A MYB transcription factor, BnMYB2, cloned from ramie (Boehmeria nivea) is involved in cadmium tolerance and accumulation

Populus euphratica R2R3-MYB transcription factor RAX2 binds ANN1 promoter to increase cadmium enrichment in Arabidopsis

The expression of R2R3-MYB transcription factor PeRAX2 increased transiently upon CdCl2 exposure (100 μM, 48 h) in leaves and roots of Populus euphratica. We observed that overexpression of PeRAX2 increased Cd2+ concentration in Arabidopsis root cells and Cd2+ amount in whole plant, which was due to the increased Cd2+ influx into root tips. However, the Cd2+ influx facilitated by PeRAX2 overexpression was substantially reduced by LaCl3 (an inhibitor of Ca2+-channels), suggesting that PeRAX2 could promote the Cd2+ entering through PM Ca2+-permeable channels (CaPCs) in the roots. It is noting that the expression of annexin1 (AtANN1), which mediates the influx of divalent cations through the PM calcium channels, was upregulated by Cd2+ in PeRAX2-transgenic Arabidopsis. Bioinformatic analysis revealed that the AtANN1 promoter (AtANN1-pro) contains four cis-elements for MYB binding. The PeRAX2 interaction with AtANN1-pro was validated by LUC reporter assay, EMSA, and Y1H assay. Our data showed that PeRAX2 binds to the AtANN1 promoter region to regulate gene transcription and that AtANN1 mediates the Cd2+ entry through CaPCs in the PM, leading to a Cd2+ enrichment in transgenic plants. The PeRAX2-stimulated Cd2+ enrichment consequently resulted in high H2O2 production in root cells of transgenic plants. The expression of AtSOD and AtPOD and activities of CAT, SOD, POD increased in the transgenic lines under Cd2+ stress. However, the Cd2+-upregulated expression and activity of antioxidative enzymes were less pronounced in the PeRAX2-overexpressed lines, compared to the wildtype and vector controls. As a result, root length and plant growth were more suppressed by Cd2+ in the transgenic lines. Our data suggest that transcriptional regulation of AtANN1 by PeRAX2 can be utilized to improve Cd2+ enrichment and phytoremediation, although the enriched Cd2+ affected antioxidant defense system and plant growth in the model species.

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.

Unveiling Innovative Approaches to Mitigate Metals/Metalloids Toxicity for Sustainable Agriculture

Due to anthropogenic activities, environmental pollution of heavy metals/metalloids (HMs) has increased and received growing attention in recent decades. Plants growing in HM-contaminated soils have slower growth and development, resulting in lower agricultural yield. Exposure to HMs leads to the generation of free radicals (oxidative stress), which alters plant morpho-physiological and biochemical pathways at the cellular and tissue levels. Plants have evolved complex defense mechanisms to avoid or tolerate the toxic effects of HMs, including HMs absorption and accumulation in cell organelles, immobilization by forming complexes with organic chelates, extraction via numerous transporters, ion channels, signaling cascades, and transcription elements, among others. Nonetheless, these internal defensive mechanisms are insufficient to overcome HMs toxicity. Therefore, unveiling HMs adaptation and tolerance mechanisms is necessary for sustainable agriculture. Recent breakthroughs in cutting-edge approaches such as phytohormone and gasotransmitters application, nanotechnology, omics, and genetic engineering tools have identified molecular regulators linked to HMs tolerance, which may be applied to generate HMs-tolerant future plants. This review summarizes numerous systems that plants have adapted to resist HMs toxicity, such as physiological, biochemical, and molecular responses. Diverse adaptation strategies have also been comprehensively presented to advance plant resilience to HMs toxicity that could enable sustainable agricultural production.

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.

