Transgenic Arabidopsis thaliana plants expressing bacterial γ-hexachlorocyclohexane dehydrochlorinase LinA.

BACKGROUND: γ-Hexachlorocyclohexane (γ-HCH), an organochlorine insecticide of anthropogenic origin, is a persistent organic pollutant (POP) that causes environmental pollution concerns worldwide. Although many γ-HCH-degrading bacterial strains are available, inoculating them directly into γ-HCH-contaminated soil is ineffective because of the low survival rate of the exogenous bacteria. Another strategy for the bioremediation of γ-HCH involves the use of transgenic plants expressing bacterial enzyme for γ-HCH degradation through phytoremediation. RESULTS: We generated transgenic Arabidopsis thaliana expressing γ-HCH dehydrochlroninase LinA from bacterium Sphingobium japonicum strain UT26. Among the transgenic Arabidopsis T2 lines, we obtained one line (A5) that expressed and accumulated LinA well. The A5-derived T3 plants showed higher tolerance to γ-HCH than the non-transformant control plants, indicating that γ-HCH is toxic for Arabidopsis thaliana and that this effect is relieved by LinA expression. The crude extract of the A5 plants showed γ-HCH degradation activity, and metabolites of γ-HCH produced by the LinA reaction were detected in the assay solution, indicating that the A5 plants accumulated the active LinA protein. In some A5 lines, the whole plant absorbed and degraded more than 99% of γ-HCH (10 ppm) in the liquid medium within 36 h. CONCLUSION: The transgenic Arabidopsis expressing active LinA absorbed and degraded γ-HCH in the liquid medium, indicating the high potential of LinA-expressing transgenic plants for the phytoremediation of environmental γ-HCH. This study marks a crucial step toward the practical use of transgenic plants for the phytoremediation of POPs.

The effects of monoculture and intercropping on photosynthesis performance correlated with growth of garlic and perennial ryegrass response to different heavy metals.

BACKGROUND: The potential of phytoremediation using garlic monoculture (MC) and intercropping (IC) system with perennial ryegrass to enhance the uptake of cadmium (Cd), chromium (Cr), and lead (Pb) were investigated. RESULTS: Positive correlations were found between MC and IC systems, with varying biomass. Production of perennial ryegrass was affected differently depending on the type of toxic metal present in the soil. Root growth inhibition was more affected than shoot growth inhibition. The total biomass of shoot and root in IC was higher than MC, increasing approximately 3.7 and 2.9 fold compared to MC, attributed to advantages in root IC crop systems. Photosystem II efficiency showed less sensitivity to metal toxicity compared to the control, with a decrease between 10.07-12.03%. Among gas exchange parameters, only Cr significantly affected physiological responses by reducing transpiration by 69.24%, likely due to leaf chlorosis and necrosis. CONCLUSION: This study exhibited the potential of garlic MC and IC with perennial ryegrass in phytoremediation. Although the different metals affect plant growth differently, IC showed advantages over MC in term biomass production.

IAA is more effective than EDTA in enhancing phytoremediation potential for cadmium and copper contaminated soils.

Enhanced phytoremediation offers a rapid and eco-friendly approach for cleaning agricultural soil contaminated with copper and cadmium which pose a direct threat to food scarcity and security. The current study aimed to compare the effectiveness of the two commonly used additives, IAA and EDTA, for the remediation of copper (Cu) and cadmium (Cd) contaminated soils using sunflower and maize. The plants were cultivated in pots under controlled conditions with four sets of treatments: control (0), Cu50/Cd50, Cu50/Cd50 + EDTA, and Cu50/Cd50 + IAA. The results showed that Cu50/Cd50 mg/kg drastically compromised the phytoremediation potential of both plants, as evident by reduced shoot and root length, and lower biomass. However, the augmentation of Cu50/Cd50 with EDTA or IAA improved the tested parameters. In sunflower, EDTA enhanced the accumulation of Cu and Cd by 58% and 21%, respectively, and improved plant biomass by 41%, compared to control treatment. However, IAA exhibited higher accumulation of Cu and Cd by 64% and 25%, respectively, and enhanced plant biomass by 43%. In case of maize, IAA was superior to EDTA which enhanced the accumulation of Cu and Cd by 87% and 32% respectively, and increased the plant biomass by 57%, compared to control treatment. Our findings demonstrate that foliar IAA is more effective than EDTA in enhancing the phytoremediation potential of sunflower and maize for Cu and Cd.

