Arabidopsis transcription factor WRKY45 confers cadmium tolerance via activating PCS1 and PCS2 expression

Unraveling cadmium tolerance mechanisms in Betula platyphylla through a hierarchical gene regulatory network in hormone signaling

Cadmium (Cd), a toxic heavy metal, is a significant pollutant that impacts plant productivity. While some studies have been conducted, the underlying mechanisms by which plants respond to Cd stress remain largely unclear. Here, we performed RNA-seq analysis of Betula platyphylla (birch) under CdCl2 treatment. The findings revealed a substantial enrichment of differentially expressed genes (DEGs) in pathways associated with plant hormones. A gene regulatory network (GRN) was constructed, and the regulatory relationships between genes were determined using a partial correlation coefficient algorithm. The GRN comprises 2151 regulatory interactions, including 7 transcription factors (TFs) from the first layer, 25 TFs from the second layer, and 168 structural genes from the third layer, all of which are linked to ten enriched biological processes. ChIP-PCR and qRT-PCR assays validated approximately 85.2 % of the predicted interactions between the first and second layers, along with 88.3 % of the interactions between the second and third layers, supporting the validity of the GRN. Eighteen genes were selected from the third layer of multiple biological pathways to analyze their functions, and the results indicated that these genes can enhance Cd tolerance in birch plants. Additionally, two TFs in the first layer, BpHD-zip7 and BpRAV1, were successfully introduced into birch plants, confirming their role in improving Cd tolerance. Our findings elucidate the regulatory mechanisms and key determinants that function in the adaptation of B. platyphylla to Cd stress.

Phytochelatins and Cadmium Mitigation: Harnessing Genetic Avenues for Plant Functional Manipulation

Among the highly toxic heavy metals, cadmium (Cd) is highlighted as a persistent environmental pollutant, posing serious threats to plants and broader ecological systems. Phytochelatins (PCs), which are synthesized by phytochelatin synthase (PCS), are peptides that play a central role in Cd mitigation through metal chelation and vacuolar sequestration upon formation of Cd-PC complexes. PC synthesis interacts with other cellular mechanisms to shape detoxification outcomes, broadening the functional scope of PCs beyond classical stress responses. Plant Cd-related processes have has been extensively investigated within this context. This perspective article presents key highlights of the panorama concerning strategies targeting the PC pathway and PC synthesis to manipulate Cd-exposed plants. It discusses multiple advances on the topic related to genetic manipulation, including the use of mutants and transgenics, which also covers gene overexpression, PCS-deficient and PCS-overexpressing plants, and synthetic PC analogs. A complementary bibliometric analysis reveals emerging trends and reinforces the need for interdisciplinary integration and precision in genetic engineering. Future directions include the design of multigene circuits and grafting-based innovations to optimize Cd sequestration and regulate its accumulation in plant tissues, supporting both phytoremediation efforts and food safety in contaminated agricultural environments.

Machine learning based prediction by PlantCdMiner and experimental validation of cadmium-responsive genes in plants

Plants have evolved diverse adaptive mechanisms to sense and respond to environmental stimuli such as cadmium stress. The regulation of gene expression plays a critical role in plant responses to abiotic stress. However, homologous genes from different plant species or even different genotypes within the same species often show divergent responses to stress, and sequence homology does not necessarily imply functional similarity. Therefore, current homology alignment approaches to predicting transcriptional response to the specific stress have inherent limitations. In this study, we trained supervised classification models using the Random Forest algorithm to predict cadmium-responsive genes based on gene sequence features in Arabidopsis thaliana, Avicennia marina, Hordeum vulgare, and Nicotiana tabacum. Our models successfully predicted transcriptional response to cadmium stress both within and across species. The results suggested that transcriptome data from well-studied species can be used to predict cadmium-responsive genes in other species lacking such data. Cis-regulatory elements analysis further revealed that MYB TFs play essential roles in cadmium stress responses. Additionally, we experimentally confirmed that the MYB TF Am06526 activates the expression of AmPCR2 using yeast one-hybrid and dual-luciferase reporter assays. Finally, we developed PlantCdMiner (https://jasonxu.shinyapps.io/PlantCdMiner/), a web-based tool that enables users to predict cadmium-responsive genes and visualize cis-regulatory elements based on genomic features using machine learning.

