The molecular mechanism of zinc and cadmium stress response in plants

ABA-regulated MAPK signaling pathway promotes hormesis in sugar beet under cadmium exposure

Sugar beet (Beta vulgaris L.) shows potential as an energy crop for cadmium (Cd) phytoremediation. To elucidate its in vivo response strategy to Cd exposure, seedlings were treated with 1, 3, and 5 mmol/L CdCl2 (Cd-1, Cd-3, and Cd-5) for 6 h, using 0 mmol/L CdCl2 (Cd-0) as the control. The results showed that Cd-3 promoted a unique "hormesis" effect, leading to superior growth performance, increased levels of chlorophyll, soluble protein, and SOD activity, and reduced MDA content in sugar beet, compared to Cd-1, Cd-5, and even Cd-0. GO and KEGG enrichments and PPI networks of transcriptomic analysis revealed that the differentially expressed genes (DEGs) were primarily involved in lipid metabolism, cellular protein catabolism, and photosynthesis. Notably, the MAPK signaling pathway was significantly enriched only under Cd-3, with the up-regulation of ABA-related core gene BvPYL9 and an increase in ABA content after 6 h of Cd exposure. Furthermore, overexpression of BvPYL9 in Arabidopsis thaliana (OE-1 and OE-2) resulted in enhanced growth (fresh weight, dry weight, and root length), as well as higher ABA and soluble protein contents under different Cd treatments. Cd-induced transcriptional responses of BvPYL9 were also evident in OE-1 and OE-2, especially at 10 µmol/L, indicated by qRT-PCR. These findings suggest that ABA-mediated MAPK signaling pathway is activated in response to Cd toxicity, with BvPYL9 being a key factor in the cascade effects for the Cd-induced hormesis in sugar beet.

The MYC2 and MYB43 transcription factors cooperate to repress HMA2 and HMA4 expression, altering cadmium tolerance in Arabidopsis thaliana

Cadmium (Cd) represents a hazardous heavy metal, prevalent in agricultural soil due to industrial and agricultural expansion. Its propensity for being absorbed by edible plants, even at minimal concentrations, and subsequently transferred along the food chain poses significant risks to human health. Accordingly, it is imperative to investigate novel genes and mechanisms that govern Cd tolerance and detoxification in plants. Here, we discovered that the transcription factor MYC2 directly binds to the promoters of HMA2 and HMA4 to repress their expression, thereby altering the distribution of Cd in plant tissues and negatively regulating Cd stress tolerance. Additionally, molecular, biochemical, and genetic analyses revealed that MYC2 interacts and cooperates with MYB43 to negatively regulate the expression of HMA2 and HMA4 and Cd stress tolerance. Notably, under Cd stress conditions, MYC2 undergoes degradation, thereby alleviating its inhibitory effect on HMA2 and HMA4 expression and plant tolerance to Cd stress. Thus, our study highlights the dynamic regulatory role of MYC2, in concert with MYB43, in regulating the expression of HMA2 and HMA4 under both normal and Cd stress conditions. These findings present MYC2 as a promising target for directed breeding efforts aimed at mitigating Cd accumulation in edible plant roots.

Posphoproteomics profiling reveals the regulatory role of a phosphorylated protein PvFBA1 in cadmium tolerance in seashore paspalum

Seashore paspalum (Paspalum vaginatum) is a warm-season and perennial turfgrass and is known for its cadmium (Cd)-stress tolerance. Here, a Phosphoproteomics analysis was performed to examine the key proteins relating to Cd tolerance in seashore paspalum. Fructose 1,6-biphosphate aldolase, PvFBA1, was identified for its phosphorylated state after exposure to Cd stress. Specifically, the phosphorylation of PvFBA1 was enhanced in several metabolic pathways, including pentose phosphate pathway (PPP), carbon fixation and biosynthesis of amino acids under Cd stress. By transforming PvFBA1 into Arabidopsis, the PvFBA1-OE plants exhibited longer roots, greater FBA activity and higher soluble sugar content than WT under 100 µM CdCl2 treatment. By expressing the PvFBA1 in yeast, a serine 50 phosphorylation site was identified as functional site. By microscale thermophoresis experiment, we indicted that PvFBA1can bind Cd directly enhancing its phosphorylation level to alleviate the damage of Cd. This finding may provide new insights into the molecular mechanisms of plants Cd tolerance.

A CC-Type Glutaredoxins GRX480 Functions in Cadmium Tolerance by Maintaining Redox Homeostasis in Arabidopsis

Cadmium (Cd) toxicity causes oxidative stress damage in plant cells. Glutaredoxins (GRXs), a type of small oxidoreductase, play a crucial role in modulating thiol redox states. However, whether GRXs act in Cd stress remains to be identified. Here, we reveal that Arabidopsis GRX480, a member of the CC-type family, enhances plant Cd stress tolerance. The GRX480 mutants exhibit enhanced sensitivity to Cd stress, manifested by shortened root, reduced biomass, lower chlorophyll and proline levels, and decreased photosynthetic efficiency compared with the wild type. The Cd concentration in GRX480 mutants is higher than the wild type, resulting from the inhibition of Cd efflux and transport genes transcription. Lower levels of GSH were detected in Cd-treated GRX480 mutants than in the wild type, indicating that GRX480 regulates plant Cd tolerance by influencing the balance between GSH and GSSG. Furthermore, the hyperaccumulation of reactive oxygen species (ROS) is associated with decreased expression of H2O2 scavenging genes in Cd-treated GRX480 mutants. Additionally, more toxic reactive carbonyl species (RCS), produced during oxidative stress, accumulate in Cd-treated GRX480 mutants than in wild type. Overall, our study establishes a critical role of GRX480 in response to Cd stress, highlighting its multifaceted contributions to detoxification and the maintenance of redox homeostasis.

Zinc/Iron-Regulated Transporter-like Protein CsZIP4 Enhances Zinc and Nitrogen Uptake and Alleviates Zinc Stresses with Nitrogen Supply in Camellia sinensis

Zinc (Zn) and nitrogen (N) are the two crucial nutrients for tea plant growth and development and contribute to the quality formation of tea fresh leaves. In this study, a zinc/iron-regulated transporter-like protein 4 gene (i.e., CsZIP4) was functionally characterized. Expression profiling showed that CsZIP4 could be induced by Zn stresses and a N deficiency. Heterologous expression of CsZIP4 in yeast revealed that CsZIP4 possessed the capacity for Zn transport but not ammonium. Moreover, CsZIP4 overexpression in Arabidopsis thaliana promoted Zn and N uptake and transport and contributed to alleviate Zn stresses by collaborating with N supply, which might be interrelated to the expression of N or Zn metabolism-related genes, such as AtNRT1.1 and AtZIP4. Additionally, CsZIP4 was localized in the plasma membrane and chloroplast, which was helpful in maintaining cellular homeostasis under a Zn excess. Furthermore, silencing of CsZIP4 in tea plants by virus-induced gene silencing increased the chlorophyll content but decreased the Zn content. Finally, the yeast one-hybrid assay demonstrated that CsbZIP2 bound to the CsZIP4 promoter. These results will shed light on the functions of CsZIP4 in the N and Zn interaction in tea plants.

Synergistic role of phenylpropanoid biosynthesis and citrate cycle pathways in heavy metal detoxification through secretion of organic acids

Excessive heavy metal contaminants in soils have serious ecological and environmental impacts, and affect plant growth and crop yields. Phytoremediation is an environmentally friendly means of lowering heavy metal concentrations in soils. In this study, we analyzed phenotypic and physiological traits, and the transcriptome and metabolome, of sheepgrass (Leymus chinensis) exposed to cadmium (Cd), lead (Pb), or zinc (Zn). Phenotypic and physiological analysis indicated that sheepgrass had strong tolerance to Cd/Pb/Zn. Transcriptomic analysis revealed that phenylpropanoid biosynthesis and organic acid metabolism were enriched among differentially expressed genes, and metabolomic analysis indicated that the citrate cycle was enriched in response to Cd/Pb/Zn exposure. Genes encoding enzymes involved in the phenylpropanoid and citrate cycle pathways were up-regulated under the Cd/Pb/Zn treatments. Organic acids significantly reduced heavy metal accumulation and improved sheepgrass tolerance of heavy metals. The results suggest that synergistic interaction of the phenylpropanoid and citrate cycle pathways in sheepgrass roots induced organic acid secretion to alleviate heavy metal toxicity. A cascade of enzymes involved in the interacting pathways could be targeted in molecular design breeding to enhance phytoremediation.

Bamboo vinegar regulates the phytoremediation efficiency of Perilla frutescens (L.) Britt. by reducing membrane lipid damage and increasing cadmium retention

The gap between serious soil heavy metals pollution and inefficient soil remediation threatens human health. This study proposed a method to improve the phytoremediation efficiency using bamboo vinegar (BV) solution and the potential mechanism was discussed. The results demonstrated that the application of BV increases the content of cadmium (Cd) in vacuole and cell wall hemicellulose 2 in leaves of Perilla frutescens. Simultaneously, it enhanced enzyme activities of superoxide dismutase and catalase in leaves. Therefore, this process alleviated the damage of Cd to functional tissues of Perilla frutescens, thus improving the tolerance of plants to Cd. Moreover, the BV application reduced the Cd content bound by root cell wall pectin fractions and insoluble phosphate, subsequently improving the ability of oxalic acids to carry Cd to the aerial parts. Consequently, the aerial parts obtained a larger amount of Cd enrichment. Overall, the Transfer Factor of Cd from roots to stems and enrichment of Cd in Perilla frutescens were maximally increased by 57.70 % and 54.03 % with the application of 50-fold and 300-fold diluted BV under 2 mg·L-1 Cd stress, respectively. The results can provide a theoretical basis for the promotion of phytoremediation of Cd-contaminated soil treatment technology.

