Cd Resistance Research Articles

Genome-wide identification and expression analysis of SpUGE gene family and heterologous expression-mediated Arabidopsis thaliana tolerance to Cd stress

The UDP-glucose 4-epimerase (UGE) enzyme plays a critical role in plant growth and responses to abiotic stressors, such as heavy metal exposure. However, UGE-mediated remodeling of cell wall polysaccharides in response to these stressors remains poorly understood in willow. This study investigated the structure, function, and expression patterns of the UGE gene family in willow, focusing on cadmium treatment to elucidate how SpUGE1 enhances Cd resistance. Six SpUGE genes were identified through whole-genome sequencing and bioinformatics analysis, and they were mapped across five chromosomes. Quantitative PCR analysis revealed that, with the exception of SpUGE3, all genes showed their highest relative expression in the leaves. Under Cd treatment, members of the SpUGE gene family displayed varying levels of responsiveness, with SpUGE1 showing a marked increase in expression over time. In transgenic Arabidopsis thaliana overexpressing SpUGE1, the cellulose, hemicellulose, lignin, and pectin content significantly increased, with cellulose levels rising by >50 % and pectin by approximately 30 %. This overexpression conferred enhanced Cd resistance by increasing cell wall thickness through elevated cell wall polysaccharides, which reduced Cd uptake. Consequently, Cd content in the cell wall, chloroplasts, and mitochondria was significantly lower than that in wild-type plants, reducing cellular damage and improving Cd resistance. Overall, this study provides valuable theoretical and experimental insights into the role of the SpUGE1 gene family in willow.

Pseudomonas consortium improves soil health and alleviates cadmium (Cd) toxicity in Brassica juncea L. via biochemical and in silico approaches

The exponential rise in Cd in the environment has raised concerns for its adequate remediation worldwide. Its non-biodegradable nature and highly migratory feature make it more toxic. Plant growth-promoting rhizobacteria (PGPR) have shown great potential in the remediation of Cd-polluted agricultural lands. PGPR is comparatively efficient, convenient and economical. PGPR application enhances plant growth and development by conferring direct and indirect benefits. This study aimed to evaluate bacterial strains, Pseudomonas putida (Pp) and Pseudomonas fluorescens (Pf), for their PGPR traits, soil physiochemical analyses, and physiological and anatomical traits of B. juncea under Cd stress. Results showed that both microbial strains shared positive interaction and had minimum inhibitory concentration (MIC) ranging from 0.8mM and 0.6mM values for Pp and Pf respectively. P. fluorescens displayed better anti-phytopathogenic activity against pathogenic fungal strains (Alterneria brassicae, Alterneria brassicola, Verticillium longisporum, Fusarium oxysporum) than P. putida. They also synthesised plant growth regulators (PGRs) such as IAA (0.146,0.156μg/ml) and GA (2.062, 2.074 μg/ml). The co-inoculation of strains improved soil organic C, P, N, and K by 283.01 %, 100.42 %, 8.89 % and 40.38 %. Also, the interactive effect of Pp and Pf recovered dry matter content (DMC) by 18.13 % in comparison to Cd-stressed plants. Moreover, the strains reduced Cd-induced H2O2 production by DAB (340.38’-3’ diaminobenzidine) staining and hence restored membrane integrity. Also, in Cd-treated B. juncea plants, the anatomical characteristics were negatively affected. However, inoculated strains induce maximum recovery as indicated by well-developed vascular elements. Genes associated with PGPR traits were mined from the NCBI database. The information compiled thereafter indicated that the genes, galU, CadR, and pgl were responsible for biofilm formation, Cd resistance and lactone synthesis. In conclusion, we reported a promising consortium having PGPR traits, that improve soil and B. juncea health under Cd toxicities. Hence, the use of such bioinoculants can be a safer substitute for chemical fertilizers.

