Metallochaperones: A critical regulator of metal homeostasis and beyond

Barriers and carriers for transition metal homeostasis in plants

Transition metals are types of metals with high chemical activity. They play critical roles in plant growth, development, reproduction, and environmental adaptation, as well as in human health. However, the acquisition, transport, and storage of these metals pose specific challenges due to their high reactivity and poor solubility. In addition, distinct yet interconnected apoplastic and symplastic diffusion barriers impede their movement throughout plants. To overcome these obstacles, plants have evolved sophisticated carrier systems to facilitate metal transport, relying on the tight coordination of vesicles, enzymes, metallochaperones, low-molecular-weight metal ligands, and membrane transporters for metals, ligands, and metal-ligand complexes. This review highlights recent advances in the homeostasis of transition metals in plants, focusing on the barriers to transition metal transport and the carriers that facilitate their passage through these barriers.

Mechanistic insight of fungal-microalgal pellets in photobioreactor for heavy-metal wastewater bioremediation

The high cost of harvesting microalgae limits their industrial application. Fungal-microalgal pellets can efficiently harvest microalgae and enhance heavy-metal adsorption. However, the molecular response mechanism of fungal-microalgal pellets under heavy-metal stress remains unclear. Fungal-microalgal pellets in a photobioreactor were used as a research object, and a 98 % harvesting efficiency could be achieved with adding exogenous carbon and nitrogen at pH 5.0-6.0 for 12 h of co-culture. Humic acid- and tryptophan-rich proteins in extracellular polymeric substances (EPS) participate in Cd(II) complexation. The Cd(II) response in fungal-microalgal pellets involves amino acids, glucose, lipids, energy metabolism, and antioxidant systems. The turning point was at 48 h. Proline, histidine, and glutamine synthesis and the adenosine-triphosphate (ATP) binding cassette (ABC) transport pathway play important roles in resistance to Cd(II) biotoxicity. This study provides a reference for the large-scale cultivation of fungal-microalgal symbiotic pellets and the practical application for industrial heavy-metal wastewater.

Copper stress in rice: Perception, signaling, bioremediation and future prospects

Copper (Cu) is an indispensable micronutrient for plants, animals, and microorganisms and plays a vital role in different physiological processes. However, excessive Cu accumulation in agricultural soil, often through anthropogenic action, poses a potential risk to plant health and crop productivity. This review article provided a comprehensive overview of the available information regarding Cu dynamics in agricultural soils, major sources of Cu contamination, factors influencing its mobility and bioavailability, and mechanisms of Cu uptake and translocation in rice plants. This review examined the impact of Cu toxicity on the germination, growth, and photosynthesis of rice plants. It also highlighted molecular mechanisms underlying Cu stress signaling and the plant defense strategy, involving chelation, compartmentalization, and antioxidant responses. This review also identified significant areas that need further research, such as Cu uptake mechanism in rice, Cu signaling process, and the assessment of Cu-polluted paddy soil and rice toxicity under diverse environmental conditions. The development of rice varieties with reduced Cu accumulation through comprehensive breeding programs is also necessary. Regulatory measures, fungicide management, plant selection, soil and environmental investigation are recommended to prevent Cu buildup in agricultural lands to achieve sustainable agricultural goals.

Transcriptome sequencing analysis of gene expression in phosphate-solubilizing bacterium 'N3' and grafted watermelon plants coping with toxicity induced by cadmium

Cadmium (Cd) is a harmful metal in soil, and reducing Cd accumulation in plants has become a vital prerequisite for maintaining food safety. Phosphate-solubilizing bacteria (PSB) can not only improve plant growth but also inhibit the transportation of metals to roots. However, data on gene expression in PSB Burkholderia sp. strain 'N3' and grafted watermelon plants dealing with Cd remain to be elucidated. In this study, core genes and metabolic pathways of strain 'N3' and grafted plants were analyzed by Illumina sequencing. Results showed that 356 and 2527 genes were upregulated in 'N3' and grafted watermelon plants, respectively, whereas 514 and 1540 genes were downregulated in 'N3' and grafted watermelon plants, respectively. Gene ontology enrichment analysis showed that signal transduction, inorganic ion transport, cell motility, amino acid transport, and metabolism pathways were marked in 'N3'. However, pathways such as secondary metabolite biosynthesis, oxidation-reduction process, electron transfer activity, and channel regulator activity were marked in the grafted plants. Six genes related to pentose phosphate, glycolysis, and gluconeogenesis metabolism were upregulated in the grafted plants. This study paves the way for developing potential strategies to improve plant growth under Cd toxicity.