Study on remediation of cadmium contaminated paddy field by ramie (Boehmeria nivea L.) floating island and its supporting technology

Ramie (Boehmeria nivea L.) is an ideal crop for cadmium (Cd) pollution remediation due to its advantages of both remediating and utilizing, however, it is mainly carried out in dry land, whose restoration effect is relatively slow. Previously, we found that the ramie plants cultivated by hydroponics has several tens of times higher Cd absorption capacity than that planted in soil. However, the issue of how to use hydroponic ramie to remediate Cd contaminated paddy fields needs to be addressed. In this study, we innovatively developed the ramie floating island technology and studied its remediation model on simulated Cd contaminated paddy fields. Different ramie varieties were used to compare the remediation effects, and the results showed that there were differences in adaptability among different varieties on floating islands and the remediation ability of the tested ramie varieties was Z2 > Z1 > Z3. Different harvested times were set to analyze the effects of harvested model on remediation, and it was suggested that multiple harvests can be carried out according to the plant growth status of ramie floating island after 30 days of remediation to achieve better remediation effects. Low water level height (5 cm) of paddy field was beneficial for the accumulation of Cd in the roots, but considering the adaptability of various ramie varieties and the effect of long-term restoration, it was recommended that the water level height of 20 cm for the cultivation of ramie floating island was more suitable. Moreover, we found that low concentration of citric acid (≤2 g L-1) or polyaspartic acid (≤3 g L-1) can improve the remediation effects for ramie floating island. Our study opens up a novel approach for ramie to remediate heavy metal pollution and provides a technical reference for water body Cd remediation by plants.

Investigation of the role of TmMYB16/123 and their targets (TmMTP1/11) in the tolerance of Taxus media to cadmium

The toxicity and stress caused by heavy metal contamination has become an important constraint to the growth and flourishing of trees. In particular, species belonging to the genus Taxus, which are the only natural source for the anti-tumor medicine paclitaxel, are known to be highly sensitive to environmental changes. To investigate the response of Taxus spp. to heavy metal stress, we analyzed the transcriptomic profiles of Taxus media trees exposed to cadmium (Cd2+). In total, six putative genes from the metal tolerance protein (MTP) family were identified in T. media, including two Cd2+ stress inducible TMP genes (TmMTP1, TmMTP11 and Taxus media). Secondary structure analyses predicted that TmMTP1 and TmMTP11, which are members of the Zn-CDF and Mn-CDF subfamily proteins, respectively, contained six and four classic transmembrane domains, respectively. The introduction of TmMTP1/11 into the ∆ycf1 yeast cadmium-sensitive mutant strain showed that TmMTP1/11 might regulate the accumulation of Cd2+ to yeast cells. To screen the upstream regulators, partial promoter sequences of the TmMTP1/11 genes were isolated using the chromosome walking method. Several myeloblastosis (MYB) recognition elements were identified in the promoters of these genes. Furthermore, two Cd2+-induced R2R3-MYB TFs, TmMYB16 and TmMYB123, were identified. Both in vitro and in vivo assays confirmed that TmMTB16/123 play a role in Cd2+ tolerance by activating and repressing the expression of TmMTP1/11 genes. The present study elucidated new regulatory mechanisms underlying the response to Cd stress and can contribute to the breeding of Taxus species with high environmental adaptability.

Exposure to multiple metals in adults and diabetes mellitus: a cross-sectional analysis

Diabetes mellitus (DM) is the most widely recognized metabolic illness with expanding morbidity among ongoing years. Its high incapacity rate and death rate badly affect individuals' quality of life. Increasing proofs backed the relationship between metal exposures with the risk of DM, but the methodological boundedness cannot clarify the complexity of the internal relationship of metal mixtures. We fitted the logistic regression model, weighted quantile sum regression model, and Bayesian kernel machine regression model to assess the relationship between the metal exposures with DM in adults who participated in the National Health and Nutrition Examination Survey 2013-2016. The metals (lead, cadmium, and copper) levels were significantly higher among diabetic compared to the healthy controls. In the logistic regression model established for each single metal, lead and manganese were associated with DM in both unadjusted and mutually adjusted models (highest vs. lowest concentration quartile). When considering all metal as a mixed exposure, we found a generally positive correlation between metal mixtures with DM (binary outcome) and glycohemoglobin (HbA1c) levels (continuous outcome). Exposure to metal mixtures was associated with an increased risk of DM and elevated levels of HbA1c.