Genome-Wide Identification and Phylogenetic Characterization of the FTIP Gene Family in Maize (Zea mays)

The maize FT-interacting protein (FTIP) gene family represents a group of multiple C2 domain and transmembrane proteins (MCTPs), characterized by their unique structural motifs and membrane-spanning regions., plays crucial roles in intercellular communication and stress responses. Here, we systematically characterized 27 ZmFTIP genes unevenly distributed across 10 maize chromosomes. Phylogenetic analysis with rice, soybean, and Arabidopsis homologs revealed five evolutionary clades with monocot-specific conservation patterns. Promoter cis-element profiling identified hormone-responsive (ABA, JA, auxin) and stress-related motifs, corroborated by differential expression under abiotic stresses and phytohormone treatments. Notably, ZmFTIP18 and ZmFTIP25 showed sustained upregulation under cadmium exposure, while ZmFTIP13 exhibited downregulation. Synteny analysis demonstrated strong conservation with monocot FTIPs, suggesting ancient evolutionary origins. This comprehensive study provides foundational insights into ZmFTIP functional diversification and potential biotechnological applications.

MIR408-encoded peptide, miPEP408, regulates cadmium stress response through sulfur assimilation pathway

Small peptides encoded by pri-miRNAs (miPEPs), have been identified as significant plant growth and development regulators. However, their roles in plant-environment interactions and heavy metal stress response remain largely unexplored. Here, we demonstrate that Arabidopsis MIR408-encoded peptide (miPEP408) plays a significant role in cadmium (Cd) stress response by modulating the sulfur assimilation pathway. Using a combination of exogenous synthetic peptide assays, CRISPR/Cas9-mediated knockout mutants (miPEP408CR), and overexpression lines (miPEP408OX), we analyzed phenotypic and molecular levels to elucidate the function of miPEP408 under Cd stress. Our results suggest that miPEP408 regulates miR408 expression and its targets in response to Cd exposure. Plants treated with exogenous miPEP408 or overexpressing miPEP408 exhibited reduced glutathione (GSH) levels, suppression of sulfur assimilation pathway genes, and heightened sensitivity to Cd. miPEP408CR plants showed enhanced GSH levels, upregulation of sulfur assimilation genes, and improved Cd detoxification. Furthermore, miPEP408 influenced the expression of Cd transporters and Cd accumulation in plants. In conclusion, this study establishes miPEP408 as a key regulator of Cd stress response in Arabidopsis, functioning through modulation of the sulfur assimilation pathway and metal transporter gene expression. These findings underscore the indispensable role of miPEPs in enhancing plant resilience to heavy metal stress.

Genome-wide identification of MYB gene family and exploration of selenium metabolism-related candidates in paper mulberry (Broussonetia papyrifera)

KEY MESSAGE

Genome-wide identified 144 MYB family members in B. papyrifera. Integrated correlation analysis and target gene-binding motif prediction indicate that BpMYB135 is vital in regulating selenium metabolism. Selenium is an essential micronutrient for maintaining the health of humans and animals. Broussonetia papyrifera, a forage tree with high nutritional value, exhibits a remarkable ability to accumulate selenium. Although previous studies have preliminarily unfolded the molecular mechanisms underlying selenium accumulation, the roles of transcription factors in regulating selenium uptake and transformation remain poorly understood. This study used various strategies including bioinformatic, physiological, and molecular experiments to explore candidates regarding Se metabolism. Briefly, 144 MYB transcription factor family members were identified and classified into four types (R1, R2R3, R1R2R3, and R4), with phylogenetic analysis further dividing them into 58 subfamilies. The promoters of those BpMYBs contain numerous cis-acting elements associated with plant growth, development, and stress response. qRT-PCR assay confirmed 8 of 15 BpMYBs exhibit a remarkable correlation with selenium content at the threshold absolute value of 0.5. Additionally, foliar application of exogenous abscisic acid (ABA), methyl jasmonate (MeJA), and salicylic acid (SA) reveals different response patterns of BpMYBs. The subcellular localization assay simultaneously verifies that the candidate BpMYB135 functions within the nucleus. Overall, this funding highlights the potential regulatory mechanisms of selenium metabolism in B. papyrifera, providing a foundation for improving its forage value through genetic modification.

