Enhanced Cd Tolerance Research Articles

The Endophytic Fungus Piriformospora Indica-Assisted Alleviation of Cadmium in Tobacco.

Increasing evidence suggests that the endophytic fungus Piriformospora indica helps plants overcome various abiotic stresses, especially heavy metals. However, the mechanism of heavy metal tolerance has not yet been elucidated. Here, the role of P. indica in alleviating cadmium (Cd) toxicities in tobacco was investigated. It was found that P. indica improved Cd tolerance to tobacco, increasing Cd accumulation in roots but decreasing Cd accumulation in leaves. The colonization of P. indica altered the subcellular repartition of Cd, increasing the Cd proportion in cell walls while reducing the Cd proportion in membrane/organelle and soluble fractions. During Cd stress, P. indica significantly enhanced the peroxidase (POD) activity and glutathione (GSH) content in tobacco. The spatial distribution of GSH was further visualized by Raman spectroscopy, showing that GSH was distributed in the cortex of P. indica-inoculated roots while in the epidermis of the control roots. A LC-MS/MS-based label-free quantitative technique evaluated the differential proteomics of P. indica treatment vs. control plants under Cd stress. The expressions of peroxidase, glutathione synthase, and photosynthesis-related proteins were significantly upregulated. This study provided extensive evidence for how P. indica enhances Cd tolerance in tobacco at physiological, cytological, and protein levels.

Ectopic expression of IMA small peptide genes confers tolerance to cadmium stress in Arabidopsis through activating the iron deficiency response

Increasing cadmium (Cd) pollution severely affects plant growth and development, posing risks to human health via food chains. The Cd toxicity could be mitigated by improving Fe nutrient in plants. IMA1 and IMA3, two novel small peptides functionally epistatic to the key transcription factor bHLH39 but independent of bHLH104, were recently identified as the newest additions to the Fe regulatory cascade, but their roles in Cd uptake and toxicity remain not addressed. Here, the functions of two IMAs and two transcription factors related to Cd tolerance were verified. Overexpression of either bHLH39 or bHLH104 in Arabidopsis showed weak roles in Cd tolerance, but overexpression of IMAs, which activates the Fe-deficient response, significantly enhanced Cd tolerance, showing greater root elongation, biomass and chlorophyll contents. The Cd contents did not show significant difference among the overexpression lines. Further investigations revealed that the tolerance of transgenic plants to Cd mainly depended on higher Fe accumulation, which decreased the MDA contents and enhanced root elongation under Cd exposure, finally contributing to attenuating Cd toxicity. Taken together, the results suggest that increasing Fe accumulation is promising for improving plant tolerance to Cd toxicity and that IMAs are potential candidates for solving Cd toxicity problem.

Genetic engineering of glycinebetaine synthesis enhances cadmium tolerance in BADH-transgenic tobacco plants via reducing cadmium uptake and alleviating cadmium stress damage

Cadmium (Cd) is a toxic non-essential elements to plants, and its accumulation in plants can affect human health through the food chain. Glycinebetaine (GB) is an effective osmotic adjustment substance for plants to resist abiotic stress, and it plays important roles in various stresses. To investigate whether endogenous GB accumulation in vivo can enhance Cd tolerance, we used betaine aldehyde dehydrogenase (BADH) transgenic tobacco plants to explore the important role of GB under Cd stress conditions. The results showed that the tobacco exposed to cadmium stress, lead to growth inhibition and biomass reduction, decreased photosynthesis, decreased the absorption of essential minerals and increased oxidative stress. However, GB accumulation in transgenic tobacco plants significantly increased Cd tolerance, as evidenced by the decreased growth inhibition, enhanced photosynthetic rate and reduced reactive oxygen species accumulation. GB can regulate Cd uptake and transport, which results in reduced Cd accumulation. Moreover, GB also reduced K+ efflux under Cd stress and regulated ion transporter genes to maintain element balance. Our findings provide a novel role of GB in enhancing Cd stress tolerance in transgenic plants and thus propose GB as a potential candidate for relieving Cd toxicity in other crops.

