OsNRAMP1 transporter contributes to cadmium and manganese uptake in rice

The chelation mechanism of neonicotinoid insecticides influencing cadmium transport and accumulation in rice at different growth stage

The combined exposure of heavy metals and organic contaminates can influence the transport and accumulation of heavy metals within the soil-rice system. However, the underlying mechanisms of this process remain largely unknown. Herein, this study investigated the influence of three neonicotinoid insecticides (NIs), including imidacloprid (IMI), clothianidin (CLO), and thiamethoxam (THI), on the Cd transport and accumulation in rice (Oryza sativa) at different growth stages. Particular focus lied on their complex interaction and key genes expression involved in Cd transport. Results showed that the interaction between Cd and NIs was the dominant factor affecting Cd transport and accumulation in rice exposed to NIs. All three NIs chelated with Cd with nitrogen (N) on the IMI and THI nitro groups, and the N on the CLO nitro guanidine group. Interestingly, this chelation behavior varied between the tillering stage and the filling/ripening stages, resulting in diverse patterns of Cd accumulation in rice tissues. During the tillering stage, all three NIs considerably inhibited Cd bioavailability and transport to the above-ground part, lowering Cd content in the stem and leaf. The inhibition was increased with stronger chelation ability in the order of IMI (-0.46 eV) > CLO (-0.41 eV) > THI (-0.11 eV), with IMI exhibiting the highest binding energy for Cd and reducing Cd transfers from root to stem by an impressive 94.49 % during the tillering stage. Conversely, during the filling/ripening stages, NIs facilitated Cd accumulation in rice roots, stems, leaves, and grains. This was mainly attributed to the generation of nitrate ions and the release of Cd2+ during the chelation between Cd and NIs under drainage condition. These findings provide theoretical basis for the treatment of combined contamination in field and deep insights into understanding the interaction of organic contaminants with heavy metals in rice culture process.

Cadmium toxicity: its' uptake and retaliation by plant defence system and ja signaling

Cadmium (Cd+2) renders multifarious environmental stresses and highly toxic to nearly all living organisms including plants. Cd causes toxicity by unnecessary augmentation of ROS that targets essential molecules and fundamental processes in plants. In response, plants outfitted a repertory of mechanisms to offset Cd toxicity. The main elements of these are Cd chelation, sequestration into vacuoles, and adjustment of Cd uptake by transporters and escalation of antioxidative mechanism. Signal molecules like phytohormones and reactive oxygen species (ROS) activate the MAPK cascade, the activation of the antioxidant system andsynergistic crosstalk between different signal molecules in order to regulate plant responses to Cd toxicity. Transcription factors like WRKY, MYB, bHLH, bZIP, ERF, NAC etc., located downstream of MAPK, and are key factors in regulating Cd toxicity responses in plants. Apart from this, MAPK and Ca2+signaling also have a salient involvement in rectifying Cd stress in plants. This review highlighted the mechanism of Cd uptake, translocation, detoxification and the key role of defense system, MAPKs, Ca2+ signals and jasmonic acid in retaliating Cd toxicity via synchronous management of various other regulators and signaling components involved under stress condition.

Multifunctional Roles of Zinc in Cadmium Transport in Soil-Rice Systems: Novel Insights from Stable Isotope Fractionation and Gene Expression

The effect of Zn on Cd accumulation in rice varies under flooding and drainage conditions, and the underlying mechanism during uptake and transport from the soil to grains remains unclear. Isotope fractionation and gene expression were investigated using pot experiments under distinct water regimes and with Zn addition to gain a deeper understanding of the molecular effects of Zn on Cd uptake and transport in rice. The higher OsHMA2 expression but constitutively lower expression of zinc-regulated, iron-regulated transporter-like protein (ZIP) family genes in roots under the drainage regime than the flooding regime caused the enrichment of nonheavy Zn isotopes in the shoots relative to roots but minimally affected Cd isotopic fractionation. Drainage regime seem to exert a striking effect on the root-to-shoot translocation of Zn rather than Cd, and increased Zn transport via OsHMA2. The changes in expression patterns in response to Zn addition were similar to those observed upon switching from the flooding to drainage regime, except for OsNRAMP1 and OsNRAMP5. However, soil solution-to-rice plants and root-to-shoot fractionation toward light Zn isotopes with Zn addition (Δ66Znrice plant-soil solution = -0.49 to -0.40‰, Δ66Znshoot-root = -0.36 to -0.27‰) indicated that Zn transport occurred via nonspecific uptake pathways and OsHMA2, respectively. Accordingly, the less pronounced and minimally varied Cd isotope fractionation suggested that OsNRAMP5 and OsHMA2 are crucial for Cd uptake and root-to-shoot transport, respectively, facilitating Cd accumulation in grains. This study demonstrated that a high Zn supply promotes Cd uptake and root-to-shoot transport in rice by sharing distinct pathways, and by utilizing a non-Zn-sensitive pathway with a high affinity for Cd.