NtZIP5A/B is involved in the regulation of Zn/Cu/Fe/Mn/Cd homeostasis in tobacco

Plants grow in soils with varying concentrations of microelements, often in the presence of toxic metals e.g. Cd. To cope, they developed molecular mechanisms to regulate metal cross-homeostasis. Understanding underlying complex relationships is key to improving crop productivity. Recent research suggests that the Zn and Cd uptake protein NtZIP5A/B [Zinc-regulated, Iron-regulated transporter-like Proteins (ZIPs)] from tobacco (Nicotiana tabacum L. v. Xanthi) is involved in the regulation of a cross-talk between the two metals. Here, we support this conclusion by showing that RNAi-mediated silencing of NtZIP5A/B resulted in a reduction of Zn accumulation and that this effect was significantly enhanced by the presence of Cd. Our data also point to involvement of NtZIP5B in regulating a cross-talk between Cu, Fe, and Mn. Using yeast growth assays, Cu (but not Fe or Mn) was identified as a substrate for NtZIP5B. Furthermore, GUS-based analysis showed that the tissue-specific activity of the NtZIP5B promoter was different in each of the Zn-/Cu-/Fe-/Mn deficiencies applied with/without Cd. The results indicate that NtZIP5B is involved in maintaining multi-metal homeostasis under conditions of Zn, Cu, Fe, and Mn deficiency, and also in the presence of Cd. It was concluded that the protein regulates the delivery of Zn and Cu specifically to targeted different root cells depending on the Zn/Cu/Fe/Mn status. Importantly, in the presence of Cd, the activity of the NtZIP5B promoter is lost in meristematic cells and increased in mature root cortex cells, which can be considered a manifestation of a defense mechanism against its toxic effects.

Efficiency of metal(loid) phytostabilization by white lupin (Lupinus albus L.), common vetch (Vicia sativa L.), and buckwheat (Fagopyrum esculentum Moench)

Erosion and leaching of metal(loid)s from contaminated sites can spread pollution to adjacent ecosystems and be a source of toxicity for living organisms. Phytostabilization consists of selecting plant species accumulating little or no metal(loid)s in aerial parts to establish a vegetation cover and thus to stabilize the contaminants in the soil. Seeds of white lupin, common vetch, and buckwheat were sown in greenhouse on soils from former French mines (Pontgibaud and Vaulry) contaminated with metal(loid)s including high concentrations of As and Pb (772 to 1064 and 121 to 12,340 mg kg-1, respectively). After 3 weeks of exposure, the growth of white lupin was less affected than that of the 2 other species probably because metal(loid) concentrations in roots and aerial parts of lupins were lower (5-20 times less Pb in lupin leaves on Pontgibaud soil and 5-10 times less As in lupin leaves on Vaulry soil than in vetch and buckwheat). To limit oxidation and/or scavenge metal(loid)s, white lupin increased the content of proline and total phenolic compounds (TPC) in leaves and roots by a factor 2 whereas buckwheat stimulated the production of TPC by a factor 1.5-2, and non-protein thiols (NPT) by factors around 1.75 in leaves and 6-12 in roots. Vetch accumulated more proline than white lupin but less NPT than buckwheat and less TPC than the 2 other plant species. The level of oxidation was however higher than in control plants for the 3 species indicating that defense mechanisms were not completely effective. Overall, our results showed that white lupin was the best species for phytostabilization but amendments should be tested to improve its tolerance to metal(loid)s.

Integrated cell wall and transcriptomic analysis revealed the mechanism underlying zinc-induced alleviation of cadmium toxicity in Cosmos bipinnatus

Plant growth is severely harmed by cadmium (Cd) contamination, while the addition of zinc (Zn) can reduce the toxic effects of Cd. However, the interaction between Cd and Zn on the molecular mechanism and cell wall of Cosmosbipinnatus is unclear. In this study, a transcriptome was constructed using RNA-sequencing. In C. bipinnatus root transcriptome data, the expression of 996, 2765, and 3023 unigenes were significantly affected by Cd, Zn, and Cd + Zn treatments, respectively, indicating different expression patterns of some metal transporters among the Cd, Zn, and Cd + Zn treatments. With the addition of Zn, the damage to the cell wall was reduced, both the proportion and content of polysaccharides in the cell wall were changed, and Cd accumulation was decreased by 32.34%. In addition, we found that Cd and Zn mainly accumulated in pectins, the content of which increased by 30.79% and 61.4% compared to the CK treatment. Thus, Zn could alleviate the toxicity of Cd to C. bipinnatus. This study revealed the interaction between Cd and Zn at the physiological and molecular levels, broadening our understanding of the mechanisms of tolerance to Cd and Zn stress in cosmos.

Protective Role of Polyethylene Glycol Towards the Damaging Effects of Cadmium

This study aimed to evaluate the role of drought-induced changes in the effects of cadmium (Cd) in plants. Cd is the most hazardous and important environmental pollutant. Water deficit is the most common environmental stress encountered by plants and affects most of the plant functions. The present study assessed the effect of Cd and water deficit on Capsicum frutescens seedlings in single and combined treatments. The seedlings of Capsicum were grown in a hydroponic solution and treated with Cd. The seedlings were subjected to water deficit with the help of polyethylene glycol (PEG). The other set of seedlings was treated with combined Cd + PEG. In the absence of PEG, maximum Cd accumulation was observed. The root and shoot growth of the seedlings were affected under all treatments with maximum inhibition in Cd. Pigment, protein and sugar contents and nitrate reductase activity decreased significantly in all treatments, while proline content increased. Induction of oxidative damage occurred through the formation of free radicals which caused alteration in electrolyte leakage, lipid peroxidation and activities of antioxidant enzymes, viz. superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase and non-enzymatic non-protein thiol content and ascorbic acid in the stressed seedlings. Water deficit buttressed the toxic effect of Cd on chilli seedlings.

Influence of Foliar Zinc Application on Cadmium and Zinc Bioaccessibility in Brassica chinensis L.: In Vitro Digestion and Chemical Sequential Extraction

Foliar zinc (Zn) application can affect the accumulation and bioaccessibility of cadmium (Cd) and Zn in crops. However, the mechanisms by which foliar Zn application influences Cd and Zn bioaccessibility remain elusive. This study examined the effects of spraying ZnSO4 and ZnNa2EDTA on bioaccessibility and chemical forms of Cd and Zn in pakchoi (Brassica chinensis L.) shoots and evaluated human health risks via pakchoi consumption. Spraying ZnSO4 reduced the concentrations of ethanol-extractable (Fethanol) and deionized water-extractable (Fd-H2O) Cd, as well as the corresponding bioaccessible Cd concentrations (20.3-66.4%) and attendant health risks of Cd, whereas spraying high-dose ZnNa2EDTA significantly increased the concentrations of both Cd forms and bioaccessible Cd. Spraying ZnSO4 and high-dose ZnNa2EDTA significantly increased the concentrations of Zn in Fethanol and Fd-H2O and the corresponding bioaccessible Zn concentrations (0.8-8.3-fold). Fethanol and Fd-H2O were the primary sources of bioaccessible Cd and Zn, contributing more than 59% of the bioaccessible Cd and Zn. These results indicate that foliar Zn application can affect Cd and Zn bioaccessibility in pakchoi mainly by modulating Cd and Zn in Fethanol and Fd-H2O. These findings provide scientific support for the development of more efficient measures to produce safe and high-quality leafy vegetables from Cd-polluted soils.

Integrative study of transcriptome and microbiome to reveal the response of Rhododendron decorum to cadmium stress

The anomalies of cadmium (Cd) in karst region pose a severe threat to plant growth and development. In this study, the responses of Rhododendron decorum to Cd stress were investigated at physiological, molecular, and endophytic microbial levels, and the potential correlation among these responses was assessed. The Cd stress impeded R. decorum growth and led to an increase in malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels, as well as enhanced superoxide dismutase (SOD) and catalase (CAT) activities. Meanwhile, Cd stress increased the Cd (up to 80 times compared to the control), sodium (Na), aluminum (Al), and zinc (Zn) contents, while decreased the magnesium (Mg) and manganese (Mn) contents in R. decorum leaves. Transcriptome suggested that Cd significantly regulated the pathways including "protein repair", "hormone-mediated signaling pathway", and "ATP-binding cassette (ABC) transporters". Additionally, q-PCR analysis showed that Cd stress significantly up-regulated the expressions of ABCB19-like and pleiotropic drug resistance, while down-regulated the expressions of indole-3-acetic acid-amido synthetase and cytokinin dehydrogenase. The Cd stress influenced the composition of endophytic microbial communities in R. decorum leaves and enhanced the interspecific bacterial associations. Furthermore, the bacterial genera Achromobacter, Aureimonas and fungal genus Vishniacozyma exhibited a high degree of connectivity with other nodes in networks constructed by the metal element contents, differentially expressed genes (DEGs), and microbial communities, respectively. These findings provide a comprehensive insight into the response of R. decorum to Cd-induced stress, which might facilitate the breeding of the Cd-tolerant R. decorum.