Effect of exogenous silicon and methyl jasmonate on the alleviation of cadmium-induced phytotoxicity in tomato plants.

In the present study, a hydroponic experiment was performed to evaluate the effect of exogenous silicon (Si) and methyl jasmonate (MeJA) on the mitigation of Cd toxicity in tomato seedlings. The results revealed that Cd-stressed plants exhibited growth inhibition, increased lipid peroxidation, and impaired photosynthetic pigment accumulation. However, Si and MeJA applied alone or in combination significantly ameliorated the above-mentioned adverse effects induced by Cd. Among all treatments, Cd+Si+MeJA treatment elevated the dry mass of roots, stems, and leaves by 317.39%, 110.85%, and 119.71%, respectively. The chlorophyll a, chlorophyll b, and carotenoid contents in Cd+Si+MeJA-treated group were dramatically elevated (p < 0.05). Meanwhile, the malondialdehyde content in roots and shoots were reduced by 32.24% and 69.94%, respectively. The Si and MeJA applied separately or in combination also resulted in a prominent decrease of Cd influxes in tomato roots; therefore, a reduction of Cd content in tomato tissues were detected, and the Cd concentration in tomato roots were decreased by 27.19%, 25.18%, and 17.51% in Cd+Si, Cd+MeJA and Cd+Si+MeJA-treated plants, respectively. Moreover, in Cd+Si+MeJA-treated group, the percentage of Cd in cell wall fraction was enhanced while that in organelle fraction was decreased as compared with Cd-stressed plants. Collectively, our findings indicated that Si and MeJA application provide a beneficial role in enhancing Cd tolerance and reducing Cd uptake in tomato plants.

Overexpression of FaHSP17.8-CII improves cadmium accumulation and tolerance in tall fescue shoots by promoting chloroplast stability and photosynthetic electron transfer of PSII

Genetic improvement could play a significant role in enhancing the Cd accumulation, translocation and tolerance in plants. In this study, for the first time, we constructed transgenic tall fescue overexpressing a class II (CII) sHSP gene FaHSP17.8-CII, which enhanced Cd tolerance and the root-to-shoot Cd translocation. After exposed to 400 μM CdCl2, two FaHSP17.8-CII overexpressing lines (OE#3 and OE#7) exhibited 30% and 40% more shoot fresh weight, respectively, relative to the wild-type (WT). Both transgenic lines showed higher tolerance to Cd, as evidenced by lower levels of electrolyte leakage and malondialdehyde compared to the WT plants under Cd stress. FaHSP17.8-CII overexpression increased shoot Cd contents 49–59% over the WT plants. The Cd translocation factor of root-to-shoot in OE grasses was 69–85% greater than WT under Cd stress. Furthermore, overexpression of FaHSP17.8-CII reduced Cd-induced damages of chloroplast ultra-structure and chlorophyll synthesis, and then improved photosystem II (PSII) function under Cd stress, which resulted in less reactive oxygen species (ROS) accumulation in OE grasses than that in WT exposed to Cd stress. The study suggests a novel FaHSP17.8-CII–PSII-ROS module to understand the mechanisms of Cd detoxification and tolerance, which provides a new strategy to improve phytoremediation efficiency in Cd-stressed grasses.

Excretion from long glandular trichomes contributes to alleviation of cadmium toxicity in Nicotiana tabacum