Effect of Genotype on Cadmium and Trace Element Accumulation in Wheat from Weakly Alkaline Cadmium-contaminated Soil

Cadmium (Cd) contamination of farmland soils leads to Cd accumulation in crops and reduced micronutrient uptake, posing grave risks to food safety. Herein, we investigated the enrichment and transportation patterns of Cd and trace elements in different parts of six wheat genotypes grown in weakly alkaline Cd-contaminated soils via pot experiments. The results revealed that the wheat grain variety with high Cd accumulation (Ningmai13) demonstrated a 1.94-fold increase compared to the variety with low accumulation (Yanong0428). The transfer factor of Cd from wheat straw to grain ranged from 0.319 to 0.761, while the transfer factor of Cd from root to straw ranged from 0.167 to 0.461. Furthermore, the concentrations of other metals in wheat grains followed the order of Zn > Mn > Fe > Cu. There was a significant positive correlation between Cd and Mn in grains, indicating a potential synergistic effect. Overall, this study provides valuable insights into the regulation of micronutrient intake to modulate Cd uptake in wheat.

Salicylic Acid's impact on Sedum alfredii growth and cadmium tolerance: Comparative physiological, transcriptomic, and metabolomic study

With the acceleration of industrialization, Cd pollution has emerged as a major threat to soil ecosystem health and food safety. Hyperaccumulating plants like Sedum alfredii Hance are considered to be used as part of an effective strategy for the ecological remediation of Cd polluted soils. This study delved deeply into the physiological, transcriptomic, and metabolomic responses of S. alfredii under cadmium (Cd) stress when treated with exogenous salicylic acid (SA). We found that SA notably enhanced the growth of S. alfredii and thereby increased absorption and accumulation of Cd, effectively alleviating the oxidative stress caused by Cd through upregulation of the antioxidant system. Transcriptomic and metabolomic data further unveiled the influence of SA on photosynthesis, antioxidant defensive mechanisms, and metal absorption enrichment pathways. Notably, the interactions between SA and other plant hormones, especially IAA and JA, played a central role in these processes. These findings offer us a comprehensive perspective on understanding how to enhance the growth and heavy metal absorption capabilities of hyperaccumulator plants by regulating plant hormones, providing invaluable strategies for future environmental remediation efforts.

Populus euphratica R2R3-MYB transcription factor RAX2 binds ANN1 promoter to increase cadmium enrichment in Arabidopsis

The expression of R2R3-MYB transcription factor PeRAX2 increased transiently upon CdCl2 exposure (100 μM, 48 h) in leaves and roots of Populus euphratica. We observed that overexpression of PeRAX2 increased Cd2+ concentration in Arabidopsis root cells and Cd2+ amount in whole plant, which was due to the increased Cd2+ influx into root tips. However, the Cd2+ influx facilitated by PeRAX2 overexpression was substantially reduced by LaCl3 (an inhibitor of Ca2+-channels), suggesting that PeRAX2 could promote the Cd2+ entering through PM Ca2+-permeable channels (CaPCs) in the roots. It is noting that the expression of annexin1 (AtANN1), which mediates the influx of divalent cations through the PM calcium channels, was upregulated by Cd2+ in PeRAX2-transgenic Arabidopsis. Bioinformatic analysis revealed that the AtANN1 promoter (AtANN1-pro) contains four cis-elements for MYB binding. The PeRAX2 interaction with AtANN1-pro was validated by LUC reporter assay, EMSA, and Y1H assay. Our data showed that PeRAX2 binds to the AtANN1 promoter region to regulate gene transcription and that AtANN1 mediates the Cd2+ entry through CaPCs in the PM, leading to a Cd2+ enrichment in transgenic plants. The PeRAX2-stimulated Cd2+ enrichment consequently resulted in high H2O2 production in root cells of transgenic plants. The expression of AtSOD and AtPOD and activities of CAT, SOD, POD increased in the transgenic lines under Cd2+ stress. However, the Cd2+-upregulated expression and activity of antioxidative enzymes were less pronounced in the PeRAX2-overexpressed lines, compared to the wildtype and vector controls. As a result, root length and plant growth were more suppressed by Cd2+ in the transgenic lines. Our data suggest that transcriptional regulation of AtANN1 by PeRAX2 can be utilized to improve Cd2+ enrichment and phytoremediation, although the enriched Cd2+ affected antioxidant defense system and plant growth in the model species.