Synergistic interaction between brassinosteroid and jasmonate pathways in rice response to cadmium toxicity

Brassinosteroids (BRs) and jasmonic acid (JA) are known to be involved in regulating plant responses to cadmium (Cd) stress. However, their specific roles and interaction in this process remain unclear. In this study, we discovered that exogenous BR alleviated Cd-mediated growth inhibition of rice seedlings. Enhanced Cd tolerance was also observed in m107, a BR-overproduction mutant. Phenotypic analysis of genetic materials involved in BR signaling confirmed the positive role of BR in regulating rice response to Cd toxicity. OsDLT, a key component in the BR signaling pathway, was found to be crucial for BR-mediated Cd tolerance. Further analysis demonstrated that activation of the BR pathway reduced the accumulation of Cd and reactive oxygen species (ROS) by modulating the expression of genes associated with Cd transport and ROS scavenging. Interestingly, transcriptome analysis indicated that the JA pathway was enriched in OsDLT-regulated differently expressed genes (DEGs). Gene expression and hormone assays showed that BR promoted the expression of JA pathway genes and JA levels in plants. Moreover, BR-induced tolerance was compromised in the JA signaling-deficient mutant osmyc2, suggesting that BR-mediated Cd resistance depends on the activation of the JA signaling pathway. Overall, our study revealed the synergistic interaction between BR and JA pathways in rice response to Cd stress, providing insights into the complex hormonal interplay in plant tolerance to heavy metals.

Machine learning phenotyping and GWAS reveal genetic basis of Cd tolerance and absorption in jute

Cadmium (Cd) is a dangerous environmental contaminant. Jute (Corchorus sp.) is an important natural fiber crop with strong absorption and excellent adaptability to metal-stressed environments, used in the phytoextraction of heavy metals. Understanding the genetic and molecular mechanisms underlying Cd tolerance and accumulation in plants is essential for efficient phytoremediation strategies and breeding novel Cd-tolerant cultivars. Here, machine learning (ML) and hyperspectral imaging (HSI) combining genome-wide association studies (GWAS) and RNA-seq reveal the genetic basis of Cd resistance and absorption in jute. ML needs a small number of plant phenotypes for training and can complete the plant phenotyping of large-scale populations with efficiency and accuracy greater than 90%. In particular, a candidate gene for Cd resistance (COS02g_02406) and a candidate gene (COS06g_03984) associated with Cd absorption are identified in isoflavonoid biosynthesis and ethylene response signaling pathways. COS02g_02406 may enable plants to cope with metal stress by regulating isoflavonoid biosynthesis involved in antioxidant defense and metal chelation. COS06g_03984 promotes the binding of Cd2+ to ETR/ERS, resulting in Cd absorption and tolerance. The results confirm the feasibility of high-throughput phenotyping for studying plant Cd tolerance by combining HSI and ML approaches, facilitating future molecular breeding.

The dynamic roles of intracellular vacuoles in heavy metal detoxification by Rhodotorula mucilaginosa.

Rhodotorula mucilaginosa (Rho) can develop a range of strategies to resist the toxicity of heavy metals. This study aimed to investigate the physiological responses and transcriptomic regulation of the fungus under different heavy metal stresses. This study applied transmission electron microscopy and RNA-seq to investigate the fungal resistance to Pb, Cd, and Cu stresses. Under Pb stress, the activated autophagy-related genes, vesicle-fusing ATPase, and vacuolar ATP synthase improved vacuolar sequestration. This offsets the loss of lipids. However, the metal sequestration by vacuoles was not improved under Cd stress. Vacuolar fusion was also inhibited following the interference of intravacuolar Ca2+ due to their similar ionic radii. Cu2+ showed the maximum toxic effects due to its lowest cellular sorption (as low as 7%) with respect to Pb2+ and Cd2+, although the efflux pumps and divalent metal ion transporters partially contributed to the detoxification. Divalent cation transporters and vacuolar sequestration are the critical strategies for Rho to resist Pb stress. Superoxide dismutase (SOD) is the main strategy for Cd resistance in Rho. The intracellular Cu level was decreased by efflux pump and divalent metal ion transporters.

GmAMT2.1/2.2-dependent ammonium nitrogen and metabolites shape rhizosphere microbiome assembly to mitigate cadmium toxicity

Cadmium (Cd), a heavy metal, is negatively associated with plant growth. AMT (ammonium transporter) genes can confer Cd resistance and enhance nitrogen (N) uptake in soybeans. The potential of AMT genes to alleviate Cd toxicity by modulating rhizosphere microbiota remains unkonwn. Here, the rhizosphere microbial taxonomic and metabolic differences in three genotypes, i.e., double knockout and overexpression lines and wild type, were identified. The results showed that GmAMT2.1/2.2 genes could induce soybean to recruit beneficial microorganisms, such as Tumebacillus, Alicyclobacillus, and Penicillium, by altering metabolites. The bacterial, fungal, and cross-kingdom synthetic microbial communities (SynComs) formed by these microorganisms can help soybean resist Cd toxicity. The mechanisms by which SynComs help soybeans resist Cd stress include reducing Cd content, increasing ammonium (NH4+-N) uptake and regulating specific functional genes in soybeans. Overall, this study provides valuable insights for the developing microbial formulations that enhance Cd resistance in sustainable agriculture.