Natural variation of TBR confers plant zinc toxicity tolerance through root cell wall pectin methylesterification

Zinc (Zn) is an essential micronutrient but can be cytotoxic when present in excess. Plants have evolved mechanisms to tolerate Zn toxicity. To identify genetic loci responsible for natural variation of plant tolerance to Zn toxicity, we conduct genome-wide association studies for root growth responses to high Zn and identify 21 significant associated loci. Among these loci, we identify Trichome Birefringence (TBR) allelic variation determining root growth variation in high Zn conditions. Natural alleles of TBR determine TBR transcript and protein levels which affect pectin methylesterification in root cell walls. Together with previously published data showing that pectin methylesterification increase goes along with decreased Zn binding to cell walls in TBR mutants, our findings lead to a model in which TBR allelic variation enables Zn tolerance through modulating root cell wall pectin methylesterification. The role of TBR in Zn tolerance is conserved across dicot and monocot plant species.

Multi-biomarker approach reveals the effects of heavy metal bioaccumulation in the foundation species Prosopis laevigata (Fabaceae)

Mining is a major economic activity in many developing countries. However, it disturbs the environment, producing enormous quantities of waste, known as mine tailings, which can have deleterious environmental impact, due to their high heavy metals (HM) content. Often, foundation species that establish on mine tailings are good candidates to study the effects of HM bioaccumulation at different levels of biological organization. Prosopis laevigata is considered a HM hyperaccumulator which presents attributes of a foundation species (FS) and establishes naturally on mine tailings. We evaluated the bioaccumulation of Cu, Pb, and Zn in P. laevigata foliar tissue, the leaf micro- and macro-morphological characters, DNA damage, and population genetic effects. In total, 80 P. laevigata individuals (20/site) belonging to four populations: The individuals from both sites (exposed and reference) bioaccumulated HMs (Pb > Cu > Zn). However, in the exposed individuals, Pb and Cu bioaccumulation was significantly higher. Also, a significant effect of macro- and micro-morphological characters was registered, showing significantly lower values in individuals from the exposed sites. In addition, we found significant differences in genotoxic damage in P. laevigata individuals, between the exposed and reference sites. In contrast, for the micro-morphological characters, none of the analyzed metals had any influence. P. laevigata did not show significant differences in the genetic structure and diversity between exposed and reference populations. However, four haplotypes and four private alleles were found in the exposed populations. Since P. laevigata is a species that establishes naturally in polluted sites and bioaccumulates HM in its foliar tissues, the resulting genetic, individual and population effects have not been severe enough to show detrimental effects; hence, P. laevigata can be a useful tool in phytoremediation strategies for soils polluted with Pb and Cu, maintaining its important ecological functions.

GhRCD1 promotes cotton tolerance to cadmium by regulating the GhbHLH12-GhMYB44-GhHMA1 transcriptional cascade

Heavy metal pollution poses a significant risk to human health and wreaks havoc on agricultural productivity. Phytoremediation, a plant-based, environmentally benign, and cost-effective method, is employed to remove heavy metals from contaminated soil, particularly in agricultural or heavy metal-sensitive lands. However, the phytoremediation capacity of various plant species and germplasm resources display significant genetic diversity, and the mechanisms underlying these differences remain hitherto obscure. Given its potential benefits, genetic improvement of plants is essential for enhancing their uptake of heavy metals, tolerance to harmful levels, as well as overall growth and development in contaminated soil. In this study, we uncover a molecular cascade that regulates cadmium (Cd2+) tolerance in cotton, involving GhRCD1, GhbHLH12, GhMYB44, and GhHMA1. We identified a Cd2+-sensitive cotton T-DNA insertion mutant with disrupted GhRCD1 expression. Genetic knockout of GhRCD1 by CRISPR/Cas9 technology resulted in reduced Cd2+ tolerance in cotton seedlings, while GhRCD1 overexpression enhanced Cd2+ tolerance. Through molecular interaction studies, we demonstrated that, in response to Cd2+ presence, GhRCD1 directly interacts with GhbHLH12. This interaction activates GhMYB44, which subsequently activates a heavy metal transporter, GhHMA1, by directly binding to a G-box cis-element in its promoter. These findings provide critical insights into a novel GhRCD1-GhbHLH12-GhMYB44-GhHMA1 regulatory module responsible for Cd2+ tolerance in cotton. Furthermore, our study paves the way for the development of elite Cd2+-tolerant cultivars by elucidating the molecular mechanisms governing the genetic control of Cd2+ tolerance in cotton.

Rhodopseudomonas palustris shapes bacterial community, reduces Cd bioavailability in Cd contaminated flooding paddy soil, and improves rice performance

Photosynthetic bacteria (PSB) are suitable to live and remediate cadmium (Cd) in the slightly oxygenated or anaerobic flooding paddy field. However, there is currently limited study on the inhibition of Cd accumulation in rice by PSB, and the relevant mechanisms has yet to be elucidated. In the current study, we firstly used Rhodopseudomonas palustris SC06 (a typical PSB) as research target and combined physiology, biochemistry, microbiome and metabolome to evaluate the mechanisms of remeding Cd pollution in paddy field and inhibiting Cd accumulation in rice. Microbiome analysis results revealed that intensive inoculation with R. palustris SC06 successfully survived and multiplied in flooding paddy soil, and significantly increased the relatively abundance of anaerobic bacteria including Desulfobacterota, Anaerolineaceae, Geobacteraceae, and Gemmatimonadaceae by 46.40 %, 45.00 %, 50.12 %, and 21.30 %, respectively. Simultaneously, the structure of microbial community was regulated to maintain relative stability in the rhizosphere soil of rice under Cd stress. In turn, these bacteria communities reduced bioavailable Cd and enhanced residual Cd in soil, and induced the upregulation of sugar and organic acids in the rice roots, which further inhibited Cd uptake in rice seedlings, and dramatically improved the photosynthetic efficiency in the leaves and the activities of antioxidative enzymes in the roots. Finally, Cd content of the roots, stems, leaves, and grains significantly decreased by 38.14 %, 69.10 %, 83.40 %, and 37.24 % comparing with the control, respectively. This study provides a new strategy for the remediation of Cd-contaminated flooding paddy fields and the safe production of rice.

Changes of Cd content in chloroplasts are mirrored by the activity of photosystem I, but not by photosystem II

We searched for a direct Cd action on the photosynthetic electron transport chain using induced chlorophyll fluorescence and P700 light absorption. Young barley and maize plants were treated with Cd in concentrations of toxic (80 μM) and nearly lethal (250 μM). The maximal and relative photochemical activities of PSI, its major limitation at the donor side, and partially acceptor-side limitation of PSII changed in agreement with Cd accumulation in the corresponding chloroplasts. Acceptor-side limitation of PSII increased with a direct Cd action at 80 μM that was overcome with an indirect Cd action at 250 μM. These alterations can be explained by Cd/Cu substitution in plastocyanin. The photochemical and nonphotochemical quenching by PSII varied diversely which cannot be explained unambiguously by any mechanism. The limitations of PSI [Y(ND), Y(NA)] and PSII (qC) were compared for the first time. They were ranged: Y(NA) < qC < Y(ND).

Effects of cadmium and zinc interactions on the physiological biochemistry and enrichment characteristics of Iris pseudacorus

Compound pollution with cadmium (Cd) and zinc (Zn) is common in nature. The effects of compounded Cd and Zn on the growth and development of Iris pseudacorus in the environment and the plant's potential to remediate heavy metals in the environment remain unclear. In this study, the effects of single and combined Cd and Zn stress on I. pseudacorus growth and the enrichment of heavy metals in I. pseudacorus seedlings were investigated. The results showed that under Cd (160 μM) and Zn (800 μM) stress, plant growth was significantly inhibited and photosynthetic performance was affected. Cd+Zn200 (160 μM + 200 μM) reduced the levels of malondialdehyde, hydrogen peroxide, and non-protein thiols by 31.29%, 53.20%, and 13.29%, respectively, in the aboveground tissues compared with levels in the single Cd treatment. However, Cd+Zn800 (160 μM + 800 μM) had no effect. Cd and Zn800 inhibited the absorption of mineral elements, while Zn200 had little effect on plants. Compared with that for Cd treatment alone, Cd + Zn200 and Cd+Zn800 reduced the Cd content in aboveground tissues by 54.15% and 49.92%, respectively, but had no significant effect on Cd in the root system. Zn significantly reduced the Cd content in subcellular components and limited the content and proportion of Cd extracted using water and ethanol. These results suggest that a low supply of Zn reduces Cd accumulation in aboveground tissues by promoting antioxidant substances and heavy metal chelating agents, thus protecting the photosynthetic systems. The addition of Zn also reduced the mobility and bioavailability of Cd to alleviate its toxicity in I. pseudacorus.

Upregulation of antioxidant enzymes contribute to the elevated tolerance of Juncus acutus offspring from metal contaminated environments

Long-term environmental exposure to metals e.g. zinc (Zn), may allow saltmarsh halophytes to develop metal tolerance to improve the chance of survival of their progeny in future metal-contaminated scenarios. Juncus acutus seeds were collected from mature parents (F0) inhabiting a legacy Zn-contaminated location (Cockle Creek) and an uncontaminated reference location (Swansea) of Lake Macquarie, NSW, Australia. Seeds (J. acutus) were exposed to Zn (0.00 mM (control), 0.01 mM (effective concentration, EC10) and 0.74 mM (EC50)) and resultant germinants (F1) were allowed to grow until 15 days. Seedling growth parameters i.e. biomass, root length and 1st leaf length, and seedling biochemical responses i.e. superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) antioxidant enzyme activity and lipid peroxidation products, malondialdehyde (MDA), were examined in order to assess if enzymes may be implicated in conferring tolerance to the offspring of metal-exposed parents. Control locations exhibited significantly greater declines in biomass and root length with Zn dose compared to seed from contaminated locations, suggesting F1 offspring from contaminated parents were conferred tolerance to Zn. Furthermore, significant upregulation of CAT and GPx enzymes were evident in the seedlings derived from parents of contaminated locations. These are the antioxidative enzymes responsible for minimizing metal-induced oxidative stress, and may, in part, be responsible for increasing seedling fitness and observed tolerance.