The B-type cyclin gene, CycB2, serves as a negative regulator of glandular trichome initiation. Through targeted knockout of NtCycB2 in Nicotiana tabacum cv. K326 using the CRISPR/Cas9 system, we created a variety, HK326, which exhibits significantly increased density and larger glandular heads of long glandular trichomes. Under Cd-stress, HK326 exhibited enhanced Cd tolerance, as demonstrated by a robust root system, strengthened cell membrane stability, and higher photosynthetic parameters. HK326 exhibited enhanced Cd-stress tolerance due to a strong excretion capacity of long glandular trichomes by forming calcium oxalate crystals. Cd mainly accumulated in tobacco shoots rather than remained in roots. Specifically, Cd levels of the HK326 shoot surface were nearly two-fold of those of K326, resulting in less Cd internally in the roots and shoots. Gene expression patterns revealed 11 Cd transporter genes that were upregulated after Cd-stress in shoots, roots, and trichomes. Among them, the NtHMA2 gene encoding heavy metal ATPases and involved in the transport of divalent heavy metal cations was expressed consistently and significantly higher in HK326 than K326, both before and after Cd-stress. NtHMA2 expression was strong in trichomes, moderate in shoots, while weak in roots. The results indicate that NtHMA2 may be involved in Cd excretion from glandular trichomes. Our findings suggest HK326 may be an appropriate candidate plant for Cd-stress tolerance.

Exogenous Hemin Confers Cadmium Tolerance by Decreasing Cadmium Accumulation and Modulating Water Status and Matter Accumulation in Maize Seedlings

Cadmium (Cd) contamination harms plant growth and human health. The application of hemin (ferroprotoporphyrin IX) can effectively relieve abiotic stresses in plants. This work investigates the effects of hemin on alleviating Cd toxicity and enhancing Cd tolerance in maize seedlings. In this study, maize seedlings were cultivated in nutrient solutions, with a combination of CdCl2 (464 μmol L−1) and hemin (100 μmol L−1). We measured plant growth status, water status, Cd concentration, and Cd distribution in maize seedlings. The results indicated that Cd stress increased Cd accumulation in plants and inhibited plant growth. However, hemin alleviated the growth inhibition and improved water balance, root morphology, and root vitality under Cd stress. Additionally, hemin increased 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), total phenolic content, and phenylalanine ammonia lyase (PAL) activity to enhance tolerance to Cd stress. Hemin reduced Cd concentration, the translocation factor (TF), and the bioconcentration factor (BCF) in maize seedlings under Cd stress. Furthermore, hemin increased Cd concentrations in the cell wall and the soluble fraction of seedling roots, which helped reduce Cd transport from root to shoot. In summary, exogenous hemin could be used for alleviating adverse impacts on maize seedling induced by Cd stress.

Response in Cadmium Tolerance of Penicillium cyclopium Westling Subsequent to Exposure to Gamma Irradiation

Role of gamma irradiation in modulating 1.1 times more cadmium (Cd) tolerance in Penicillium cyclopium Westling has been detailed in this paper. Augmentation in metal tolerance was recognized by escalation in response to Cadmium and Cd removal efficacies than that of their un-irradiated group. FTIR spectra and electron microscopic photographs further strengthen the role of low absorbed dose of gamma in modulating Cd tolerance in P.cyclopium. Up regulated activities of anti-oxidatives in gamma exposed fungal groups might be the reason for enhanced Cd tolerance than that of their un-irradiated counter parts. This findings reveal a positive and eco-friendly step for heavy metal bioremediation and metal stressed lignocellulosic waste degradation.

The tonoplast-localized transporter OsABCC9 is involved in cadmium tolerance and accumulation in rice

Cadmium (Cd) is a highly toxic element to living organisms, and its accumulation in the edible portions of crops poses a potential threat for human health. The molecular mechanisms underlying Cd detoxification and accumulation are not fully understood in plants. In this study, the involvement of a C-type ABC transporter, OsABCC9, in Cd tolerance and accumulation in rice was investigated. The expression of OsABCC9 was rapidly induced by Cd treatment in a concentration-dependent manner in the root. The transporter, localized on the tonoplast, was mainly expressed in the root stele under Cd stress. OsABCC9 knockout mutants were more sensitive to Cd and accumulated more Cd in both the root and shoot compared to the wild-type. Moreover, the Cd concentrations in the xylem sap and grain were also significantly increased in the knockout lines, suggesting that more Cd was distributed from root to shoot and grain in the mutants. Heterologous expression of OsABCC9 in yeast enhanced Cd tolerance along with an increase of intracellular Cd content. Taken together, these results indicated that OsABCC9 mediates Cd tolerance and accumulation through sequestration of Cd into the root vacuoles in rice.