Endoplasmic reticulum stress response modulator OsbZIP39 regulates cadmium accumulation via activating the expression of defensin-like gene OsCAL2 in rice

Accumulation of cadmium (Cd) in rice is not only harmful to the growth of plants but also poses a threat to human health. Exposure to Cd triggers unfolded protein response (UPR) within cells, a process that is still not completely understood. The study demonstrated that the lack of OsbZIP39, an essential endoplasmic reticulum (ER)-resident regulator of the UPR, resulted in decreased Cd intake and reduced Cd levels in the roots, stems, and grains of rice. Upon exposure to Cd stress, GFP-OsbZIP39 translocated from ER to nucleus, initiating UPR. Further investigation revealed that Cd treatment caused changes in sphingolipid levels in the membrane, influencing the localization and activation of OsbZIP39. Yeast one-hybrid and dual-LUC assays were conducted to validate the interaction between activated OsbZIP39 and the promoter of the defensin-like gene OsCAL2, resulting in an increase in its expression. Different variations were identified in the coding region of OsbZIP39, which may explain the varying levels of Cd accumulation observed in the indica and japonica subspecies. Under Cd treatment, OsbZIP39ind exhibited a more significant enhancement in the transcription of OsCAL2 compared to OsbZIP39jap. Our data suggest that OsbZIP39 positively regulates Cd uptake in rice, offering an encouraging objective for the cultivation of low-Cd rice.

Metabolomics and physio-chemical analyses of mulberry plants leaves response to manganese deficiency and toxicity reveal key metabolites and their pathways in manganese tolerance

Introduction

Manganese (Mn) plays a pivotal role in plant growth and development. Aside aiding in plant growth and development, Mn as heavy metal (HM) can be toxic in soil when applied in excess. Morus alba is an economically significant plant, capable of adapting to a range of environmental conditions and possessing the potential for phytoremediation of contaminated soil by HMs. The mechanism by which M. alba tolerates Mn stresses remains obscure.

Methods

In this study, Mn concentrations comprising sufficiency (0.15 mM), higher regimes (1.5 mM and 3 mM), and deficiency (0 mM and 0.03 mM), were applied to M. alba in pot treatment for 21 days to understand M. alba Mn tolerance. Mn stress effects on the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular CO2 concentration (Ci), chlorophyll content, plant morphological traits, enzymatic and non-enzymatic parameters were analyzed as well as metabolome signatures via non-targeted LC-MS technique.

Results

Mn deficiency and toxicity decrease plant biomass, Pn, Ci, Gs, Tr, and chlorophyll content. Mn stresses induced a decline in the activities of catalase (CAT) and superoxide dismutase (SOD), while peroxidase (POD) activity, and leaf Mn content, increased. Soluble sugars, soluble proteins, malondialdehyde (MDA) and proline exhibited an elevation in Mn deficiency and toxicity concentrations. Metabolomic analysis indicates that Mn concentrations induced 1031 differentially expressed metabolites (DEMs), particularly amino acids, lipids, carbohydrates, benzene and derivatives and secondary metabolites. The DEMs are significantly enriched in alpha-linolenic acid metabolism, biosynthesis of unsaturated fatty acids, galactose metabolism, pantothenate and CoA biosynthesis, pentose phosphate pathway, carbon metabolism, etc.

Discussion and conclusion

The upregulation of Galactinol, Myo-inositol, Jasmonic acid, L-aspartic acid, Coproporphyrin I, Trigonelline, Pantothenol, and Pantothenate and their significance in the metabolic pathways makes them Mn stress tolerance metabolites in M. alba. Our findings reveal the fundamental understanding of DEMs in M. alba's response to Mn nutrition and the metabolic mechanisms involved, which may hold potential significance for the advancement of M. alba genetic improvement initiatives and phytoremediation programs.

CIP1, a CIPK23-interacting transporter, is implicated in Cd tolerance and phytoremediation

Environmental pollution from cadmium (Cd) presents a serious threat to plant growth and development. Therefore, it's crucial to find out how plants resist this toxic metal to develop strategies for remediating Cd-contaminated soils. In this study, we identified CIP1, a transporter protein, by screening interactors of the protein kinase CIPK23. CIP1 is located in vesicles membranes and can transport Cd2+ when expressed in yeast cells. Cd stress specifically induced the accumulation of CIP1 transcripts and functional proteins, particularly in the epidermal cells of the root tip. CIKP23 could interact directly with the central loop region of CIP1, phosphorylating it, which is essential for the efficient transport of Cd2+. A loss-of-function mutation of CIP1 in wild-type plants led to increased sensitivity to Cd stress. Conversely, tobacco plants overexpressing CIP1 exhibited improved Cd tolerance and increased Cd accumulation capacity. Interestingly, this Cd accumulation was restricted to roots but not shoots, suggesting that manipulating CIP1 does not risk Cd contamination of plants' edible parts. Overall, this study characterizes a novel Cd transporter, CIP1, with potential to enhance plant tolerance to Cd toxicity while effectively eliminating environmental contamination without economic losses.