Physiological, transcriptome and gene functional analysis provide novel sights into cadmium accumulation and tolerance mechanisms in kenaf

Kenaf is considered to have great potential for remediation of heavy metals in ecosystems. However, studies on molecular mechanisms of root Cd accumulation and tolerance are still inadequate. In this study, two differently tolerant kenaf cultivars were selected as materials and the physiological and transcriptomic effects were evaluated under Cd stress. This study showed that 200 µmol/L CdCl2 treatment triggered the reactive oxygen species (ROS) explosion and membrane lipid peroxidation. Compared with the Cd-sensitive cultivar 'Z', the Cd-tolerant cultivar 'F' was able to resist oxidative stress in cells by producing higher antioxidant enzyme activities and increasing the contents of ascorbic acid (AsA) and glutathione (GSH). The root cell wall of 'F' exhibited higher polysaccharide contents under Cd treatment, providing more Cd-binding sites. There were 3,439 differentially expressed genes (DEGs) that were co-regulated by Cd treatment in two cultivars. Phenylpropanoid biosynthesis and plant hormone signal transduction pathways were significantly enriched by functional annotation analysis. DEGs associated with pectin, cellulose, and hemi-cellulose metabolism were involved in Cd chelation of root cell wall; V-ATPases, ABCC3 and Narmp3 could participated in vacuolar compartmentalization of Cd; PDR1 was responsible for Cd efflux; the organic acid transporters contributed to the absorption of Cd in soil. These genes might have played key roles in kenaf Cd tolerance and Cd accumulation. Moreover, HcZIP2 was identified to be involved in Cd uptake and transport in kenaf. Our findings provide a deeper understanding of the molecular pathways underlying Cd accumulation and detoxification mechanisms in kenaf.

Alleviating the adverse effects of Cd-Pb contamination through the application of silicon fertilizer: Enhancing soil microbial diversity and mitigating heavy metal contamination

The use of silicon fertilizer (SF) as a means of remediating cadmium (Cd) and lead (Pb) pollution has proven to be beneficial. However, the mechanism via which SF enhances soil quality and crop productivity under Cd- and Pb-contaminated soil (S) remains unclear. This study investigated the impacts of chemical fertilizer, mineral SF (MSF), and organic SF (OSF) on microbial community structure, activity of nutrient acquisition enzymes, and growth of tobacco in the presence of S condition. SF significantly reduced the contents of Cd and Pb in soil under S condition by 6.92-42.43% and increased plant height and leaf area by 15.27-81.77%. Moreover, the use of SF was observed to increase the efficiency of soil carbon and phosphorus cycling under S condition by 6.88-23.08%. Concurrently, SF was found to play a crucial role in facilitating the establishment of a complex, efficient, and interdependent molecular ecological network among soil microorganisms. In this context, Actinobacteriota, Bacteroidota, Ascomycota, and Basidiomycota were observed to be integral components of this network. SF was found to have a substantial positive impact on the metabolic functions and organismal systems of soil microorganisms. Moreover, the combined utilization of the Mantel test and partial least squares path model provided empirical evidence supporting the assertion that the administration of SF had a positive impact on both soil nutrient acquisition enzyme activity and tobacco growth, which was attributed to the enhancement of soil microbial diversity resulting from the application of SF. Furthermore, compared with MSF, OSF has advantages in reducing soil Pb and Cd content, promoting tobacco agronomic traits, increasing the number of key microbial communities, and maintaining the structural stability of microbial networks. The aforementioned findings, therefore, suggest that the OSF played a pivotal role in alleviating the adverse impacts of S, thereby demonstrating its efficacy in this particular process.

Stable Isotope Analyses Reveal Impact of Fe and Zn on Cd Uptake and Translocation by Theobroma cacao

High concentrations of toxic cadmium (Cd) in soils are problematic as the element accumulates in food crops such as rice and cacao. A mitigation strategy to minimise Cd accumulation is to enhance the competitive uptake of plant-essential metals. Theobroma cacao seedlings were grown hydroponically with added Cd. Eight different treatments were used, which included/excluded hydroponic or foliar zinc (Zn) and/or iron (Fe) for the final growth period. Analyses of Cd concentrations and natural stable isotope compositions by multiple collector ICP-MS were conducted. Cadmium uptake and translocation decreased when Fe was removed from the hydroponic solutions, while the application of foliar Zn-EDTA may enhance Cd translocation. No significant differences in isotope fractionation during uptake were found between treatments. Data from all treatments fit a single Cd isotope fractionation model associated with sequestration (seq) of isotopically light Cd in roots and unidirectional mobilisation (mob) of isotopically heavier Cd to the leaves (ε114Cdseq-mob = -0.13‱). This result is in excellent agreement with data from an investigation of 19 genetically diverse cacao clones. The different Cd dynamics exhibited by the clones and seen in response to different Fe availability may be linked to similar physiological processes, such as the regulation of specific transporter proteins.

Assessment of metal pollution and effects of physicochemical factors on soil microbial communities around a landfill

The physicochemical properties, chemical fractions of six metals (Cu, Zn, Pb, Cd, Cr, and Mn), and microbial communities of soil around a typical sanitary landfill were analyzed. The results indicate that soils around the landfill were from neutral to weak alkalinity. The contents of organic matter (OM), total nitrogen (TN), total phosphorous (TP), and activities of catalase, cellulase, and urease were significantly higher in landfill soils than those in background soils. Negative correlations were found between pH and metals. Cr was the dominant metal. Cu, Pb, Cr, and Mn were accumulated in the nearby farmland soils. Cd had the highest percentage of exchangeable fraction (33.7%-51.8%) in landfill and farmland soils, suggesting a high bioavailability to the soil environment affected by the landfill. Pb, Cr, and Mn existed mostly in oxidable fraction, and Cu and Zn were dominant in residual fraction. There was a low risk of soil metals around the landfill based on the RI values, while according to RAC classification, Cd had high to very high environmental risk. The MisSeq sequencing results showed that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla of bacteria, and the most abundant phylum of fungi was Ascomycota. The NMDS analysis revealed that the landfill could influence soil fungal communities more intensely than bacterial communities. TN, cellulase, and bioavailable metals (Pb-Bio and Cr-Bio) were identified to have main influences on microbial communities. Pb-Bio was the most dominant driving factor for bacterial community structures. For fungi, Pb-Bio was significantly negatively related to Olpidiomycota and Cr-Bio had a significantly negative correlation with Ascomycota. It manifests that bioavailable metals play important roles in assessing environmental risks and microbial community structures of soil around landfill.

Uptake and transport mechanisms of rare earth hyperaccumulators: A review

Due to their use in a number of advanced electronic technologies, Rare earth elements (REEs) have recently emerged as a key strategic resource for many nations worldwide. The significant increase in demand for REEs has thus greatly increased the mining of these substances, but this industrial-scale expansion of mining activities also poses potential risks to the surrounding environment, flora, fauna, and humans. Hence efficient REE remediation is one potential remediation process involving in situ clean-up of contaminated soil which has gained much attention in recent years, due to its low cost and lack of secondary pollution. However, some crucial aspects of phytoremediation, such as the precise-mechanisms of absorption, transport, and tolerance of REEs by hyperaccumulators -are poorly understood. This review briefly discusses the environmental risks associated with excess REEs, the efficacy of phytoremediation technologies coupled with, appropriate hyperaccumulator species to migrate REEs exposure. While REEs hyperaccumulator species should ideally be large-biomass trees and shrubs suitable for cropping in subtropical regions areas, such species have not yet been found. Specifically, this review focuses on the factors affecting the bioavailability of REEs in plants, where organic acids are critical ligands promoting efficient transport and uptake. Thus the uptake, transport, and binding forms of REEs in the above-ground parts of hyperaccumulators, especially the transporters isolated from the heavy metal transporter families, are discussed in detail. Finally, having summarized the current state of research in this area, this review proceeds to discuss current knowledge gaps and research directions. With a focus on hyperaccumulators, this review serves as a basis for future phytoremediation strategies of rare earth mining-impacted environments and addresses ecosystem/environmental degradation issues resulting from such mining activity.

OsPDR20 is an ABCG metal transporter regulating cadmium accumulation in rice

Cadmium (Cd) is a non-essential toxic heavy metal, seriously posing high environmental risks to human health. Digging genetic resources relevant to functional genes is important for understanding the metal absorption and accumulation in crops and bioremediation of Cd-polluted environments. This study investigated a functionally uncharacterized ATP binding cassette transporter G family (ABCG) gene encoding a Pleiotropic Drug Resistance 20 (PDR20) type metal transporter which is localized to the plasma membrane of rice. OsPDR20 was transcriptionally expressed in almost all tissues and organs in lifespan and was strongly induced in roots and shoots of young rice under Cd stress. Ectopic expression of OsPDR20 in a yeast mutant ycf1 sensitive to Cd conferred cellular tolerance with less Cd accumulation. Knockdown of OsPDR20 by RNA interference (RNAi) moderately attenuated root/shoot elongation and biomass, with reduced chlorophylls in rice grown under hydroponic medium with 2 and 10 µmol/L Cd, but led to more Cd accumulation. A field trial of rice grown in a realistic Cd-contaminated soil (0.40 mg/kg) showed that RNAi plants growth and development were also compromised compared to wild-type (WT), with smaller panicles and lower spikelet fertility but little effect on yield of grains. However, OsPDR20 suppression resulted in unexpectedly higher levels of Cd accumulation in rice straw including lower leaves and culm and grain. These results suggest that OsPDR20 is actively involved in Cd accumulation and homeostasis in rice crops. The increased Cd accumulation in the RNAi plants has the potential application in phytoremediation of Cd-polluted wetland soils.

