) is a Mediterranean crop, member of the Asteraceae family, characterized by high production of biomass and secondary metabolites and by a good adaptation to climate change, usable in green chemistry, nutraceutical, and pharmaceutical sectors. Recent studies demonstrated the ability of cardoon to grow up in a stressful environment, which is associated with enhanced biosynthesis of biologically active compounds in these plants, and this effect is increased by abiotic stresses (salt, heat, pollution, and drought stress) that characterize many world marginal areas, affected by the climate changes. The plant response to these stresses consists in implementing different processes that modify some plant biological functions, such as alleviating both cellular hyperosmolarity and ion disequilibrium or synthesizing antioxidant molecules. The aim of this work was to investigate different cardoon response mechanisms to abiotic stresses and to evaluate their influence on the biologically active compounds biosynthesis. Following this purpose, we analyzed the ability of cardoon seeds to germinate under different salt stress conditions, and on the sprouts obtained, we measured the total phenol content and the antioxidant activity. Moreover, the growth of cardoon seedlings grown under heavy metals stress conditions was monitored, and the expression levels of heavy metal transport-associated genes were analyzed. The results showed the ability of cardoon plants to tolerate abiotic stress, thanks to different defense mechanisms and the possibility to obtain biomass with high content of biologically active molecules by exploiting the natural tolerance of this species for abiotic stresses. Moreover, we identified some important genes encoding for metal transportation that may be involved in arsenic and cadmium uptake and translocation in C. cardunculus. Then, this species can be considered as a promising crop for green chemistry and energy in marginal lands.

Transcriptome analysis reveals comprehensive responses to cadmium stress in maize inoculated with arbuscular mycorrhizal fungi

Biological strategy of utilization of plants-microbe's interactions to remediate cadmium (Cd) contaminated soils is effective and practical. However, limited evidence at transcriptome level is available about how microbes work with host plants to alleviate Cd stress. In the present study, comparative transcriptomic analysis was performed between maize seedlings inoculated with arbuscular mycorrhizal (AM) fungi and non-AM fungi inoculation under distinct concentrations of CdCl₂ (0, 25, and 50 mg per kg soil). Significantly higher levels of Cd were found in root tissues of maize colonized by AM fungi, whereas, Cd content was reduced as much as 50% in leaf tissues when compared to non-AM seedlings, indicating that symbiosis between AM fungi and maize seedlings can significantly block translocation of Cd from roots to leaf tissues. Moreover, a total of 5827 differentially expressed genes (DEG) were determined and approximately 68.54% DEGs were downregulated when roots were exposed to high Cd stress. In contrast, 67.16% (595) DEGs were significantly up-regulated when seedlings were colonized by AM fungi under 0 mg CdCl₂. Based on hierarchical clustering analysis, global expression profiles were split into eight distinct clusters. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that hundreds of genes functioning in plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling pathway and glutathione metabolism were enriched. Furthermore, MapMan pathway analysis indicated a more comprehensive overview response, including hormone metabolism, especially in JA, glutathione metabolism, transcription factors and secondary metabolites, to Cd stress in mycorrhizal maize seedlings. These results provide an overview, at the transcriptome level, of how inoculation of maize seedlings by AM fungi could facilitate the relief of Cd stress.

Mechanisms underlying enhanced Cd translocation and tolerance in roots of Populus euramericana in response to nitrogen fertilization

A pot experiment was conducted to evaluate how nitrogen (N) availability influences cadmium (Cd) absorption, translocation and stress tolerance in roots of Populus euramericana. Seedling growth was sensitive to N deficiency, but it was unaltered by Cd exposure. Cadmium absorption by roots was promoted by N deficiency, resulting in a higher root Cd concentration compared to the N-sufficient condition. Fine-root length was tightly correlated (R² = 0.73) with Cd concentration in roots, indicating that vigorous fine-root proliferation under N deficiency contributed to active absorption and accumulation of Cd in roots. Despite accumulation in roots, Cd translocation from roots to shoots was less active under N deficiency compared to N sufficiency. This was related to elevated glutathione reductase (GR) activity and glutathione (GSH) levels in roots after N application, which may not only promote antioxidant defence, but also facilitate the formation of GSH-Cd complexes that are uploaded into root cylinders. Nitrogen application also promoted antioxidant defense in roots via increased production of phytohormones and the level of enzymatic and non-enzymatic antioxidants. Transcript levels for genes responsible for antioxidant defense, Cd detoxification and Cd uploading were increased in roots by N application. The N-stimulated Cd tolerance, detoxification and uploading in roots are factors likely to promote Cd translocation from roots to shoots, which may enhance the biological capacity of this poplar species for phytoremediation of Cd pollution.

New insight into the molecular basis of cadmium stress responses of wild paper mulberry plant by transcriptome analysis

BACKGROUND

Heavy metal contamination is becoming a limitation to the utilization of soil and the distribution of vegetation. In particular, cadmium (Cd) pollution has had a serious impact on the food chain. Broussonetia papyrifera is a widely distributed pioneer tree species of heavy metal contaminated areas with important economic value. However, little is known about the genomic background of the Cd-tolerance mechanism in B. papyrifera.

