Harnessing an arbuscular mycorrhizal fungus to improve the adaptability of a facultative metallophytic poplar (Populus yunnanensis) to cadmium stress: Physiological and molecular responses

Rhizophagus Irregularis regulates flavonoids metabolism in paper mulberry roots under cadmium stress

Broussonetia papyrifera is widely found in cadmium (Cd) contaminated areas, with an inherent enhanced flavonoids metabolism and inhibited lignin biosynthesis, colonized by lots of symbiotic fungi, such as arbuscular mycorrhizal fungi (AMF). However, the physiological and molecular mechanisms by which Rhizophagus irregularis, an AM fungus, regulates flavonoids and lignin in B. papyrifera under Cd stress remain unclear. Here, a pot experiment of B. papyrifera inoculated and non-inoculated with R. irregularis under Cd stress was carried out. We determined flavonoids and lignin concentrations in B. papyrifera roots by LC-MS and GC-MS, respectively, and measured the transcriptional levels of flavonoids- or lignin-related genes in B. papyrifera roots, aiming to ascertain the key components of flavonoids or lignin, and key genes regulated by R. irregularis in response to Cd stress. Without R. irregularis, the concentrations of eriodictyol, quercetin and myricetin were significantly increased under Cd stress. The concentrations of eriodictyol and genistein were significantly increased by R. irregularis, while the concentration of rutin was significantly decreased. Total lignin and lignin monomer had no alteration under Cd stress or with R. irregularis inoculation. As for flavonoids- or lignin-related genes, 26 genes were co-regulated by Cd stress and R. irregularis. Among these genes, BpC4H2, BpCHS8 and BpCHI5 were strongly positively associated with eriodictyol, indicating that these three genes participate in eriodictyol biosynthesis and were involved in R. irregularis assisting B. papyrifera to cope with Cd stress. This lays a foundation for further research revealing molecular mechanisms by which R. irregularis regulates flavonoids synthesis to enhance tolerance of B. papyrifera to Cd stress.

Physiological response and molecular mechanism of Quercus variabilis under cadmium stress

Heavy metal pollution is a global environmental problem, and Quercus variabilis has a stronger tolerance to Cd stress than do other species. We aimed to explore the physiological response and molecular mechanisms of Q. variabilis to Cd stress. In this study, the antioxidant enzyme activities of leaves were determined, while the photosynthetic parameters of leaves were measured using Handy PEA, and ion fluxes and DEGs in the roots were investigated using noninvasive microtest technology (NMT) and RNA sequencing techniques, respectively. Cd stress at different concentrations and for different durations affected the uptake patterns of Cd2+ and H+ by Q. variabilis and affected the photosynthetic efficiency of leaves. Moreover, there was a positive relationship between antioxidant enzyme (CAT and POD) activity and Cd concentration. Transcriptome analysis revealed that many genes, including genes related to the cell wall, glutathione metabolism, ion uptake and transport, were significantly upregulated in response to cadmium stress in Q. variabilis roots. WGCNA showed that these DEGs could be divided into eight modules. The turquoise and blue modules exhibited the strongest correlations, and the most significantly enriched pathways were the phytohormone signaling pathway and the phenylpropanoid biosynthesis pathway, respectively. These findings suggest that Q. variabilis can bolster plant tolerance by modulating signal transduction and increasing the synthesis of compounds, such as lignin, under Cd stress. In summary, Q. variabilis can adapt to Cd stress by increasing the activity of antioxidant enzymes, and regulating the fluxes of Cd2+ and H+ ions and the expression of Cd stress-related genes.