Transcriptome analysis reveals the role of polysaccharide biosynthesis in the detoxification of Dendrobium nobile under zinc stress

Plants can bind excessive heavy metals by synthesizing compounds to alleviate the harm caused by heavy metals. To reveal the mechanism by which Dendrobium nobile alleviates zinc stress, metabolome combined transcriptome analysis was used in this research. The results showed that zinc was mainly enriched in the roots and leaves and the biomass of the roots and leaves of D. nobile decreased significantly by 18.21 % and 49.22 % (P < 0.05) compared to the control (CK), respectively. Meanwhile, the contents of nonprotein thiol(NPT), glutathione(GSH), and phytochelatins (PCs) in the roots were significantly increased by 48.8 %, 78.3 %, and 45.4 % compared to CK, respectively. Through TEM testing, it was found that D. nobile exhibited toxic symptoms. Metabolome analysis showed that the metabolites of D. nobile under zinc stress were mainly enriched in biosynthesis of other secondary metabolites and carbohydrate metabolism. Nova-seq results identified 1202 differentially expressed genes(DEGs), of which 603 were upregulated and 599 were downregulated. Through GO and KEGG annotation analysis of these DEGs, it was found that PMR6 and PECS-2.1, SS1 and GLU3 genes were significantly upregulated, leading to an increase in the biosynthesis of xylan, pectin, starch and other polysaccharides in D. nobile. These polysaccharides can form a "Polysaccharide-Zn" with excess zinc. Meanwhile, the GSTs in glutathione metabolism were significantly upregulated, leading to a significant increase in the content of NPT, GSH, and PCs. These zinc complexes were transported to vacuoles through ABC transporters for compartmentalization, effectively alleviating the damage of zinc. The results can provide new insights for phytoremediation and quality assurance of medicinal D. nobile.

A Pseudomonas Plant Growth Promoting Rhizobacterium and Arbuscular Mycorrhiza differentially modulate the growth, photosynthetic performance, nutrients allocation, and stress response mechanisms triggered by a mild Zinc and Cadmium stress in tomato

This study aimed to assess the effectiveness of plant growth-promoting rhizobacteria (PGPR; Pseudomonas strain So_08) and arbuscular mycorrhizal fungi (AMF; Rhizoglomus irregulare BEG72 and Funneliformis mosseae BEG234) in mitigating the detrimental effects of cadmium (Cd) and zinc (Zn) stress in tomato plants. Plant biomass, root morphology, leaf relative water content, membrane stability, photosynthetic performance, chlorophyll content, and heavy metals (HMs) accumulation were determined. Furthermore, an ionomic profile was conducted to investigate whether microbial inoculants affected the uptake and allocation of macro- and micronutrients. Metabolomics with pathway analysis of both roots and leaves was performed to unravel the mechanisms underlying the differential responses to HMs stress. The findings revealed that the levels of HMs did not significantly affect plant growth parameters; however, they affected membrane stability, photosynthetic performance, nutrient allocation, and chlorophyll content. Cadmium was mainly accumulated in roots, whilst Zn exhibited accumulation in various plant organs. Our findings demonstrate the beneficial effects of PGPR and AMF in mitigating Cd and Zn stress in tomato plants. The microbial inoculations improved physiological parameters and induced differential accumulation of macro- and micronutrients, modulating nutrient uptake balance. These results provide insights into the mechanisms underlying the plant-microbe interactions and highlight the differential modulation of the biosynthetic pathways of secondary metabolites related to oxidative stress response, membrane lipids stability, and phytohormone crosstalk.

NPs-Ca promotes Cd accumulation and enhances Cd tolerance of rapeseed shoots by affecting Cd transfer and Cd fixation in pectin

The use of rapeseed (Brassica napus) as a hyperaccumulator plant has shown great promise for the remediation of cadmium (Cd) contaminated soils. Nanosized materials (NPs) have been shown to mitigate heavy metal toxicity in plants, but it is unknown how l-aspartate nano-calcium (NPs-Ca) affects Cd uptake, transport, and tolerance in rapeseed. A soil pot experiment was conducted with two treatments: a control treatment (CK) with 2.16 g CaCl2 and NPs-Ca treatment with 6.00 g NPs-Ca, to evaluate the effects and mechanisms of NPs-Ca on Cd tolerance in rapeseed. Compared to CaCl2, NPs-Ca promoted Cd transportation from roots to shoots by up-regulating the expression of Cd transport genes (ABCC12, HMA8, NRAM6, ZIP6, CAX4, PCR2, and HIP6). Therefore, NPs-Ca increased Cd accumulation in rapeseed shoots by 39.4%. Interestingly, NPs-Ca also enhanced Cd tolerance in the shoots, resulting in lower hydrogen peroxide (H2O2) accumulation and proline content, as well as higher antioxidant enzyme activities (POD, CAT). Moreover, NPs-Ca reduced the activity of pectin-degrading enzymes (polygalacturonase: PG, β-galactosidase: β-GAL), promoted the activity of pectin methyl esterase (PME), and changed transcription levels of related genes (PME, PMEI, PG, PGIP, and β-GAL). NPs-Ca treatment also significantly increased the Cd content in cell walls by 59.8%, that is, more Cd was immobilized in cell walls, and less Cd entered organelles in shoots of NPs-Ca treatment due to increased pectin content and degree of pectin demethylation. Overall, NPs-Ca increased Cd accumulation in rapeseed shoots by promoting Cd transport from roots to shoots. And meantime, NPs-Ca enhanced Cd tolerance of shoots by inhibiting pectin degradation, promoting pectin demethylation and increasing Cd fixation in pectin. These findings suggest that NPs-Ca can improve the potential of rapeseed as a hyperaccumulator for the remediation of Cd-contaminated soil and the protection of the environment. Furthermore, the study provides a theoretical basis for the application of NPs-Ca in the phytoremediation of Cd-contaminated soils with hyperaccumulating plants.

Populus euphratica plant cadmium resistance 2 mediates Cd tolerance by root efflux of Cd ions in poplar

KEY MESSAGE

Populus euphratica PePCR2 increases Cd resistance by functioning as a Cd extrusion pump and by mediating the expression of genes encoding other transporters. Cadmium (Cd) is a non-essential, toxic metal that negatively affects plant growth. Plant cadmium resistance (PCR) proteins play key roles in the response to heavy metal stress. In this study, we isolated the gene PePCR2 encoding a plant PCR from Populus euphratica. PePCR2 gene transcription was induced by Cd, and its transcript level peaked at 24 h after exposure, at a level approximately 18-fold higher than that at 0 h. The PePCR2 protein was localized to the plasma membrane. Compared with yeast cells harboring the empty vector, yeast cells expressing PePCR2 showed enhanced Cd tolerance and a lower Cd content. Compared with wild-type (WT) plants, poplar overexpressing PePCR2 showed higher Cd resistance. Net Cd2+ efflux measurements showed that Cd2+ efflux from the roots was 1.5 times higher in the PePCR2-overexpressing plants than in WT plants. Furthermore, compared with WT plants, the PePCR2-overexpressing plants showed increased transcript levels of ABCG29, HMA5, PDR2, YSL7, and ZIP1 and decreased transcript levels of NRAMP6, YSL3, and ZIP11 upon exposure to Cd. These data show that PePCR2 increased Cd resistance by acting as a Cd extrusion pump and/or by regulating other Cd2+ transporters to decrease Cd toxicity in the cytosol. The results of this study identify a novel plant gene with potential applications in Cd removal, and provide a theoretical basis for reducing Cd toxicity and protecting food safety.

The Potential of Bioaugmentation-Assisted Phytoremediation Derived Maize Biomass for the Production of Biomethane via Anaerobic Digestion

Anthropogenic behaviors are causing the severe build-up of heavy metal (HM) pollutants in the environment, particularly in soils. Amongst a diversity of remediation technologies, phytoremediation is an environmentally friendly technology that, when coupling tolerant plants to selected rhizospheric microorganisms, can greatly stimulate HM decontamination of soils. Maize (Zea mays) is a plant with the reported capacity for HM exclusion from contaminated soil but also has energetic importance. In this study, Zea mays was coupled with Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), and Cupriavidus sp. strain 1C2, a plant growth-promoting rhizobacteria (PGPR), as a remediation approach to remove Cd and Zn from an industrial contaminated soil (1.2 mg Cd kg-1 and 599 mg Zn kg-1) and generate plant biomass, by contrast to the conservative development of the plant in an agricultural (with no metal pollution) soil. Biomass production and metal accumulation by Z. mays were monitored, and an increase in plant yield of ca. 9% was observed after development in the contaminated soil compared to the soil without metal contamination, while the plants removed ca. 0.77% and 0.13% of the Cd and Zn initially present in the soil. The resulting biomass (roots, stems, and cobs) was used for biogas generation in several biomethane (BMP) assays to evaluate the potential end purpose of the phytoremediation-resulting biomass. It was perceptible that the HMs existent in the industrial soil did not hinder the anaerobic biodegradation of the biomass, being registered biomethane production yields of ca. 183 and 178 mL of CH4 g-1 VS of the complete plant grown in non-contaminated and contaminated soils, respectively. The generation of biomethane from HM-polluted soils' phytoremediation-derived maize biomass represents thus a promising possibility to be a counterpart to biogas production in an increasingly challenging status of renewable energy necessities.

