Plasma-Membrane-Localized Transporter NREET1 is Responsible for Rare Earth Element Uptake in Hyperaccumulator Dicranopteris linearis

Organic Cation Transporter Mediates the Uptake of Quaternary Ammonium Compounds in Arabidopsis

Quaternary ammonium compounds (QACs), widely used in consumer products and pharmaceuticals, are increasingly released into soils and can accumulate in plants, posing significant ecological and health risks. While plant uptake mechanisms for QACs remain poorly characterized, this study identifies organic cation transporter 1 (OCT1) as a potential mediator of QAC absorption in Arabidopsis. Root uptake experiments demonstrated reduced QAC accumulation under treatments with metabolic and OCT inhibitors. Transcriptional upregulation of AtOCT1 in QAC-exposed wild-type plants, along with functional validation through yeast heterologous expression systems, implicated this transporter in cationic pollutant absorption. Comparative analysis revealed 12%-42% lower root QAC concentrations in AtOCT1 mutants compared to wild-type plants, while overexpression lines exhibited 9.4%-43% increases in accumulation alongside enhanced sensitivity. Molecular docking simulations demonstrated stronger binding affinities between AtOCT1 and QACs compared to its native substrate L-carnitine, with microscale thermophoresis confirming direct interactions. Quantitative structure-activity relationship analysis identified electronic energy, molecular weight, and polarizability as critical determinants of AtOCT1-mediated transport efficiency. These findings establish the biological and structural role of AtOCT1 in cationic pollutant uptake, advancing mechanistic understanding of transporter-mediated plant accumulation of ionizable organic pollutants.

Harnessing hyperaccumulator plants to recover technology-critical metals: where are we at?

Since its inception over three decades ago, phytomining has finally reached the stage of commercial-scale implementation, at least for nickel. Much potential remains to be realised for other elements, notably cobalt, selenium, and thallium, but this requires scientific impetus leveraging recent advances in insights garnered from molecular mechanisms of hyperaccumulation, domestication and agronomic development. These advances will also enable us to (genetically) improve hyperaccumulators for use in phytomining by targeted breeding, as well as synthetic biology approaches.

The Soil-Plant Continuity of Rare Earth Elements: Insights into an Enigmatic Class of Xenobiotics and Their Interactions with Plant Structures and Processes

Rare earth elements (REEs) are increasingly present in the environment owing to their extensive use in modern industries, yet their interactions with plants remain poorly understood. This review explores the soil-plant continuum of REEs, focusing on their geochemical behavior in soil, the mechanisms of plant uptake, and fractionation processes. While REEs are not essential for plant metabolism, they interact with plant structures and interfere with the normal functioning of biological macromolecules. Accordingly, the influence of REEs on the fundamental physiological functions of plants is reviewed, including calcium-mediated signalling and plant morphogenesis. Special attention is paid to the interaction of REEs with photosynthetic machinery and, particularly, the thylakoid membrane. By examining both the beneficial effects at low concentrations and toxicity at higher levels, this review provides some mechanistic insights into the hormetic action of REEs. It is recommended that future research should address knowledge gaps related to the bioavailability of REEs to plants, as well as the short- and long-range transport mechanisms responsible for REE fractionation. A better understanding of REE-plant interactions will be critical in regard to assessing their ecological impact and the potential risks in terms of agricultural and natural ecosystems, to ensure that the benefits of using REEs are not at the expense of environmental integrity or human health.

Solar-Driven Nanofluidic Ion Regulation for Fractional Salt Crystallization and Reutilization