Effects of mycorrhizal symbiosis and Ulva lactuca seaweed extract on growth, carbon/nitrogen metabolism, and antioxidant response in cadmium-stressed sorghum plant

In our study on the effect of cadmium (Cd) toxicity (200 µM) on the growth of Sorghum bicolor (L.) Moench plants, cultivated with arbuscular mycorrhizal fungi (AMF) (Glomus intraradices) and/or under seaweed treatment (3% Ulva lactuca extract) (U. lactuca), we found that AMF increased the tolerance of sorghum to cadmium stress, either alone or in combination with the seaweed treatment. Morphological parameters were higher in these two culture conditions, with increased chlorophyll content. AMF reduced Cd accumulation in roots and inhibited its translocation to the aerial part, while seaweed treatment alone significantly increased Cd accumulation in leaves and roots without affecting plant growth compared to stressed witnesses. Treatment with AMF and/or U. lactuca attenuated oxidative stress, measured by activation of superoxide dismutase, and resulted in a significant decrease in malondialdehyde and superoxide ions (O2-) in treated plants. Furthermore, it induced significant alterations in carbon and nitrogen metabolic pathways, with a significant increase in the activity of enzymes such as glutamine synthetase, glutamate synthase (GOGAT), glutamate dehydrogenase, phosphoenolpyruvate carboxylase, aspartate aminotransferase and isocitrate dehydrogenase in the leaves of each treated plant. These results confirm that AMF, U. lactuca algae extract and their combination can improve the biochemical parameters of sorghum under Cd stress, through modification of the antioxidant response on one hand, and improved nitrogen absorption and assimilation efficiency on the other.

Identification of cadmium phytoavailability in response to cadmium transformation and changes in soil pH and electrical conductivity

Owing to complex changes in the soil environment, determining cadmium (Cd) phytoavailability is challenging. We devised a soil-wheat system to monitor alterations in soil pH, electrical conductivity (EC), and Cd transformation under various rates of calcium chloride and/or low-molecular-weight organic acids (LMWOAs) addition. The findings indicate that decreasing soil pH value, increasing soil EC value, and Cd transformation affect the phytoextraction of Cd. The exchangeable Cd and transformation of Cd under shifts in soil pH and EC contribute differentially to the phytoextracted Cd. The level of potentially phytoavailable Cd was identified through complete wheat cultivation in which the soil pH decreased by 0.47 unit and soil EC increased by 600-1000 μS cm-1, resembling the concentration of 0.01 M LMWOAs extractable Cd, when transitioning from paddy to dryland soil. Based on considering the phytoextracted Cd as the phytoavailable Cd throughout a complete wheat growth term, the threshold for phytoavailable Cd in soil, ensuring the safety of wheat grain (limit: 0.1 mg kg-1), is determined to be 2.90 μg kg-1. Maintaining control over Cd phytoavailability in soil emerges as the key factor in ensuring the safety of wheat grain cultivation.

Function and Characteristic Analysis of Candidate PEAR Proteins in Populus yunnanensis

PEAR proteins are a type of plant-specific DNA binding with one finger (Dof) transcription factors that play a key role in the regulation of plant growth, especially during phloem cell growth and seed germination in Arabidopsis. However, the identification, characteristics and function of PEAR proteins, particularly in woody plants, need to be further studied. In the present study, 43 candidate PEAR proteins harboring the conserved Zf-Dof domain were obtained in Populus yunnanensis. Based on phylogenetic and structural analysis, 10 representative PEAR candidates were selected, belonging to different phylogenetic groups. The functions of PEAR proteins in the stress response, signal transduction, and growth regulation of stem cambium and roots undergoing vigorous cell division in Arabidopsis were revealed based on their expression patterns as characterized by qRT-PCR analysis, in accordance with the results of cis-element analysis. In vitro experiments showed that the interaction of transcription factor (E2F) and cyclin indirectly reflects the growth regulation function of PEAR through light signaling and cell-cycle regulation. Therefore, our results provide new insight into the identity of PEAR proteins and their function in stress resistance and vigorous cell division regulation of tissues in P. yunnanensis, which may serve as a basis for further investigation of the functions and characteristics of PEAR proteins in other plants.