The OsZIP2 transporter is involved in root-to-shoot translocation and intervascular transfer of cadmium in rice

Cadmium (Cd) is a toxic metal that poses serious threats to human health. Rice is a major source of dietary Cd but how rice plants transport Cd to the grain is not fully understood. Here, we characterize the function of the ZIP (ZRT, IRT-like protein) family protein, OsZIP2, in the root-to-shoot translocation of Cd and intervascular transfer of Cd in nodes. OsZIP2 is localized at the plasma membrane and exhibited Cd2+ transport activity when heterologously expressed in yeast. OsZIP2 is strongly expressed in xylem parenchyma cells in roots and in enlarged vascular bundles in nodes. Knockout of OsZIP2 significantly enhanced root-to-shoot translocation of Cd and alleviated the inhibition of root elongation by excess Cd stress; whereas overexpression of OsZIP2 decreased Cd translocation to shoots and resulted in Cd sensitivity. Knockout of OsZIP2 increased Cd allocation to the flag leaf but decreased Cd allocation to the panicle and grain. We further reveal that the variation of OsZIP2 expression level contributes to grain Cd concentration among rice germplasms. Our results demonstrate that OsZIP2 functions in root-to-shoot translocation of Cd in roots and intervascular transfer of Cd in nodes, which can be used for breeding low Cd rice varieties.

Dynamic transcriptome profiling revealed a key gene ZmJMJ20 and pathways associated with cadmium stress in maize

Cadmium (Cd) pollution in soil poses a global concern due to its serious impacts on human health and ecological security. In plants, tremendous efforts have been made to identify some key genes and pathways in Cd stress responses. However, studies on the roles of epigenetic factors in response to Cd stress were still limited. In the study, we first gain insight into the gene expression dynamics for maize seedlings under 0 h, 12 h, and 72 h Cd stress. As a result, six distinct groups of genes were identified by hierarchical clustering and principal component analysis. The key pathways associated with 12 h Cd stress were protein modifications including protein ubiquitination, signal transduction by protein phosphorylation, and histone modification. Whereas, under 72 h stress, main pathways were involved in biological processes including phenylalanine metabolism, response to oxygen-containing compounds and metal ions. Then to be noted, one of the most highly expressed genes at 12 h under Cd treatment is annotated as histone demethylases (ZmJMJ20). The evolutionary tree analysis and domain analysis showed that ZmJMJ20 belonged to the JmjC-only subfamily of the Jumonji-C (JmjC) family, and ZmJMJ20 was conserved in rice and Arabidopsis. After 72 h of Cd treatment, the zmjmj20 mutant created by EMS treatment manifested less severe chlorosis/leaf yellowing symptoms compared with wild-type plants, and there was no significant difference in Fv/Fm and φPSII value before and after Cd treatment. Moreover, the expression levels of several photosynthesis-related down-regulated genes in EMS mutant plants were dramatically increased compared with those in wild-type plants at 12 h under Cd treatment. Our results suggested that ZmJMJ20 plays an important role in the Cd tolerance response pathway and will facilitate the development of cultivars with improved Cd stress tolerance.

Safe utilization and remediation potential of the mulberry-silkworm system in heavy metal-contaminated lands: A review

Mulberry cultivation and silkworm rearing hold a prominent position in the agricultural industries of many Asian countries, contributing to economic growth, sustainable development, and cultural heritage preservation. Applying the soil-mulberry-silkworm system (SMSS) to heavy metal (HM)-contaminated areas is significant economically, environmentally, and socially. The ultimate goal of this paper is to review the main research progress of SMSS under HM stress, examining factors affecting its safe utilization and remediation potential for HM-contaminated soils. HM tolerance of mulberry and silkworms relates to their growth stages. Based on the standards for HM contaminants in various mulberry and silkworm products and the bioconcentration factor of HMs at different parts of SMSS, we calculated maximum safe Cd and Pb levels for SMSS application on contaminated lands. Several remediation practices demonstrated mulberry's ability to grow on barren lands, absorb various HMs, while silkworm excreta can adsorb HMs and improve soil fertility. Considering multiple factors influencing HM tolerance and accumulation, we propose a decision model to guide SMSS application in polluted areas. Finally, we discussed the potential of using molecular breeding techniques to screen or develop varieties better suited for HM-contaminated regions. However, actual pollution scenarios are often complex, requiring consideration of multiple factors. More large-scale applications are crucial to enhance the theoretical foundation for applying SMSS in HM pollution risk areas.