Transcriptomic analysis reveals the molecular mechanisms of Boehmeria nivea L. in response to antimonite and antimonate stresses

Soil antimony (Sb) pollution is a global concern that threatens food security and human health. Boehmeria nivea L. (ramie) is a promising phytoremediation plant exhibiting high tolerance and enrichment capacity for Sb. To reveal the molecular mechanisms and thus enhance the ramie uptake, transport, and detoxification of Sb with practical strategies, a hydroponic experiment was conducted to compare the physiological and transcriptomic responses of ramie towards antimonite (Sb(Ⅲ)) and antimonate (Sb(Ⅴ)). Phenotypic results showed that Sb(Ⅲ) had a stronger inhibitory effect on the growth of ramie. Root Sb content under Sb(Ⅲ) was 2.43 times higher than that in Sb(Ⅴ) treatment. Based on the ribonucleic acid sequencing (RNA-Seq) technique, 3915 and 999 significant differentially expressed genes (DEGs) were identified under Sb(Ⅲ) and Sb(Ⅴ), respectively. Transcriptomic analysis revealed that ramie showed different adaptation strategies to Sb(Ⅲ) and Sb(V). Key DEGs and their involved pathways such as catalytic activity, carbohydrate metabolisms, phenylpropanoid biosynthesis, and cell wall modification were identified to perform crucial roles in Sb tolerance and detoxification. Two heavy metal-associated domain-type genes, six heavy metal-associated isoprenylated plant proteins, and nine ABC transporters showed possible roles in the transport and detoxification of Sb. The significant upregulation of NRAMP5 and three NIPs suggested their roles in the transport of Sb(V). This study is the basis for future research to identify the exact genes and biological processes that can effectively enhance Sb accumulation or improve plant tolerance to Sb, thereby promoting the phytoremediation of Sb-polluted soils.

The R2R3-MYB transcription factor ThRAX2 recognized a new element MYB-T (CTTCCA) to enhance cadmium tolerance in Tamarix hispida

R2R3-MYB transcription factors play an important role in plant development and response to various environmental stresses. In this study, a new R2R3-MYB gene, named ThRAX2, was isolated from T. hispida. ThRAX2 has an open reading frame (ORF) of 1191 bp and encodes a protein of 396 amino acids. ThRAX2 was localized in the nucleus. The overexpression of ThRAX2 in Arabidopsis and T. hispida significantly increased Cadmium (Cd) tolerance. Moreover, the accumulation of cadmium in roots and leaves was significantly reduced. The TF-centred Y1H and Y1H results showed that ThRAX2 was able to specifically bind a new cis-element (MYB-T, CTTCCA). The promoters of some Cd-responsive genes, such as ThSOS1, ThCKX3, ThCAX3A, ThMYB78, ThMIP2, ThTPS4, and ThSOD2, all contained 1-3 MYB-T sequences. Furthermore, chromatin immunoprecipitation-polymerase chain reaction (ChIP-PCR) and ChIPquantitative (q)PCR showed that the ThRAX2 gene can bind to ThSOS1, ThCKX3, ThCAX3A and ThMYB78 promoter fragments, including the MYB-T motif. Meanwhile, the qRTPCR results also showed that the expression trends of ThSOS1, ThCKX3, ThCAX3A and ThMYB78 were similar to that of ThRAX2. This finding suggests that Cd tolerance of the ThRAX2 gene may regulate the expression of some downstream genes through specific recognition of the MYB-T motif and participate in regulating intracellular ion homeostasis, transport, and protein activity or enhance antioxidant enzyme activity. This study found a novel cis-acting element that binds ThRAX2 to regulate Cd tolerance, which lays the foundation for the ThRAX2 regulatory mechanism of Cd stress. This study provides a genetic and theoretical basis for the bioremediation of Cd-contaminated land by cultivating transgenic plants in the future.