The Role of Lignin in the Compartmentalization of Cadmium in Maize Roots Is Enhanced by Mycorrhiza

In nature, arbuscular mycorrhizal fungi (AMF) play a crucial role in the root systems of plants. They can help enhance the resistance of host plants by improving the compartmentalization of toxic metal contaminants in the cell walls (CWs). However, the functions and responses of various CW subfractions to mycorrhizal colonization under Cd exposure remain unknown. Here we conducted a study to investigate how Cd is stored in the cell walls of maize roots colonized by Funneliformis mosseae. Our findings indicate that inoculating the roots with AMF significantly lowers the amount of Cd in the maize shoots (63.6 ± 6.54 mg kg-1 vs. 45.3 ± 2.19 mg kg-1, p < 0.05) by retaining more Cd in the mycorrhized roots (224.0 ± 17.13 mg kg-1 vs. 289.5 ± 8.75 mg kg-1, p < 0.01). This reduces the adverse effects of excessive Cd on the maize plant. Additional research on the subcellular distribution of Cd showed that AMF colonization significantly improves the compartmentalization of 88.2% of Cd in the cell walls of maize roots, compared to the 80.8% of Cd associated with cell walls in the non-mycorrhizal controls. We observed that the presence of AMF did not increase the amount of Cd in pectin, a primary binding site for cell walls; however, it significantly enhanced the content of lignin and the proportion of Cd in the total root cell walls. This finding is consistent with the increased activity of lignin-related enzymes, such as PAL, 4CL, and laccase, which were also positively impacted by mycorrhizal colonization. Fourier transform infrared spectroscopy (FTIR) results revealed that AMF increased the number and types of functional groups, including -OH/-NH and carboxylate, which chelate Cd in the lignin. Our research shows that AMF can improve the ability of maize plants to tolerate Cd by reducing the amount of Cd transferred from the roots to the shoots. This is achieved by increasing the amount of lignin in the cell walls, which binds with Cd and prevents it from moving through the plant. This is accomplished by activating enzymes related to lignin synthesis and increasing the exposure of Cd-binding functional groups of lignin. However, more direct evidence on the immobilization of Cd in the mycorrhiza-altered cell wall subfractions is needed.

An ultralight and flexible nanofibrillated cellulose/chitosan aerogel for efficient chromium removal: Adsorption-reduction process and mechanism

Heavy metals in water are critical global environmental problems. In particular, the anionic heavy metal chromium (Cr) has carcinogenic and genotoxic risks on human health. To this end, an ultralight and flexible nanofibrillated cellulose (NFC)/chitosan (CS) aerogel was developed only by freeze-drying combined with physical thermal cross-linking for efficient one step co-removal of Cr(VI) and Cr(III). The maximum adsorption capacity of Cr(VI) and total Cr calculated according to the Langmuir model was 197.33 and 134.12 mg/g, respectively. Even in the presence of competing soluble organics, anions and oil contaminants, the resulting NFC/CS-5 aerogels showed excellent selectivity. The aerogel exhibited outstanding mechanical integrity, remaining intact after 17 compressions in air and underwater. Meanwhile, after 5 adsorption-desorption cycles, the aerogel was easy to regenerate and maintained a high regeneration efficiency of 80.25%. Importantly, self-assembled NFC/CS-5 aerogel filter connected with the peristaltic pump could purify 752 mL of industrial wastewater with Cr(VI) pre-concentration capacity of 49.71 mg/g. XPS and FT-IR verified that electrostatic interactions, reduction and complexation acted as the main driving forces for the adsorption process. Moreover, such aerogel possessed broad application prospects for alleviating heavy metal pollution in agriculture.

Pleiotropic melatonin-mediated responses on growth and cadmium phytoextraction of Brassica napus: A bioecological trial for enhancing phytoremediation of soil cadmium