Changes in secondary metabolites contents and stress responses in Salvia miltiorrhiza via ScWRKY35 overexpression: Insights from a wild relative Salvia castanea

Salvia castanea Diels, a close wild relative to the medicinal plant, Salvia miltiorrhiza Bunge, primarily grows in high-altitude regions. While the two species share similar active compounds, their content varies significantly. WRKY transcription factors are key proteins, which regulate plant growth, stress response, and secondary metabolism. We identified 46 ScWRKY genes in S. castanea and found that ScWRKY35 was a highly expressed gene associated with secondary metabolites accumulation. This study aimed to explore the role of ScWRKY35 gene in regulating the accumulation of secondary metabolites and its response to UV and cadmium (Cd) exposure in S. miltiorrhiza. It was found that transgenic S. miltiorrhiza hairy roots overexpressing ScWRKY35 displayed upregulated expression of genes related to phenolic acid synthesis, resulting in increased salvianolic acid B (SAB) and rosmarinic acid (RA) contents. Conversely, tanshinone pathway gene expression decreased, leading to lower tanshinone levels. Further, overexpression of ScWRKY35 upregulated Cd transport protein HMA3 in root tissues inducing Cd sequestration. In contrast, the Cd uptake gene NRAMP1 was downregulated, reducing Cd absorption. In response to UV radiation, ScWRKY35 overexpression led to an increase in the accumulation of phenolic acid and tanshinone contents, including upregulation of genes associated with salicylic acid (SA) and jasmonic acid (JA) synthesis. Altogether, these findings highlight the role of ScWRKY35 in enhancing secondary metabolites accumulation, as well as in Cd and UV stress modulation in S. miltiorrhiza, which offers a novel insight into its phytochemistry and provides a new option for the genetic improvement of the plants.

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.

The Uptake, Transfer, and Detoxification of Cadmium in Plants and Its Exogenous Effects

Cadmium (Cd) exerts a toxic influence on numerous crucial growth and development processes in plants, notably affecting seed germination rate, transpiration rate, chlorophyll content, and biomass. While considerable advances in Cd uptake and detoxification of plants have been made, the mechanisms by which plants adapt to and tolerate Cd toxicity remain elusive. This review focuses on the relationship between Cd and plants and the prospects for phytoremediation of Cd pollution. We highlight the following issues: (1) the present state of Cd pollution and its associated hazards, encompassing the sources and distribution of Cd and the risks posed to human health; (2) the mechanisms underlying the uptake and transport of Cd, including the physiological processes associated with the uptake, translocation, and detoxification of Cd, as well as the pertinent gene families implicated in these processes; (3) the detrimental effects of Cd on plants and the mechanisms of detoxification, such as the activation of resistance genes, root chelation, vacuolar compartmentalization, the activation of antioxidant systems and the generation of non-enzymatic antioxidants; (4) the practical application of phytoremediation and the impact of incorporating exogenous substances on the Cd tolerance of plants.

Mechanisms of chloride to promote the uptake and accumulation of cadmium in rice (Oryza sativa L.)

Cadmium (Cd) contamination in rice ecosystems posed a critical challenge to global food security and environmental health. This study aimed to unveil the key mechanisms trough hydroponic experiments by which chloride (Cl-) promoted the absorption and accumulation of cadmium (Cd) in rice plants. The findings elucidated that the addition of Cl- increased Cd uptake by rice roots (5.1 % ∼ 61 %), acting both directly by enhancing root morphology and indirectly through regulating of the main transporter genes of Cd. The study unveiled that Cl- addition significantly improves Cd bioavailability in roots, which was discernible through the augmentation of Cd concentration and proportion in subcellular fractions, coupled with elevated energy values in key cellular components. Moreover, Cl- addition further augmented the intricate process of Cd transport from roots to shoots (16.1- 86.7 %), which was mainly attributed to the underexpression of OsHMA3 and the decrease in the formation of sulfuhydryl substances. This research provides a comprehensive understanding of the complex mechanisms governing Cd dynamics in rice plants in the presence of Cl-. By elucidating these processes, our findings not only contribute to fundamental knowledge in plant metal uptake but also hold promising implications for mitigating Cd contamination in rice cultivation systems.

Foliar application protected vegetable against poisonous element cadmium and mitigated human health risks

Foliar application has been reported as an effective method to facilitate plant growth and mitigate cadmium (Cd) accumulation. However, the application of foliar fertilizers on plant production, Cd uptake and health risks of Solanaceae family remains unknown. In this study, four foliar fertilizers were applied to investigate their effects on the production, Cd accumulation and human health risk assessment of two varieties of pepper (Capsicum annuum L.) and eggplant (Solanum melongena L.), respectively. Compared with CK, the foliar application increased vegetable production to 104.16 %-123.70 % in peppers, and 100.83 %-105.17 % in eggplants, accordingly. The application of foliar fertilizers largely decreased Cd TF (transportation factor) by up to 23.32 % in JY, 18.37 % in GJ of pepper varieties, and up to 14.47 % in ZL, 15.24 % in HGR of eggplant varieties. Moreover, Cd BAF (bioaccumulation factor) also declined to different extents after the application of foliar fertilizers. As for human health risk assessments, foliar application diminished the hazard index (HI) and carcinogenic risk (CR) of both pepper and eggplant varieties. The results concluded that the application of composed foliar fertilizers was most effective, and could be a promising alternative for the improvement of vegetable production and mitigation of vegetable Cd accumulation and human health risks as well. The results further highlighted the understanding of foliar fertilizer application on vegetable production and health risks, which benefited better vegetable safe production and further guaranteed human health.