Exogenous Melatonin Enhances Cd Tolerance and Phytoremediation Efficiency by Ameliorating Cd-Induced Stress in Oilseed Crops: A Review

Heavy metal pollution is of increasing global concern as it adversely impacts different spheres including pedosphere, hydrosphere, biosphere, and humansphere. Cadmium (Cd) contamination of agriculture soil has become a thoughtful challenge across the globe due to uncontrolled anthropogenic activities, limiting agricultural productivity and disturbing eco-environment sustainability. Sustainable mitigation strategies are, therefore, required for effective Cd decontamination. Biostimulation is a promising method to improve and stimulate life processes of plants in general and oilseed crops in particular, without posing threats to eco-environment sustainability and safer food production. Melatonin (N-acetyl-5-methoxytryptamine), a recognized pleiotropic molecule, has emerged as a research highlight regarding its role as an effective natural plant growth promoter, a broad spectrum antioxidant, and more specifically an efficient biostimulator to improve Cd-induced tolerance of plants for phytoremediation purposes and simultaneous biofuel production. This review provides a novel insight to understand the multifunctional role of melatonin in improving Cd phytoremediation capacity together with reducing phytotoxicity in oilseed crops, which was not previously assessed. Among oilseed crops, Brassicaceae spp. have unique stress adaptive mechanisms with exceptionally high Cd accumulating capabilities, apart from the diverse agri-horticultural importance. Interestingly, the discovery of dynamic approaches regarding melatonin application helped to better understand the basic mechanisms involved in melatonin-mediated responses against Cd stress in oilseed crops. Our review will provide a useful basis for the development of alternative strategies to genetically engineer low-Cd-content oilseed crops, with the aim of improving eco-friendly crop production and ensuring food safety. Furthermore, future researches will be supposed to provide more genetic evidences about Cd-induced melatonin regulation in higher plants.

Regulating effects of silicon on Cd-accumulation and stress-resistant responding in rice seedling.

Silicon (Si) application could significantly alleviate the toxic effects of cadmium (Cd) on the growth and development of rice. Here, we examined the regulatory effects of Si on Cd accumulation and stress response in rice seedlings through a hydroponic root separation test. The results showed that the biomass of rice seedlings decreased significantly under Cd stress, while the addition of Si could alleviate such negative effect. The uptake, transfer, and accumulation of Cd in rice seedling were significantly affected by Si addition under Cd stress. Si application under the unilateral Cd stress (Si-Cd+Si, Si-Cd) increased Cd-retention coefficient of root by 83.3%-83.6%, which restricted the transfer of Cd from root to aboveground. However, the treatment with Si added to the non-stressed side (Si-Cd) elevated the uptake and accumulation of Cd in rice seedling, with the accumulation in root being increased by 48.2% when compared to the treatment under the unilateral Cd stress without the addition of Si (CK-Cd). The treatment with Si added in two sides (Si-Cd+Si) decreased the uptake of Cd both in root and aboveground parts by 36.7% and 54.9%, respectively. The addition of Si under bilateral Cd stress (Cd-Cd+Si) significantly reduced the Cd uptake of both the root and aboveground parts by 57.8% and 46.5%, respectively, compared to the treatment of bilateral Cd stress (Cd-Cd). Higher Si concentration in rice seedling was found under the Cd stress. More Si was accumulated in rice seedling to resist the Cd stress when Si was added. The addition of Si affected the absorption of other metal elements in rice seedlings, including calcium (Ca), magnesium (Mg) and manganese (Mn). The concentrations of Ca and Mg in root and aboveground parts were significantly increased by Si addition under bilateral Cd-stress (Cd-Cd+Si), but Mn concentration was changed with the stress degree of Cd. The activities of superoxide dismutase (SOD) and peroxidase (POD) in root were affected by Si under Cd stress, especially for the Si-Cd treatment. The activity of POD in the root of the Cd-stress side and that of SOD in non-stress side were significantly increased, which benefit to scavenging the free radicals induced by Cd stress. In conclusion, Si could regulate the growth of rice seedlings, the uptake of elements such as Cd and Si, and the antioxidant reaction of the root system under the Cd stress. High Si concentration in plant is conducive to enhancing Cd tolerance.