Transcriptomic Analysis of Differentially Expressed Genes in Arabidopsis thaliana Overexpressing BnMYB2 from Boehmeria nivea under Cadmium Stress

Boehmeria nivea (ramie) is an important fiber crop with strong tolerance to cadmium (Cd). In our previous study, a novel MYB transcription factor gene from ramie, BnMYB2, was found to positively regulate Cd tolerance and accumulation in the transgenic Arabidopsis thaliana lines. Herein, transcriptome sequencing was performed to identify the differentially expressed genes involved in cadmium response between the wild-type (WT) and BnMYB2 overexpressed lines; 1598 differentially expressed genes (DEGs) were detected in the shoot. GO and KEGG analysis indicated that the majority of DEGs belonged to the categories of transcription factors, plant hormone signal transduction and nitrogen metabolism. The expression level of the Ib subgroup bHLH genes (AtbHLH38, AtbHLH39, AtbHLH100 and AtbHLH101) and nitrogen assimilation-related genes (AtNIA1, AtNIA2, AtNIR1 and AtASN2) were significantly higher than that of WT, accompanied with the positive changes in iron (Fe) and total nitrogen content in the shoot of BnMYB2 overexpression lines. Several DEGs belonging to the bZIP transcription factor family or SAUR family were also found up-regulated in the transgenic plants. These results provide important clues for elucidating how the molecular mechanisms of BnMYB2 regulate plant response to Cd stress.

Transcriptional Regulatory Network of Plant Cadmium Stress Response

Cadmium (Cd) is a non-essential heavy metal with high toxicity to plants. Plants have acquired specialized mechanisms to sense, transport, and detoxify Cd. Recent studies have identified many transporters involved in Cd uptake, transport, and detoxification. However, the complex transcriptional regulatory networks involved in Cd response remain to be elucidated. Here, we provide an overview of current knowledge regarding transcriptional regulatory networks and post-translational regulation of the transcription factors involved in Cd response. An increasing number of reports indicate that epigenetic regulation and long non-coding and small RNAs are important in Cd-induced transcriptional responses. Several kinases play important roles in Cd signaling that activate transcriptional cascades. We also discuss the perspectives to reduce grain Cd content and improve crop tolerance to Cd stress, which provides a theoretical reference for food safety and the future research of plant varieties with low Cd accumulation.

Molecular Breeding and Drought Tolerance in Chickpea

Cicer arietinum L. is the third greatest widely planted imperative pulse crop worldwide, and it belongs to the Leguminosae family. Drought is the utmost common abiotic factor on plants, distressing their water status and limiting their growth and development. Chickpea genotypes have the natural ability to fight drought stress using certain strategies viz., escape, avoidance and tolerance. Assorted breeding methods, including hybridization, mutation, and marker-aided breeding, genome sequencing along with omics approaches, could be used to improve the chickpea germplasm lines(s) against drought stress. Root features, for instance depth and root biomass, have been recognized as the greatest beneficial morphological factors for managing terminal drought tolerance in the chickpea. Marker-aided selection, for example, is a genomics-assisted breeding (GAB) strategy that can considerably increase crop breeding accuracy and competence. These breeding technologies, notably marker-assisted breeding, omics, and plant physiology knowledge, underlined the importance of chickpea breeding and can be used in future crop improvement programmes to generate drought-tolerant cultivars(s).