Two aquaporins, PIP1;1 and PIP2;1, mediate the uptake of neonicotinoid pesticides in plants

Neonicotinoids (NEOs), a large class of organic compounds, are a type of commonly used pesticide for crop protection. Their uptake and accumulation in plants are prerequisites for their intra- and intercellular movements, transformation, and function. Understanding the molecular mechanisms that underpin NEO uptake by plants is crucial for effective application, which remains elusive. Here, we demonstrate that NEOs enter plant cells primarily through the transmembrane symplastic pathway and accumulate mainly in the cytosol. Two plasma membrane intrinsic proteins discovered in Brassica rapa, BraPIP1;1 and BraPIP2;1, were found to encode aquaporins (AQPs) that are highly permeable to NEOs in different plant species and facilitate NEO subcellular diffusion and accumulation. Their conserved transport function was further demonstrated in Xenopus laevis oocyte and yeast assays. BraPIP1;1 and BraPIP2;1 gene knockouts and interaction assays suggested that their proteins can form functional heterotetramers. Assessment of the potential of mean force indicated a negative correlation between NEO uptake and the energy barrier of BraPIP1;1 channels. This study shows that AQPs transport organic compounds with greater osmolarity than previously thought, providing new insight into the molecular mechanisms of organic compound uptake and facilitating innovations in systemic pesticides.

OsGLP8-7 interacts with OsPRX111 to detoxify excess copper in rice

Lignin is a phenolic biopolymer generated from phenylpropanoid pathway in the secondary cell wall and is required for defense of plants against various stress. Although the fact of stress-induced lignin deposition has been clearly demonstrated, it remains largely elusive how the formation of lignin is promoted under Cu stress. The present study showed that OsGLP8-7, an extracellular glycoprotein of rice (Oryza sativa L.), plays an important function against Cu stress. The loss function of OsGLP8-7 results in Cu sensitivity whereas overexpression of OsGLP8-7 scavenges Cu-induced superoxide anion (O2•-). OsGLP8-7 interacts with apoplastic peroxidase111 (OsPRX111) and elevates OsPRX111 stability when exposed to excess Cu. In OsGLP8-7 overexpressing (OE) lines, the retention of Cu within cell wall limiting Cu uptake into cytoplasm is attributed to the enhanced lignification required for Cu tolerance. Exogenous application of a lignin inhibitor can impair the Cu tolerance of transgenic Arabidopsis lines overexpressing OsGLP8-7. In addition, co-expression of OsGLP8-7 and OsPRX111 genes in tobacco leaves leads to an improved lignin deposition compared to leaves expressing each gene individually or the empty vector. Taken together, our findings provided the convincing evidences that the interaction between OsGLP8-7 and OsPRX111 facilitates effectively lignin polymerization, thereby contributing to Cu tolerance in rice.

Glomus versiforme and intercropping with Sphagneticola calendulacea decrease Cd accumulation in maize

Little information is available on the influence of the compound use of intercropping (IN) and arbuscular mycorrhizal fungus (AMF) on Cd accumulation and the expression of Cd transporter genes in two intercropped plants. A pot experiment was conducted to study the influences of IN and AMF-Glomus versiforme on growth and Cd uptake of two intercropped plants-maize and Cd hyperaccumulator Sphagneticola calendulacea, and the expression of Cd transporter genes in maize in Cd-polluted soils. IN, AMF and combined treatments of IN and AMF (IN + AMF) obviously improved biomass, photosynthesis and total antioxidant capacities of two plants. Moreover, single and compound treatments of IN and AMF evidently reduced Cd contents in maize, and the greatest decreases appeared in the compound treatment. However, Cd contents of S. calendulacea in IN, AMF and IN + AMF groups were notably improved. Furthermore, the single and compound treatments of IN and AMF significantly downregulated the expression levels of Nramp1, HMA1, ABCC1 and ABCC10 in roots and leaves, and the largest decreases were observed in the combined treatment. Our work first revealed that the combined use of IN and AMF appeared to have a synergistic effect on decreasing Cd content by downregulating the expression of Cd transporter genes in maize.