UCL23 hierarchically regulated by WRKY51-miR528 mediates cadmium uptake, tolerance, and accumulation in rice

In humans, cadmium (Cd) toxicity caused by contaminated environments is associated with numerous chronic diseases. Breeding rice with low Cd accumulation is now deemed critical for sustainable agriculture development. Here, we elucidate the crucial functions of UCLACYANIN 23 (UCL23), a small copper protein, in Cd absorption, tolerance, and accumulation through modulation of reactive oxygen signals in rice. Additionally, we demonstrate that WRKY51 binds to promoters of UCL23 and miR528, a post-transcriptional regulator of UCL23, thereby contributing to Cd regulation in a dual-modulatory manner. Furthermore, we show that the natural variation of UCL23 is important for the differential accumulation of Cd in rice grains. Finally, we reveal that Indica rice harboring the major Japonica haplotype of UCL23 significantly reduces Cd uptake in roots and Cd accumulation in grains. Together, our study not only reveals a regulatory cascade in Cd regulation but also provides valuable resources for breeding low-Cd rice cultivars.

Transcriptomic and metabolomic analyses of Tartary buckwheat roots during cadmium stress

Cadmium (Cd) can adversely damage plant growth. Therefore, understanding the control molecular mechanisms of Cd accumulation will benefit the development of strategies to reduce Cd accumulation in plants. This study performed transcriptomic and metabolomic analyses on the roots of a Cd-tolerant Tartary buckwheat cultivar following 0 h (CK), 6 h (T1), and 48 h (T2) of Cd treatment. The fresh weight and root length were not significantly inhibited under the T1 treatment but they were in the T2 treatment. The root's ultrastructure was seriously damaged in T2 but not in T1 treatment. This was evidenced by deformed cell walls, altered shape and number of organelles. A total of 449, 999 differentially expressed genes (DEGs) and eight, 37 differentially expressed metabolites (DEMs) were identified in the CK versus T1 and CK versus T2 comparison, respectively. DEGs analysis found that the expression of genes related to cell wall function, glutathione (GSH) metabolism, and phenylpropanoid biosynthesis changed significantly during Cd stress. Several WRKY, MYB, ERF, and bHLH transcription factors and transporters also responded to Cd treatment. Our results indicate that Cd stress affects cell wall function and GSH metabolism and that changes in these pathways might contribute to mechanisms of Cd tolerance in Tartary buckwheat.

WRKY45 positively regulates salinity and osmotic stress responses in Arabidopsis

Salt damage is a major issue that causes a decline in crop yield. WRKY transcription factors (TFs) extensively regulate plant biotic and abiotic stress responses, growth, and development. WRKY45 is crucial in regulating leaf senescence, low phosphorus responses, and cadmium stress response in Arabidopsis. However, the involvement of WRKY45 in salinity and osmotic stress responses is unclear. Here, we report that WRKY45 plays a vital role in responding to salinity and osmotic stress. NaCl and sorbitol treatments upregulate WRKY45 expression. Furthermore, the overexpression of WRKY45 (WRKY45-OXs) may enhance the tolerance of Arabidopsis to salinity and osmotic stress. Moreover, the root length, fresh weight, chlorophyll, and proline content were significantly higher in WRKY45-OXs than in the wide type (WT) Col-0 plants after salt or PEG treatment, whereas malondialdehyde and reactive oxygen species (ROS) levels were significantly lower than in the WT plants. Correspondingly, the overexpression of WRKY45 modulated the expression of stress-responsive genes. Dual luciferase assay and electrophoretic mobility shift assay further confirmed that WRKY45 can activate the promoter of RD29A by directly binding to specific W-box cis-acting elements. Overall, our experimental evidence suggesting that WRKY45 mainly acts as a key regulator coordinating the response to high salinity and osmotic stress through mechanisms dependent on ABA signaling along with enhanced antioxidant capacity.