Inoculation with Rhizobacteria Enhanced Tolerance of Tomato (Solanum lycopersicum L.) Plants in Response to Cadmium Stress

In this study, cadmium (Cd)-tolerant bacteria Serratia sp. D23 (D23) and Sphingomonas sp. D36 (D36) were isolated from Cd-contaminated rhizospheric soil. Both strains have indole-3-acetic acid production, phosphate solubilization and siderophores production ability. A hydroponic experiment was performed to evaluate the effect of D23 and D36 on Cd toxicity and Cd content in tomato plants. The results indicated that under Cd-stressed condition, D23 and D36 inoculation increased photosynthetic pigment content in tomato leaves and decreased malonyldialdehyde level in tomato roots (p < 0.05). Both strains could alleviate Cd-induced inhibition of dry mass accumulation, D23 inoculation increased the root and leaf dry mass by 44.95% and 99.13%, while D36 treatment increased the root and leaf dry mass by 41.56% and 46.81%, respectively. Besides, D23 treatment reduced the Cd content in tomato root by 46.70%, and D36 inoculation reduced the Cd content in root and leaf by and 27.63% and 35.41%. Moreover, the expression of stress-related genes, including Hsp90, MT2 and Nramp3 were enhanced by bacterial inoculation. The subcellular localization of Cd and the activity of antioxidant enzyme were also influenced by D23 and D36 colonization. Taken together, rhizobacteria D23 and D36 could alleviate Cd toxicity and reduce Cd concentration in tomato plants via alleviating oxidative stress, modulating Cd subcellular localization and upregulating stress-related gene expression. This study provides evidence of enhancing Cd tolerance in tomato plants via rhizosphere bacteria and will be helpful to establish bacterial-assisted approach for alleviating heavy metal toxicity in plants.

Transcriptome analysis and association mapping reveal the genetic regulatory network response to cadmium stress in Populus tomentosa.

Long non-coding RNAs (lncRNAs) play essential roles in plant abiotic stress responses, but the response of lncRNA-mediated genetic networks to cadmium (Cd) treatment remain elusive in trees, the promising candidates for phytoremediation of Cd contamination. We identified 172 Cd-responsive lncRNAs and 295 differentially expressed target genes in the leaves of Cd-treated Populus tomentosa. Functional annotation revealed that these lncRNAs were involved in various processes, including photosynthesis, hormone regulation, and phenylalanine metabolism. Association studies identified 78 significant associations, representing 14 Cd-responsive lncRNAs and 28 target genes for photosynthetic and leaf physiological traits. Epistasis uncovered 83 pairwise interactions among these traits, revealing Cd-responsive lncRNA-mediated genetic networks for photosynthesis and leaf physiology in P. tomentosa. We focused on the roles of two Cd-responsive lncRNA-gene pairs, MSTRG.22608.1-PtoMYB73 and MSTRG.5634.1-PtoMYB27, in Cd tolerance of Populus, and detected insertions/deletions within lncRNAs as polymorphisms driving target gene expression. Genotype analysis of lncRNAs and heterologous overexpression of PtoMYB73 and PtoMYB27 in Arabidopsis indicated their effects on enhancing Cd tolerance, photosynthetic rate, and leaf growth, and the potential interaction mechanisms of PtoMYB73 with abiotic stresses. Our study identifies the genetic basis for the response of Populus to Cd treatment, facilitating genetic improvement of Cd tolerance in trees.

CAX3 (cation/proton exchanger) mediates a Cd tolerance by decreasing ROS through Ca elevation in Arabidopsis.