Analysis of WRKY Resistance Gene Family in Boehmeria nivea (L.) Gaudich: Crosstalk Mechanisms of Secondary Cell Wall Thickening and Cadmium Stress

A total of 60 WRKY family genes of ramie were identified in the ramie. The genes were unevenly distributed across 14 chromosomes in the specie and highly concentrated (72%) in the distal telomeric region. Phylogenetic analysis placed these genes into seven distinct subfamilies groups: I, II (a, b, c, d, e), and III, with group IIc containing only the variant of heptapetide sequence (WRKYGKK). Segmental duplication events (41.7%) was found to be the main driver of BnGWRKY evolution. Thirty eight from among the genes showed collinear relationships with WRKY genes from Arabidopsis thaliana, Cannabis sativa, Oryza sativa, and Zea mays. The number and density of stress and hormone responsives cis-acting elements were comparably higher than other elements, with abundant ARE and rare LTR cis-acting elements indicating the long-standing adaptability of ramie to its natural environment. GO and KEGG enrichment analysis of the WRKY target genes revealed their involvement in response to stimuli, immune system processes, transporter protein activity and antioxidant activity. Expression analysis show that most WRKYs were activated by the cadmium stress, more especially the BnGWRKY2, BnGWRKY15, BnGWRKY20, BnGWRKY50 and BnGWRKY58. Combining transcriptome, orthologous gene relationships and qPCR result, we established the possible involvement of BnGWRKY50 and BnGWRKY58 in crosstalk mechanism between secondary cell wall thickening and Cd²⁺ stress. This provided information into the role of BnGWRKY proteins in ramie secondary wall development and cadmium stress response to, and could serve as basis for improvement of the ramie.

Genome-wide identification of myeloblastosis gene family and its response to cadmium stress in Ipomoea aquatica

The myeloblastosis (MYB) proteins perform key functions in mediating cadmium (Cd) tolerance of plants. Ipomoea aquatica has strong adaptability to Cd Stress, while the roles of the I. aquatica MYB gene family with respect to Cd stress are still unclear. Here, we identified a total of 183 MYB genes in the I. aquatica genome (laMYB), which were classified into 66 1R-type IaMYB, 112 2R-type IaMYB, four 3R-type IaMYB, and one 4R-type IaMYB based on the number of the MYB repeat in each gene. The analysis of phylogenetic tree indicated that most of IaMYB genes are associated with the diverse biological processes including defense, development and metabolism. Analysis of sequence features showed that the IaMYB genes within identical subfamily have the similar patterns of the motif distributions and gene structures. Analysis of gene duplication events revealed that the dispersed duplication (DSD) and whole-genome duplication (WGD) modes play vital roles in the expansion of the IaMYB gene family. Expression profiling manifests that approximately 20% of IaMYB genes had significant role in the roots of I. aquatica under Cd stress. Promoter profiling implied that the differentially expressed genes might be induced by environmental factors or inherent hormones and thereby execute their function in Cd response. Remarkably, the 2R-type IaMYB157 with abundant light-responsive element G-box and ABA-responsive element ABRE in its promoter region exhibited very strong response to Cd stress. Taken together, our findings provide an important candidate IaMYB gene for further deciphering the molecular regulatory mechanism in plant with respect to Cd stress.

Early gene expression response of barley root tip to toxic concentrations of cadmium