Homocysteine S-Methyltransferase 3 Positively Regulates Cadmium Tolerance in Maize

The increasing contamination of agricultural soils with cadmium (Cd) poses a significant threat to human health and global food security. Plants initiate a series of mechanisms to reduce Cd toxicity. However, the response of maize to Cd toxicity remains poorly understood. In this study, we identified that ZmHMT3, which encodes a homocysteine S-methyltransferases family protein, acted as a regulator of Cd tolerance in maize. Subcellular localization and in situ PCR exhibited that ZmHMT3 was localized in the cytoplasm and predominantly expressed in the phloem. Overexpression of ZmHMT3 enhanced Cd tolerance and reduced Cd concentration in both shoots and roots. In contrast, ZmHMT3 mutants attenuated Cd tolerance but did not change shoot Cd concentration. Heterologous overexpression of ZmHMT3 in rice enhanced Cd tolerance and reduced grain Cd concentration. Transcriptome analysis revealed that ZmHMT3 upregulated the expression of stress-responsive genes, especially glutathione S-transferases (GSTs) and transcription factors, including MYBs, NACs and WRKYs, and modulates the expression of different ATP-binding cassette (ABC) transporters, thereby enhancing Cd tolerance. Collectively, these findings highlight the pivotal role of ZmHMT3 in Cd tolerance and as a candidate gene for improving Cd tolerance in elite maize varieties.

Integrated comparative transcriptome and weighted gene co-expression network analysis provide valuable insights into the response mechanisms of Alisma orientale to cadmium stress

Cadmium (Cd) pollution poses a serious challenge to the quality and safe utilization of traditional Chinese medicine plants as well as human health. In this study, seedlings of the medicinal plant species Alisma orientale were subjected to different levels of Cd stress for 7 days to investigate the effects of Cd stress on its growth, physiological response, and transcriptome profiling. The results showed that under different Cd stress levels, the growth of A. orientale displayed an inverted U-shaped dose response curve as low-dose stimulation and high-dose inhibition. Cd was mainly enriched in roots in the high concentration treatment, and Cd content reached maximum under 200-μM Cd stress. Cd stress-induced indicators including H2O2 (14.1-228.8 % in leaves; 29.7-131.7 % in roots) and MDA (22.0-161.1 % in leaves; 30.0-201.1 % in roots) showed different degree of increase, except under 200-μM Cd stress, which had a slight decrease. Antioxidant enzyme system (SOD, POD and CAT) and nonenzymatic substances (SS, SP, total flavonoid and total polyphenols) played a key role to mitigate Cd toxic effects. Transcriptome analysis revealed 26,442 significantly differentially expressed genes, and plant-pathogen interactions and phenylpropanoid biosynthesis were identified as two key pathways. Through WGCNA joint analysis, the transcription factor genes R2R3-MYB (AoMYB12) and WRKY (AoWRKY5 and AoWRKY6) were identified as hub regulators of A. orientale in response to Cd stress. Our study provides experimental data on the effects of Cd stress on A. orientale growth and Cd accumulation in different plant parts, and investigated the transcriptomic and physio-biochemical features, advancing our understanding of the response and detoxification mechanisms of plants under Cd stress.

Overexpression of tae-miR9670 enhances cadmium tolerance in wheat by targeting mTERFs without yield penalty

Cadmium (Cd) is a widely distributed heavy metal that poses significant hazards to both crop productivity and human health. MicroRNAs (miRNAs) play pivotal roles in plant growth, development and responses to environmental stresses, yet little is known about their roles in regulating Cd tolerance in wheat. In this study, we identified tae-miR9670, a Triticeae-specific miRNA, as responsive to Cd exposure in wheat through miRNAome analysis. Tae-miR9670 can target genes that encode mitochondrial transcription termination factors (mTERFs), mediating their mRNA cleavage and suppressing their expression. Overexpression of tae-miR9670 significantly enhanced Cd tolerance in wheat seedlings, as demonstrated by increased biomass and reduced levels of malondialdehyde (MDA), H2O2, and Cd content. Consequently, multiple downstream genes involved in ROS scavenging, detoxification and heavy metal transport were upregulated in tae-miR9670 overexpression plants. Moreover, the grain Cd content in mature plants overexpressing tae-miR9670 was reduced by over 60 % compared to wild-type controls. Our results also indicated that overexpressing tae-miR9670 in wheat preserved yield-related traits, thereby overcoming the trade-off between stress resistance and grain yield. Overall, our findings provide new insights into the role of tae-miR9670 in Cd tolerance in wheat and its potential application in breeding low-Cd cultivars.

