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.

Transition metal ions are critically important across all kingdoms of life. The chemical properties of iron, copper, zinc, manganese, cobalt, and nickel make them very attractive for use as cofactors in metalloenzymes and/or metalloproteins. Their versatile chemistry in aqueous solution enables them to function both as electron donors and acceptors, and thus participate in both reduction and oxidation reactions respectively. Transition metal ions can also function as nonredox multidentate coordination sites that play essential roles in macromolecular structure and function. Malfunction in transition metal transport and homeostasis has been linked to a wide number of human diseases including cancer, diabetes, and neurodegenerative disorders. Transition metal transporters are central players in the physiology of transition metals whereby they move transition metals in and out of cellular compartments. In this review, we provide a comprehensive overview of in vitro reconstitution of the activity of integral membrane transition metal transporters and discuss strategies that have been successfully implemented to overcome the challenges. We also discuss recent advances in our understanding of transition metal transport mechanisms and the techniques that are currently used to decipher the molecular basis of transport activities of these proteins. Deep mechanistic insights into transition metal transport systems will be essential to understand their malfunction in human diseases and target them for potential therapeutic strategies.

Vesicular sequestration is a potential strategy for enhancing plant tolerance to cadmium (Cd) and arsenic (As). In this study, the ectopic overexpression of yeast-derived ScSMF2 in Arabidopsis thaliana was found to enhance the accumulation and tolerance of Cd and As in transgenic plants. ScSMF2 was localized on vacuole membranes and formed puncta structures in plant cells when agro-infiltrated for transient expression. Transgenic Arabidopsis showed less retardation on root elongation and shoot weight and more accumulation of Cd, As (III) and As (V) when cultured on medium containing Cd or As. Overexpression of ScSMF2 promoted accumulation of Cd and arsenic in transgenic Arabidopsis, which were over twice higher than in WT plants when cultured in soil. This study provides insights into the mechanisms involved in the vesicular sequestration of heavy metals in plant and presents a potential strategy for enhancing the phytoremediation capacity of plants toward heavy metals.
Ectopic overexpression of the yeast Mn2+ transporter SMF2 in Arabidopsis thaliana substantially boosts the accumulation and tolerance to Cd and As in plants. This augmentation is attributed to the enhanced efficacy of intracellular vesicle sequestration, thereby bolstering the capacity of plants to sequester and detoxify these toxic heavy metals. This investigation introduces a potential approach for cultivating plants with improved phytoremediation capabilities, thereby advancing eco-friendly and sustainable remediation initiatives against heavy metal pollution.

Cadmium (Cd) is a toxic metal that poses serious threats to human health. Rice is a major source of dietary Cd but how rice plants transport Cd to the grain is not fully understood. Here, we characterize the function of the ZIP (ZRT, IRT-like protein) family protein, OsZIP2, in the root-to-shoot translocation of Cd and intervascular transfer of Cd in nodes. OsZIP2 is localized at the plasma membrane and exhibited Cd2+ transport activity when heterologously expressed in yeast. OsZIP2 is strongly expressed in xylem parenchyma cells in roots and in enlarged vascular bundles in nodes. Knockout of OsZIP2 significantly enhanced root-to-shoot translocation of Cd and alleviated the inhibition of root elongation by excess Cd stress; whereas overexpression of OsZIP2 decreased Cd translocation to shoots and resulted in Cd sensitivity. Knockout of OsZIP2 increased Cd allocation to the flag leaf but decreased Cd allocation to the panicle and grain. We further reveal that the variation of OsZIP2 expression level contributes to grain Cd concentration among rice germplasms. Our results demonstrate that OsZIP2 functions in root-to-shoot translocation of Cd in roots and intervascular transfer of Cd in nodes, which can be used for breeding low Cd rice varieties.

Metal homeostasis is maintained by the uptake, storage and efflux of metal ions that are necessary for the survival of the bacterium. Homeostasis is mostly regulated by a group of transporters categorized as ABC transporters and P-type ATPases. On the other hand, efflux pumps often play a role in drug-metal cross-resistance. Here, with the help of antibiotic sensitivity, antibiotic/dye accumulation and semi-quantitative biofilm formation assessments we report the ability of Rv3270, a P-type ATPase known for its role in combating Mn2+ and Zn2+ metal ion toxicity in Mycobacterium tuberculosis, in influencing the extrusion of multiple structurally unrelated drugs and enhancing the biofilm formation of Escherichia coli and Mycobacterium smegmatis. Overexpression of Rv3270 increased the tolerance of host cells to norfloxacin, ofloxacin, sparfloxacin, ampicillin, oxacillin, amikacin and isoniazid. A significantly lower accumulation of norfloxacin, ethidium bromide, bocillin FL and levofloxacin in cells harbouring Rv3270 as compared to host cells indicated its role in enhancing efflux activity. Although over-expression of Rv3270 did not alter the susceptibility levels of levofloxacin, rifampicin and apramycin, the presence of a sub-inhibitory concentration of Zn2+ resulted in low-level tolerance towards these drugs. Of note, the expression of Rv3270 enhanced the biofilm-forming ability of the host cells strengthening its role in antimicrobial resistance. Therefore, the study indicated that the over-expression of Rv3270 enhances the drug efflux activity of the micro-organism where zinc might facilitate drug-metal cross-resistance for some antibiotics.