Phosphorus-Solubilizing Bacteria Enhance Cadmium Immobilization and Gene Expression in Wheat Roots to Reduce Cadmium Uptake.

The application of phosphorus-solubilizing bacteria is an effective method for increasing the available phosphorus content and inhibiting wheat uptake of heavy metals. However, further research is needed on the mechanism by which phosphorus-solubilizing bacteria inhibit cadmium (Cd) uptake in wheat roots and its impact on the expression of root-related genes. Here, the effects of strain Klebsiella aerogenes M2 on Cd absorption in wheat and the expression of root-related Cd detoxification and immobilization genes were determined. Compared with the control, strain M2 reduced (64.1-64.6%) Cd uptake by wheat roots. Cd fluorescence staining revealed that strain M2 blocked the entry of exogenous Cd into the root interior and enhanced the immobilization of Cd by cell walls. Forty-seven genes related to Cd detoxification, including genes encoding peroxidase, chalcone synthase, and naringenin 3-dioxygenase, were upregulated in the Cd+M2 treatment. Strain M2 enhanced the Cd resistance and detoxification activity of wheat roots through the regulation of flavonoid biosynthesis and antioxidant enzyme activity. Moreover, strain M2 regulated the expression of genes related to phenylalanine metabolism and the MAPK signaling pathway to enhance Cd immobilization in roots. These results provide a theoretical basis for the use of phosphorus-solubilizing bacteria to remediate Cd-contaminated fields and reduce Cd uptake in wheat.

A novel OsGST gene encoding 9glutathione reductase negatively regulates cadmium accumulation in rice

Cadmium (Cd) accumulates in rice and then moves up the food chain, causing serious health problems for humans. Glutathione S-transferase (GST) binds exogenous hazardous compounds to glutathione (GSH), which performs a variety of roles in plant responses to Cd stress. Here, Cd stimulated the transcripts of a novel OsGST gene, and the OsGST protein, which was localized in the nucleus and cytoplasm, was also induced by Cd. In OsGST deletion mutant lines generated by CRISPR/Cas9, more Cd was accumulated, and Cd hypersensitive phenotypes were observed, while transgenic lines overexpressing OsGST exhibited enhanced Cd tolerance and less Cd accumulation. Further analysis indicated that the osgst mutants exhibited considerably greater reactive oxygen species (ROS) and higher GSH level, and the antioxidant activity associated genes’ expression were down-regulated, imply that OsGST controlled rice Cd accumulation and resistance through preserving the equilibrium of the GSH and redox in rice.

Overexpression of histone demethylase gene SlJMJ18 and SlJMJ23 from tomato confers cadmium tolerance by regulating metal transport and hormone content in Arabidopsis

A lower concentration of cadmium (Cd), a hazardous and non-essential element for plant growth, will have deleterious effects on plants and endanger human health. Histone demethylase (JHDM) is important for plants' ability to withstand abiotic stress, according to an increasing number of studies. The degree of expression of the SlJMJ18 and SlJMJ23 genes in different tomato tissues was confirmed by this study. These two genes were responsive to the heavy metals Cd, Hg, Pb, and Cu stress, according to fluorescence quantification and GUS staining. Interestingly, the overexpression transgenic Arabidopsis plants of two genes have different responses to Cd stress. While SlJMJ18-OE lines consistently display Cd resistance but an early-flowering phenotype, SlJMJ23-OE plants have sensitivity during the post-germination stage and then greater tolerance to Cd stress. It was discovered that these two genes may affect cadmium tolerance of plants by regulating the expression of hormone synthesis related genes and hormone contents (BRs and ABA). Moreover, SlJMJ23 may resist cadmium stress by increasing the total phenol content in plants. The functional significance of JMJs is better understood in this study, which also offers a theoretical foundation for the use of molecular technology to develop plants resistant to Cd and an experimental basis for the efficient use of land resources.

Silicon Dioxide Nanoparticles-Based Amelioration of Cd Toxicity by Regulating Antioxidant Activity and Photosynthetic Parameters in a Line Developed from Wild Rice.