Phytoremediation potential of monocotyledonous plants in the sediments of the Uben River, Gujarat, India

Phytoremediation is a basic eco-friendly technique that uses to treat contaminated water and soil. The plants that remediate the water and soil by their absorption process and improve the water and sediment fertility or decrease the contamination. Form this experiment our finding suggest that the contamination decrease in majority from starting point to end point, it means plants plays the most important role in clean-up the environment and its cost-efficient method to improve the quality of water and soil. This study was carried out on Uben River which is around 50kms long and we covered around 41.88kms of area which divided into six locations. in soil minerals (Ca2+, Mg2+, Na+ and K+) from Up-stream to Down-stream the concentration of minerals is in decreasing order but in heavy metals (Cu2+, Zn2+, Fe2+ and Mn2+) the concentration data is varying. We selected plants that grow around riverbanks belongs to family Cyperaceae, Poaceae, Typhaceae. Most of the plants accumulate high Fe2+ concentrations in their root while in the shoots have low concentration observed from our data. For the statistical validation of data, we perform Grouped Component Analysis (GCA) and Radial Cluster Hierarchy (RCH) analysis. Further we included pollution indices: Contamination factor (CF), Degree of contamination (Cd), Geo accumulation index (Igeo).

Overexpression of PavHIPP16 from Prunus avium enhances cold stress tolerance in transgenic tobacco

BACKGROUND

The heavy metal-associated isoprenylated plant protein (HIPP) is an important regulatory element in response to abiotic stresses, especially playing a key role in low-temperature response.

RESULTS

This study investigated the potential function of PavHIPP16 up-regulated in sweet cherry under cold stress by heterologous overexpression in tobacco. The results showed that the overexpression (OE) lines' growth state was better than wild type (WT), and the germination rate, root length, and fresh weight of OE lines were significantly higher than those of WT. In addition, the relative conductivity and malondialdehyde (MDA) content of the OE of tobacco under low-temperature treatment were substantially lower than those of WT. In contrast, peroxidase (POD), superoxide dismutase (SOD), catalase (CAT) activities, hydrogen peroxide (H2O2), proline, soluble protein, and soluble sugar contents were significantly higher than those of WT. Yeast two-hybrid assay (Y2H) and luciferase complementation assay verified the interactions between PavbHLH106 and PavHIPP16, suggesting that these two proteins co-regulated the cold tolerance mechanism in plants. The research results indicated that the transgenic lines could perform better under low-temperature stress by increasing the antioxidant enzyme activity and osmoregulatory substance content of the transgenic plants.

CONCLUSIONS

This study provides genetic resources for analyzing the biological functions of PavHIPPs, which is important for elucidating the mechanisms of cold resistance in sweet cherry.

Effects of environmental metal and metalloid pollutants on plants and human health: exploring nano-remediation approach

Metal and metalloid pollutants severely threatens environmental ecosystems and human health, necessitating effective remediation strategies. Nanoparticle (NPs)-based approaches have gained significant attention as promising solutions for efficient removing heavy metals from various environmental matrices. The present review is focused on green synthesized NPs-mediated remediation such as the implementation of iron, carbon-based nanomaterials, metal oxides, and bio-based NPs. The review also explores the mechanisms of NPs interactions with heavy metals, including adsorption, precipitation, and redox reactions. Critical factors influencing the remediation efficiency, such as NPs size, surface charge, and composition, are systematically examined. Furthermore, the environmental fate, transport, and potential risks associated with the application of NPs are critically evaluated. The review also highlights various sources of metal and metalloid pollutants and their impact on human health and translocation in plant tissues. Prospects and challenges in translating NPs-based remediation from laboratory research to real-world applications are proposed. The current work will be helpful to direct future research endeavors and promote the sustainable implementation of metal and metalloid elimination.