Role of SbNRT1.1B in cadmium accumulation is attributed to nitrate uptake and glutathione-dependent phytochelatins biosynthesis

Phytoremediation of cadmium (Cd)-polluted soil by using sweet sorghum displays a tremendous potential as it is a fast-growing, high biomass and Cd tolerant energy plant. Previous study has demonstrated SbNRT1.1B expression change is in accordance with enhanced Cd accumulation by external nitrate supply in sweet sorghum. Nevertheless, underlying mechanism of SbNRT1.1B response to Cd stress is still elusive. SbNRT1.1B exhibited a positive response to Cd stress in sweet sorghum. Overexpressing SbNRT1.1B increased primary root length, shoot fresh weight, nitrate and chlorophyll concentrations compared with Col-0 under Cd stress, while complementary SbNRT1.1B rescued these decreased values in mutant chl1-5. Cd concentrations in overexpressing SbNRT1.1B, complementary SbNRT1.1B and Col-0 lines were 3.2-4.1, 2.5-3.1 and 1.2-2.1 folds of that in chl1-5. Consistent with Cd concentrations, non-protein thiol (NPT), reduced glutathione (GSH) and phytochelatins (PCs) concentrations as well as the related genes expression levels showed the same trends under Cd stress. GSH biosynthesis inhibitor failed to reverse the patterns of GSH-dependent PCs concentrations changes in different lines, suggesting that SbNRT1.1B plays an upstream role in GSH-dependent PCs biosynthesis under Cd treatment. Altogether, SbNRT1.1B enhances nitrate concentrations contributing to increased chlorophyll concentrations and GSH-dependent PCs metabolites biosynthesis, thereby improving growth and Cd concentrations in plants.

Soybean PHR1-regulated low phosphorus-responsive GmRALF22 promotes phosphate uptake by stimulating the expression of GmPTs

Phosphorus (P) is an essential macronutrient for plant growth and development. Rapid alkalisation factors (RALFs) play crucial roles in plant responses to nutrient stress. However, the functions of Glycine max RALFs (GmRALFs) under low P (LP) stress remain elusive. In this study, we first identified 27 GmRALFs in soybean and then revealed that, under LP conditions, GmRALF10, GmRALF11, and GmRALF22 were induced in both roots and leaves, whereas GmRALF5, GmRALF6, and GmRALF25 were upregulated in leaves. Furthermore, GmRALF22 was found to be the target gene of the transcription factor GmPHR1, which binds to the P1BS cis-element in the promoter of GmRALF22 via electrophoretic mobility shift assay and dual-luciferase experiments. Colonisation with Bacillus subtilis which delivers GmRALF22, increases the expression of the high-affinity phosphate (Pi) transporter genes GmPT2, GmPT11, GmPT13, and GmPT14, thus increasing the total amount of dry matter and soluble Pi in soybeans. RNA sequencing revealed that GmRALF22 alleviates LP stress by regulating the expression of jasmonic acid- (JA-), salicylic acid- (SA-), and immune-related genes. Finally, we verified that GmRALF22 was dependent on FERONIA (FER) to promote Arabidopsis primary root growth under LP conditions. In summary, the GmPHR1-GmRALF22 module positively regulates soybean tolerance to LP.

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.

The transcription factor OsNAC5 regulates cadmium accumulation in rice

Cadmium (Cd) is a hazardous heavy metal that threatens human health through the consumption of contaminated rice. To mitigate Cd accumulation in rice grains, it is crucial to reduce Cd uptake. Nevertheless, the transcriptional mechanisms governing Cd uptake in rice remain largely unknown. This research identifies the transcription factor OsNAC5 in Oryza sativa as a positive regulator of the Cd transporter gene OsNRAMP1, thereby influencing Cd uptake. OsNAC5 is predominantly expressed in the roots, resides in the nucleus, and is upregulated by Cd-induced hydrogen peroxide (H2O2). Knocking out OsNAC5 results in lower Cd concentrations in both shoots and roots and heightens sensitivity to Cd. The expression of OsNRAMP1, enhanced by Cd stress, is dependent on OsNAC5. OsNAC5 binds to "CATGTG" motifs in the OsNRAMP1 promoter, activating its expression. The loss of OsNAC5 function leads to reduced Cd accumulation in rice grains. Our findings provide insights into the transcriptional regulation of Cd stress response in rice and propose biotechnological strategies to lower Cd uptake in crops.

