Comparative transcriptome analysis reveals candidate genes related to cadmium accumulation and tolerance in two almond mushroom (Agaricus brasiliensis) strains with contrasting cadmium tolerance

A nationwide study of heavy metal(loid)s in agricultural soils and the soil-grown black morel Morchella sextelata in China

The accumulation of heavy metal(loid)s (HMs) in soil-grown mushrooms poses potential health risks. Morchella sextelata (black morel) is a typical soil-grown mushroom with a rapidly expanding cultivation area. This study investigated the distribution of arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc in 213 pairs of soil and morel samples collected from 29 provincial administrative regions in China, together with the nutritional contents in the morel samples. The HM contents in the arable soils used to cultivate morels were 2.4-33.1 times higher than those in desert soils, while the HM contents in arable-soil morels were 2.9-155.9 times higher than desert morels. The HM contents of morels and their cultivation soils were significantly correlated (0.465 ≤ R ≤ 0.778, P < 0.001). Furthermore, the enrichment factors of most HMs were higher in arable soils than in desert soils (P < 0.05), except Hg. A considerable proportion of the arable soils produced morels with HMs exceeding the risk control standards (RCSs) for food and the health-risk thresholds of dietary intake. In comparison, HMs in morels from desert soils were far below the RCSs and health-risk thresholds. In addition, desert morels contained higher contents of crude proteins, total polysaccharides, and free amino acids (P < 0.001). These findings indicate that growing morels in desert soils is a way of green production that provides mushroom products with improved safety and nutrition.

Exogenous selenium mitigates cadmium uptake and accumulation in two rice (Oryza sativa L.) varieties in cadmium-contaminated soil

Rice grown in cadmium (Cd)-contaminated soil, is a potential threat to human health, but exogenous selenium (Se) application on rice can mitigate Cd toxicity. However, the mechanisms underlying Se mitigation of Cd stress in ratoon rice (RR) are still poorly understood. We conducted a pot experiment with moderate Cd-contaminated yellow-brown paddy soil on two rice varieties 'Taoyouxiangzhan' (TX) and 'Liangyou 6326'(LY). For all treatments, 1.0 mg kg-1 sodium selenite solution was added to soil. Treatment T1 was sodium selenite only, and in the other treatments 100 mg L-1 Se solution was sprayed on the leaves at seedling stage (T2), at tillering stage (T3), and in early anthesis stage (T4). Se treatments decreased Cd accumulation in rice grains and herbage. Under foliar spraying 100 mg L-1 Se at the seedling + 1.0 mg kg-1 Se in soil (T2), leaf Cd content decreased 16.95% in the current season and grains content decreased 46.67% in the subsequent season. Furthermore, grain Se content increased 0.94 mg kg-1 for the TX variety combined with the analysis of Cd bio-accumulation factor in grains, and Se treatments effectively decreased Cd grain concentrations due to reduced Cd translocation from roots to grains. TX variety rice showed a more pronounced response to Se treatments than LY.

Copper Is Accumulated as Copper Sulfide Particles, and Not Bound to Glutathione, Phytochelatins or Metallothioneins, in the Marine Alga Ulva compressa (Chlorophyta)

To analyze the mechanism of copper accumulation in the marine alga Ulva compressa, it was cultivated with 10 μM of copper, with 10 μM of copper and increasing concentrations of a sulfide donor (NaHS) for 0 to 7 days, and with 10 μM of copper and a concentration of the sulfide acceptor (hypotaurine) for 5 days. The level of intracellular copper was determined as well as the level of glutathione (GSH) and phytochelatins (PCs) and the expression of metallothioneins (UcMTs). The level of intracellular copper in the algae treated with copper increased at day 1, slightly increased until day 5 and remained unchanged until day 7. The level of copper in the algae cultivated with copper and 100 or 200 μM of NaHS continuously increased until day 7 and the copper level was higher in the algae cultivated with 200 μM of NaHS compared to 100 μM of NaHS. In contrast, the level of intracellular copper decreased in the algae treated with copper and hypotaurine. The level of intracellular copper did not correlate with the level of GSH or with the expression of UcMTs, and PCs were not detected in response to copper, or copper and NaHS. Algae treated with copper and with copper and 200 μM of NaHS for 5 days were visualized by TEM and the elemental composition of electrondense particles was analyzed by EDXS. The algae treated with copper showed electrondense particles containing copper and sulfur, but not nitrogen, and they were mainly located in the chloroplast, but also in the cytoplasm. The algae treated with copper and NaHS showed a higher level of electrondense particles containing copper and sulfur, but not nitrogen, and they were located in the chloroplast, and in the cytoplasm. Thus, copper is accumulated as copper sulfide insoluble particles, and not bound to GSH, PCs or UcMTs, in the marine alga U. compressa.

