Cadmium stress alters gene expression of DNA mismatch repair related genes in Arabidopsis seedlings

Uptake of hematite nanoparticles in maize and their role in cell cycle dynamics, PCNA expression and mitigation of cadmium stress

Cadmium toxicity is considered a major threat to several crops worldwide. Hematite nanoparticles (NPs), due to their small size and large specific surface area, could be applied as an adsorbent for toxic heavy metals in soil. Also, they serve as an efficient nano-fertilizer, promoting Fe availability and biomass production in plants, thus enabling Cd²⁺ -induced stress tolerance. The phytotoxicity of five different concentrations of hematite NPs, ranging from 500 to 8,000 mg·kg^-1 , and Cd²⁺ concentrations (110 or 130 mg·kg^-1 Cd²⁺ ) alone or combined with 500 mg·kg^-1 NPs was evaluated in maize. The changes in fresh weight, element analysis, cell cycle regulation, DNA banding patterns and proliferating cell nuclear antigen (PCNA) expression were used as biomarkers. The results revealed that increased fresh weight and fewest polymorphic DNA bands were detectable after treatment with 500 mg·kg^-1 NPs. However, at 8,000 mg·kg^-1 NPs, PCNA expression increased significantly, which resulted in cell cycle arrest at the G1/S checkpoint in roots. Significant reductions in fresh weight, altered nutrient profiles and cell cycle perturbations are considered symptoms of Cd²⁺ toxicity in maize. Conversely, amending 500 mg·kg^-1 NPs with 130 mg·kg^-1 Cd²⁺ increased fresh weight, Fe concentration and genomic template stability, while reducing Cd²⁺ uptake and PCNA1 expression. Overall, 8,000 mg·kg^-1 hematite NPs interfered with the cellular homeostatic balance of maize, resulting in a cascade of genotoxic events, leading to growth inhibition. Although 500 mg·kg^-1 hematite NPs alleviated Cd²⁺ -induced DNA damage to a certain extent, their impact on cell cycle progression requires further verification.

Mechanisms of Enterobacter bugandensis TJ6 immobilization of heavy metals and inhibition of Cd and Pb uptake by wheat based on metabolomics and proteomics

Microbial passivation remediation of heavy metal-contaminated farmland has attracted increasing attention. However, the molecular mechanism by which heavy metal-immobilizing bacteria inhibit the uptake of Cd and Pb by wheat is not clear. Herein, a heavy metal-immobilizing bacterium, Enterobacter bugandensis TJ6, was used to reveal its immobilization mechanisms of Cd and Pb and inhibition of Cd and Pb uptake by wheat using metabolomics and proteomics. Compared with the control, strain TJ6 significantly reduced (44.7%-56.6%) the Cd and Pb contents of wheat roots and leaves. Strain TJ6 reduced the Cd and Pb concentrations by adsorption, intracellular accumulation, and bioprecipitation in solution. Untargeted metabolomics showed that strain TJ6 produced indole-3-acetic acid (IAA), betaine, and arginine under Cd and Pb stress, significantly improving the resistance of strain TJ6 and wheat to Cd and Pb. Label-free proteomics showed that 143 proteins were upregulated and 61 proteins were downregulated in wheat roots in the presence of strain TJ6. The GO items of the differentially expressed proteins (DEPs) involved in protein-DNA complexes, DNA packaging complexes, and peroxidase activity were enriched. In addition, the ability of wheat roots to synthesize abscisic acid and jasmonic acid was improved. In conclusion, strain TJ6 reduced Cd and Pb uptake in wheat through its own adsorption of Cd and Pb and regulation of wheat root DNA repair ability, plant hormone levels, and antioxidant activities. These results provide new insights and a theoretical basis for the application of heavy metal-immobilizing bacteria in safe wheat production.