WRKY Transcription Factors in Response to Metal Stress in Plants: A Review

Heavy metals in soil can inflict direct damage on plants growing within it, adversely affecting their growth height, root development, leaf area, and other physiological traits. To counteract the toxic impacts of heavy metals on plant growth and development, plants mitigate heavy metal stress through mechanisms such as metal chelation, vacuolar compartmentalization, regulation of transporters, and enhancement of antioxidant functions. WRKY transcription factors (TFs) play a crucial role in plant growth and development as well as in responses to both biotic and abiotic stresses; notably, heavy metal stress is classified as an abiotic stressor. An increasing number of studies have highlighted the significant role of WRKY proteins in regulating heavy metal stress across various levels. Upon the entry of heavy metal ions into plant root cells, the production of reactive oxygen species (ROS) is triggered, leading to the phosphorylation and activation of WRKY TFs through MAPK cascade signaling. Activated WRKY TFs then modulate various physiological processes by upregulating or downregulating the expression of downstream genes to confer heavy metal tolerance to plants. This review provides an overview of the research advancements regarding WRKY TFs in regulating heavy metal ion stress-including cadmium (Cd), arsenic (As), copper (Cu)-and aluminum (Al) toxicity.

Mechanisms of Cadmium stress response in watermelon: Insights from physiological, transcriptomic, and metabolic analyses

Cadmium (Cd) contamination of soil may lead to Cd stress for plants, which significantly hinders plant growth and development, posing a risk to human health through the consumption of Cd-contaminated foods. Watermelon (Citrullus lanatus), a widely consumed fruit, is particularly affected by Cd stress globally, yet the mechanisms underlying its response are not well understood. Here, we subjected watermelon seedlings to simulated Cd stress treatment and explored the physiological, transcriptomic, and metabolic response. Our findings revealed that Cd stress treatment led to increased accumulation of reactive oxygen species (ROS) in watermelon leaves. Transcriptome sequencing unveiled a multitude of osmotic and oxidative stress-responsive genes, including peroxidase (POD), MYB, voltage-dependent anion channel (SLAC1), and ABC transporter. KEGG enrichment analysis highlighted the predominant enrichment of Cd stress-responsive genes in pathways such as glutathione (GSH) metabolism, MAPK signaling, and biosynthesis of secondary metabolites. Within the GSH metabolism pathway, several glutathione S-transferase (GST) genes were up-regulated, alongside phytochelatin synthetase (PCS) genes involved in phytochelatin synthesis. In the MAPK signaling pathway, genes associated with ABA and ethylene signal transduction showed up-regulation following Cd stress. Metabolomic analysis demonstrated that Cd stress enhanced the production of amino acids, phenolamines, and esters. Overall, our study elucidates that watermelon responds to Cd stress by activating its antioxidant system, GSH metabolism pathway, MAPK signal pathway, and biosynthesis of key metabolites. These findings offer valuable insights for the remediation of heavy metal pollution in soil affecting plant life.

Metal transport proteins and transcription factor networks in plant responses to cadmium stress

Cadmium (Cd) contamination poses a significant threat to agriculture and human health due to its high soil mobility and toxicity. This review synthesizes current knowledge on Cd uptake, transport, detoxification, and transcriptional regulation in plants, emphasizing the roles of metal transport proteins and transcription factors (TFs). We explore transporter families like NRAMP, HMA, ZIP, ABC, and YSL in facilitating Cd movement within plant tissues, identifying potential targets for reducing Cd accumulation in crops. Additionally, regulatory TF families, including WRKY, MYB, bHLH, and ERF, are highlighted for their roles in modulating gene expression to counteract Cd toxicity. This review consolidates the existing literature on plant-Cd interactions, providing insights into established mechanisms and identifying gaps for future research. Understanding these mechanisms is crucial for developing strategies to enhance plant tolerance, ensure food safety, and promote sustainable agriculture amidst increasing heavy-metal pollution.