Increased ascorbic acid synthesis by overexpression of AcGGP3 ameliorates copper toxicity in kiwifruit

The widespread application of copper (Cu) -based fertilizers and pesticides could increase the accumulation of Cu in kiwifruit. According to a global survey, red- and yellow-fleshed kiwifruit contained more elevated amounts of Cu than green-fleshed kiwifruit due to weaker disease resistance and higher use of Cu pesticides. Intriguingly, our research revealed that external and endogenous ascorbic acid (AsA) reduced the phenotypic and physiological injury of Cu toxicity in kiwifruit. Cu stress assays and transcriptional analysis have shown that Cu treatment for 12 h significantly increased the AsA content in kiwifruit leaves and up-regulated key genes involved in AsA biosynthesis, such as GDP-L-galactose phosphorylase3 (GGP3) and GDP-mannose-3',5'-epimerase (GME). Overexpressing GGP3 in transgenic kiwifruit significantly increased the endogenous AsA content of kiwifruit, which was beneficial in mitigating Cu toxicity by decreasing levels of reactive oxygen species, malondialdehyde, and electrolyte leakage, as well as reducing damage to the chloroplast structure and photosystem II. This study presented a novel strategy to ameliorate plant Cu stress by increasing the endogenous antioxidant (AsA) content through transgenesis.

Reduction in PLANT DEFENSIN 1 expression in Arabidopsis thaliana results in increased resistance to pathogens and zinc toxicity

Ectopic expression of defensins in plants correlates with their increased capacity to withstand abiotic and biotic stresses. This applies to Arabidopsis thaliana, where some of the seven members of the PLANT DEFENSIN 1 family (AtPDF1) are recognised to improve plant responses to necrotrophic pathogens and increase seedling tolerance to excess zinc (Zn). However, few studies have explored the effects of decreased endogenous defensin expression on these stress responses. Here, we carried out an extensive physiological and biochemical comparative characterization of (i) novel artificial microRNA (amiRNA) lines silenced for the five most similar AtPDF1s, and (ii) a double null mutant for the two most distant AtPDF1s. Silencing of five AtPDF1 genes was specifically associated with increased aboveground dry mass production in mature plants under excess Zn conditions, and with increased plant tolerance to different pathogens - a fungus, an oomycete and a bacterium, while the double mutant behaved similarly to the wild type. These unexpected results challenge the current paradigm describing the role of PDFs in plant stress responses. Additional roles of endogenous plant defensins are discussed, opening new perspectives for their functions.

Unveiling Cacao Rootstock-Genotypes with Potential Use in the Mitigation of Cadmium Bioaccumulation

The accumulation of high cadmium (Cd) levels in cacao beans (Theobroma cacao) generate several commercial and health issues. We hypothesized that cacao phenotypic and genotypic diversity could provide new insights to decrease Cd accumulation in cacao beans. Nine cacao rootstock genotypes were evaluated for up to 90 days under 0, 6, and 12 (mg·kg-1) of CdCl2 exposure and Cd content and plant growth dynamics were measured in leaves, stems, and roots. Data revealed that all cacao genotypes studied here were highly tolerant to Cd, since they presented tolerance index ≥ 60%. In shoots, EET61 and PA46 presented the higher (~270 mg·kg DW-1) and lower (~20 mg·kg DW-1) Cd concentration, respectively. Accordingly, only the EET61 showed an increase in the shoot cadmium translocation factor over the 90 days of exposure. However, when analyzing cadmium allocation to different organs based on total plant dry mass production, none of the genotypes maintained high Cd compartmentalization into roots, since P46, which was the genotype with the highest allocation of Cd to the roots, presented only 20% of total cadmium per plant in this plant organ and 80% allocated into the shoots, under Cd 12 (mg·kg-1) and after 90 days of exposure. Thus, genotypic/phenotypic variability in cacao rootstocks may provide valuable strategies for maximizing the reduction in Cd content in shoots. In this sense, IMC67 and PA46 were the ones that stood out in the present study.

Cadmium up Taking and Allocation in Wood Species Associated to Cacao Agroforestry Systems and Its Potential Role for Phytoextraction

Trees in cacao Agroforestry systems (AFS) may present a high potential for cadmium (Cd) phytoextraction, helping to reduce Cd in cacao (Theobroma cacao L.) plants grown in contaminated soils. To assess this potential, four forest fine-woody species commonly found in cacao high-productive sites in Colombia (Tabebuia rosea, Terminalia superba, Albizia guachapele, and Cariniana pyriformis) were exposed to contrasting CdCl2 contamination levels (0, 6, and 12 ppm) on a hydroponic medium. Growth dynamics, tolerance index (TI), and Cd concentration and allocation in leaves, stems, and roots were evaluated for up to 90 days after initial exposure. T. superba, A. guachapele, and C. pyriformis were classified as moderately tolerant (TI > 0.6), and T. rosea was considered a sensitive species (TI < 0.35) under 12 ppm Cd contamination. Despite showing a high stem Cd concentration, C. pyriformis also showed the lowest relative growth rate. Among the evaluated forest species, A. guachapele exhibited the highest Cd accumulation capacity per plant (2.02 mg plant-1) but also exhibited a higher Cd allocation to leaves (4%) and a strong decrease in leaf and stem dry mass after 90 days of exposure (~75% and 50% respectively, compared to control treatments). Taking together all the favorable features exhibited by T. superba as compared to other CAFS tree species and recognized phytoextractor tree species in the literature, such as Cd hyperaccumulation, high tolerance index, low Cd concentration in leaves, and high Cd allocation to the stem (harvestable as wood), this species is considered to have a high potential for cadmium phytoextraction in cocoa agroforestry systems.

Molecular insights into rare earth element (REE)-mediated phytotoxicity and its impact on human health

Rare earth elements (REEs) that include 15 lanthanides, scandium, and yttrium are a special class of elements due to their remarkable qualities such as magnetism, corrosion resistance, luminescence, and electroconductivity. Over the last few decades, the implication of REEs in agriculture has increased substantially, which was driven by rare earth element (REE)-based fertilizers to increase crop growth and yield. REEs regulate different physiological processes by modulating the cellular Ca2+ level, chlorophyll activities, and photosynthetic rate, promote the protective role of cell membranes, and increase the plant's ability to withstand various stresses and other environmental factors. However, the use of REEs in agriculture is not always beneficial because REEs regulate plant growth and development in dose-dependent manner and excessive usage of them negatively affects plants and agricultural yield. Moreover, increasing applications of REEs together with technological advancement is also a rising concern as they adversely impact all living organisms and disturb different ecosystems. Several animals, plants, microbes, and aquatic and terrestrial organisms are subject to acute and long-term ecotoxicological impacts of various REEs. This concise overview of REEs' phytotoxic effects and implications on human health offers a context for continuing to sew fabric scraps to this incomplete quilt's many layers and colors. This review deals with the applications of REEs in different fields, specifically agriculture, the molecular basis of REE-mediated phytotoxicity, and the consequences for human health.

EcAGL enhances cadmium tolerance in transgenic Arabidopsis thaliana through inhibits cadmium transport and ethylene synthesis pathway

Cadmium (Cd) is a highly toxic heavy metal with severe impacts on plant growth and development. Although a multitude of plants have acquired strong tolerance to Cd stress, the underlying molecular mechanism has not been fully elucidated. Here, we identified a Agamous-like MADS-box gene (EcAGL) from Erigeron canadensis. The expression of EcAGL was obviously raised under Cd stress and subcellular localization indicated EcAGL was localized in the nucleus. Overexpression of EcAGL in Arabidopsis thaliana showed marked alleviation of the Cd-induced reduction; Compared to wild-type lines, the antioxidant enzymes activities were increased in EcAGL overexpressing lines under Cd stress. The roots Cd content of transgenic lines was not different with the control plants, whereas significant reduction in shoots Cd content was detected in the transgenic lines, indicating that this gene can enhance Cd tolerance by reducing Cd accumulation in Arabidopsis. Moreover, the expression levels of heavy metal ATPase (AtHMA2 and AtHMA3) and natural resistance-associated macrophage protein (AtNRAMP5) genes in the root of transgenic lines decreased under Cd stress, indicating that EcAGL likely hampered the Cd transport pathway. Gene expression profiles in shoot showed that EcAGL likely modulates the expression of 1-aminocyclopropane-1-carboxylic acid synthase gene (AtACS2), which is involved in the ethylene synthesis pathway, to strengthen the tolerance to Cd. Collectively, these results indicate that EcAGL plays a significant role in regulating Cd tolerance in E. canadensis by alleviating oxidative stress, Cd transport and affecting the ethylene biosynthesis pathway, providing new insight into the molecular mechanism underlying plant tolerance to Cd stress.

Photosynthetic Efficiency of Marchantia polymorpha L. in Response to Copper, Iron, and Zinc

Metal micronutrients are essential for plant nutrition, but their toxicity threshold is low. In-depth studies on the response of light-dependent reactions of photosynthesis to metal micronutrients are needed, and the analysis of chlorophyll a fluorescence transients is a suitable technique. The liverwort Marchantia polymorpha L., a model organism also used in biomonitoring, allowed us to accurately study the effects of metal micronutrients in vivo, particularly the early responses. Gametophytes were treated with copper (Cu), iron (Fe) or zinc (Zn) for up to 120 h. Copper showed the strongest effects, negatively affecting almost the entire light phase of photosynthesis. Iron was detrimental to the flux of energy around photosystem II (PSII), while the acceptor side of PSI was unaltered. The impact of Fe was milder than that of Cu and in both cases the structures of the photosynthetic apparatus that resisted the treatments were still able to operate efficiently. The susceptibility of M. polymorpha to Zn was low: although the metal affected a large part of the electron transport chain, its effects were modest and short-lived. Our results may provide a contribution towards achieving a more comprehensive understanding of response mechanisms to metals and their evolution in plants, and may be useful for supporting the development of biomonitoring techniques.