Over-expression of CAX3 encoding a cation/proton exchanger enhances Cd tolerance by decreasing ROS (Reactive Oxygen Species) through activating anti-oxidative enzymes via elevation of Ca level in Arabidopsis CAXs (cation/proton exchangers) are involved in the sequestration of cations such as Mn, Li, and Cd, as well as Ca, from cytosol into the vacuole using proton gradients. In addition, it has been reported that CAX1, 2 and 4 are involved in Cd tolerance. Interestingly, it has been reported that CAX3 expressions were enhanced by Cd in Cd-tolerant transgenic plants expressing Hb1 (hemoglobin 1) or UBC1 (Ub-conjugating enzyme 1). Therefore, to investigate whether CAX3 plays a role in increasing Cd tolerance, CAX3 of Arabidopsis and tobacco were over-expressed in Arabidopsis thaliana. Compared to control plants, both transgenic plants displayed an increase in Cd tolerance, no change in Cd accumulation, and enhanced Ca levels. In support of these, AtCAX3-Arabidopsis showed no change in expressions of Cd transporters, but reduced expressions of Ca exporters and lower rate of Ca efflux. By contrast, atcax3 knockout Arabidopsis exhibited a reduced Cd tolerance, while the Cd level was not altered. The expression of Δ90-AtCAX3 (deletion of autoinhibitory domain) increased Cd and Ca tolerance in yeast, while AtCAX3 expression did not. Interestingly, less accumulation of ROS (H2O2 and O2-) was observed in CAX3-expressing transgenic plants and was accompanied with higher antioxidant enzyme activities (SOD, CAT, GR). Taken together, CAX3 over-expression may enhance Cd tolerance by decreasing Cd-induced ROS production by activating antioxidant enzymes and by intervening the positive feedback circuit between ROS generation and Cd-induced spikes of cytoplasmic Ca.

Indole-3-butyric acid priming reduced cadmium toxicity in barley root tip via NO generation and enhanced glutathione peroxidase activity.

Activation of GPX and enhanced NO level play a key role in IBA-mediated enhanced Cd tolerance in young barley roots. Application of exogenous indole-3-acetic acid (IAA) or an IAA precursor improves the tolerance of plants to heavy metals. However, the physiology of these tolerance mechanisms remains largely unknown. Therefore, we studied the priming effect of indole-3-butyric acid (IBA), an IAA precursor, on mild and severe cadmium (Cd) stress-induced responses in roots of young barley seedlings. IBA, similarly to mild Cd stress, significantly increased the glutathione peroxidase (GPX) activity in the apexes of barley roots, which remained elevated after the IBA pretreatment as well. IBA pretreatment-evoked high nitric oxide generation in roots effectively reduced the high superoxide level under the severe Cd stress, leading to less toxic peroxynitrite accumulation accompanied by markedly reduced Cd-induced cell death. On the other hand, the IBA-evoked changes in IAA homeostasis resulted in root growth reorientation from longitudinal elongation to radial swelling. However, the application of an IAA signaling inhibitor, following the activation of defense responses by IBA, was able to promote root growth even at high concentrations of Cd. Based on the results, it can be concluded that the application of IBA, as an effective activator of Cd tolerance mechanisms in young barley roots, and the subsequent use of an IAA signaling inhibitor for the inhibition of root morphogenic responses induced by altered auxin metabolism, results in a high degree of root Cd tolerance, helping it to withstand even the transient exposure to lethal Cd concentration without the absolute inhibition of root growth.

Characterization of the Heavy-Metal-Associated Isoprenylated Plant Protein (HIPP) Gene Family from Triticeae Species.