Differential expression pattern of the proteome in response to cadmium stress based on proteomics analysis of wheat roots

BACKGROUND

Heavy metal cadmium (Cd) is a common environmental pollutant in soils, which has an negative impacts on crop growth and development. At present, cadmium has become a major soil and water heavy metal pollutant, which not only causes permanent and irreversible health problems for humans, but also causes a significant reduction in crop yields.

RESULTS

This study examined the chemical forms of Cd in the roots of two wheat varieties (M1019 and Xinong20) by continuous extraction and analyzed differences in distribution characteristics of Cd in the root cell wall, cytoplasm, and organelles by elemental content determination and subcellular separation. Furthermore, we conducted proteomics analysis of the roots of the two varieties under Cd pollution using mass spectrometry quantitative proteomics techniques. A total of 11,651 proteins were identified, of which 10,532 proteins contained quantitative information. In addition, the differentially expressed proteins in the two varieties were related to DNA replication and repair, protein metabolism, and the glutathione metabolism pathway.

CONCLUSION

The results of this study improve our understanding of the mechanism of plant responses to Cd stress.

Lasting DNA Damage and Aberrant DNA Repair Gene Expression Profile Are Associated with Post-Chronic Cadmium Exposure in Human Bronchial Epithelial Cells

Cadmium (Cd) is a widespread environmental pollutant and carcinogen. Although the exact mechanisms of Cd-induced carcinogenesis remain unclear, previous acute/chronic Cd exposure studies have shown that Cd exerts its cytotoxic and carcinogenic effects through multiple mechanisms, including interference with the DNA repair system. However, the effects of post-chronic Cd exposure remain unknown. Here, we establish a unique post-chronic Cd-exposed human lung cell model (the "CR0" cells) and investigate the effects of post-chronic Cd exposure on the DNA repair system. We found that the CR0 cells retained Cd-resistant property even though it was grown in Cd-free culture medium for over a year. The CR0 cells had lasting DNA damage due to reduced DNA repair capacity and an aberrant DNA repair gene expression profile. A total of 12 DNA repair genes associated with post-chronic Cd exposure were identified, and they could be potential biomarkers for identifying post-chronic Cd exposure. Clinical database analysis suggests that some of the DNA repair genes play a role in lung cancer patients with different smoking histories. Generally, CR0 cells were more sensitive to chemotherapeutic (cisplatin, gemcitabine, and vinorelbine tartrate) and DNA damaging (H₂O₂) agents, which may represent a double-edged sword for cancer prevention and treatment. Overall, we demonstrated for the first time that the effects of post-chronic Cd exposure on human lung cells are long-lasting and different from that of acute and chronic exposures. Findings from our study unveiled a new perspective on Cd-induced carcinogenesis-the post-chronic exposure of Cd. This study encourages the field of post-exposure research which is crucial but has long been ignored.

Comparative transcriptome analysis of duckweed (Landoltia punctata) in response to cadmium provides insights into molecular mechanisms underlying hyperaccumulation

Cadmium (Cd) is a detrimental environmental pollutant. Duckweeds have been considered promising candidates for Cd phytoremediation. Although many physiological studies have been conducted, the molecular mechanisms underlying Cd hyperaccumulation in duckweeds are largely unknown. In this study, clone 6001 of Landoltia punctata, which showed high Cd tolerance, was obtained by large-scale screening of over 200 duckweed clones. Subsequently, its growth, Cd flux, Cd accumulation, and Cd distribution characteristics were investigated. To further explore the global molecular mechanism, a comprehensive transcriptome analysis was performed. For RNA-Seq, samples were treated with 20 μM CdCl₂ for 0, 1, 3, and 6 days. In total, 9,461, 9,847, and 9615 differentially expressed unigenes (DEGs) were discovered between Cd-treated and control (0 day) samples. DEG clustering and enrichment analysis identified several biological processes for coping with Cd stress. Genes involved in DNA repair acted as an early response to Cd, while RNA and protein metabolism would be likely to respond as well. Furthermore, the carbohydrate metabolic flux tended to be modulated in response to Cd stress, and upregulated genes involved in sulfur and ROS metabolism might cause high Cd tolerance. Vacuolar sequestration most likely played an important role in Cd detoxification in L. punctata 6001. These novel findings provided important clues for molecular assisted screening and breeding of Cd hyperaccumulating cultivars for phytoremediation.