An extremely hazardous heavy metal called cadmium (Cd) is frequently released into the soil, causing a considerable reduction in plant productivity and safety. In an effort to reduce the toxicity of Cd, silicon dioxide nanoparticles were chosen because of their capability to react with metallic substances and decrease their adsorption. This study examines the processes that underlie the stress caused by Cd and how SiO2NPs may be able to lessen it through modifying antioxidant defense, oxidative stress, and photosynthesis. A 100 μM concentration of Cd stress was applied to the hydroponically grown wild rice line, and 50 μM of silicon dioxide nanoparticles (SiO2NPs) was given. The study depicted that when 50 μM SiO2NPs was applied, there was a significant decrease in Cd uptake in both roots and shoots by 30.2% and 15.8% under 100 μM Cd stress, respectively. The results illustrated that Cd had a detrimental effect on carotenoid and chlorophyll levels and other growth-related traits. Additionally, it increased the levels of ROS in plants, which reduced the antioxidant capability by 18.8% (SOD), 39.2% (POD), 32.6% (CAT), and 25.01% (GR) in wild rice. Nevertheless, the addition of silicon dioxide nanoparticles reduced oxidative damage and the overall amount of Cd uptake, which lessened the toxicity caused by Cd. Reduced formation of reactive oxygen species (ROS), including MDA and H2O2, and an increased defense system of antioxidants in the plants provided evidence for this. Moreover, SiO2NPs enhanced the Cd resistance, upregulated the genes related to antioxidants and silicon, and reduced metal transporters' expression levels.

Integrated proteomics, transcriptomics, and metabolomics offer novel insights into Cd resistance and accumulation in Poa pratensis

Kentucky bluegrass (Poa pratensis L., KB) demonstrates superior performance in both cadmium (Cd) accumulation and tolerance; however, the regulatory mechanisms and detoxification pathways in this species remain unclear. Therefore, phenotype, root ultrastructure, cell wall components, proteomics, transcriptomics, and metabolomics were analyzed under the hydroponic system to investigate the Cd tolerance and accumulation mechanisms in the Cd-tolerant KB variety ‘Midnight (M)’ and the Cd-sensitive variety ‘Rugby II (R)’ under Cd stress. The M variety exhibited higher levels of hydroxyl and carboxyl groups as revealed by Fourier transform infrared spectroscopy spectral analysis. Additionally, a reduced abundance of polysaccharide degradation proteins was observed in the M variety. The higher abundance of glutathione S-transferase and content of L-cysteine-glutathione disulfide and oxidized glutathione in the M variety may contribute to better performance of the M variety under Cd stress. Additionally, the R variety had an enhanced content of carboxylic acids and derivatives, increasing the Cd translocation capacity. Collectively, the down-regulation of cell wall polysaccharide degradation genes coupled with the up-regulation of glutathione metabolism genes enhances the tolerance to Cd stress in KB. Additionally, lignification of the endodermis and the increase in carboxylic acids and derivatives play crucial roles in the redistribution of Cd in KB.

The Cd resistant mechanism of Proteus mirabilis Ch8 through immobilizing and detoxifying

Cadmium (Cd) pollution is a serious global environmental problem, which requires a global concern and practical solutions. Microbial remediation has received widespread attention owing to advantages, such as environmental friendliness and soil amelioration. However, Cd toxicity also severely deteriorates the remediation performance of functional microorganisms. Analyzing the mechanism of bacterial resistance to Cd stress will be beneficial for the application of Cd remediation. In this study, the bacteria strain, up to 1400 mg/L Cd resistance, was employed and identified as Proteus mirabilis Ch8 (Ch8) through whole genome sequence analyses. The results indicated that the multiple pathways of immobilizing and detoxifying Cd maintained the growth of Ch8 under Cd stress, which also possessed high Cd extracellular adsorption. Firstly, the changes in surface morphology and functional groups of Ch8 cells were observed under different Cd conditions through SEM-EDS and FTIR analyses. Under 100 mg/L Cd, Ch8 cells exhibited aggregation and less flagella; the Cd biosorption of Ch8 was predominately by secreting exopolysaccharides (EPS) and no significant change of functional groups. Under 500 mg/L Cd, Ch8 were present irregular polymers on the cell surface, some cells with wrapping around; the Cd biosorption capacity exhibited outstanding effects (38.80 mg/g), which was mainly immobilizing Cd by secreting and interacting with EPS. Then, Ch8 also significantly enhanced the antioxidant enzyme activity and the antioxidant substance content under different Cd conditions. The activities of SOD and CAT, GSH content of Ch8 under 500 mg/L Cd were significantly increased by 245.47%, 179.52%, and 241.81%, compared to normal condition. Additionally, Ch8 significantly induced the expression of Acr A and Tol C (the resistance-nodulation-division (RND) efflux pump), and some antioxidant genes (SodB, SodC, and Tpx) to reduce Cd damage. In particular, the markedly higher expression levels of SodB under Cd stress. The mechanism of Ch8 lays a foundation for its application in solving soil remediation.