Heavy-metal-associated (HMA) isoprenylated plant proteins (HIPPs) only exist in vascular plants. They play important roles in responses to biotic/abiotic stresses, heavy-metal homeostasis, and detoxification. However, research on the distribution, diversification, and function of HIPPs in Triticeae species is limited. In this study, a total of 278 HIPPs were identified from a database from five Triticeae species, and 13 were cloned from Haynaldia villosa. These genes were classified into five groups by phylogenetic analysis. Most HIPPs had one HMA domain, while 51 from Clade I had two, and all HIPPs had good collinear relationships between species or subgenomes. In silico expression profiling revealed that 44 of the 114 wheat HIPPs were dominantly expressed in roots, 43 were upregulated under biotic stresses, and 29 were upregulated upon drought or heat treatment. Subcellular localization analysis of the cloned HIPPs from H. villosa showed that they were expressed on the plasma membrane. HIPP1-V was upregulated in H. villosa after Cd treatment, and transgenic wheat plants overexpressing HIPP1-V showed enhanced Cd tolerance, as shown by the recovery of seed-germination and root-growth inhibition by supplementary Cd. This research provides a genome-wide overview of the Triticeae HIPP genes and proved that HIPP1-V positively regulates Cd tolerance in common wheat.

Characterization of a phytochelatin synthase gene from Ipomoea pes-caprae involved in cadmium tolerance and accumulation in yeast and plants

Phytochelatin synthases (PCSs) play a crucial part in heavy metal tolerance in plants via the synthesis of phytochelatins (PCs), which can chelate heavy metals (HMs) in the vacuole and decrease cell damage. Plant PCSs are commonly designated as key genes for phytoremediation. In this study, we identified a PCS gene (IpPCS1) from Ipomoea pes-caprae and investigated its role in regulating cadmium (Cd) tolerance and accumulation. The expression of a truncated IpPCS1t in yeast could complement the Cd-sensitive phenotype of the ycf1Δ mutant strain, as well as improve the Cd tolerance of the wild-type yeast strain, while promoting Cd accumulation in the yeast cells. The expression of IpPCS1 was induced in I. pes-caprae plants under Cd treatment. Compared with IpPCS1, the lack of a C-terminal in IpPCS1t did not affect its Cd tolerance, but might restrict the zinc (Zn) detoxification in yeast. The overexpression of IpPCS1t in Arabidopsis could improve the Cd tolerance slightly and had little impact on Cd accumulation in transgenic plant. Our results indicated that IpPCS1 has certain potential application value in Cd tolerance and detoxification, therefore provides a useful genetic resource for enhancing Cd tolerance and improving the Cd phytoremediation capacity of plants or organisms. In addition, our research is the first time to discover a new possible Cd activation site in the C-terminal of IpPCS1.

Transcription Factor GmWRKY142 Confers Cadmium Resistance by Up-Regulating the Cadmium Tolerance 1-Like Genes.

Cadmium (Cd) is a widespread pollutant that is toxic to living organisms. Previous studies have identified certain WRKY transcription factors, which confer Cd tolerance in different plant species. In the present study, we have identified 29 Cd-responsive WRKY genes in Soybean [Glycine max (L.) Merr.], and confirmed that 26 of those GmWRKY genes were up-regulated, while 3 were down-regulated. We have also cloned the novel, positively regulated GmWRKY142 gene from soybean and investigated its regulatory mechanism in Cd tolerance. GmWRKY142 was highly expressed in the root, drastically up-regulated by Cd, localized in the nucleus, and displayed transcriptional activity. The overexpression of GmWRKY142 in Arabidopsis thaliana and soybean hairy roots significantly enhanced Cd tolerance and lead to extensive transcriptional reprogramming of stress-responsive genes. ATCDT1, GmCDT1-1, and GmCDT1-2 encoding cadmium tolerance 1 were induced in overexpression lines. Further analysis showed that GmWRKY142 activated the transcription of ATCDT1, GmCDT1-1, and GmCDT1-2 by directly binding to the W-box element in their promoters. In addition, the functions of GmCDT1-1 and GmCDT1-2, responsible for decreasing Cd uptake, were validated by heterologous expression in A. thaliana. Our combined results have determined GmWRKYs to be newly discovered participants in response to Cd stress, and have confirmed that GmWRKY142 directly targets ATCDT1, GmCDT1-1, and GmCDT1-2 to decrease Cd uptake and positively regulate Cd tolerance. The GmWRKY142-GmCDT1-1/2 cascade module provides a potential strategy to lower Cd accumulation in soybean.