MicroRNA-encoded regulatory peptides modulate cadmium tolerance and accumulation in rice

MicroRNAs (miRNAs) are small noncoding RNAs that play a vital role in plant responses to abiotic and biotic stresses. Recently, it has been discovered that some primary miRNAs (pri-miRNAs) encode regulatory short peptides called miPEPs. However, the presence of miPEPs in rice, and their functions in response to abiotic stresses, particularly stress induced by heavy metals, remain poorly understood. Here, we identified a functional small peptide (miPEP156e) encoded by pri-miR156e that regulates the expression of miR156 and its target SPL genes, thereby affecting miR156-mediated cadmium (Cd) tolerance in rice. Overexpression of miPEP156e led to decreased uptake and accumulation of Cd and reactive oxygen species (ROS) levels in plants under Cd stress, resulting in improved rice Cd tolerance, as observed in miR156-overexpressing lines. Conversely, miPEP156e mutants displayed sensitivity to Cd stress due to the elevated accumulation of Cd and ROS. Transcriptome analysis further revealed that miPEP156e improved rice Cd tolerance by modulating Cd transporter genes and ROS scavenging genes. Our study provides insights into the regulatory mechanism of miPEP156e in rice response to Cd stress and demonstrates the potential of miPEPs as an effective tool for improving crop abiotic stress tolerance.

Genome-wide identification and evolutionary analysis of the NRAMP gene family in the AC genomes of Brassica species

BACKGROUND

Brassica napus, a hybrid resulting from the crossing of Brassica rapa and Brassica oleracea, is one of the most important oil crops. Despite its significance, B. napus productivity faces substantial challenges due to heavy metal stress, especially in response to cadmium (Cd), which poses a significant threat among heavy metals. Natural resistance-associated macrophage proteins (NRAMPs) play pivotal roles in Cd uptake and transport within plants. However, our understanding of the role of BnNRAMPs in B. napus is limited. Thus, this study aimed to conduct genome-wide identification and bioinformatics analysis of three Brassica species: B. napus, B. rapa, and B. oleracea.

RESULTS

A total of 37 NRAMPs were identified across the three Brassica species and classified into two distinct subfamilies based on evolutionary relationships. Conservative motif analysis revealed that motif 6 and motif 8 might significantly contribute to the differentiation between subfamily I and subfamily II within Brassica species. Evolutionary analyses and chromosome mapping revealed a reduction in the NRAMP gene family during B. napus evolutionary history, resulting in the loss of an orthologous gene derived from BoNRAMP3.2. Cis-acting element analysis suggested potential regulation of the NRAMP gene family by specific plant hormones, such as abscisic acid (ABA) and methyl jasmonate (MeJA). However, gene expression pattern analyses under hormonal or stress treatments indicated limited responsiveness of the NRAMP gene family to these treatments, warranting further experimental validation. Under Cd stress in B. napus, expression pattern analysis of the NRAMP gene family revealed a decrease in the expression levels of most BnNRAMP genes with increasing Cd concentrations. Notably, BnNRAMP5.1/5.2 exhibited a unique response pattern, being stimulated at low Cd concentrations and inhibited at high Cd concentrations, suggesting potential response mechanisms distinct from those of other NRAMP genes.

CONCLUSIONS

In summary, this study indicates complex molecular dynamics within the NRAMP gene family under Cd stress, suggesting potential applications in enhancing plant resilience, particularly against Cd. The findings also offer valuable insights for further understanding the functionality and regulatory mechanisms of the NRAMP gene family.

NRAMPs and manganese: Magic keys to reduce cadmium toxicity and accumulation in plants

Cadmium (Cd), a toxic heavy metal, poses significant threats to both crop production and human health worldwide. Manganese (Mn), an essential micronutrient, plays a crucial role in plant growth and development. NRAMPs (Natural Resistance-Associated Macrophage Proteins) function as common transporters for both Cd and Mn. Deep understanding of the regulatory mechanisms governing NRAMP-mediated Cd and Mn transport is imperative for developing the crop varieties with high tolerance and low accumulation of Cd. This review reported the advance in studies on the fundamental properties and classification of NRAMPs in plants, and structural characteristics, expression patterns, and diverse functions of NRAMP genes across different plant species. We highlighted the pivotal role of NRAMPs in Cd/Mn uptake and transport in plants as a common transporter. Finally, we also comprehensively discussed over the strategies for reducing Cd uptake and accumulation in plants through using antagonism of Mn over Cd and altering the expression of NRAMP genes.