Effective remediation and phytotoxicity assessment of oxytetracycline and Cd co-contaminated soil using biochar

Heavy metal-antibiotic complex contamination in soil has raised much attention. Biochar is a common soil conditioner and pollutant barrier agent. However, there has rare research about biochar control effectiveness on heavy metals and antibiotics in plant-soil system. This work evaluated the impact of applying unmodified biochar (M) and H3PO4-modified biochar (PM) on Cd, OTC, and antibiotic resistance genes (ARGs) distribution in pakchoi (Brassica chinensis L.) and soil by pot experiment. Biochar can improve quality, antioxidative defense responses of plant and enzymes activity, physiochemical properties, microbial community of soil. The content of OTC, Cd, and ARGs in pakchoi were significantly reduced after applying biochar. There was a 73.08–78.48 % decrease rate in relative abundance of ARGs, a 58.96 %–59.66 % decrease rate in OTC content, and a 71.65 %–79.64 % decrease rate in available Cd content when biochar had been added to soil with OTC and Cd contaminations. The addition of 1.5 % biochar converted exchangeable Cd to residual fraction. Furthermore, applying PM biochar led to a greater reduction in Cd mobility and OTC in soil and their accumulation in pakchoi compared to M biochar. The biochar also mitigated the OTC and Cd phytotoxicity and improved plant quality and soil enzymes activity. Biochar could reduce Proteobacteria, Actinobacteria, Planctomycetes, Gemmatimonadetes, and Firmicutes abundancies. Soil organic matter accounted for the greatest proportion of variation in ARGs. Overall, the use of biochar, particularly PM biochar, was a promising approach for remediating soil contaminated with multiple pollutants.

Identification and characterization of the critical genes encoding Cd-induced enhancement of SOD isozymes activities in Zhe-Maidong (Ophiopogon japonicus).

Superoxide dismutase (SOD) protects plants from abiotic stress-induced reactive oxygen species (ROS) damage. Here, the effects of cadmium (Cd) exposure on ROS accumulation and SOD isozymes, as well as the identification of significant SOD isozyme genes, were investigated under different Cd stress treatments to Zhe-Maidong (Ophiopogon japonicus). The exposure to Cd stress resulted in a notable elevation in the SOD activity in roots. Cu/ZnSODa and Cu/ZnSODb were the most critical SOD isozymes in response to Cd stress, as indicated by the detection results for SOD isozymes. A total of 22 OjSOD genes were identified and classified into three subgroups, including 10 OjCu/ZnSODs, 6 OjMnSODs, and 6 OjFeSODs, based on the analysis of conserved motif and phylogenetic tree. Cu/ZnSOD-15, Cu/ZnSOD-18, Cu/ZnSOD-20, and Cu/ZnSOD-22 were the main genes that control the increase in SOD activity under Cd stress, as revealed via quantitative PCR and transcriptome analysis. Additionally, under various heavy metal stress (Cu2+, Fe2+, Zn2+, Mn2+), Cu/ZnSOD-15, Cu/ZnSOD-18, and Cu/ZnSOD-22 gene expression were significantly upregulated, indicating that these three genes play a critical part in resisting heavy metal stress. The molecular docking experiments performed on the interaction between oxygen ion (O2•-) and OjSOD protein have revealed that the critical amino acid residues involved in the binding of Cu/ZnSOD-22 to the substrate were Pro135, Ile136, Ile140, and Arg144. Our findings provide a solid foundation for additional functional investigations on the OjSOD genes, as well as suggestions for improving genetic breeding and agricultural management strategies to increase Cd resistance in O. japonicus.