A Comprehensive Review on the Roles of Metals Mediating Insect-Microbial Pathogen Interactions

Insects and microbial pathogens are ubiquitous and play significant roles in various biological processes, while microbial pathogens are microscopic organisms that can cause diseases in multiple hosts. Insects and microbial pathogens engage in diverse interactions, leveraging each other's presence. Metals are crucial in shaping these interactions between insects and microbial pathogens. However, metals such as Fe, Cu, Zn, Co, Mo, and Ni are integral to various physiological processes in insects, including immune function and resistance against pathogens. Insects have evolved multiple mechanisms to take up, transport, and regulate metal concentrations to fight against pathogenic microbes and act as a vector to transport microbial pathogens to plants and cause various plant diseases. Hence, it is paramount to inhibit insect-microbe interaction to control pathogen transfer from one plant to another or carry pathogens from other sources. This review aims to succinate the role of metals in the interactions between insects and microbial pathogens. It summarizes the significance of metals in the physiology, immune response, and competition for metals between insects, microbial pathogens, and plants. The scope of this review covers these imperative metals and their acquisition, storage, and regulation mechanisms in insect and microbial pathogens. The paper will discuss various scientific studies and sources, including molecular and biochemical studies and genetic and genomic analysis.

An analysis of differentially expressed and differentially m6A-modified transcripts in soybean roots treated with lead

Lead is one of the most common toxic heavy metal pollutants in nature, and exposure to lead can cause serious toxicity to many organisms. In this study, we collected root growth data from soybean plants exposed to lead for seven days and confirmed that lead significantly inhibited root growth. We performed a transcriptome-wide m6A methylation analysis to study the response of soybean RNA methylation groups to lead. The m6A modified regions were enriched near the 3'UTR region and stop codon, and m6A methylation was positively correlated with transcript abundance. In the presence of lead, the transcriptome range of m6A RNA methylation peaks increased, and we identified 1144 m6A modification peaks and 1094 differentially expressed genes. The integration of m6A methylation and transcriptomic results enabled us to identify 16 candidate genes whose transcripts were differentially methylated and differentially expressed under lead stress. Annotation results suggest that these genes may promote abiotic stress tolerance by impacting lead uptake, transport, and accumulation through ROS pathways, enzymes, transporters, and hormones. These results provide candidate genes for future studies of lead stress tolerance mechanisms in soybean roots and provide genetic resources for studying plant heavy metal stress in soybean breeding.

Functional characterization of a DNA-damage repair/tolerance 100 (DRT100) gene in Sedum alfredii Hance for genome stability maintenance and Cd hypertolerance

Cd contamination is a world-wild concern for its toxicity and accumulation in food chain. Sedum alfredii Hance (Crassulaceae) is a zinc (Zn) and cadmium (Cd) hyperaccumulator native to China and widely applied for the phytoremediation at Zn or Cd contaminated sites. Although many studies report the uptake, translocation and storage of Cd in S. alfredii Hance, limited information is known about the genes and underlying mechanisms of genome stability maintenance under Cd stress. In this study, a gene resembling DNA-damage repair/toleration 100 (DRT100) was Cd inducible and designated as SaDRT100. Heterologous expression of SaDRT100 gene in yeasts and Arabidopsis thaliana enhanced Cd tolerance capability. Under Cd stress, transgenic Arabidopsis with SaDRT100 gene exhibited lower levels of reactive oxygen species (ROS), fewer Cd uptake in roots and less Cd-induced DNA damage. Evidenced by the subcellular location in cellular nucleus and expression in aerial parts, we suggested the involvement of SaDRT100 in combating Cd-induced DNA damage. Our findings firstly uncovered the roles of SaDRT100 gene in Cd hypertolerance and genome stability maintenance in S. alfredii Hance. The potential functions of DNA protection make SaDRT100 gene a candidate in genetic engineering for phytoremediation at multi-component contaminated sites.

The glutathione-dependent alarm triggers signalling responses involved in plant acclimation to cadmium

Cadmium (Cd) uptake from polluted soils inhibits plant growth and disturbs physiological processes, at least partly due to disturbances in the cellular redox environment. Although the sulfur-containing antioxidant glutathione is important in maintaining redox homeostasis, its role as an antioxidant can be overruled by its involvement in Cd chelation as a phytochelatin precursor. Following Cd exposure, plants rapidly invest in phytochelatin production, thereby disturbing the redox environment by transiently depleting glutathione concentrations. Consequently, a network of signalling responses is initiated, in which the phytohormone ethylene is an important player involved in the recovery of glutathione levels. Furthermore, these responses are intricately connected to organellar stress signalling and autophagy, and contribute to cell fate determination. In general, this may pave the way for acclimation (e.g. restoration of glutathione levels and organellar homeostasis) and plant tolerance in the case of mild stress conditions. This review addresses connections between these players and discusses the possible involvement of the gasotransmitter hydrogen sulfide in plant acclimation to Cd exposure.

ʟ-glutamic acid modulates antioxidant defense systems and nutrient homeostasis in lentil (Lens culinaris Medik.) under copper toxicity

Copper (Cu), an essential micronutrient, can generate reactive oxygen species (ROS) at its supra-optimal level in living cells as a transition metal, thus producing oxidative stress in plants. Therefore, protecting plants from Cu-induced oxidative stress via the exogenous application of chemical substances, particularly L-glutamic acid (L-Glu), could be a viable strategy for mitigating the toxicity of Cu. The aim of our present study was to investigate how ʟ-Glu protects lentil seedlings from oxidative stress produced by toxic Cu and allows them to survive under Cu toxicity. The results exhibited that when lentil seedlings were exposed to excessive Cu, their growth was inhibited and their biomass decreased due to an increase in Cu accumulation and translocation to the root, shoot, and leaves. Exposure to toxic Cu also depleted photosynthetic pigments, imbalanced water content, and other essential nutrients, increased oxidative stress, and reduced enzymatic and non-enzymatic antioxidants. However, pre-treatment of ʟ-Glu improved the phenotypic appearance of lentil seedlings, which was distinctly evidenced by higher biomass production, maintenance of water balance, and an increase in photosynthetic pigments when exposed to toxic Cu. ʟ-Glu also protected the seedlings from Cu-induced oxidative stress by reducing the oxidative stress marker, specifically by the efficient action of enzymatic and non-enzymatic antioxidants, particularly ascorbate, catalase, monodehydroascorbate, and glutathione peroxidase and maintaining redox balance. Furthermore, ʟ-Glu assisted in maintaining the homeostasis of Cu and other nutrient in the roots, shoots, and leaves of lentil. Collectively, our results provide evidence of the mechanism of ʟ-Glu-mediated protective role in lentil against Cu toxicity, thus proposed as a potential chemical for managing Cu toxicity not only in lentil but also other plants.

Characteristics of cadmium accumulation and tolerance in apple plants grown in different soils

Cadmium (Cd) is a nonessential element and highly toxic to apple tree. However, Cd accumulation, translocation and tolerance in apple trees planted in different soils remain unknown. To investigate soil Cd bioavailability, plant Cd accumulation, physiological changes as well as gene expression patterns in apple trees grown in five different soils, 'Hanfu' apple seedlings were planted in orchard soils collected from Maliangou village (ML), Desheng village (DS), Xishan village (XS), Kaoshantun village (KS) and Qianertaizi village (QT), and subjected to 500 μM CdCl₂ for 70 d. Results showed that soils of ML and XS had higher content of organic matter (OM), clay and silt, and cation exchange capacity (CEC) but lower sand content than the other soils, thereby reduced Cd bioavailability, which could be reflected by lower concentrations and proportions of acid-soluble Cd but higher concentrations and proportions of reducible and oxidizable Cd. The plants grown in soils of ML and XS had relatively lower Cd accumulation levels and bio-concentration factors than those grown in the other soils. Excess Cd reduced plant biomass, root architecture, and chlorophyll content in all plants but to relatively lesser degree in those grown in soils of ML and XS. The plants grown in soils of ML, XS and QT had comparatively lower reactive oxygen species (ROS) content, less membrane lipid peroxidation, and higher antioxidant content and enzyme activity than those grown in soils of DS and KS. Transcript levels of genes regulating Cd uptake, transport and detoxification such as HA11, VHA4, ZIP6, IRT1, NAS1, MT2, MHX, MTP1, ABCC1, HMA4 and PCR2 displayed significant differences in roots of plants grown in different soils. These results indicate that soil types affect Cd accumulation and tolerance in apple plants, and plants grown in soils with higher OM content, CEC, clay and silt content and lower sand content suffer less Cd toxicity.