Solar water evaporation (SWE) has emerged as an appealing method for water and salt recovery from hypersaline wastewater. However, different ions usually transfer and accumulate uncontrollably during ion-water separation, making salt fractionalization impractical for conventional SWE, and the resulting mixed salts are hard to use and still require significant costs for disposal. To achieve salt fractionalization and reutilization, achieving ion-water and ion-ion separation simultaneously are crucial in advancing SWE toward sustainability. Here, we present a wood-derived nanofluidic solar-driven fractional crystallizer that regulates the ion transfer processes and extracts nearly pure salt from a mixture of salts. SWE continuously induces capillary flow to propel and concentrate the ions in the wood channels. Meanwhile, engineered functional groups on the channel walls dominate the ion separation process via differentiated interactions with different ions. During ion transfer through channels, SO42- approaches the channel wall to compete for the positive charges and propels Cl- away, slowing SO42- transport and enlarging the transport energy barrier gap (2.65 to 19.28 kJ mol-1) between SO42- and Cl-. Through in situ observation, positive charges on the channel wall make SO42- lag Cl- 12.4 times that of bare Wood-D, accounting for the enhanced ion separation and the consequent fractional salt crystallization.

Root Zn sequestration transporter heavy metal ATPase 3 from Odontarrhena chalcidica enhance Cd tolerance and accumulation in Arabidopsis thaliana

The Ni hyperaccumulator Odontarrhena chalcidica (formerly Alyssum murale), exhibits a significant capacity to accumulate Zn in the roots. However, the molecular mechanisms underlying the variation in Ni and Zn accumulation are poorly understood. Here, we isolated a homolog of heavy metal ATPase 3 from O. chalcidica (OcHMA3) and characterized its functions using heterologous systems. Phylogenetic analysis revealed that OcHMA3 protein shares 87.6 % identity with AtHMA3, with similar metal binding sites to other HMA3 proteins. Heterologous expression of OcHMA3 in yeast increased sensitivity to Cd, Ni and Zn, suggesting it functions as a broad-specificity transporter. Further investigation showed OcHMA3 is constitutively expressed in the roots and localized to the tonoplast. Overexpression of OcHMA3 in A. thaliana shoots increased its roots Zn concentrations by 41.9 % - 74.1 %. However, overexpression of OcHMA3 in roots enhanced its tolerance to Cd and increased roots Cd concentrations by 50.9 % - 90.6 %. Our findings indicated OcHMA3 is responsible for Zn sequestration in root vacuoles, likely leading to Zn retention in roots and subsequent Ni hyperaccumulation in shoots. This study elucidates the molecular mechanism of Ni and Zn accumulation in O. chalcidica, and identifies OcHMA3 as a potential gene for developing Zn-rich plants and for phytoextraction in Cd-contaminated soils.

Distribution and migration of rare earth elements in sediment profile near a decommissioned uranium hydrometallurgical site in South China: Environmental implications

Rare earth elements have garnered increasing attention due to their strategic properties and chronic toxicity to humans. To better understand the content, migration, and ecological risk of rare earth elements in a 180 cm depth sediment profile downstream of a decommissioned uranium hydrometallurgical site in South China, X-ray powder diffraction (XRD) and High-resolution transmission electron microscope (HRTEM) were additionally used to quantify and clarify the mineral composition features. The results showed a high enrichment level of total rare earth elements in the sediment depth profile (range: 129.6-1264.3 mg/kg); the concentration variation of light rare earth elements was more dependent on depth than heavy rare earth elements. Overall, there was an obvious enrichment trend of light rare earth elements relative to heavy rare earth elements and negative anomalies of Ce and Eu. The fractionation and anomaly of rare earth elements in sediments were closely related to the formation and weathering of iron-bearing minerals and clay minerals, as confirmed by the correlation analysis of rare earth elements with Fe (r2 = 0.77-0.90) and Al (r2 = 0.50-0.71). The mineralogical composition of sediments mainly consisted of quartz, feldspar, magnetite, goethite, and hematite. Pollution assessment based on the potential ecological risk index, pollution load index (PLI), enrichment factor, and geological accumulation index (Igeo) showed that almost all the sediments had varying degrees of pollution and a high level of ecological risk. This study implied that continued environmental supervision and management are needed to secure the ecological health in terms of rare earth elements enrichment around a decommissioned uranium hydrometallurgical site. The findings may provide valuable insights for other uranium mining and hydrometallurgical areas globally.