Exogenous Application of Amino Acids Alleviates Toxicity in Two Chinese Cabbage Cultivars by Modulating Cadmium Distribution and Reducing Its Translocation

Plants communicate underground by secreting multiple amino acids (AAs) through their roots, triggering defense mechanisms against cadmium (Cd) stress. However, the specific roles of the individual AAs in Cd translocation and detoxification remain unclear. This study investigated how exogenous AAs influence Cd movement from the roots to the shoots in Cd-resistant and Cd-sensitive Chinese cabbage cultivars (Jingcui 60 and 16-7 cultivars). The results showed that methionine (Met) and cysteine (Cys) reduced Cd concentrations in the shoots of Jingcui 60 by approximately 44% and 52%, and in 16-7 by approximately 43% and 32%, respectively, compared to plants treated with Cd alone. However, threonine (Thr) and aspartic acid (Asp) did not show similar effects. Subcellular Cd distribution analysis revealed that AA supplementation increased Cd uptake in the roots, with Jingcui 60 preferentially storing more Cd in the cell wall, whereas the 16-7 cultivar exhibited higher Cd concentrations in the organelles. Moreover, Met and Cys promoted the formation of Cd-phosphate in the roots of Jingcui 60 and Cd-oxalate in the 16-7 cultivar, respectively. Further analysis showed that exogenous Cys inhibited Cd transport to the xylem by downregulating the expression of HMA2 in the roots of both cultivars, and HMA4 in the 16-7 cultivar. These findings provide insights into the influence of exogenous AAs on Cd partitioning and detoxification in Chinese cabbage plants.

Overexpression of BnaA10.WRKY75 Decreases Cadmium and Salt Tolerance via Increasing ROS Accumulation in Arabidopsis and Brassica napus L

Soil is indispensable for agricultural production but has been seriously polluted by cadmium and salt in recent years. Many crops are suffering from this, including rapeseed, the third largest global oilseed crop. However, genes simultaneously related to both cadmium and salt stress have not been extensively reported yet. In this study, BnaA10.WRKY75 was screened from previous RNA-seq data related to cadmium and salt stress and further analyses including sequence comparison, GUS staining, transformation and qRT-PCR were conducted to confirm its function. GUS staining and qRT-PCR results indicated BnaA10.WRKY75 was induced by CdCl2 and NaCl treatment. Sequence analysis suggested BnaA10.WRKY75 belongs to Group IIc of the WRKY gene family and transient expression assay showed it was a nuclear localized transcription factor. BnaA10.WRKY75-overexpressing Arabidopsis and rapeseed plants accumulated more H2O2 and O2- and were more sensitive to CdCl2 and NaCl treatment compared with untransformed plants, which may be caused by the downregulation of BnaC03.CAT2. Our study reported that BnaA10.WRKY75 increases sensitivity to cadmium and salt stress by disrupting the balance of reactive oxygen species both in Arabidopsis and rapeseed. The results support the further understanding of the mechanisms underlying cadmium and salt tolerance and provide BnaA10.WRKY75 as a valuable gene for rapeseed abiotic stress breeding.

NtARF11 positively regulates cadmium tolerance in tobacco by inhibiting expression of the nitrate transporter NtNRT1.1

Heavy metal cadmium (Cd) is widespread in contaminated soil and an important factor limiting plant growth. NO3- (nitrate) affects Cd uptake and thus changes Cd tolerance in plants; however, the underlying molecular regulatory mechanisms have not yet been elucidated. Here, we analyzed a novel gene, NtARF11 (auxin response factor), which regulates Cd tolerance in tobacco via the NO3- uptake pathway, through experiments with NtARF11-knockout and NtARF11-overexpression transgenic tobacco lines. NtARF11 was highly expressed under Cd stress in tobacco plants. Under Cd stress, overexpression of NtARF11 enhanced Cd tolerance in tobacco compared to that in wild-type tobacco, as shown by the low Cd concentration, high chlorophyll concentration, and low accumulation of reactive oxygen species in NtARF11-overexpressing tobacco. Moreover, low NO3- concentrations were observed in NtARF11-overexpressing tobacco plants. Further analyses revealed direct binding of NtARF11 to the promoter of the nitrate transporter NtNRT1.1, thereby negatively regulating its expression in tobacco. Notably, NtNRT1.1 knockout reduced NO3- uptake, which resulted in low Cd concentrations in tobacco. Altogether, these results demonstrate that the NtARF11-NtNRT1.1 module functions as a positive regulator of Cd tolerance by reducing the Cd uptake in tobacco, providing new insights for improving Cd tolerance of plants through genetic engineering.