Effects of biochar amendment on relieving cadmium stress and reducing cadmium accumulation in pepper

Biochar is widely used in agricultural soils or heavy metal-polluted soils to improve the quality of the soils, which would affect the growth of the plant. However, the information of biochars' effect on the plant growth was still lacking, especially for the physiological response of the plant. Pot experiments were used to examine the effect of willow-derived biochars at two temperatures (450 and 600 °C) on cadmium (Cd) accumulation in pepper and to reveal the response of physiological parameters to exogenous Cd stress (1 and 5 mg/kg). The results showed that the accumulation of Cd in pepper roots was higher than that in pepper shoots. For low level of Cd treatments, high additional rates of the biochars could obviously reduce the accumulation of Cd in the pepper roots. Moreover, there was a negative correlation between the C content of the biochar-amended soils and the Cd content of the pepper root, suggesting that the application of biochar to the soil decreased the Cd accumulation in the root. A positive relationship between the H/C ratios of biochar-amended soils and their corresponding Cd concentrations in pepper root indicated that low thermal temperature-derived biochar could play an important role in immobilizing Cd in the soil. Furthermore, on the condition of low Cd level of treatments, the malondialdehyde content decreased in biochar-amended soils, especially at high biochar application rate. The chlorophyll content increased with increasing the rates of the biochar application. The physiological parameters indirectly proved that the application of biochar did not always alleviate the toxic effects of Cd on pepper leaves at high Cd concentration.

Cadmium adsorption on plant- and manure-derived biochar and biochar-amended sandy soils: impact of bulk and surface properties

To investigate the role of the bulk and surface composition of both biochar and biochar-amended soils in the adsorption of Cd(2+), as well as the influence of different biochars added to the soils on Cd(2+) adsorption, swine-manure-derived biochars (BSs) and wheat-straw-derived biochars (BWs) were produced at 300, 450, and 600°C. These biochars were added to a sandy soil to investigate the effect of biochars on the adsorption of Cd(2+) by soil. The significantly higher surface C content of the amended soils compared to their bulk C content suggests that the minerals of the biochar-amended soils are most likely covered primarily by biochars. The maximum adsorption capacity (Qmax,total) of the BSs was 10-15 times higher than that of the BWs due to the high polarity and ash content of the BSs. The polarity ((N+O)/C) of the low-temperature biochars greatly affected their Cd(2+) adsorption. The Qmax,total of the BS-amended soils increased with increasing dose, whereas the Qmax,total of the BW-amended soils showed the opposite behavior, which was attributed to the different surface composition characteristics of the two types of soil. The BSs were more effective in immobilizing Cd(2+) upon application to the soil relative to the BWs. This study elucidates the spatial distribution of biochars in biochar-amended soils and highlights the importance of the surface composition of the investigated samples in Cd(2+) adsorption.

Copper-mediated genotoxic stress is attenuated by the overexpression of the DNA repair gene MtTdp2α (tyrosyl-DNA phosphodiesterase 2) in Medicago truncatula plants