Advancing phytomining: Harnessing plant potential for sustainable rare earth element extraction

Rare earth elements (REEs) are pivotal for advanced technologies, driving a surge in global demand. Import dependency on clean energy minerals raises concerns about supply chain vulnerabilities and geopolitical risks. Conventional REEs productionis resource-intensive and environmentally harmful, necessitating a sustainable supply approach. Phytomining (agromining) utilizes plants for eco-friendly REE extraction, contributing to the circular economy and exploiting untapped metal resources in enriched soils. Critical parameters like soil pH, Casparian strip, and REE valence influence soil and plant uptake bioavailability. Hyperaccumulator species efficiently accumulate REEs, serving as energy resources. Despite a lack of a comprehensive database, phytomining exhibits lower environmental impacts due to minimal chemical usage and CO2 absorption. This review proposes phytomining as a system for REEs extraction, remediating contaminated areas, and rehabilitating abandoned mines. The phytomining of REEs offers a promising avenue for sustainable REEs extraction but requires technological advancements to realize its full potential.

Rare earth elements perturb root architecture and ion homeostasis in Arabidopsis thaliana

Rare earth elements (REEs) are crucial elements for current high-technology and renewable energy advances. In addition to their increasing usage and their low recyclability leading to their release into the environment, REEs are also used as crop fertilizers. However, little is known regarding the cellular and molecular effects of REEs in plants, which is crucial for better risk assessment, crop safety and phytoremediation. Here, we analysed the ionome and transcriptomic response of Arabidopsis thaliana exposed to a light (lanthanum, La) and a heavy (ytterbium, Yb) REE. At the transcriptome level, we observed the contribution of ROS and auxin redistribution to the modified root architecture following REE exposure. We found indications for the perturbation of Fe homeostasis by REEs in both roots and leaves of Arabidopsis suggesting competition between REEs and Fe. Furthermore, we propose putative ways of entry of REEs inside cells through transporters of microelements. Finally, similar to REE accumulating species, organic acid homeostasis (e.g. malate and citrate) appears critical as a tolerance mechanism in response to REEs. By combining ionomics and transcriptomics, we elucidated essential patterns of REE uptake and toxicity response of Arabidopsis and provide new hypotheses for a better evaluation of the impact of REEs on plant homeostasis.

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.

Co-cropping vetiver grass and legume for the phytoremediation of an acid mine drainage (AMD) impacted soil

Acid mine drainage (AMD) is a form of environmental pollution from mining activity that can negatively affect soil environments by acidification, salinisation, and metal(loid) contamination. The use of plants to remediate (phytoremediation) these impacted environments while generating plant-based value is a promising approach to more accessible and cost-benefiting restoration of post-mining, marginal lands. In this study, a 3-month growth-chamber pot experiment was conducted to investigate the influence of co-cropping two plant species, Chrysopogon zizanioides (vetiver grass) and the legume Medicago truncatula (barrel clover) with a wheat straw biochar amendment on the phytostabilisation of metal(loid)s Cr, Zn, and As and the phytoextraction of rare earth element (REE) in an AMD impacted soil from a gold mining region in South Africa. The results showed that co-cropping with vetiver significantly lowered the legume's Cr, Zn, and As root contents by 80%, 32% and 54%, respectively, and improved the plant's overall metal(loid) tolerance by increasing its translocation from root to shoot tissue. The biochar further inhibited root uptake of Cr and Zn, by 71% and 36%, and increased the legume biomass by 40%. Both plant species and cropping treatments exhibited low REE extraction capabilities by shoot tissue, which accounted for less than 0.2% of total soil REE contents. The study shows that co-cropping with vetiver and biochar amendment are effective tools for the phytoremediation of AMD impacted soil mainly by lowering plant uptake and improving plant metal(loid) tolerance. Likely mechanisms at play include the alteration of rhizosphere chemistry and species-specific physiological and molecular responses. These effects offer support for the phytostabilisation of AMD impacted soil with the generation of plant-based value through dual (and safe) cultivation (phytoprotection) rather than through REE recovery from plant biomass (phytoextraction). These techniques could allow for the simultaneous restoration of post-mining, mining-impacted and marginal lands with agricultural production.