How plants respond to heavy metal contamination: a narrative review of proteomic studies and phytoremediation applications.

MAIN CONCLUSION: Heavy metal pollution caused by human activities is a serious threat to the environment and human health. Plants have evolved sophisticated defence systems to deal with heavy metal stress, with proteins and enzymes serving as critical intercepting agents for heavy metal toxicity reduction. Proteomics continues to be effective in identifying markers associated with stress response and metabolic processes. This review explores the complex interactions between heavy metal pollution and plant physiology, with an emphasis on proteomic and biotechnological perspectives. Over the last century, accelerated industrialization, agriculture activities, energy production, and urbanization have established a constant need for natural resources, resulting in environmental degradation. The widespread buildup of heavy metals in ecosystems as a result of human activity is especially concerning. Although some heavy metals are required by organisms in trace amounts, high concentrations pose serious risks to the ecosystem and human health. As immobile organisms, plants are directly exposed to heavy metal contamination, prompting the development of robust defence mechanisms. Proteomics has been used to understand how plants react to heavy metal stress. The development of proteomic techniques offers promising opportunities to improve plant tolerance to toxicity from heavy metals. Additionally, there is substantial scope for phytoremediation, a sustainable method that uses plants to extract, sequester, or eliminate contaminants in the context of changes in protein expression and total protein behaviour. Changes in proteins and enzymatic activities have been highlighted to illuminate the complex effects of heavy metal pollution on plant metabolism, and how proteomic research has revealed the plant's ability to mitigate heavy metal toxicity by intercepting vital nutrients, organic substances, and/or microorganisms.

γ-Aminobutyric acid (GABA) priming alleviates acid-aluminum toxicity to roots of creeping bentgrass via enhancements in antioxidant defense and organic metabolites remodeling.

MAIN CONCLUSION: γ-Aminobutyric acid alleviates acid-aluminum toxicity to roots associated with enhanced antioxidant metabolism as well as accumulation and transportation of citric and malic acids. Aluminum (Al) toxicity has become the main limiting factor for crop growth and development in acidic soils and is further being aggravated worldwide due to continuous industrial pollution. The current study was designed to examine effects of GABA priming on alleviating acid-Al toxicity in terms of root growth, antioxidant defense, citrate and malate metabolisms, and extensive metabolites remodeling in roots under acidic conditions. Thirty-seven-day-old creeping bentgrass (Agrostis stolonifera) plants were used as test materials. Roots priming with or without 0.5 mM GABA for 3 days were cultivated in standard nutrient solution for 15 days as control or subjected to nutrient solution containing 5 mM AlCl3·6H2O for 15 days as acid-Al stress treatment. Roots were sampled for determinations of root characteristics, physiological and biochemical parameters, and metabolomics. GABA priming significantly alleviated acid-Al-induced root growth inhibition and oxidative damage, despite it promoted the accumulation of Al in roots. Analysis of metabolomics showed that GABA priming significantly increased accumulations of organic acids, amino acids, carbohydrates, and other metabolites in roots under acid-Al stress. In addition, GABA priming also significantly up-regulated key genes related to accumulation and transportation of malic and citric acids in roots under acid-Al stress. GABA-regulated metabolites participated in tricarboxylic acid cycle, GABA shunt, antioxidant defense system, and lipid metabolism, which played positive roles in reactive oxygen species scavenging, energy conversion, osmotic adjustment, and Al ion chelation in roots.

GhRCD1 promotes cotton tolerance to cadmium by regulating the GhbHLH12-GhMYB44-GhHMA1 transcriptional cascade.