RESULTS

The CdCl₂ responsive physiology was evaluated and proved to be involved in antioxidase activity and active oxygen species (ROS) accumulation. The leaf and root transcriptomes derived from B. papyrifera grown under normal and CdCl₂ stress conditions were systematically investigated using the Illumina HiSeq method. A total of 180,678,660 bp (27.1 GB) clean reads were assembled into 589,487 high-quality unigenes, of which 256,025 (43.43% of the total) and 250,251 (42.45% of the total) were aligned in Gene Ontology (GO) and Protein family (Pfam), respectively. A total of 24,414 differentially expressed genes (DEGs) were GO-annotated into 53, 23, 55, and 60 terms from the transcriptomes of root and leaf tissues under Cd stress and control conditions. A total of 117,547 Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology (KO)-annotated DEGs were enriched in at least 47 KEGG pathway terms among the four comparisons. Many genes encoding important transcription factors (e.g., auxin/indole-3-acetic acid (AUX/IAA), basic helix-loop-helix (bHLH), DNA-binding one zinc finger (Dof), and MYB) and proteins involved in plant-pathogen interactions, phenylpropanoid biosynthesis, plant hormone signal transduction, oxidative phosphorylation, carbon fixation, peroxisomes, flavonoid biosynthesis, and glutathione metabolism, among others, were substantially upregulated under CdCl₂ stress.

CONCLUSIONS

These genes represent important candidates for studying Cd-response mechanisms and molecular biology of B. papyrifera and related species. Our findings provide a genomic sequence resource for functional genetic assignments in B. papyrifera, which will help elucidate the molecular mechanisms of its Cd-stress responses and facilitate the bioremediation of heavy metal contaminated areas via breeding of new stress-tolerant cultivars.

The walnut JrVHAG1 gene is involved in cadmium stress response through ABA-signal pathway and MYB transcription regulation

BACKGROUND

Vacuolar H⁺-ATPase (V-ATPase) is a vital protein complex involved in abiotic stress response in plants. The G subunit of Juglans regia (JrVHAG1) was previously identified as a drought tolerance-related gene involved in the ABA (abscisic acid)-signal pathway. Heavy metal stress is becoming a major detriment for plant growth, development, and production. In order to understand the role of JrVHAG1, the potential function mechanism of JrVHAG1 exposed to CdCl₂ stress was confirmed in this study.

RESULTS

Transcription of JrVHAG1 was induced by ABA and increased to 58.89-fold (roots) and 7.38-fold (leaves) and by CdCl₂ to 2.65- (roots) and 11.42-fold (leaves) relative to control, respectively. Moreover, when treated simultaneously with ABA and CdCl₂ (ABA+CdCl₂), JrVHAG1 was up-regulated to 110.13- as well as 165.42-fold relative to control in the roots and leaves, accordingly. Compared to the wild type (WT) Arabidopsis plants, the transgenic plants with overexpression of JrVHAG1 (G2, G6, and G9) exhibited increased seed germination rate, biomass accumulation, proline content, and activities of superoxide dismutase (SOD) and peroxidase (POD) under ABA, CdCl₂, and ABA+CdCl₂ treatments. In contrast, the reactive oxygen species (ROS) staining, malondialdehyde (MDA) content, hydrogen dioxide (H₂O₂) content, as well as electrolyte leakage (EL) rates of transgenic seedlings were all lower than those of WT exposed to ABA, CdCl₂ and ABA+CdCl₂ stresses. Furthermore, a 1200 bp promoter fragment of JrVHAG1 was isolated by analyzing the genome of J. regia, in which the cis-elements were identified. This JrVHAG1 promoter fragment showed expression activity that was enhanced significantly when subjected to the above treatments. Yeast one-hybrid assay and transient expression analysis demonstrated that JrMYB2 specifically bound to the MYBCORE motif and shared similar expression patterns with JrVHAG1 under ABA, CdCl₂ and ABA+CdCl₂ stress conditions.

CONCLUSIONS

Our results suggested that the JrVHAG1 gene functions as a CdCl₂ stress response regulator by participating in ABA-signal pathway and MYB transcription regulation network. JrVHAG1 gene is a useful candidate gene for heavy metal stress tolerance in plant molecular breeding.

Toxic Effects and Molecular Mechanism of Different Types of Silver Nanoparticles to the Aquatic Crustacean Daphnia magna

Silver nanoparticles (AgNPs) have been assessed to have a high exposure risk for humans and aquatic organisms. Toxicity varies considerably between different types of AgNPs. This study aimed to investigate the toxic effects of AgNPs with different particle sizes (40 and 110 nm) and different surface coatings (sodium citrate and polyvinylpyrrolidone, PVP) on Daphnia magna and their mechanisms of action. The results revealed that the citrate-coated AgNPs were more toxic than PVP-coated AgNPs and that the 40 nm AgNPs were more toxic than the 110 nm AgNPs. Transcriptome analysis further revealed that the toxic effects of AgNPs on D. magna were related to the mechanisms of ion binding and several metabolic pathways, such as the "RNA polymerase" pathway and the "protein digestion and absorption" pathway. Moreover, the principal component analysis (PAC) results found that surface coating was the major factor that determines the toxicities compared to particle size. These results could help us better understand the possible mechanism of AgNP toxicity in aquatic invertebrates at the transcriptome level and establish an important foundation for revealing the broad impacts of nanoparticles on aquatic environments.