Cadmium biosorption and mechanism investigation using two cadmium-tolerant microorganisms isolated from rhizosphere soil of rice

Microbial remediation of cadmium-contaminated soil offers advantages like environmental friendliness, cost-effectiveness, and simple operation. However, the efficacy of this remediation process relies on obtaining dominant strains and a comprehensive understanding of their Cd adsorption mechanisms. This study identified two Cd-resistant bacteria, Burkholderia sp. 1–22 and Bacillus sp. 6–6, with significant growth-promoting effects from rice rhizosphere soil. The strains showed remarkable Cd resistance up to ∼200 mg/L and alleviated Cd toxicity by regulating pH and facilitating bacterial adsorption of Cd. FTIR analysis showed crucial surface functional groups, like carboxyl and amino groups, on bacteria played significant roles in Cd adsorption. The strains could induce CdCO3 formation via a microbially induced calcium precipitation (MICP) mechanism, confirmed by SEM-EDS, X-ray analysis, and elemental mapping. Pot experiments showed these strains significantly increased organic matter and enzyme activity (e.g., urease, sucrase, peroxidase) in the rhizosphere soil versus the control group. These changes are crucial for restricting Cd mobility. Furthermore, strains 6–6 and 1–22 significantly enhance plant root detoxification of Cd, alleviating toxicity. Notably, increased pH likely plays a vital role in enhancing Cd precipitation and adsorption by strains, converting free Cd into non-bioavailable forms.

Knockout of OsHMA3 in an indica rice increases cadmium sensitivity and inhibits plant growth

Cadmium (Cd) is a heavy metal that poses harm to both plants and humans. OsHMA3, a member of the heavy metal ATPase (HMA) family, plays a crucial role in sequestering Cd into the vacuoles of roots, thereby limiting its accumulation in rice grains. However, the response of rice plants to Cd under complete loss-of-function of OsHMA3 remains unclear. In this study, we successfully generated OsHMA3 null mutants in an indica variety 93 − 11 using CRISPR/Cas9 technology. A Cd resistance experiment revealed that the Oshma3 mutants exhibited increased sensitivity to Cd compared to the wild-type at a tested concentration of 10 µM CdCl2. Furthermore, the seedlings of Oshma3 mutant lines displayed inhibited plant growth in the presence of 1 µM Cd, specifically suppressing aboveground growth. As expected, knockout lines of OsHMA3 showed lower Cd accumulation in roots but higher concentrations in shoots compared to wild-type plants, highlighting the role of OsHMA3 in root-to-shoot Cd translocation. We further performed RNA sequencing analysis on wild-type and Oshma3 plants under control and Cd treatment conditions and found that differentially expressed genes were mainly enriched in metal ion binding, integral component of the membranes, and biosynthesis pathways for secondary metabolites triggered by exposure to Cd. When grown in a paddy field, the Oshma3 mutants exhibited shorter plant height, lower seed setting rate, and higher Cd accumulation in grains compared to wild-type plants. Our results indicate that knockout of OsHMA3 in the 93 − 11 variety increases sensitivity to Cd and inhibits plant growth.

Comparative transcriptome combined with physiological analyses revealed key genes and pathways for cadmium tolerance in wild-type and mutant microalgae Dunaliella salina

Cadmium (Cd) has become one of the major contaminants in aquatic ecosystems. The microalgae Dunaliella salina is known as a cadmium (Cd) accumulator and shows a high level of tolerance to Cd, but improved Cd tolerance and relevant mechanisms are still required for investigation. In this study, two mutant strains (M1 and M2) of D. salina with high Cd resistance were obtained by chemical mutagenesis. In the normal medium, there were no differences between the two mutant strains and the wild-type strain in biochemical and physiological indicators. However, the two mutant strains showed high Cd resistance, rapid growth rate, and good Cd accumulation capacity in the medium containing high levels of Cd compared with the wild strain, which may be involved in increases in protein content, accumulation of carotenoids and chlorophylls, and glutathione reductase (GR) activity. We identified 829, 587, and 740 differentially expressed genes (DEGs) from the Cd/Control, Cd + M1/Cd, and Cd + M2/Cd sample groups by transcriptome analysis, respectively. The main DEGs were found in the ribosome, DNA replication, photosynthesis-antenna, and photosynthesis pathways after KEGG enrichment. There were 39 DEGs involved in the photosynthesis and photosynthesis-antenna pathways, of which 28 DEGs were down-regulated by Cd in the wild-type strain but remained relatively unchanged in the mutant strains. Under Cd exposure, the mutant strains showed higher mRNA levels of most DEGs involved in the ribosome and DNA replication pathways than the wild strain. Taken together, the present study will help us understand the mechanism of Cd tolerance in microalgae, and provide candidate genes and key pathways for phytoremediation.