Heavy metal pollution poses a significant risk to human health and wreaks havoc on agricultural productivity. Phytoremediation, a plant-based, environmentally benign, and cost-effective method, is employed to remove heavy metals from contaminated soil, particularly in agricultural or heavy metal-sensitive lands. However, the phytoremediation capacity of various plant species and germplasm resources display significant genetic diversity, and the mechanisms underlying these differences remain hitherto obscure. Given its potential benefits, genetic improvement of plants is essential for enhancing their uptake of heavy metals, tolerance to harmful levels, as well as overall growth and development in contaminated soil. In this study, we uncover a molecular cascade that regulates cadmium (Cd2+) tolerance in cotton, involving GhRCD1, GhbHLH12, GhMYB44, and GhHMA1. We identified a Cd2+-sensitive cotton T-DNA insertion mutant with disrupted GhRCD1 expression. Genetic knockout of GhRCD1 by CRISPR/Cas9 technology resulted in reduced Cd2+ tolerance in cotton seedlings, while GhRCD1 overexpression enhanced Cd2+ tolerance. Through molecular interaction studies, we demonstrated that, in response to Cd2+ presence, GhRCD1 directly interacts with GhbHLH12. This interaction activates GhMYB44, which subsequently activates a heavy metal transporter, GhHMA1, by directly binding to a G-box cis-element in its promoter. These findings provide critical insights into a novel GhRCD1-GhbHLH12-GhMYB44-GhHMA1 regulatory module responsible for Cd2+ tolerance in cotton. Furthermore, our study paves the way for the development of elite Cd2+-tolerant cultivars by elucidating the molecular mechanisms governing the genetic control of Cd2+ tolerance in cotton.

UDP-glycosyltransferase UGT96C10 functions as a novel detoxification factor for conjugating the activated dinitrotoluene sulfonate in switchgrass.

Dinitrotoluene sulfonates (DNTSes) are highly toxic hazards regulated by the Resource Conservation and Recovery Act (RCRA) in the United States. The trinitrotoluene (TNT) red water formed during the TNT purification process consists mainly of DNTSes. Certain plants, including switchgrass, reed and alfalfa, can detoxify low concentrations of DNTS in TNT red water-contaminated soils. However, the precise mechanism by which these plants detoxify DNTS remains unknown. In order to aid in the development of phytoremediation resources with high DNTS removal rates, we identified and characterized 1-hydroxymethyl-2,4-dinitrobenzene sulfonic acid (HMDNBS) and its glycosylated product HMDNBS O-glucoside as the degradation products of 2,4-DNT-3-SO3Na, the major isoform of DNTS in TNT red water-contaminated soils, in switchgrass via LC-MS/MS- and NMR-based metabolite analyses. Transcriptomic analysis revealed that 15 UDP-glycosyltransferase genes were dramatically upregulated in switchgrass plants following 2,4-DNT-3-SO3Na treatment. We expressed, purified and assayed the activity of recombinant UGT proteins in vitro and identified PvUGT96C10 as the enzyme responsible for the glycosylation of HMDNBS in switchgrass. Overexpression of PvUGT96C10 in switchgrass significantly alleviated 2,4-DNT-3-SO3Na-induced plant growth inhibition. Notably, PvUGT96C10-overexpressing transgenic switchgrass plants removed 83.1% of 2,4-DNT-3-SO3Na in liquid medium after 28 days, representing a 3.2-fold higher removal rate than that of control plants. This work clarifies the DNTS detoxification mechanism in plants for the first time, suggesting that PvUGT96C10 is crucial for DNTS degradation. Our results indicate that PvUGT96C10-overexpressing plants may hold great potential for the phytoremediation of TNT red water-contaminated soils.

Multiomics and biotechnologies for understanding and influencing cadmium accumulation and stress response in plants.

Cadmium (Cd) is one of the most toxic heavy metals faced by plants and, additionally, via the food chain, threatens human health. It is principally dispersed through agro-ecosystems via anthropogenic activities and geogenic sources. Given its high mobility and persistence, Cd, although not required, can be readily assimilated by plants thereby posing a threat to plant growth and productivity as well as animal and human health. Thus, breeding crop plants in which the edible parts contain low to zero Cd as safe food stuffs and harvesting shoots of high Cd-containing plants as a route for decontaminating soils are vital strategies to cope with this problem. Recently, multiomics approaches have been employed to considerably enhance our understanding of the mechanisms underlying (i) Cd toxicity, (ii) Cd accumulation, (iii) Cd detoxification and (iv) Cd acquisition tolerance in plants. This information can be deployed in the development of the biotechnological tools for developing plants with modulated Cd tolerance and detoxification to safeguard cellular and genetic integrity as well as to minimize food chain contamination. The aim of this review is to provide a current update about the mechanisms involved in Cd uptake by plants and the recent developments in the area of multiomics approach in terms of Cd stress responses, as well as in the development of Cd tolerant and low Cd accumulating crops.