A novel antimony metallochaperone AntC in Comamonas testosteroni JL40 and its application in antimony immobilization

The microbial metabolism of toxic antimony (Sb) and the bioremediation of Sb-contaminated environments have attracted significant attention recently. This study identified an Sb(III) metallochaperone AntC in the Sb(III) efflux operon antRCA of Comamonas testosteroni JL40. The deletion of AntC significantly increased the intracellular Sb content in strain JL40 and concomitantly diminished resistance to Sb(III). By contrast, the complementary expression of AntC in the knockout strain resulted in a substantial recovery of Sb(III) resistance. The site-directed mutagenesis assay demonstrated the three conserved cysteine (Cys) residues (Cys30, Cys34, and Cys36) play an essential role in the binding of Sb(III) to AntC and its transfer. The function of the metallochaperone AntC was further investigated in an Sb(III) sensitive bacterium Escherichia coli AW3110 (Δars). The co-expression of AntC and AntA in AW3110 cells resulted in a four-fold increase in minimum inhibitory concentrations (MICs) toward Sb(III), while the intracellular Sb content decreased five-fold compared to cells expressing AntA alone. In addition, a genetically modified E. coli strain was engineered to co-express AntC and the Sb uptake protein GlpF, showing an eight-fold increase in Sb absorption and achieving a remarkable 90% removal of Sb from the solution. This engineered strain was also applied in a hydroponic experiment, displaying a significant 80% reduction in Sb uptake by rice seedlings. This finding provides new insights into the mechanisms of bacterial Sb detoxification and a potential bioremediation strategy for Sb pollution.

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.

Farmland phytoremediation in bibliometric analysis

Phytoremediation is an environmentally friendly, economical, and sustainable technique for restoring farmland. It can remove heavy metals and organic pollutants from the soil through the implementation of hyperaccumulator plants. In recent years, it has garnered significant interest from academic and industrial sectors. This article screened 368 research papers from the Web of Science core collection database related to farmland phytoremediation and conducted a bibliometric analysis of the domain based on CiteSpace. The paper intuitively demonstrates the most influential countries, the most productive institutions, the most contributing groups of authors, and the primary sources of farmland phytoremediation research domain. The findings additionally indicate that the research hotspots include: (1) mechanisms and principles of phytoremediation, (2) the improvement of restoration efficiency, (3) the economic, ecological, and sustainable development of phytoremediation. The exploration of plants with potential to accumulate heavy metals and produce large amounts of biomass is the research frontier within the field of farmland phytoremediation. Additionally, this bibliometric analysis can help scholars willing to work in this research field by concisely understanding the overall research field and frontiers. With the continuous improvement of phytoremediation and its combination with other remediation technologies, the future of farmland remediation will have a promising prospect.

A transposable element-derived siRNAs involve DNA hypermethylation at the promoter of OsGSTZ4 for cadmium tolerance in rice

Environmental contaminants such as cadmium (Cd) pose high risks to crop production and human health. The genetic basis for regulation of Cd stress-responsive genes for plant adaptation to adverse environments remains poorly understood. In this study, we characterized a rice Zeta family glutathione-S-transferase (OsGSTZ4) gene for Cd detoxification. Heterologous expression of OsGSTZ4 in a yeast (Saccharomyces cerevisiae) conferred cellular Cd tolerance. Transgenic rice overexpressing OsGSTZ4 improved plant growth, attenuated Cd-induced toxicity, and accumulated more Cd in roots. OsGSTZ4 transcription was rapidly induced 3 h after Cd exposure and then declined to the basal level. This was followed by (days after Cd treatment) by CHH hypermethylation (by 41.2 %) at a MITE (Miniature Inverted-repeat Transposable Element) transposable element (TE) inserted in the 5'-untranscribed region (UTR) (-1,722 ∼ -1,392 bp) of OsGSTZ4. Meanwhile, three 24-nt siRNAs derived from the TE (-1,722 ∼ -1,471 bp) were detected and was also rapidly enriched under Cd stress. To validate the possibility that Cd-induced change in OsGSTZ4 expression correlates with the siRNAs-involved CHH methylation through an RdDM (RNA-directed DNA methylation) pathway, genetic analyses were performed. We found that the CHH methylation at the promoter and transcript level of OsGSTZ4 were compromised in the osdrm2 (loss of function for CHH methylation) and osrdr2i (defective in RNA-dependent RNA polymerase 2) but did not change in other types of methyltransferases such as osmet1, ossdg714 or osros1. Promoter deletion analyses confirmed that the siRNA target sequences were essential for the proper expression of OsGSTZ4. Our studies reveal an unusual feedback mechanism by which the Cd-induced rapid OsGSTZ4 expression for Cd tolerance would interplay with the late CHH hypermethylation to silence the TE through the 24-nt siRNAs- and Osdrm2-mediated RdDM pathway, and help understand the diversity of gene regulation via an epigenetic mechanism for rice adaptation to the environmental stress.