Effects of exogenous nitric oxide and ethylenediaminetetraacetic acid on cadmium toxicity and accumulation in ryegrass

The effects of exogenous nitric oxide (NO) and ethylenediaminetetraacetic acid (EDTA) on cadmium toxicity and accumulation in ryegrass (Lolium perenne L.) were studied in a hydroponic experiment. The results show that in plants without Cd application, addition of EDTA and sodium nitroprusside (SNP, an exogenous NO donor) significantly reduced the plant height, root length, and root activity of ryegrass, and significantly increased the O2*- generation rate and H2O2 and malondialdehyde (MDA) content in the aboveground and underground parts of ryegrass. Cadmium stress significantly inhibited ryegrass growth. Addition of SNP or EDTA alleviated Cd toxicity, and addition of both had a better effect. Compared with Cd alone, the shoot height and root length in the Cd+EDTA+SNP treatment increased by 68.8 and 59.6 %, and plant fresh and dry masses by 62.6 and 60.0 %, respectively. Also, the superoxide dismutase activity in the shoots and roots increased by 32.5 and 67.6 %, the peroxidase activity by 49.8 and 67.6 %, the ascorbate peroxidase activity by 134 and 102 %, the MDA content decreased by 30.4 and 21.8 %, and the O2*- generation rate by 29.0 and 26.1 %, respectively. At the same time, Cd content in the shoots and roots increased significantly by 89.7 and 30.2 %, respectively. Overall, the results suggest that exogenous NO could enhance Cd tolerance of ryegrass, but addition of EDTA could promote plant Cd uptake. Combined application of NO and EDTA increased Cd accumulation in the aboveground parts of ryegrass. In this experiment, the treatment of 100 &#181;M CdCl2 + 0.25 mM EDTA + 50 &#956;M SNP showed the best effects in promoting Cd accumulation in ryegrass and enhancing its Cd tolerance.

Melatonin confers cadmium tolerance by modulating critical heavy metal chelators and transporters in radish plants.

Cadmium (Cd) is an environmental pollutant that causes health hazard to living organisms. Melatonin (MT) has emerged as a ubiquitous pleiotropic molecule capable of coordinating heavy metal (HM) stresses in plants. However, it remains unclear how melatonin mediates Cd homeostasis and detoxification at transcriptional and/or post-transcriptional levels in radish. Herein, the activities of five key antioxidant enzymes were increased, while root and shoot Cd contents were dramatically decreased by melatonin. A combined small RNA and transcriptome sequencing analysis showed that 14 differentially expressed microRNAs (DEMs) and 966 differentially expressed genes (DEGs) were shared between the Cd and Cd+MT conditions. In all, 23 and ten correlated miRNA-DEG pairs were identified in Con vs. Cd and Con vs. Cd+MT comparisons, respectively. Several DEGs encoding yellow stripe 1-like (YSL), heavy metal ATPases (HMA), and ATP-binding cassette (ABC) transporters were involved in Cd transportation and sequestration in radish. Root exposure to Cd2+ induced several specific signaling molecules, which consequently trigger some HM chelators, transporters, and antioxidants to achieve reactive oxygen species (ROS) scavenging and detoxification and eliminate Cd toxicity in radish plants. Notably, transgenic analysis revealed that overexpression of the RsMT1 (Metallothionein 1) gene could enhance Cd tolerance of tobacco plants, indicating that the exogenous melatonin confers Cd tolerance, which might be attributable to melatonin-mediated upregulation of RsMT1 gene in radish plants. These results could contribute to dissecting the molecular basis governing melatonin-mediated Cd stress response in plants and pave the way for high-efficient genetically engineering low-Cd-content cultivars in radish breeding programs.