Transcriptomic and physiological analyses of Trichoderma citrinoviride HT-1 assisted phytoremediation of Cd contaminated water by Phragmites australis.

Plant growth promoting microbe assisted phytoremediation is considered a more effective approach to rehabilitation than the single use of plants, but underlying mechanism is still unclear. In this study, we combined transcriptomic and physiological methods to explore the mechanism of plant growth promoting microbe Trichoderma citrinoviride HT-1 assisted phytoremediation of Cd contaminated water by Phragmites australis. The results show that the strain HT-1 significantly promoted P. australis growth, increased the photosynthetic rate, enhanced antioxidant enzyme activities. The chlorophyll content and the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were increased by 83.78%, 23.17%, 47.60%, 97.14% and 12.23% on average, and decreased the content of malondialdehyde (MDA) by 31.10%. At the same time, strain HT-1 improved the absorption and transport of Cd in P. australis, and the removal rate of Cd was increased by 7.56% on average. Transcriptome analysis showed that strain HT-1 induced significant up-regulated the expression of genes related to oxidative phosphorylation and ribosome pathways, and these upregulated genes promoted P. australis remediation efficiency and resistance to Cd stress. Our results provide a mechanistic understanding of plant growth promoting microbe assisted phytoremediation under Cd stress.

Arsenic stress triggers active exudation of arsenic-phytochelatin complexes from Lupinus albus roots.

Arsenic (As) contamination of soils threatens the health of millions globally through accumulation in crops. While plants detoxify As via phytochelatin (PC) complexation and efflux of arsenite from roots, arsenite efflux mechanisms are not fully understood. Here, white lupin (Lupinus albus) was grown in semi-hydroponics, and exudation of glutathione (GSH) derivatives and PCs in response to As was measured using LC-MS/MS. Inhibiting synthesis of the PC precursor GSH with l-buthionine sulfoximine (BSO) or ABC transporters with vanadate drastically reduced (>22%) GSH derivative and PC2 exudation, but not PC3 exudation. This was accompanied by As hypersensitivity in plants treated with BSO and moderate sensitivity with vanadate treatment. Investigating As-PC complexation revealed two distinct As-PC complexes, As bound to GSH and PC2 (GS-As-PC2) and As bound to PC3 (As-PC3), in exudates of As-treated lupin plants. Vanadate inhibited As-PC exudation, while BSO inhibited both the synthesis and exudation of As-PC complexes. These results demonstrate a role for GSH derivatives and PC exudation in lupin As tolerance and reveal As-PC exudation as a new potential mechanism contributing to active As efflux in plants. Overall, this study uncovers insights into rhizosphere As detoxification with potential to help mitigate pollution and reduce As accumulation in crops.

Habitat-specific allocations of elements in Atriplex lentiformis seeds indicate adaptation to metal toxicity.

Self-sustaining vegetation in metal-contaminated areas is essential for rebuilding ecological resilience and community stability in degraded lands. Metal-tolerant plants originating from contaminated post-mining areas may hold the key to successful plant establishment and growth. Yet, little is known about the impact of metal toxicity on reproductive strategies, metal accumulation, and allocation patterns at the seed stage. Our research focused on the metal tolerant Atriplex lentiformis. Specifically, we examined the effects of toxic metal(loid) concentration in soils on variability in its reproductive strategies, including germination patterns, elemental uptake, and allocation within the seeds. We employed advanced imaging techniques like synchrotron X-ray fluorescence microscopy (2D scans and 3D tomograms) combined with inductively coupled plasma mass spectrometry to reveal significant differences in metal(loid) concentration and distribution within the seed structures of A. lentiformis from contrasting habitats. Exclusive Zn hotspots of high concentrations were found in the seeds of the metallicolous accession, primarily in the sensitive tissues of shoot apical meristems and root zones of the seed embryos. Our findings offer novel insights into phenotypic variability and metal tolerance and accumulation in plants from extreme environments. This knowledge can be applied to enhance plant survival and performance in land restoration efforts.

Phytoremediation: a transgenic perspective in omics era.