BcaSOD1 enhances cadmium tolerance in transgenic Arabidopsis by regulating the expression of genes related to heavy metal detoxification and arginine synthesis

Cadmium (Cd), which is a nonessential heavy metal element for organisms, can have a severe impact on the growth and development of organisms that absorb excessive Cd. Studies have shown that Brassica carinata, a semiwild oil crop, has strong tolerance to various abiotic stresses, and RNA-seq has revealed that the B. carinata superoxide dismutase gene (BcaSOD1) likely responds to Cd stress. To elucidate the BcaSOD1 function involved in tolerance of Cd stress, we cloned the coding sequences of BcaSOD1 from a purple B. carinata accession and successfully transferred it into Arabidopsis thaliana. The subcellular localization results demonstrated that BcaSOD1 was primarily located in the plasma membrane, mitochondria and nucleus. Overexpression of BcaSOD1 in transgenic Arabidopsis (OE) effectively decreased the toxicity caused by Cd stress. Compared to the WT (wild type lines), the OE lines exhibited significantly increased activities of antioxidant enzymes (APX, CAT, POD, and SOD) after exposure to 2.5 mM CdCl2. The Cd content of underground (root) in the OE line was dominantly higher than that in the WT; however, the Cd content of aboveground (shoot) was comparable between the OE and WT types. Moreover, the qRT‒PCR results showed that several heavy metal detoxification-related genes (AtIREG2, AtMTP3, AtHMA3, and AtNAS4) were significantly upregulated in the roots of OE lines under Cd treatment, suggesting that these genes are likely involved in Cd absorption in the roots of OE lines. In addition, both comparable transcriptome and qRT-PCR analyses revealed that exogenous BcaSOD1 noticeably facilitates detoxification by stimulating the expression of two arginine (Arg) biosynthesis genes (AtGDH1 and AtGDH2) while inhibiting the expression of AtARGAH1, a negative regulator in biosynthesis of Arg. The Arg content was subsequently confirmed to be significantly enhanced in OE lines under Cd treatment, indicating that BcaSOD1 likely strengthened Cd tolerance by regulating the expression of Arg-related genes. This study demonstrates that BcaSOD1 can enhance Cd tolerance and reveals the molecular mechanism of this gene, providing valuable insights into the molecular mechanism of Cd tolerance in plants.

Safe Production Strategies for Soil-Covered Cultivation of Morel in Heavy Metal-Contaminated Soils

Morel is a popular edible mushroom with considerable medicinal and economic value which has garnered global popularity. However, the increasing heavy metal (HM) pollution in the soil presents a significant challenge to morels cultivation. Given the susceptibility of morels to HM accumulation, the quality and output of morels are at risk, posing a serious food safety concern that hinders the development of the morel industry. Nonetheless, research on the mechanism of HM enrichment and mitigation strategies in morel remains scarce. The morel, being cultivated in soil, shows a positive correlation between HM content in its fruiting body and the HM content in the soil. Therefore, soil remediation emerges as the most practical and effective approach to tackle HM pollution. Compared to physical and chemical remediation, bioremediation is a low-cost and eco-friendly approach that poses minimal threats to soil composition and structure. HMs easily enriched during morels cultivation were examined, including Cd, Cu, Hg, and Pb, and we assessed soil passivation technology, microbial remediation, strain screening and cultivation, and agronomic measures as potential approaches for HM pollution prevention. The current review underscores the importance of establishing a comprehensive system for preventing HM pollution in morels.

Pleurotus pulmonarius Strain: Arsenic(III)/Cadmium(II) Accumulation, Tolerance, and Simulation Application in Environmental Remediation

The arsenic (As, III) and cadmium (Cd, II) accumulation and tolerance traits of a new strain Pleurotus pulmonarius MT were evaluated, and the utilization of the strain for repairing contaminated liquid and soil was explored. The hypha cultivated in potato dextrose agar (PDA) exhibited medium or high Cd accumulation (0 to 320 mg/L), medium Cd tolerance (maximum tolerated concentration, MTC ≥ 640 mg/L), medium As accumulation (0 to 80 mg/L), and high As tolerance (MTC > 1280 mg/L). The hypha has application potential in processes related to the removal of Cd and As in aqueous pollutants at concentrations of 80 mg/L Cd and 20 mg/L As. The trends obtained for the fruiting bodies of P. pulmonarius MT seemed to deviate from those of the hypha of this strain. The results show that the fruiting bodies featured medium As accumulation (0 to 40 mg/kg), medium As tolerance (MTC > 160 mg/kg), medium Cd accumulation (0 to 10 mg/kg), and high Cd tolerance (MTC > 1280 mg/kg). The fruiting bodies of P. pulmonarius MT were utilized in processes related to the recovery of Cd and As in substrates, that is, 12% contaminated soil mixed with 50 mg/kg Cd and 200 mg/kg As; thus, the hypha and fruiting bodies of P. pulmonarius MT can be used for the decontamination of water and soil containing As(III) and Cd(II).