AtERF13 and AtERF6 double knockout fine-tunes growth and the transcriptome to promote cadmium tolerance in Arabidopsis

The toxic heavy metal cadmium (Cd) restricts plant growth. However, how plants fine-tune their growth to modulate Cd resistance has not been determined. Ethylene response factors (ERFs) are key regulators of Cd stress, and Arabidopsis thaliana ERF13 and ERF6 (AtERF13 and AtERF6) negatively regulate growth. We previously demonstrated that AtERF13 is a transcriptional activator that binds a Cd-responsive element. Herein, we report that Arabidopsis plants improve Cd tolerance by repressing AtERF13 and AtERF6. We found that AtERF13 and AtERF6 were strongly downregulated by Cd stress and that AtERF6 weakly bound Cd-responsive elements. Moreover, AtERF13 physically interacted with AtERF6. Importantly, AtERF13 and AtERF6 double knockout mutants, but not single mutants or overexpression lines, grew better, tolerated more Cd and had higher Cd contents than did the wild type. Comparative transcriptome analysis revealed that the double mutants regulate the defense response to cope with Cd toxicity. Accordingly, we propose that, upon Cd stress, Arabidopsis plants repress AtERF13 and AtERF6 to relieve their growth inhibition effects and adjust the transcriptome to adapt to Cd stress, leading to increased Cd tolerance. Our findings thereby provide deep mechanical insights into how dual-function transcription factors fine-tune growth and the transcriptome to promote Cd tolerance in plants.

Cysteine and thiosulfate promoted cadmium immobilization in strain G303 by the formation of extracellular CdS

Bacteria have evolved a variety of strategies to defend themselves against cadmium toxicity, however, the specific mechanisms involved in the enhancement of bacterial cadmium resistance by sulfur sources are unclear. In this study, a novel cadmium (Cd)-tolerant bacterium, Stenotrophomonas geniculata G303, was isolated from activated sludge. The growth of strain G303 under diverse Cd concentrations was investigated, and the minimum inhibitory concentration of Cd was found to be 1 mM. Strain G303 effectively remove 94.7 % of Cd after 96 h of culture. Extracellular CdS was detected using multiple methods, with the CdS formed being aggregated in the biofilm. The addition of cysteine and thiosulfate to the medium significantly enhanced the Cd resistance and removal capacity of strain G303. Integrated genomic and proteomic analyses revealed that heavy metal transporters cooperate to resist Cd stress. Cysteine and thiosulfate improved Cd tolerance in strain G303 by upregulating nitrogen and energy metabolism. Proteins associated with nitrate reduction likely played a pivotal role in cysteine and thiosulfate metabolism. Notably, cysteine synthase and the SUF system played crucial roles in CdS formation. This study systematically explored the impact of cysteine and thiosulfate on the Cd resistance of strain G303, deepening our understanding of the microbial response mechanism to heavy metals.

Co-inoculation of rhizobia and AMF improves growth, nutrient uptake, and cadmium resistance of black locust grown in sand culture.

Rhizobia and arbuscular mycorrhizal fungi (AMF) are symbiotic microorganisms important for plants grown in nutrient-deficient and heavy metal-contaminated soils. However, it remains unclear how plants respond to the coupled stress by heavy metal and nitrogen (N) deficiency under co-inoculation. Here, we investigated the synergistic effect of Mesorhizobium huakuii QD9 and Funneliformis mosseae on the response of black locust (Robinia pseudoacacia L.) grown in sand culture to cadmium (Cd) under N deficiency conditions. The results showed that single inoculation of AMF improved the growth and Cd resistance of black locust, co-inoculation improved the most. Compared to non-inoculated controls, co-inoculation mediated higher biomass and antioxidant enzyme activity, reduced oxidative stress, and promoted nodulation, mycorrhizal colonization, photosynthetic capacity, and N, P, Fe and Mg acquisition when exposed to Cd. This increase was significantly higher under N deficiency compared to N sufficiency. In addition, the uptake of Cd by co-inoculated black locust roots increased, but Cd translocation to the above-ground decreased under both N deficiency and sufficiency. Thus, in the tripartite symbiotic system, not merely metabolic processes but also Cd uptake increased under N deficiency. However, enhanced Cd detoxification in the roots and reduced allocation to the shoot likely prevent Cd toxicity and rather stimulated growth under these conditions.