Source apportionment and transfer characteristics of Pb in a soil-rice-human system, Jiulong River Basin, southeast China

The source apportionment and transfer of Pb in a paddy soil-rice-human system within the Jiulong River Basin in southeast China was investigated by analyzing (1) the chemical fractionation of Pb in paddy soils using a modified BCR four-step sequential extraction procedure, and (2) the bioaccessibility of Pb in both paddy soils and rice grains using a Simple Bioaccessibility Extraction Test method. In addition, a qualitative Pb isotopic model was used in combination with IsoSource software to quantify the contribution of potential Pb sources. The results show the enrichment of Pb in agro-ecosystems in the Jiulong River Basin. Contaminant Pb in paddy soils was mainly present in the reducible (42.9%) and the residual fractions (27.1%). The average bioaccessibility of Pb in rice grains was significantly higher than that in paddy soil, with values of 77.85% and 37.44%, respectively. Lead in paddy soils was primarily derived from agricultural (35.3%), natural (25.5%), industrial (24.5%) and coal combustion sources (14.7%), while Pb in rice grains was primarily derived from coal combustion (54.1%), agricultural (35.1%), industrial (6.0%) and natural sources (4.8%). The bioaccessible Pb was mainly derived from anthropogenic sources [agricultural (42.3% for soil and 25.3% for grain) and coal combustion sources (25.3% for soil and 59.3% for grain)]. Lead isotopic ratios are an effective tracer of Pb transfer from potential sources to rice plants and within the rice plants. Rice plants absorb Pb from the soil and the atmosphere through the roots and leaves, respectively. Most of the Pb was accumulated in roots. The integrated use of chemical fractionation, bioaccessibility and Pb isotopic data provides an effective method to study the source apportionment and transfer characteristics of Pb in paddy soil-rice-human systems.

Selenium alleviates cadmium and copper toxicity in Gracilaria lemaneiformis (rhodophyta) with contrasting detoxification strategies

Selenium (Se) is a beneficial element for plants, and can be used to mitigate the toxicity of heavy metals. However, the detoxification of Se in macroalgae, a crucial part of aquatic ecosystem productivity, has rarely been reported. In the present study, a red macroalga Gracilaria lemaneiformis was exposed to non-essential metal cadmium (Cd) or essential metal copper (Cu) with addition of different levels of Se. We then examined the changes in growth rate, metal accumulation, metal uptake rate, subcellular distribution, as well as thiol compound induction in this alga. Se addition alleviated Cd/Cu-induced stress in G. lemaneiformis by regulating cellular metal accumulation and intracellular detoxification. Specifically, supplementation of low-level Se displayed a significant decrease in Cd accumulation, and thus alleviated the growth inhibition induced by Cd. This may be caused by the inhibitory effect of endogenous Se instead of exogenous Se on Cd uptake. Although Se addition increased bioaccumulation of Cu in G. lemaneiformis, the important intracellular metal chelators, phytochelatins (PCs), were massively induced to alleviate Cu-induced growth inhibition. High-dose Se addition did not deteriorate but failed to normalize the growth of algae under metal stress conditions. Reduction in Cd accumulation or induction of PCs by Cu could not suppress the toxicity of Se above safe levels. Se addition also altered metal subcellular distribution in G. lemaneiformis, which might affect the subsequent metal trophic transfer. Our results demonstrated that the detoxification strategies of Se between Cd and Cu were different in macroalgae. Elucidating the protective mechanisms of Se against metal stress may help us better apply Se to regulate metal accumulation, toxicity, and transfer in aquatic environment.

TGase-induced Cd tolerance by boosting polyamine, nitric oxide, cell wall composition and phytochelatin synthesis in tomato

In highly intensive greenhouse vegetable production, soil acidification was caused by excessive fertilization, increasing cadmium (Cd) concentrations in the vegetables, which bears environmental hazards and is a negative influence on vegetables and humans. Transglutaminases (TGases), a central mediator for certain physiological effects of polyamines (PAs) in the plant kingdom, play important roles in plant development and stress response. Despite increased research on the crucial role of TGase in protecting against environmental stresses, relatively little is known about the mechanisms of Cd tolerance. In this study, we found, TGase activity and transcript level, which was upregulated by Cd, and TGase-induced Cd tolerance related to endogenous bound PAs increase and formation of nitric oxide (NO). Plant growth of tgase mutants was hypersensitive to Cd, chemical complementation by putrescine, sodium nitroprusside (SNP, nitric oxide donor) or gain of function TGase experiments restore Cd tolerance. α-diflouromethylornithine (DFMO, a selective ODC inhibitor) and 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, NO scavenger), were respectively found declined drastically endogenous bound PA and NO content in TGase overexpression plants. Likewise, we reported that TGase interacted with polyamine uptake protein 3 (Put3), and the silencing of Put3 largely reduced TGase-induced Cd tolerance and bound PAs formation. This salvage strategy depends on TGase-regulated synthesis of bound PAs and NO that is able to positively increase the concentration of thiol and phytochelatins, elevate Cd in the cell wall, as well as induce the levels of expression Cd uptake and transport genes. Collectively, these findings indicate that TGase-mediated enhanced levels of bound PA and NO acts as a vital mechanism to protect the plant from Cd-caused toxicity.

24-Epibrassinolide confers zinc stress tolerance in watermelon seedlings through modulating antioxidative capacities and lignin accumulation

Zinc (Zn) is an important element in plants, but over-accumulation of Zn is harmful. It is well-known that brassinolide (BR) plays a key role in the regulation of abiotic stress responses in plants. However, the effects of brassinolide on alleviating Zn phytotoxicity in watermelon (Citrullus lanatus L.) seedlings are not clear. The purpose of this study was to study the effect of 24-epibrassinolide (EBR, one of the bioactive BRs) on Zn tolerance of watermelon seedlings and its potential resistance mechanism. Exposure to excessive Zn significantly inhibited shoot and root fresh weight of watermelon, but this could be significantly alleviated by the optimum 0.05 μM EBR. Exogenous spraying EBR increased the pigments and alleviated oxidative damage caused by Zn through reducing Zn accumulation and the levels of reactive oxygen species (ROS) and malonaldehyde (MDA) and increasing the activities of antioxidant enzymes and contents of ascorbic acid (AsA) and glutathione (GSH). Importantly, the relative mRNA levels of antioxidant genesincluding Cu/Zn-superoxidedismutase (Cu-Zn SOD), catalase (CAT), ascorbic acid peroxidase (APX), and glutathione reductase (GR) were significantly induced after EBR treatment. In addition, EBR pre-treatment induced lignin accumulation under Zn stress, and the activity of phenylalanine ammonia-lyase (PAL) and 4-coumaric ligase (4CL), two key enzymes regulating lignin synthesis, also tended to be consistent. Collectively, the present research proves the beneficial effects of EBR in response to Zn stress through enhancing antioxidant defense and lignin accumulation and provides a new insight into the mechanism of BR-enhancing heavy metal tolerance.

Novel mechanisms of cadmium tolerance and Cd-induced fungal stress in wheat: Transcriptomic and metagenomic insights

Although several studies on the effects of cadmium (Cd) on wheat have been reported, the gene expression profiles of different wheat tissues in response to gradient concentrations of Cd, and whether soil microorganisms are involved in the damage to wheat remain to be discovered. To gain further insight into the molecular mechanisms of Cd-resistance in wheat, we sowed bread wheat (Triticum aestivum) in artificially Cd-contaminated soil and investigated the transcriptomic response of the wheat roots, stems, and leaves to gradient concentrations of Cd, as well as the alteration of the soil microbiome. Results indicated that the root bioaccumulation factors increased with Cd when concentrations were < 10 mg/kg, but at even higher concentrations, the bioaccumulation factors decreased, which is consistent with the overexpression of metal transporters and other genes related to Cd tolerance. In the Cd-contaminated soil, the abundance of fungal pathogens increased, and the antimicrobial response in wheat root was observed. Most of the differentially expressed genes (DEGs) of wheat changed significantly when the Cd concentration increased above 10 mg/kg, and the transcriptional response is much greater in roots than in stems and leaves. The DEGs are mainly involved in Cd transport and chelation, antioxidative stress, antimicrobial responses, and growth regulation. COPT3 and ZnT1 were identified for the first time as the major transporters responding to Cd in wheat. Overexpression of the nicotianamine synthase and pectinesterase genes suggested that nicotianamine and pectin are the key chelators in Cd detoxification. endochitinase, chitinase, and snakin2 were involved in the anti-fungal stress caused by Cd-induced cell damage. Several phytohormone-related DEGs are involved in the root's growth and repair. Overall, this study presents the novel Cd tolerance mechanisms in wheat and the changes in soil fungal pathogens that increase plant damage.

Regulatory module WRKY33-ATL31-IRT1 mediates cadmium tolerance in Arabidopsis

Cadmium (Cd) is one of the most dangerous environmental pollutants among heavy metals, and threatens food safety and human health by accumulating in plant sink tissues. Here, we report a novel regulatory cascade that profoundly influences Cd tolerance in Arabidopsis. Phenotypic analysis showed that an insertional knockdown mutation at the Arabidopsis Tóxicos en Levadura 31 (ATL31) locus resulted in hypersensitivity to Cd stress, most likely due to a significant increase in Cd accumulation. Consistently, ATL31-overexpressing lines exhibited enhanced Cd stress tolerance and reduced Cd accumulation. Further, IRON-REGULATED TRANSPORTER 1 (IRT1) was identified, and yeast two-hybrid, co-immunoprecipitation and bimolecular fluorescence complementation assays demonstrated its interaction with ATL31. Biochemical, molecular, and genetic analyses showed that IRT1 is targeted by ATL31 for ubiquitin-conjugated degradation in response to Cd stress. Intriguingly, transcription of ATL31 was strongly induced by Cd stress. In addition, transgenic and molecular analyses showed that WRKY33 directly activated the transcription of ATL31 in response to Cd stress and positively regulated Cd tolerance. Genetic analysis indicated that ATL31 acts upstream of IRT1 and downstream of WRKY33 to regulate Cd tolerance. Our study revealed that the WRKY33-ATL31-IRT1 module plays a crucial role in timely blocking Cd absorption to prevent metal toxicity in Arabidopsis.