Methyl jasmonate reduces cadmium toxicity by enhancing phenol and flavonoid metabolism and activating the antioxidant defense system in pigeon pea (Cajanus cajan)

Cadmium (Cd) is absorbed by plant roots from soil along with essential nutrients and affects plant growth and productivity. Methyl jasmonate (Me-JA) play important roles to mitigate Cd toxicity in plants. We have investigated the role of Me-JA to ameliorate Cd toxicity in Pigeon pea (Cajanus cajan). Plant root growth, biomass, cellular antioxidant defense system and expression of key regulatory genes in molecular and signaling process have been analyzed. Two Cajanus cajan varieties AL-882 and PAU-881 were grown at 25 °C, 16/8h light/dark conditions in three biological replicates at 5 mM Cd concentration, three concentration of Me-JA (0, 10 nM, 100 nM) and two concentrations in combination of Me-JA + Cd (10 nM Me-JA +5 mM Cd, 100 nM Me-JA +5 mM Cd). The seedlings were exposed to Cd stress consequently plants showed decrease in primary root growth (60.71%, in AL-882 and 8.33%, in PAU-881), shoot and root biomass and antioxidant enzymes activities. Me-JA treatment resulted in increased primary root growth (63.64%, in AL-882) and overall plant biomass. Oxidative stress generated due to Cd stress was counter balanced by Me-JA treatment. Me-JA reduced H2O2 free radicals formation and enhanced antioxidant enzyme activities and phenolic content in stressed seedlings. Me-JA treatment increased expression of CALM, IP3, CDPK2, MPKs (involved in calcium and kinase signaling pathways) and reduced expression of metal transporters (IRT1 and HMA3) genes. This reduction in metal transporters gene expression is a probable reason for low toxicity effect of Cd in root after Me-JA treatment which has potential implications in reducing the risk of Cd in the food chain.

Dose dependent effect of nitrogen on the phyto extractability of Cd in metal contaminated soil using Wedelia trilobata

Cadmium (Cd) is one of the toxic heavy metal that negatively affect plant growth and compromise food safety for human consumption. Nitrogen (N) is an essential macronutrient for plant growth and development. It may enhance Cd tolerance of invasive plant species by maintaining biochemical and physiological characteristics during phytoextraction of Cd. A comparative study was conducted to evaluate the phenotypical and physiological responses of invasive W. trilobata and native W. chinensis under low Cd (10 µM) and high Cd (80 µM) stress, along with different N levels (i.e., normal 91.05 mg kg-1 and low 0.9105 mg kg-1). Under low-N and Cd stress, the growth of leaves, stem and roots in W. trilobata was significantly increased by 35-23%, 25-28%, and 35-35%, respectively, compared to W. chinensis. Wedelia trilobata exhibited heightened antioxidant activities of catalase and peroxidase were significantly increased under Cd stress to alleviate oxidative stress. Similarly, flavonoid content was significantly increased by 40-50% in W. trilobata to promote Cd tolerance via activation of the secondary metabolites. An adverse effect of Cd in the leaves of W. chinensis was further verified by a novel hyperspectral imaging technology in the form of normalized differential vegetation index (NDVI) and photochemical reflectance index (PRI) compared to W. trilobata. Additionally, W. trilobata increased the Cd tolerance by regulating Cd accumulation in the shoots and roots, bolstering its potential for phytoextraction potential. This study demonstrated that W. trilobata positively responds to Cd with enhanced growth and antioxidant capabilities, providing a new platform for phytoremediation in agricultural lands to protect the environment from heavy metals pollution.

Detoxification and catabolism of mesotrione and fomesafen facilitated by a Phase II reaction acetyltransferase in rice

INTRODUCTION

The excessive dosage of pesticides required for agronomic reality results in growing contamination of pesticide residues in environment, thus bringing high risks to crop production and human health.