Phytoremediation is an environmental safety strategy that might serve as a viable preventative approach to reduce soil contamination in a cost-effective manner. Using plants to remediate pollution from the environment is referred to as phytoremediation. In the past few decades, plants have undergone genetic manipulation to overcome inherent limitations by using genetically modified plants. This review illustrates the eco-friendly process of cleaning the environment using transgenic strategies combined with omics technologies. Herbicides tolerance and phytoremediation abilities have been established in genetically modified plants. Transgenic plants have eliminated the pesticides atrazine and metolachlor from the soil. To expand the application of genetically engineered plants for phytoremediation process, it is essential to test strategies in the field and have contingency planning. Omics techniques were used for understanding various genetic, hormonal, and metabolic pathways responsible for phytoremediation in soil. Transcriptomics and metabolomics provide useful information as resources to understand the mechanisms behind phytoremediation. This review aims to highlight the integration of transgenic strategies and omics technologies to enhance phytoremediation efficiency, emphasizing the need for field testing and comprehensive planning for successful implementation.

Alleviation of heavy metals chromium, cadmium and lead and plant growth promotion in Vigna radiata L. plant using isolated Pseudomonas geniculata.

Plants exposed to heavy metals (HMs) stress negatively affect their development and production capacity. Chromium (Cr), Cadmium (Cd), and Lead (Pb) are the most common hazardous trace metals in agriculture. The physiological, biochemical, and molecular characteristics of crops are being affected. Phytoremediation is a method to alleviate heavy metals from the contaminated soil. The study aims to evaluate the phytoremediation ability of Vigna radiata L. (mung bean) in the absence and the presence of multi-metal tolerant and plant growth promoting Pseudomonas geniculata strain TIU16A3 isolated from soil of tannery industrial estate, Kolkata, West Bengal, India. The strain was further assessed with increasing concentrations of Cr, Cd, and Pb (10, 20, 40, and 80 µg/mL) when the mung bean plant was a test crop. The strain significantly increased plant growth, chlorophyll content, increased level of antioxidant enzymes such as superoxide dismutase, peroxidase, and catalase, and decreased oxidative stress indicators like H2O2 and electrolyte leakage in the presence of Cr, Cd, and Pb as compared to plants grown in the absence of Pseudomonas geniculata strain. Shoot length responsive gene (Aux/IAA) in the presence of heavy metal alone and Pseudomonas geniculata treated Cd and Cr showed higher relative expression of (Aux/IAA) compared to Pb. Due to these intrinsic abilities, Pseudomonas geniculata strain TIU16A3 can be a plant growth promoter and thus can help in the remediation of heavy metal (Cr, Cd, and Pb) contaminated soil.

Plant growth-promoting bacteria isolated from earthworms enhance spinach growth and its phytoremediation potential in metal-contaminated soils.

The aim of this study was to evaluate the impact of metal-tolerant plant growth-promoting bacteria (PGPB) isolated from the chloragogenous tissue of Aporrectodea molleri, which represents a unique habitat. Our objectives were to investigate their effects on the growth of Spinacia oleracea under heavy metal stress and assess their potential for enhancing phytoremediation capabilities. The experiment was conducted in an alkaline soil contaminated with 7 mg kg-1 of cadmium, 100 mg kg-1 of nickel, 150 mg kg-1 of copper, 300 mg kg-1 of Zinc, and mg kg-1 of 600 Manganese. The results showed that heavy metal stress considerably diminished root (42.8%) and shoot length (60.1%), biomass (80%), chlorophyll content (41%), soil alkaline (45%), and acid (51%) phosphatases (42%) and urease (42%). However, soil inoculation with bacterial isolates remarkably improved plant growth. Soil bioaugmentation increased spinach growth (up to 74.5% for root length, up to 106.3% for shoot length, and up to 5.5 folds for fresh biomass) while significantly increasing soil enzyme activity and NPK content. Multivariate data analysis indicated that soil inoculation with Bacillus circulans TC7 promoted plant growth while limiting metal bioaccumulation, whereas Pseudomonas sp. TC33 and Bacillus subtilis TC34 increased metal bioaccumulation in spinach tissues while minimizing their toxicity. Our study confirms that earthworms are a reservoir of multi-beneficial bacteria that can effectively improve phytoremediation efficiency and mitigate the toxic effects of heavy metals on plant growth. Further studies are needed to investigate the long-term effects and feasibility of using these isolates as a consortium in field applications.

Arabidopsis response to copper is mediated by density and root exudates: Evidence that plant density and toxic soils can shape plant communities.