Melatonin (MT) has recently gained significant scientific interest, though its mechanism of action in enhancing plant vigor, cadmium (Cd) tolerance, and Cd phytoremediation processes are poorly understood. Therefore, here we investigated the beneficial role of MT in improving growth and Cd remediation potential of rapeseed (Brassica napus). Plants, with or without MT (200 µM L^-1), were subjected to Cd stress (30 mg kg¹). Without MT, higher Cd accumulation (up to 99%) negatively affected plant growth and developmental feature as well as altered expression of several key genes (DEGs) involved in different molecular pathways of B. napus. As compared to only Cd-stressed counterparts, MT-treated plants exhibited better physiological performance as indicated by improved leaf photosynthetic and gaseous exchange processes (3-48%) followed by plant growth (up to 50%), fresh plant biomass (up to 45%), dry plant biomass (up to 32%), and growth tolerance indices (up to 50%) under Cd exposure. MT application enhanced Cd tolerance and phytoremediation capacity of B. napus by augmenting (1) Cd accumulation in plant tissues and its translocation to above-ground parts (by up to 45.0%), (2) Cd distribution in the leaf cell wall (by up to 42%), and (3) Cd detoxification by elevating phytochelatins (by up to 8%) and metallothioneins (by upto 14%) biosynthesis, in comparison to Cd-treated plants. MT played a protective role in stabilizing hydrogen peroxide and malondialdehyde levels in the tissue of the Cd-treated plants by enhancing the content of osmolytes (proline and total soluble protein) and activities of antioxidant enzymes (SOD, CAT, APX and GR). Transcriptomic analysis revealed that MT regulated 1809 differentially expressed genes (828 up and 981 down) together with 297 commonly expressed DEGs (CK vs Cd and Cd vs CdMT groups) involved in plant-pathogen interaction pathway, protein processing in the endoplasmic reticulum pathway, mitogen-activated protein kinase signaling pathway, and plant hormone signal transduction pathway which ultimately promoted plant growth and Cd remediation potential in the Cd-stressed plants. These results provide insights into the unexplored pleiotropic beneficial action of MT in enhancing in the growth and Cd phytoextraction potential of B. napus, paving the way for developing Cd-tolerant oilseed crops with higher remediation capacity as a bioecological trial for enhancing phytoremediation of hazardous toxic metals in the environment.

Contributions of ectomycorrhizal fungi in a reclaimed poplar forest (Populus yunnanensis) in an abandoned metal mine tailings pond, southwest China

Reclamation using fast-growing trees has great potential for agroforestry development on former non-ferrous metal mining areas. However, the functional traits of ectomycorrhizal fungi (ECMF) and the relationship between ECMF and reclaimed trees remain unknown. Here, the restoration of ECMF and their functions in reclaimed poplar (Populus yunnanensis) growing in a derelict metal mine tailings pond were investigated. We identified ECMF belonging to 15 genera in 8 families, suggesting the occurrence of spontaneous diversification as poplar reclamation progressed. We described a previously unknown ectomycorrhizal relationship between poplar roots and Bovista limosa. Our results showed that B. limosa PY5 alleviated the phytotoxicity of Cd and enhanced poplar heavy metal tolerance, resulting in increased plant growth due to reduced Cd accumulation in host tissues. As part of the improved metal tolerance mechanism, PY5 colonization activated antioxidant systems, enhanced the conversion of Cd into inactive chemical forms, and promoted the compartmentalization of Cd into host cell walls. These results suggest that introducing adaptative ECMF may be an alternative to bioaugmenting reforestation and phytomanagement programs of fast-growing native trees in the barren metal mining and smelting areas.

Integrating physiological and transcriptome analyses clarified the molecular regulation mechanism of PyWRKY48 in poplar under cadmium stress