OBJECTIVES

This study aims to unveil a novel mechanism for catabolism of two pesticides MTR and FSA facilitated by an uncharacterized Phase II reaction enzyme termed acetyltransferase-1 (ACE1) in rice and to make assessment of its potential for bioremediation to minimize the risks to crop production and food safety.

METHODS

We developed genetically improved cultivars overexpressing OsACE1 (OE) and knockout mutant lines by CRISPR-Cas9 technology to identify the MTR and FSA detoxic and metabolic functions and characterized their metabolites and conjugates by HPLC-LTQ-MS/MS.

RESULTS

OsACE1 overexpression conferred rice resistance to toxicity of MTR/FSA compared to wild-type, manifested by improved plant elongation and biomass, attenuated cellular injury, and increased chlorophyll accumulation. The OE plants accumulated significantly less parent MTR/FSA and more degradative metabolites, and removed MTR/FSA from their growth medium by 1.38 and 1.61 folds over the wild-type. In contrast, knocking out OsACE1 led to compromised growth fitness and intensified toxic symptoms under MTR/FSA stress and accumulation of more toxic MTR and FSA in rice. The reduced metabolites of MTR and FSA detected in the Cas9 plants suggest the impaired capability of OsACE1 function.

CONCLUSIONS

These results signified that OsACE1 expression is required for detoxifying the two poisoning chemicals in rice and plays a critical role in accelerating breakdown of the pesticides mainly through Phase II reaction mechanism pathways.

Heavy Metal-Associated Isoprenylated Plant Proteins (HIPPs) at Plasmodesmata: Exploring the Link between Localization and Function

Heavy metal-associated isoprenylated plant proteins (HIPPs) are a metallochaperone-like protein family comprising a combination of structural features unique to vascular plants. HIPPs possess both one or two heavy metal-binding domains and an isoprenylation site, facilitating a posttranslational protein lipid modification. Recent work has characterized individual HIPPs across numerous different species and provided evidence for varied functionalities. Interestingly, a significant number of HIPPs have been identified in proteomes of plasmodesmata (PD)-nanochannels mediating symplastic connectivity within plant tissues that play pivotal roles in intercellular communication during plant development as well as responses to biotic and abiotic stress. As characterized functions of many HIPPs are linked to stress responses, plasmodesmal HIPP proteins are potentially interesting candidate components of signaling events at or for the regulation of PD. Here, we review what is known about PD-localized HIPP proteins specifically, and how the structure and function of HIPPs more generally could link to known properties and regulation of PD.

The Effect of Cadmium on Plants in Terms of the Response of Gene Expression Level and Activity

Cadmium (Cd) is a heavy metal that can cause damage to living organisms at different levels. Even at low concentrations, Cd can be toxic to plants, causing harm at multiple levels. As they are unable to move away from areas contaminated by Cd, plants have developed various defence mechanisms to protect themselves. Hyperaccumulators, which can accumulate and detoxify heavy metals more efficiently, are highly valued by scientists studying plant accumulation and detoxification mechanisms, as they provide a promising source of genes for developing plants suitable for phytoremediation techniques. So far, several genes have been identified as being upregulated when plants are exposed to Cd. These genes include genes encoding transcription factors such as iron-regulated transporter-like protein (ZIP), natural resistance associated macrophage protein (NRAMP) gene family, genes encoding phytochelatin synthases (PCs), superoxide dismutase (SOD) genes, heavy metal ATPase (HMA), cation diffusion facilitator gene family (CDF), Cd resistance gene family (PCR), ATP-binding cassette transporter gene family (ABC), the precursor 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and precursor 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) multigene family are also influenced. Thanks to advances in omics sciences and transcriptome analysis, we are gaining more insights into the genes involved in Cd stress response. Recent studies have also shown that Cd can affect the expression of genes related to antioxidant enzymes, hormonal pathways, and energy metabolism.