PREMISE: Plants grown at high densities show increased tolerance to heavy metals for reasons that are not clear. A potential explanation is the release of citrate by plant roots, which binds metals and prevents uptake. Thus, pooled exudates at high plant densities might increase tolerance. We tested this exclusion facilitation hypothesis using mutants of Arabidopsis thaliana defective in citrate exudation. METHODS: Wild type Arabidopsis and two allelic mutants for the Ferric Reductase Defective 3 (FRD3) gene were grown at four densities and watered with copper sulfate at four concentrations. Plants were harvested before bolting and dried. Shoot biomass was measured, and shoot material and soil were digested in nitric acid. Copper contents were determined by atomic absorption. RESULTS: In the highest-copper treatment, density-dependent reduction in toxicity was observed in the wild type but not in FRD3 mutants. For both mutants, copper concentrations per gram biomass were up to seven times higher than for wild type plants, depending on density and copper treatment. In all genotypes, total copper accumulation was greater at higher plant densities. Plant size variation increased with density and copper treatment because of heterogeneous distribution of copper throughout the soil. CONCLUSIONS: These results support the hypothesis that citrate exudation is responsible for density-dependent reductions in toxicity of metals. Density-dependent copper uptake and growth in contaminated soils underscores the importance of density in ecotoxicological testing. In soils with a heterogeneous distribution of contaminants, competition for nontoxic soil regions may drive size hierarchies and determine competitive outcomes.

Perfluorooctanesulfonic Acid Alters the Plant's Phosphate Transport Gene Network and Exhibits Antagonistic Effects on the Phosphate Uptake.

Per- and polyfluoroalkyl substances (PFASs), with significant health risks to humans and wildlife, bioaccumulate in plants. However, the mechanisms underlying plant uptake remain poorly understood. This study deployed transcriptomic analysis coupled with genetic and physiological studies using Arabidopsis to investigate how plants respond to perfluorooctanesulfonic acid (PFOS), a long-chain PFAS. We observed increased expressions of genes involved in plant uptake and transport of phosphorus, an essential plant nutrient, suggesting intertwined uptake and transport processes of phosphorus and PFOS. Furthermore, PFOS-altered response differed from the phosphorus deficiency response, disrupting phosphorus metabolism to increase phosphate transporter (PHT) transcript. Interestingly, pht1;2 and pht1;8 mutants showed reduced sensitivity to PFOS compared to that of the wild type, implying an important role of phosphate transporters in PFOS sensing. Furthermore, PFOS accumulated less in the shoots of the pht1;8 mutant, indicating the involvement of PHT1;8 protein in translocating PFOS from roots to shoots. Supplementing phosphate improved plant's tolerance to PFOS and reduced PFOS uptake, suggesting that manipulating the phosphate source in PFOS-contaminated soils may be a promising strategy for minimizing PFOS uptake by edible crops or promoting PFOS uptake during phytoremediation. This study highlighted the critical role of phosphate sensing and transport system in the uptake and translocation of PFOS in plants.

Serendipita indica Drives Sulfur-Related Microbiota in Enhancing Growth of Hyperaccumulator Sedum alfredii and Facilitating Soil Cadmium Remediation.

Endophytic fungus Serendipita indica can bolster plant growth and confer protection against various biotic and abiotic stresses. However, S. indica-reshaped rhizosphere microecology interactions and root-soil interface processes in situ at the submicrometer scale remain poorly understood. We combined amplicon sequencing and high-resolution nano X-ray fluorescence (nano-XRF) imaging of the root-soil interface to reveal cadmium (Cd) rhizosphere processes. S. indica can successfully colonize the roots of Sedum alfredii Hance, which induces a remarkable increase in shoot biomass by 211.32% and Cd accumulation by 235.72%. Nano-XRF images showed that S. indica colonization altered the Cd distribution in the rhizosphere and facilitated the proximity of more Cd and sulfur (S) to enter the roots and transport to the shoot. Furthermore, the rhizosphere-enriched microbiota demonstrated a more stable network structure after the S. indica inoculation. Keystone species were strongly associated with growth promotion and Cd absorption. For example, Comamonadaceae are closely related to the organic acid cycle and S bioavailability, which could facilitate Cd and S accumulation in plants. Meanwhile, Sphingomonadaceae could release auxin and boost plant biomass. In summary, we construct a mutualism system for beneficial fungi and hyperaccumulation plants, which facilitates high-efficient remediation of Cd-contaminated soils by restructuring the rhizosphere microbiota.