Comparative Transcriptomic Analysis of Root Cadmium Responses in Two Chinese Rice Cultivars Yuzhenxiang and Xiangwanxian 12

Cadmium (Cd) pollution in paddy soil is an increasingly serious issue in rice production. It has been reported that there is a higher or lower grain Cd accumulation in the rice cultivars Yuzhenxiang (YZX) or Xiangwanxian 12 (XWX), respectively. To better manage the Cd pollution problem, the genes that might play vital roles in governing the difference in root Cd responses between these two rice cultivars were examined. In this study, the results of RNA sequencing (RNA-seq) showed that there were 341 and 161 differentially expressed genes in the roots of YZX and XWX after Cd exposure, respectively. Among these genes, 7 genes, such as Os06g0196300 (OsJ_019618), Os07g0570700 (OsJ_24808), ADI1, GDCSH, HSFB2C, PEX11-4, and CLPB1, possessed higher degree nodes with each other, through interaction analysis by the STRING (search tool for the retrieval of interacting genes/proteins) software, suggesting that they might play vital roles in Cd response. Based on GO enrichment analysis, 41 differently expressed genes after Cd treatment in YZX or XWX were identified to be related to Cd response. Through comparative transcriptomic analysis, 257 genes might be associated with the root Cd response difference between YZX and XWX. Furthermore, we supposed that ADI1, CFBP1, PEX11-4, OsJ_019618, OsJ_24808, GDCSH, CLPB1, LAC6, and WNK3 might be implicated in Cd response based on the combined analysis of RT-qPCR, interaction, and GO annotation analysis. In conclusion, the numerous genes that might be related to Cd stress response and root Cd response difference between YZX and XWX at the booting stage may be of benefit for the development of rice varieties with low Cd consumption.

Effects of cadmium stress on physiological indexes and fruiting body nutritions of Agaricus brasiliensis

In this study, 0, 0.5, 1, 1.5, 2, 4, 6 and 8 mg·kg^-1 of cadmium were added to the cultivation materials. In order to study the effects of different concentrations of Cd stress on J1 and J77, the contents of antioxidant enzymes, proline and malondialdehyde, Cd content, agronomic traits and yield of fruiting bodies of Agaricus brasiliensis were determined, and the nutritional components such as polysaccharide, triterpene, protein, total sugar and total amino acid were determined. The results showed that the physiological indexes of strain J1 and J77 changed regularly under different concentrations of Cd stress. J1 was a high absorption and low tolerance variety, while J77 was a low absorption and high tolerance variety. Low concentration of Cd promoted the growth of strain J1, and higher concentration of Cd promoted the growth of strain J77. The contents of protein and total amino acids in the two strains changed greatly, followed by polysaccharides, which indicated that Cd stress had the greatest impact on the three nutrients, and other nutrients were not sensitive to Cd stress.

Fungal-Metal Interactions: A Review of Toxicity and Homeostasis

Metal nanoparticles used as antifungals have increased the occurrence of fungal-metal interactions. However, there is a lack of knowledge about how these interactions cause genomic and physiological changes, which can produce fungal superbugs. Despite interest in these interactions, there is limited understanding of resistance mechanisms in most fungi studied until now. We highlight the current knowledge of fungal homeostasis of zinc, copper, iron, manganese, and silver to comprehensively examine associated mechanisms of resistance. Such mechanisms have been widely studied in Saccharomyces cerevisiae, but limited reports exist in filamentous fungi, though they are frequently the subject of nanoparticle biosynthesis and targets of antifungal metals. In most cases, microarray analyses uncovered resistance mechanisms as a response to metal exposure. In yeast, metal resistance is mainly due to the down-regulation of metal ion importers, utilization of metallothionein and metallothionein-like structures, and ion sequestration to the vacuole. In contrast, metal resistance in filamentous fungi heavily relies upon cellular ion export. However, there are instances of resistance that utilized vacuole sequestration, ion metallothionein, and chelator binding, deleting a metal ion importer, and ion storage in hyphal cell walls. In general, resistance to zinc, copper, iron, and manganese is extensively reported in yeast and partially known in filamentous fungi; and silver resistance lacks comprehensive understanding in both.