An investigation of zinc isotope fractionation in cacao (Theobroma cacao L.) and comparison of zinc and cadmium isotope compositions in hydroponic plant systems under high cadmium stress

This study aims to establish whether zinc (Zn) and cadmium (Cd) share similar physiological mechanisms for uptake and translocation in cacao plants (Theobroma cacao L.). Multiple-collector ICP-MS was used to determine the Zn stable isotope compositions in the roots, stems and leaves of 19 diverse cacao genotypes grown in hydroponics with 20 µmol L^-1 CdCl₂. Additional plants of one genotype were grown in hydroponic solutions containing lower Cd concentrations (0 and 5 µmol L^-1 added CdCl₂). Regardless of the Cd concentration used in the exposures, the Zn stable isotope compositions show the same systematic patterns in plant organs, with δ⁶⁶Zn_root > δ⁶⁶Zn_stem > δ⁶⁶Zn_leaf (δ⁶⁶Zn denotes relative differences in ⁶⁶Zn/⁶⁴Zn ratios in parts per thousand). The mean Zn stable isotope fractionation between the plants and the hydroponic solutions was ε⁶⁶Zn_uptake = -1.15 ± 0.36‰ (2SD), indicating preferential uptake of isotopically light Zn by plants from the hydroponic solution. The mean  stable isotope fractionation factor associated with translocation of Zn from roots to shoots, ε⁶⁶Zn_seq-mob =  + 0.52 ± 0.36‰ (2SD), shows that isotopically heavy Zn is preferentially sequestered in the cacao roots, whilst isotopically light Zn is mobilised to the leaves. A comparison with the Cd stable isotope compositions of the same plants shows that both isotopically light Zn and Cd are preferentially taken up by cacao plants. In contrast to Zn, however, the cacao roots retain isotopically light Cd and transfer isotopically heavy Cd to the leaves.

Transport and Environmental Risks of Propachlor Within the Soil-Plant-Water Phase as Affected by Dissolved Organic Matter as a Nonionic Surfactant

Propachlor is a widely used acylaniline herbicide for weeding annual gramineous and dicot plants in farmland. As a toxic agricultural chemical, it is overused in crop production and has become one of the most serious environmental pollutants. Yet, understanding the impact of environmental factors on its behavior in farmland soils is critically important for healthy crop production and food safety. In this study, we characterized the effect of dissolved organic matter (DOM) extracted from rice straw on the mobility behavior of propachlor in farmland soil using comprehensive approaches such as the batch equilibrium experiment, soil thin-layer chromatography, soil column leaching, and wheat bioaccumulation with Triton X-100 (TX-100) as a reference surfactant. The application of DOM at 60 and 120 mg DOC L^-1 and TX-100 at 96, 192, and 288 mg L^-1 reduced the sorption and increased the desorption of propachlor in soil. Freundlich constant K _f values (sorption) of propachlor declined with the expansion of DOM and TX-100 concentrations. The addition of DOM and TX-100 increased the mobility of propachlor and the total concentration of propachlor in the leachate of soil columns. The retention factors (R _f) were evaluated in the soil thin-layer chromatography as 0.741 and 0.772 (for DOM) and 0.731, 0.763, and 0.791 (for TX-100), all of which were greater than the control (0.710) under the treatment. The application of DOM or TX-100 reduced root growth (biomass) and increased bioaccumulation of propachlor in the roots and shoots of wheat. The outcome of the study can provide important references for the rational use of propachlor and help agronomic management to minimize pesticide contamination in realistic crop production.

A Green Approach Used for Heavy Metals 'Phytoremediation' Via Invasive Plant Species to Mitigate Environmental Pollution: A Review

Heavy metals (HMs) normally occur in nature and are rapidly released into ecosystems by anthropogenic activities, leading to a series of threats to plant productivity as well as human health. Phytoremediation is a clean, eco-friendly, and cost-effective method for reducing soil toxicity, particularly in weedy plants (invasive plant species (IPS)). This method provides a favorable tool for HM hyperaccumulation using invasive plants. Improving the phytoremediation strategy requires a profound knowledge of HM uptake and translocation as well as the development of resistance or tolerance to HMs. This review describes a comprehensive mechanism of uptake and translocation of HMs and their subsequent detoxification with the IPS via phytoremediation. Additionally, the improvement of phytoremediation through advanced biotechnological strategies, including genetic engineering, nanoparticles, microorganisms, CRISPR-Cas9, and protein basis, is discussed. In summary, this appraisal will provide a new platform for the uptake, translocation, and detoxification of HMs via the phytoremediation process of the IPS.