Arsenite Antiporter PvACR3 Driven by Its Native Promoter Increases Leaf Arsenic Accumulation in Tobacco.

Pteris vittata is the first-reported arsenic (As) hyperaccumulator, which has been applied to phytoremediation of As-contaminated soil. PvACR3, a key arsenite (AsIII) antiporter, plays an important role in As hyperaccumulation in P. vittata. However, its functions in plants are not fully understood. In this study, the PvACR3 gene was heterologously expressed in tobacco, driven by its native promoter (ProPvACR3). After growing at 5 µM AsIII or 10 µM AsV in hydroponics for 1-5 days, PvACR3-expression enhanced the As levels in leaves by 66.4-113 and 51.8-101%, without impacting the As contents in the roots or stems. When cultivated in As-contaminated soil, PvACR3-expressed transgenic plants accumulated 47.9-85.5% greater As in the leaves than wild-type plants. In addition, PvACR3-expression increased the As resistance in transgenic tobacco, showing that enhanced leaf As levels are not detrimental to its overall As tolerance. PvACR3 was mainly expressed in tobacco leaf veins and was likely to unload AsIII from the vein xylem vessels to the mesophyll cells, thus elevating the leaf As levels. This work demonstrates that heterologously expressing PvACR3 under its native promoter specifically enhances leaf As accumulation in tobacco, which helps to reveal the As-hyperaccumulation mechanism in P. vittata and to enhance the As accumulation in plant leaves for phytoremediation.

Novel Phosphate Transporter-B PvPTB1;1/1;2 Contribute to Efficient Phosphate Uptake and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata.

Arsenic (As) contamination in soil poses a potential threat to human health via crop uptake. As-hyperaccumulator Pteris vittata serves as a model plant to study As uptake and associated mechanisms. This study focuses on a novel P/AsV transport system mediated by low-affinity phosphate transporter-B 1 family (PTB1) in P. vittata. Here, we identified two plasma-membrane-localized PTB1 genes, PvPTB1;1/1;2, in vascular plants for the first time, which were 4.4-40-fold greater in expression in P. vittata than in other Pteris ferns. Functional complementation of a yeast P-uptake mutant and enhanced P accumulation in transgenic Arabidopsis thaliana confirmed their role in P uptake. Moreover, the expression of PvPTB1;1/1;2 facilitated the transport and accumulation of As in both yeast and A. thaliana shoots, demonstrating a comparable AsV uptake capacity. Microdissection-qPCR analysis and single-cell transcriptome analysis collectively suggest that PvPTB1;1/1;2 are specifically expressed in the epidermal cells of P. vittata roots. PTB1 may play a pivotal role in efficient P recycling during phytate secretion and hydrolysis in P. vittata roots. In summary, the dual P transport mechanisms consisting of high-affinity Pht1 and low-affinity PTB1 may have contributed to the efficient P/As uptake in P. vittata, thereby contributing to efficient phytoremediation for As-contaminated soils.

Cadmium toxicity promotes hormonal imbalance and induces the expression of genes involved in systemic resistances in barley.

Cadmium (Cd) is a widely distributed pollutant that adversely affects plants' metabolism and productivity. Phytohormones play a vital role in the acclimation of plants to metal stress. On the other hand, phytohormones trigger systemic resistances, including systemic acquired resistance (SAR) and induced systemic resistance (ISR), in plants in response to biotic interactions. The present study aimed to investigate the possible induction of SAR and ISR pathways in relation to the hormonal alteration of barley seedlings in response to Cd stress. Barley seedlings were exposed to 1.5 mg g-1 Cd in the soil for three days. The nutrient content, oxidative status, phytohormones profile, and expression of genes involved in SAR and ISR pathways of barley seedlings were examined. Cd accumulation resulted in a reduction in the nutrient content of barley seedlings. The specific activity of superoxide dismutase and the hydrogen peroxide content significantly increased in response to Cd toxicity. Abscisic acid, jasmonic acid, and ethylene content increased under Cd exposure. Cd treatment resulted in the upregulation of NPR1, PR3, and PR13 genes in SAR pathways. The transcripts of PAL1 and LOX2.2 genes in the ISR pathway were also significantly increased in response to Cd treatment. These findings suggest that hormonal-activated systemic resistances are involved in the response of barley to Cd stress.