Our study highlights the use of the DNA repair gene MtTdp2α as a tool for improving the plant response to heavy metal stress. Tyrosyl-DNA phosphodiesterase 2 (Tdp2), involved in the removal of DNA topoisomerase II-mediated DNA damage and cell proliferation/differentiation signalling in animal cells, is still poorly characterised in plants. The Medicago truncatula lines Tdp2α-13c and Tdp2α-28 overexpressing the MtTdp2α gene and control (CTRL) line were exposed to 0.2 mM CuCl2. The DNA diffusion assay revealed a significant reduction in the percentage of necrosis caused by copper in the aerial parts of the Tdp2α-13c and Tdp2α-28 plants while neutral single cell gel electrophoresis highlighted a significant decrease in double strand breaks (DSBs), compared to CTRL. In the copper-treated Tdp2α-13c and Tdp2α-28 lines there was up-regulation (up to 4.0-fold) of genes encoding the α and β isoforms of Tyrosyl-DNA phosphodiesterase 1, indicating the requirement for Tdp1 function in the response to heavy metals. As for DSB sensing, the MtMRE11, MtRAD50 and MtNBS1 genes were also significantly up-regulated (up to 2.3-fold) in the MtTdp2α-overexpressing plants grown under physiological conditions, compared to CTRL line, and then further stimulated in response to copper. The basal antioxidant machinery was always activated in all the tested lines, as indicated by the concomitant up-regulation of MtcytSOD and MtcpSOD genes (cytosolic and chloroplastic Superoxide Dismutase), and MtMT2 (type 2 metallothionein) gene. The role of MtTdp2α gene in enhancing the plant response to genotoxic injury under heavy metal stress is discussed.

In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 μM) and high (50 μM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

A PLAC8-containing protein from an endomycorrhizal fungus confers cadmium resistance to yeast cells by interacting with Mlh3p

Cadmium is a genotoxic pollutant known to target proteins that are involved in DNA repair and in antioxidant defence, altering their functions and ultimately causing mutagenic and carcinogenic effects. We have identified a PLAC8 domain-containing protein, named OmFCR, by a yeast functional screen aimed at identifying genes involved in cadmium resistance in the endomycorrhizal fungus Oidiodendron maius. OmFCR shows a remarkable specificity in mediating cadmium resistance. Both its function and its nuclear localization in yeast strictly depend on the interaction with Mlh3p, a subunit of the mismatch repair (MMR) system. Although proteins belonging to the PLAC8 family are widespread in eukaryotes, they are poorly characterized and their biological role still remains elusive. Our work represents the first report about the potential role of a PLAC8 protein in physically coupling DNA lesion recognition by the MMR system to appropriate effectors that affect cell cycle checkpoint pathways. On the basis of cell survival assays and yeast growth curves, we hypothesize that, upon cadmium exposure, OmFCR might promote a higher rate of cell division as compared to control cells.

Effects of selected heavy metals (Pb, Cu, Ni, and Cd) in the aquatic medium on the restoration potential and accumulation in the stem cuttings of the terrestrial plant, Talinum triangulare Linn

The heavy metal (Cu, Pb, Ni, and Cd) accumulation capacity of the stem cuttings of the terrestrial, ornamental plant, Talinum triangulare was assessed in hydroponic medium. The stem cuttings of T. triangulare, grew well in distilled water regenerating roots and aerial parts. On exposure to various concentrations of Cu, Pb, Ni, and Cd, a concentration dependent decrease was observed in the number of leaves produced and roots regenerated and an increase in the number of days required for the initiation of roots. The number of leaves produced showed an increasing trend in almost all treatment concentrations of Cu, Pb, Ni, and Cd with an increase in the duration of experiment, whereas, with an increase in the treatment concentration of metals a significant (P < 0.05) decrease was observed in the number of leaves produced. The number of days required for root initiation in metal solutions, however, increased with increasing concentration of Cu, Pb, Ni, and Cd. The root development was completely arrested from 10 mg l(-1) of Ni and 4 mg l(-1) of Cd. Compared to the control, a significant decrease was recorded in the number of roots produced in all treatment concentrations of Cu, Pb, Ni, and Cd. Pink colouration of metal solution consequent to leaching of plant pigment from T. triangulare was observed which was not persistent and disappeared after a few days. Decaying of stem was observed when exposed to Ni and Cd but not to Cu and Pb. Although, copper accumulation by T. triangulare at treatment concentration of 15 and 20 mg l(-1) exceeded 1,000 mg kg(-1) dry matter, necessary pot culture experiment is required before "T. triangulare" can be definitely classified as a Cu hyperaccumulator.