Already a short-term Cd treatment induces changes in gene expression in barley root tips via IAA and ROS signaling during mild and severe Cd stress, respectively. Even a short, 30 min, Cd treatment of roots induced a considerable alteration in gene expression in the barley root tips within an hour after the treatments. The very early activation of MYB1 transcription factor expression is partially regulated by auxin signaling in mildly stressed seedlings. An increase in allene oxide cyclase and NADPH oxidase expression was a distinguishing feature of root tips response to mild Cd stress and their expression is activated via IAA signaling. Meanwhile, early changes in the level of dehydrin transcripts were detected in moderately and severely stressed root tips, and their induction is related to altered ROS homeostasis in cells. The early activation of glutathione peroxidase expression by mild Cd stress indicates the involvement of IAA in the signaling process. In contrast, early ascorbate peroxidase expression was induced only with Cd treatment causing severe stress and ROS play central roles in its induction. The expression of cysteine protease was activated similarly in both mildly and severely Cd-stressed roots; consequently, both increased IAA and ROS levels take part in the regulation of cysteine protease expression. The Cd-evoked accumulation of BAX Inhibitor-1 mRNA was characteristic for moderately and severely stressed roots. Whereas decreased IAA level did not affect its expression, rotenone-mediated ROS depletion markedly reduced the Cd-induced expression of BAX Inhibitor-1. An early increase of alternative oxidase levels in the root tip cells indicated that the reduction of mitochondrial superoxide generation is an important component of barley root response to severe Cd stress.

Cross-Kingdom Comparative Transcriptomics Reveals Conserved Genetic Modules in Response to Cadmium Stress

It is known that organisms have developed various mechanisms to cope with cadmium (Cd) stress, while we still lack a system-level understanding of the functional isomorphy among them. In the present study, a cross-kingdom comparison was conducted among Escherichia coli, Saccharomyces cerevisiae, and Chlamydomonas reinhardtii, through toxicological tests, comparative transcriptomics, as well as conventional functional genomics. An equivalent level of Cd stress was determined via inhibition tests. Through transcriptome comparison, the three organisms exhibited differential gene expression under the same Cd stress relative to the corresponding no-treatment control. Results from functional enrichment analysis of differentially expressed genes (DEGs) showed that four metabolic pathways responsible for combating Cd stress were commonly regulated in the three organisms, including antioxidant reactions, sulfur metabolism, cell wall remodeling, and metal transport. In vivo expression patterns of 43 DEGs from the four pathways were further examined using quantitative PCR and resulted in a relatively comparable dynamic of gene expression patterns with transcriptome sequencing (RNA-seq). Cross-kingdom comparison of typical Cd stress-responding proteins resulted in the detection of 12 groups of homologous proteins in the three species. A class of potential metal transporters were subjected to cross-transformation to test their functional complementation. An ABC transporter gene in E. coli, possibly homologous to the yeast ycf1, was heterologously expressed in S. cerevisiae, resulting in enhanced Cd tolerance. Overall, our findings indicated that conserved genetic modules against Cd toxicity were commonly regulated among distantly related microbial species, which will be helpful for utilizing them in modifying microbial traits for bioremediation.

IMPORTANCE Research is establishing a systems biology view of biological response to Cd stress. It is meaningful to explore whether there is regulatory isomorphy among distantly related organisms. A transcriptomic comparison was done among model microbes, leading to the identification of a conserved cellular model pinpointing the generic strategies utilized by microbes for combating Cd stress. A novel E. coli transporter gene substantially increased yeast’s Cd tolerance. Knowledge on systems understanding of the cellular response to metals provides the basis for developing bioengineering remediation technology.

Regulatory hubs and strategies for improving heavy metal tolerance in plants: Chemical messengers, omics and genetic engineering

Heavy metal (HM) accumulation in the agricultural soil and its toxicity is a major threat for plant growth and development. HMs disrupt functional integrity of the plants, induces altered phenological and physiological responses and slashes down qualitative crop yield. Chemical messengers such as phytohormones, plant growth regulators and gasotransmitters play a crucial role in regulating plant growth and development under metal toxicity in plants. Understanding the intricate network of these chemical messengers as well as interactions of genes/metabolites/proteins associated with HM toxicity in plants is necessary for deciphering insights into the regulatory circuit involved in HM tolerance. The present review describes (a) the role of chemical messengers in HM-induced toxicity mitigation, (b) possible crosstalk between phytohormones and other signaling cascades involved in plants HM tolerance and (c) the recent advancements in biotechnological interventions including genetic engineering, genome editing and omics approaches to provide a step ahead in making of improved plant against HM toxicities.