WRKY transcription factors (TFs) play an important role in regulating plant growth and responses to environmental stress. However, the molecular mechanism of WRKY to cadmium (Cd) stress is unclear, which prevents phytoremediation of Cd-contaminated soil from widely application. To determine the underlying mechanism, PyWRKY48-overexpressing poplars were obtained (OE-32 and OE-67) to study the Cd tolerance and accumulation in poplars. Results showed that the Cd content in the aboveground part of the two transgenic poplar lines were 1.57 and 1.99 times higher than that of wild type (WT), and lateral roots, GSH, PCs content and GST activity increased significantly. RNA-seq. data about transgenic and WT poplars revealed that 2074 differentially expressed genes (DEGs) in roots, 4325 in leaves, and 499 in both tissues. And these DEGs were mainly concentrated in ABC transport protein (PaABC), heavy-metal binding protein (PaHIPP), and transportation and loading of xylem (PaNPF, PaBSP) proteins, and they enhanced Cd accumulation. Meanwhile, PyWRKY48 increased the Cd tolerance of transgenic poplars by up-regulating the expression of PaGRP, PaPER and PaPHOS, which encode cell wall proteins, antioxidant enzyme, and heavy metal-associated proteins, respectively. In addition, overexpression PyWRKY48 promoted poplar growth by increasing the chlorophyll and carotenoid content. ENVIRONMENTAL IMPLICATION: This study generated PyWRKY48-overexpressing poplars and functionally verified them in Cd-contaminated soil, to analyze the effects of the gene on poplar growth, Cd tolerance and Cd accumulation. RNA seq. data revealed that several genes are involved in Cd exposure. This may provide a strong molecular basis and new ideas for improving the phytoremediation efficiency of Cd-contaminated soils. Importantly, the transgenic poplars grew better and accumulated more Cd than the wild-type. Therefore, PyWRKY48-overexpressing poplars could be considered useful for mitigating environmental pollution.

Reconditioning of plant metabolism by arbuscular mycorrhizal networks in cadmium contaminated soils: Recent perspectives

Cadmium (Cd) is one of the most perilous nonessential heavy metal for plants, owing to its high water solubility and obstruction with various physiological and biochemical processes. It enters food chain via plant uptake from contaminated soil, posing a grave menace to ecosystem and mankind. Green remediation comprises approaches intended at prudent use of natural resources for increasing profits to humans and environment. Arbuscular mycorrhizal (AM) fungi are considered a promising green technological tool for remedial of Cd-polluted soils. They are naturally associated with root system of plants in Cd-contaminated soils, evidencing their tolerance to Cd. AM can decrease Cd uptake by plants broadly through two strategies: (1) extracellular mechanisms involving Cd chelation by root exudates, binding to fungal cell wall/structures or to the glycoprotein glomalin; (2) intracellular means involving transfer via hyphal network, detoxification and vacuolar sequestration mediated by complexation of Cd with glutathione (GSH), phytochelatins (PCs), metallothioneins (MTs) and polyphosphate granules. Additionally, mycorrhizal symbiosis facilitates reconditioning of plants' metabolism primarily through dilution effect, increased water and mineral uptake. Recently, AM-induced remodelling of root cell wall synthesis has been reported to improve plant vigor and survival under Cd stressed environments. The present article highlights Cd impacts on AM growth, its diversity in Cd contaminated soils, and variations among diverse AM fungal species for imparting plant Cd tolerance. The most recent perspectives on AM-mediated Cd tolerance mechanisms in plants, including cellular and molecular studies have also been reviewed for successful utilization of these beneficial microbes in sustainable agriculture.

Regulation mechanism of plant response to heavy metal stress mediated by endophytic fungi

Endophytic fungi exist widely in plants and play an important role in the growth and adaptation of plants. They could be used in phytoremediation techniques against heavy metal contaminated soil since beneficial microbial symbionts can endow plants with resistance to external heavy metal stresses. This review summarized the regulation mechanism of plant response to heavy metal stress mediated by endophytic fungi. Potential endophytic fungi in enhancing plant's adaption to heavy metal stresses include arbuscular mycorrhizal fungi, dark septate endophytic fungi, plant growth promoting endophytic fungi. The mechanisms involve coevolution strategy, immune regulation and detoxification transport to improve the ability of plants to adapt to heavy metal stress. They can increase the synthesis of host hormones and maintaining the balance of endogenous hormones, strengthen osmotic regulation, regulate carbon and nitrogen metabolism, and increase immune activity, antioxidant enzyme and glutathione activity. They also help to improve the detoxification transport and heavy metal emission capacity of the host by significantly producing iron carrier, metallothionein and 1-aminocyclopropane-1-carboxylic acid deaminase. The combination of endophytic fungi and hyperaccumulation plants provides a promising technology for the ecological restoration of heavy metal contaminated soil. Endophytic fungi reserves further development on enhancing host plant's adaptability to heavy metal stresses.