A Golgi-Located Transmembrane Nine Protein Gene TMN11 Functions in Manganese/Cadmium Homeostasis and Regulates Growth and Seed Development in Rice

Metal transporters play crucial roles in plant nutrition, development, and metal homeostasis. To date, several multi-proteins have been identified for metal transport across the plasma membrane and tonoplast. Nevertheless, Golgi endomembrane metal carriers and their mechanisms are less documented. In this study, we identified a new transmembrane nine (TMN) family gene, TMN11, which encodes a Mn transport protein that was localized to the cis-Golgi endomembrane in rice. OsTMN11 contains a typically conserved long luminal N-terminal domain and nine transmembrane domains. OsTMN11 was ubiquitously expressed over the lifespan of rice and strongly upregulated in young rice under excess Mn(II)/Cd(II) stress. Ectopic expression of OsTMN11 in an Mn-sensitive pmr1 mutant (PMR1 is a Golgi-resident Mn exporter) yeast (Saccharomyces cerevisiae) restored the defective phenotype and transported excess Mn out of the cells. As ScPMR1 mediates cellular Mn efflux via a vesicle-secretory pathway, the results suggest that OsTMN11 functions in a similar manner. OsTMN11 knockdown (by RNAi) compromised the growth of young rice, manifested as shorter plant height, reduced biomass, and chlorosis under excessive Mn and Cd conditions. Two lifelong field trials with rice cropped in either normal Mn supply conditions or in Cd-contaminated farmland demonstrated that knockdown of OsTMN11 impaired the capacity of seed development (including panicle, spikelet fertility, seed length, grain weight, etc.). The mature RNAi plants contained less Mn but accumulated Cd in grains and rice straw, confirming that OsTMN11 plays a fundamental role in metal homeostasis associated with rice growth and development even under normal Mn supply conditions.

Metal ion availability and homeostasis as drivers of metabolic evolution and enzyme function

Metal ions are potent catalysts and have been available for cellular biochemistry at all stages of evolution. Growing evidence suggests that metal catalysis was critical for the origin of the very first metabolic reactions. With approximately 80% of modern metabolic pathways being dependent on metal ions, metallocatalysis and homeostasis continue to be essential for intracellular metabolic networks and physiology. However, the genetic network that controls metal ion homeostasis and the impact of metal availability on metabolism is poorly understood. Here, we review recent work on gene and protein evolution relevant for better understanding metal ion biology and its role in metabolism. We highlight the importance of analysing the origin and evolution of enzyme catalysis in the context of catalytically relevant metal ions, summarise unanswered questions essential for developing a comprehensive understanding of metal ion homeostasis and advocate for the consideration of metal ion properties and availability in the design and directed evolution of novel enzymes and pathways.

Molecular Mechanisms Underlying Mimosa acutistipula Success in Amazonian Rehabilitating Minelands

Mimosa acutistipula is endemic to Brazil and grows in ferruginous outcrops (canga) in Serra dos Carajás, eastern Amazon, where one of the largest iron ore deposits in the world is located. Plants that develop in these ecosystems are subject to severe environmental conditions and must have adaptive mechanisms to grow and thrive in cangas. Mimosa acutistipula is a native species used to restore biodiversity in post-mining areas in canga. Understanding the molecular mechanisms involved in the adaptation of M. acutistipula in canga is essential to deduce the ability of native species to adapt to possible stressors in rehabilitating minelands over time. In this study, the root proteomic profiles of M. acutistipula grown in a native canga ecosystem and rehabilitating minelands were compared to identify essential proteins involved in the adaptation of this species in its native environment and that should enable its establishment in rehabilitating minelands. The results showed differentially abundant proteins, where 436 proteins with significant values (p < 0.05) and fold change ≥ 2 were more abundant in canga and 145 in roots from the rehabilitating minelands. Among them, a representative amount and diversity of proteins were related to responses to water deficit, heat, and responses to metal ions. Other identified proteins are involved in biocontrol activity against phytopathogens and symbiosis. This research provides insights into proteins involved in M. acutistipula responses to environmental stimuli, suggesting critical mechanisms to support the establishment of native canga plants in rehabilitating minelands over time.