Symbiotic nitrogen fixation carried out by the interaction between legumes and rhizobia is the main source of nitrogen in natural ecosystems and in sustainable agriculture. For the symbiosis to be viable, nutrient exchange between the partners is essential. Transition metals are among the nutrients delivered to the nitrogen-fixing bacteria within the legume root nodule cells. These elements are used as cofactors for many of the enzymes controlling nodule development and function, including nitrogenase, the only known enzyme able to convert N2 into NH3 . In this review, we discuss the current knowledge on how iron, zinc, copper, and molybdenum reach the nodules, how they are delivered to nodule cells, and how they are transferred to nitrogen-fixing bacteria within.

The natural resistance-associated macrophage protein (NRAMP) gene family assists in the transport of metal ions in plants. However, the role and underlying physiological mechanism of NRAMP genes under heavy metal toxicity in perennial trees remain to be elucidated. In Prunus persica, five NRAMP family genes were identified and named according to their predicted phylogenetic relationships. The expression profiling analysis indicated that PpNRAMPs were significantly induced by excess manganese (Mn), iron, zinc, and cadmium treatments, suggesting their potential role in heavy metal uptake and transportation. Notably, the expression of PpNRAMP5 was tremendously increased under Mn toxicity stress. Heterologous expression of PpNRAMP5 in yeast cells also confirmed Mn transport. Suppression of PpNRAMP5 through virus-induced gene silencing enhanced Mn tolerance, which was compromised when PpNRAMP5 was overexpressed in peach. The silencing of PpNRAMP5 mitigated Mn toxicity by dramatically reducing Mn contents in roots, and effectively reduced the chlorophyll degradation and improved the photosynthetic apparatus under Mn toxicity stress. Therefore, PpNRAMP5-silenced plants were less damaged by oxidative stress, as signified by lowered H2O2 contents and O2•- staining intensity, also altered the reactive oxygen species (ROS) homeostasis by activating enzymatic antioxidants. Consistently, these physiological changes showed an opposite trend in the PpNRAMP5-overexpressed peach plants. Altogether, our findings suggest that downregulation of PpNRAMP5 markedly reduces the uptake and transportation of Mn, thus activating enzymatic antioxidants to strengthen ROS scavenging capacity and photosynthesis activity, thereby mitigating Mn toxicity in peach plants.

Iron is an essential micronutrient for all types of organisms; however, iron has chemical properties that can be harmful to cells. Because iron is both necessary and potentially damaging, insects have homeostatic processes that control the redox state, quantity, and location of iron in the body. These processes include uptake of iron from the diet, intracellular and extracellular iron transport, and iron storage. Early studies of iron-binding proteins in insects suggested that insects and mammals have surprisingly different mechanisms of iron homeostasis, including different primary mechanisms for exporting iron from cells and for transporting iron from one cell to another, and subsequent studies have continued to support this view. This review summarizes current knowledge about iron homeostasis in insects, compares insect and mammalian iron homeostasis mechanisms, and calls attention to key remaining knowledge gaps.

Arsenic (As) has become natural health hazard for millions of people across the world due to its distribution in the food chain. Naturally, it is present in different oxidative states of inorganic [As(V) and As(III)] and organic (DMA, MMA and TMA) forms. Among different mitigation approaches, microbe mediated mitigation of As toxicity is an effective and eco-friendly approach. The present study involves the characterization of bacterial strains containing arsenite methyltransferase (Pseudomonas oleovorans, B4.10); arsenate reductase (Sphingobacterium puteale, B4.22) and arsenite oxidase (Citrobacter sp., B5.12) activity with plant growth promoting (PGP) traits. Efficient reduction of grain As content by 61 % was observed due to inoculation of methyltransferase containing B4.10 as compared to B4.22 (47 %) and B5.12 (49 %). Reduced bioaccumulation of As in root (0.339) and shoot (0.166) in presence of B4.10 was found to be inversely related with translocation factor for Mn (3.28), Fe (0.073), and Se (1.82). Bioaccumulation of these micro elements was found to be associated with the modulated expression of different mineral transporters (OsIRT2, OsFRO2, OsTOM1, OsSultr4;1, and OsZIP2) in rice shoot. Improved dehydrogenase (407 %), and β-glucosidase (97 %) activity in presence of P. oleovorans (B4.10) as compared to arsenate reductase (198 and 50 %), and arsenite oxidase (134 and 69 %) containing bacteria was also observed. Our finding confers the potential of methyltransferase positive P. oleovorans (B4.10) for As stress amelioration. Reduced grain As uptake was found to be mediated by improved plant growth and nutrient uptake associated with enhanced soil microbial activity.

Aluminum (Al) toxicity causes severe reduction in crop yields in acidic soil. The natural resistance-associated macrophage proteins (NRAMPs) play an important role in the transport of mineral elements in plants. Recently, OsNrat1 and SbNrat1 were reported specifically to transport trivalent Al ions. In this study, we functionally characterized ZmNRAMP4, a gene previously identified from RNA-Seq data from Al-treated maize roots, in response to Al exposure in maize. ZmNRAMP4 was predominantly expressed in root tips and was specifically induced by Al stress. Yeast cells expressing ZmNRAMP4 were hypersensitive to Al, which was associated with Al accumulation in yeast. Furthermore, overexpression of ZmNRAMP4 in Arabidopsis conferred transgenic plants with a significant increase in Al tolerance. However, expression of ZmNRAMP4, either in yeast or in Arabidopsis, had no effect on the response to cadmium stress. Taken together, these results underlined an internal tolerance mechanism involving ZmNRAMP4 to enhance Al tolerance via cytoplasmic sequestration of Al in maize.