Influence of arbuscular mycorrhizal fungi on bioaccumulation and bioavailability of As and Cd: A meta-analysis

Increasing industrial activity has led to a growing risk of arsenic (As) and cadmium (Cd) accumulations and biomagnifications in plants and humans. Arbuscular mycorrhizal fungi (AMF) have been extensively studied as a soil amendment owing to their capability to reduce the accumulation of As and Cd in plant tissues. However, a quantitative and data-based consensus has yet to be reached on the effect of AMF on As and Cd bioaccumulation and bioavailability. Here, a meta-analysis was conducted to quantitatively evaluate the impact of AMF using 1430 individual observations from 194 articles. The results showed that AMF inoculation caused a decrease in shoot and root As and Cd accumulation compared to control, and the reduction rates were affected by experimental duration, P fertilizer, AMF species, plant family, plant lifecycle, and soil properties. Intermediate experimental duration (lasting 56-112 days) and no P fertilizer favored AMF to reduce the shoot As and root Cd accumulation. Compared to other plant families, the reduction in As and Cd accumulation in legumes was the greatest, following AMF inoculation. The soils with alkaline, high organic carbon (OC), and low available phosphorus (AP) appeared to be more favorable for AMF to reduce As accumulation in plant tissues, while soils with low AP were more conducive to reducing the Cd accumulation in plant tissues. In addition, AMF inoculation increased pH (1.92%), OC (6.27%), easily-extractable glomalin-related soil protein (EE-GRSP) (29.36%), and total glomalin-related soil protein (T-GRSP) (29.99%), and reduced bioavailable As (0.52%) and Cd (2.35%) in soils compared to control. Overall, the meta-analysis provides valuable guidelines for the optimal use of AMF in different plant-soil systems.

Rhizophagus irregularis enhances tolerance to cadmium stress by altering host plant hemp (Cannabis sativa L.) photosynthetic properties

Arbuscular mycorrhizal fungi (AMF) are widespread and specialized soil symbiotic fungi, and the establishment of their symbiotic system is of great importance for adversity adaptation. To reveal the growth and photosynthetic characteristics of AMF-crop symbionts in response to heavy metal stress, this experiment investigated the effects of Rhizophagus irregularis (Ri) inoculation on the growth, photosynthetic gas exchange parameters, and chlorophyll fluorescence characteristics of hemp (Cannabis sativa L.) at a Cd concentration of 80 mg/kg. The results showed that (1) under Cd stress, the biomass of each plant structure in the Ri treatment was significantly higher than that in the noninoculation treatment (P < 0.05); (2) under Cd stress, the transpiration rate, stomatal conductance, net photosynthetic rate, PSII efficiency, apparent electron transport rate and photochemical quenching coefficient of the Ri inoculation group reached a maximum, with increases ranging from 1% to 28%; (3) inoculation of Ri significantly reduced Cd enrichment in leaves, which in turn significantly increased the transpiration rate, stomatal conductance, electron transfer rate, net photosynthetic rate and photosynthetic intensity, protecting PSII (P < 0.05); and (4) by measuring the light response curves of different treatments, the light saturation points of hemp inoculated with the Ri treatment reached 1448.4 μmol/m²/s, and the optical compensation point reached 24.0 μmol/m²/s under Cd stress. The Ri-hemp symbiont demonstrated high adaptability to weak light and high utilization efficiency of strong light under Cd stress. Our study showed that Ri-hemp symbiosis improves adaptation to Cd stress and promotes plant growth by regulating the photosynthetic gas exchange parameters and chlorophyll fluorescence parameters of plants. The Ri-hemp symbiosis is a promising technology for improving the productivity of Cd-contaminated soil.