A metal chaperone OsHIPP16 detoxifies cadmium by repressing its accumulation in rice crops

Cadmium (Cd) is an environmentally polluted toxic heavy metal and seriously risks food safety and human health through food chain. Mining genetic potentials of plants is a crucial step for limiting Cd accumulation in rice crops and improving environmental quality. This study characterized a novel locus in rice genome encoding a Cd-binding protein named OsHIPP16, which resides in the nucleus and near plasma membrane. OsHIPP16 was strongly induced by Cd stress. Histochemical analysis with pHIPP16::GUS reveals that OsHIPP16 is primarily expressed in root and leaf vascular tissues. Expression of OsHIPP16 in the yeast mutant strain ycf1 sensitive to Cd conferred cellular tolerance. Transgenic rice overexpressing OsHIPP16 (OE) improved rice growth with increased plant height, biomass, and chlorophyll content but with a lower degree of oxidative injury and Cd accumulation, whereas knocking out OsHIPP16 by CRISPR-Cas9 compromised the growth and physiological response. A lifelong trial with Cd-polluted soil shows that the OE plants accumulated much less Cd, particularly in brown rice where the Cd concentrations declined by 11.76-34.64%. Conversely, the knockout oshipp16 mutants had higher levels of Cd with the concentration in leaves being increased by 26.36-35.23% over the wild-type. These results suggest that adequate expression of OsHIPP16 would profoundly contribute to Cd detoxification by regulating Cd accumulation in rice, suggesting that both OE and oshipp16 mutant plants have great potentials for restricting Cd acquisition in the rice crop and phytoremediation of Cd-contaminated wetland soils.

Effects of cadmium stress on the morphology, physiology, cellular ultrastructure, and BvHIPP24 gene expression of sugar beet (Beta vulgaris L.)

To clarify the mechanism of the response of sugar beet (Beta vulgaris L.) to cadmium (Cd) stress, this study investigated changes in the phenotype, physiological indexes, and subcellular structure of B. vulgaris under Cd treatment and the transcriptional pattern of the BvHIPP24 gene (a heavy metal-associated isoprenylated plant protein involved in heavy metal detoxification). The plant height and shoot and root growth of B. vulgaris seedlings were inhibited to some extent under 0.5 and 1 mM Cd, with gradually wilting and yellowing of leaves and dark brown roots. When the Cd concentration was increased, malondialdehyde content and the activities of peroxidase, superoxide dismutase, and glutathione S-transferase increased differentially. qPCR indicated that the expression of BvHIPP24 was induced by different concentrations of Cd. Although transmission electron microscopy revealed damage to nuclei, mitochondria, and chloroplasts, B. vulgaris exhibited strong adaptability to 0.5 mM Cd according to a comprehensive analysis using the membership function. The results showed that B. vulgaris may reduce cell damage and improve its Cd tolerance by regulating functional gene expression and antioxidant enzymes. This study increases our understanding of the Cd-tolerance mechanism of B. vulgaris and provides insights into the use of B. vulgaris in Cd bioremediation.

OsZIP11 is a trans-Golgi-residing transporter required for rice iron accumulation and development

Iron (Fe) is a mineral nutrient necessary for plant growth and development. Whether the rice ZRT/IRT-like protein family metal transporter OsZIP11 is involved in Fe transport has not been functionally defined. The objective of the study is to figure out the essential role of the uncharacterized OsZIP11 played in rice growth, development, and iron accumulation, particularly in seeds. Transient subcellular location assays show that OsZIP11 was targeted to the trans-Golgi network. OsZIP11 was preferentially expressed in the rice tissues (or organs) at later flowering and seed development stages. Transcripts of OsZIP11 were significantly induced under Fe but not under zinc (Zn), copper (Cu) or manganese (Mn) deficiency. Yeast (Saccharomyces cerevisiae) transformed with OsZIP11 sequences displayed an active iron input which turned out that excessive iron accumulated in the cells. Knocking out OsZIP11 by CRISPR-Cas9 approach led to the attenuated rice growth and physiological phenotypes, depicting shorter plant height, reduced biomass, chlorosis (a symptom of lower chlorophyll concentration), and over-accumulation of malondialdehyde (complex representing the peroxidation of membrane lipids) in rice plantlets. The field trials demonstrated that OsZIP11 mutation impaired the capacity of seed development, with shortened panicle and seed length, compromised spikelet fertility, and reduced grain per plant or 1000-grain weight. Knocking out OsZIP11 also lowered the accumulation of iron in the brown rice by 48-51% compared to the wild-type. Our work pointed out that OsZIP11 is required for iron acquisition for rice growth and development.