Changes in secondary metabolites contents and stress responses in Salvia miltiorrhiza via ScWRKY35 overexpression: Insights from a wild relative Salvia castanea

Salvia castanea Diels, a close wild relative to the medicinal plant, Salvia miltiorrhiza Bunge, primarily grows in high-altitude regions. While the two species share similar active compounds, their content varies significantly. WRKY transcription factors are key proteins, which regulate plant growth, stress response, and secondary metabolism. We identified 46 ScWRKY genes in S. castanea and found that ScWRKY35 was a highly expressed gene associated with secondary metabolites accumulation. This study aimed to explore the role of ScWRKY35 gene in regulating the accumulation of secondary metabolites and its response to UV and cadmium (Cd) exposure in S. miltiorrhiza. It was found that transgenic S. miltiorrhiza hairy roots overexpressing ScWRKY35 displayed upregulated expression of genes related to phenolic acid synthesis, resulting in increased salvianolic acid B (SAB) and rosmarinic acid (RA) contents. Conversely, tanshinone pathway gene expression decreased, leading to lower tanshinone levels. Further, overexpression of ScWRKY35 upregulated Cd transport protein HMA3 in root tissues inducing Cd sequestration. In contrast, the Cd uptake gene NRAMP1 was downregulated, reducing Cd absorption. In response to UV radiation, ScWRKY35 overexpression led to an increase in the accumulation of phenolic acid and tanshinone contents, including upregulation of genes associated with salicylic acid (SA) and jasmonic acid (JA) synthesis. Altogether, these findings highlight the role of ScWRKY35 in enhancing secondary metabolites accumulation, as well as in Cd and UV stress modulation in S. miltiorrhiza, which offers a novel insight into its phytochemistry and provides a new option for the genetic improvement of the plants.

The Uptake, Transfer, and Detoxification of Cadmium in Plants and Its Exogenous Effects

Cadmium (Cd) exerts a toxic influence on numerous crucial growth and development processes in plants, notably affecting seed germination rate, transpiration rate, chlorophyll content, and biomass. While considerable advances in Cd uptake and detoxification of plants have been made, the mechanisms by which plants adapt to and tolerate Cd toxicity remain elusive. This review focuses on the relationship between Cd and plants and the prospects for phytoremediation of Cd pollution. We highlight the following issues: (1) the present state of Cd pollution and its associated hazards, encompassing the sources and distribution of Cd and the risks posed to human health; (2) the mechanisms underlying the uptake and transport of Cd, including the physiological processes associated with the uptake, translocation, and detoxification of Cd, as well as the pertinent gene families implicated in these processes; (3) the detrimental effects of Cd on plants and the mechanisms of detoxification, such as the activation of resistance genes, root chelation, vacuolar compartmentalization, the activation of antioxidant systems and the generation of non-enzymatic antioxidants; (4) the practical application of phytoremediation and the impact of incorporating exogenous substances on the Cd tolerance of plants.

Transcriptome Analysis Reveals the Stress Tolerance Mechanisms of Cadmium in Zoysia japonica

Cadmium (Cd) is a severe heavy metal pollutant globally. Zoysia japonica is an important perennial warm-season turf grass that potentially plays a role in phytoremediation in Cd-polluted soil areas; however, the molecular mechanisms underlying its Cd stress response are unknown. To further investigate the early gene response pattern in Z. japonica under Cd stress, plant leaves were harvested 0, 6, 12, and 24 h after Cd stress (400 μM CdCl2) treatment and used for a time-course RNA-sequencing analysis. Twelve cDNA libraries were constructed and sequenced, and high-quality data were obtained, whose mapped rates were all higher than 94%, and more than 601 million bp of sequence were generated. A total of 5321, 6526, and 4016 differentially expressed genes were identified 6, 12, and 24 h after Cd stress treatment, respectively. A total of 1660 genes were differentially expressed at the three time points, and their gene expression profiles over time were elucidated. Based on the analysis of these genes, the important mechanisms for the Cd stress response in Z. japonica were identified. Specific genes participating in glutathione metabolism, plant hormone signal and transduction, members of protein processing in the endoplasmic reticulum, transporter proteins, transcription factors, and carbohydrate metabolism pathways were further analyzed in detail. These genes may contribute to the improvement of Cd tolerance in Z. japonica. In addition, some candidate genes were highlighted for future studies on Cd stress resistance in Z. japonica and other plants. Our results illustrate the early gene expression response of Z. japonica leaves to Cd and provide some new understanding of the molecular mechanisms of Cd stress in Zosia and Gramineae species.