Enhanced cadmium phytoremediation capacity of poplar is associated with increased biomass and Cd accumulation under nitrogen deposition conditions

Nitrogen (N) deposition plays a significant role in soil cadmium (Cd) phytoremediation, and poplar has been considered for the remediation of contaminated soil because of its enormous biomass and strong Cd resistance. To reveal the underlying physiological and root phenotypic mechanisms of N deposition affecting Cd phytoextraction in poplar, we assessed root phenotypic characteristics, Cd absorption and translocation, chlorophyll fluorescence performance, and antioxidant enzyme activities of a clone of Populus deltoides × P. nigra through combined greenhouse Cd and N experiments. Our results showed that Cd significantly changed the root phenotype by reducing root length, tip number, and diameter. Cd also caused the peroxidation of lipids, damaged the photosystem II (PSII) reaction centre, and reduced photosynthetic capacity, resulting in a decrease in biomass accumulation in poplar. The N60 (60 kg N·ha^-1·yr^-1) and N90 (90 kg N·ha^-1·yr^-1) treatments promoted the net photosynthetic rate of poplar by increasing the activity of antioxidant enzymes and proline content and repairing the PSII reaction centre, thus increasing the biomass accumulation of poplar exposed to Cd stress. Simultaneously, the N60 and N90 treatments might have increased Cd uptake from the soil by upregulating total root length, root tips, and fine root length. Cd mainly accumulated in roots and stems but not in leaves. The N30 (30 kg N·ha^-1·yr^-1) treatment had no obvious effects on these parameters compared with the single Cd treatment. Consequently, our study suggested that adequate N can improve biomass and Cd accumulation to enhance the phytoremediation capacity of poplar for Cd, which might be related to the improvement of leaf physiological defence and the change in root phenotypic characteristics.

Insights into growth-promoting effect of nanomaterials: Using transcriptomics and metabolomics to reveal the molecular mechanisms of MWCNTs in enhancing hyperaccumulator under heavy metal(loid)s stress

Carbon nanotubes present potential applications in soil remediation, particularly in phytoremediation. Yet, how multi-walled carbon nanotubes (MWCNTs) induced hyperaccumulator growth at molecular level remains unclear. Here, physio-biochemical, transcriptomic, and metabolomic analyses were performed to determine the effect of MWCNTs on Solanum nigrum L. (S. nigrum) growth under cadmium and arsenic stresses. 500 mg/kg MWCNTs application significantly promoted S. nigrum growth, especially for root tissues. Specially, MWCNTs application yields 1.38-fold, 1.56-fold, and 1.37-fold enhancement in the shoot length, root length, and fresh biomass, respectively. Furthermore, MWCNTs significantly strengthened P and Fe absorption in roots, as well as the activities of antioxidative enzymes. Importantly, the transcriptomic analysis indicated that S. nigrum gene expression was sensitive to MWCNTs, and MWCNTs upregulated advantageous biological processes under heavy metal(loid)s stress. Besides, MWCNTs reprogramed metabolism that related to defense system, leading to accumulation of 4-hydroxyphenylpyruvic acid (amino acid), 4-hydroxycinnamic acid (xenobiotic), and (S)-abscisic acid (lipid). In addition, key common pathways of differentially expressed metabolites and genes, including "tyrosine metabolism" and "isoquinoline alkaloid biosynthesis" were selected via integrating transcriptome and metabolome analyses. Combined omics technologies, our findings provide molecular mechanisms of MWCNTs in promoting S. nigrum growth, and highlight potential application of MWCNTs in soil remediation.

Research Progress and Potential Functions of AMF and GRSP in the Ecological Remediation of Metal Tailings

Metal mining generates a considerable amount of tailings. Arbuscular mycorrhizal fungi (AMF) have potential value for the ecological remediation of tailings from metal mining, despite problems with these tailings, such as loose structure, high heavy-metal concentration and low organic matter and microbial diversity. This review summarizes both the application and physiological functions of AMF, and plant symbiotic systems, in the ecological remediation of tailings from metal mining. The review also includes an in-depth analysis of the characteristics, structural composition, and potential functions of glomalin-related soil protein (GRSP), a release product of mycorrhizal fungi, in the ecological remediation of tailings from metal mining. This review is expected to provide a basis for the application of arbuscular mycorrhizal fungi remediation technology in the ecological remediation of tailings from metal mining.