Genetic engineering low-arsenic and low-cadmium rice grain

Rice is prone to take up the toxic elements arsenic (As) and cadmium (Cd) from paddy soil through the transporters for other essential elements. Disruption of these essential transporters usually adversely affects the normal growth of rice and the homeostasis of essential elements. Here we report on developing low-As and low-Cd rice grain through the co-overexpression of OsPCS1, OsABCC1, and OsHMA3 genes under the control of the rice OsActin1 promoter. Co-overexpression of OsPCS1 and OsABCC1 synergistically decreased As concentration in the grain. Overexpression of OsPCS1 also decreased Cd concentration in the grain by restricting the xylem-to-phloem Cd transport in node I, but paradoxically caused Cd hypersensitivity as the overproduced phytochelatins in OsPCS1-overexpressing plants suppressed OsHMA3-dependent Cd sequestration in vacuoles and promoted Cd transport from root to shoot. Co-overexpression of OsHAM3 and OsPCS1 overcame this suppression and complemented the Cd hypersensitivity. Compared with non-transgenic rice control, co-overexpression of OsABCC1, OsPCS1, and OsHMA3 in rice decreased As and Cd concentrations in grain by 92.1% and 98%, respectively, without causing any defect in plant growth and reproduction or of mineral nutrients in grain. Our research provides an effective approach and useful genetic materials for developing low-As and low-Cd rice grain.

Silica nanoparticles inhibit cadmium uptake by the protozoan Tetrahymena thermophila without the need for adsorption

The simultaneous presence of nanoparticles (NPs) and heavy metals in the environment may affect their mutual biological uptake. Although previous studies showed that NPs could alter the cellular uptake of heavy metals by their adsorption of heavy metals, whether they could affect metal uptake without the need for adsorption is unknown. This study examined the effects of silica (SiO2) NPs on the uptake of Cd ion by the protozoan Tetrahymena thermophila. We found that, even with negligible levels of adsorption, SiO2 NPs at concentrations of 3 to 100 mg/L inhibited Cd uptake. This inhibitory effect decreased as the ambient Cd concentration increased from 1 to 100 μg/L, suggesting the involvement of at least two transporters with different affinities for Cd. The transporters were subsequently identified by the specific protein inhibitors amiloride and tariquidar as NCX and ABCB1, which are responsible for the uptake of Cd at low and high Cd levels, respectively. RT-qPCR and molecular dynamics simulation further showed that the inhibitory effects of SiO2 NPs were attributable to the down-regulated expression of the genes Ncx and Abcb1, steric hindrance of Cd uptake by NCX and ABCB1, and the shrinkage of the central channel pore of the transporters in the presence of SiO2 NPs. SiO2 NPs more strongly inhibited Cd transport by NCX than by ABCB1, due to the higher binding affinity of SiO2 NPs with NCX. Overall, our study sheds new light on a previously overlooked influence of NPs on metal uptake and the responsible mechanism.

Predicting Cd accumulation in rice and identifying nonlinear effects of soil nutrient elements based on machine learning methods

The spatial mismatch of Cd content in soil and rice causes difficulties in environmental management for paddy soil. To investigate the influence of soil environment on the accumulation of Cd in rice grain, we conducted a paired field sampling in the middle of the Xiangjiang River basin, examining the relationships between soil properties, soil nutrient elements, Cd content, plant uptake factor (PUFCd), and translocation factors in different rice organs (root, shoot, and grain). The total soil Cd (CdT) and available Cd (CdA) contents and PUFCd showed large spatial variability with ranges of 0.31-6.19 mg/kg, 0.03-3.07 mg/kg, and 0.02-3.51, respectively. Soil pH, CdT, CdA, and the contents of soil nutrient elements (Mg, Mn, Ca, P, Si, and B) were linearly correlated with grain Cd content (Cdg) and PUFCd. The decision tree analysis identified nonlinear effects of Si, Zn and Fe on rice Cd accumulation, which suggested that low Si and high Zn led to high Cdg, and low Si and Fe caused high PUFCd. Using the soil nutrient elements as predictor variables, random forest models successfully predicted the Cdg and PUFCd and performed better than multiple linear regressions. It suggested the impacts of soil nutrient elements on rice Cd accumulation should receive more attention.

Expression of Sailx suchowensis SsIRT9 enhances cadmium accumulation and alters metal homeostasis in tobacco

Cadmium (Cd) contamination in soils is of great concern for plant growth and human health. Willow (Salix spp.) is a promising phytoextractor because of its high biomass production. However, as a non-hyperaccumulator, willow has a low competitive ability in extraction of Cd. Thus, improving Cd concentrations in developing tissues is one of the primary tasks. Here, our study uncovers a novel SsIRT9 gene from Sailx suchowensis which manipulates plant Cd accumulation. SsIRT9 was more highly expressed in willow roots than other SsIRT genes. As a plasma membrane-localized protein, when expressed in yeast, SsIRT9 retarded cell growth more severely than other SsIRT proteins in the presence of Cd. Furthermore, SsIRT9 was cloned and expressed in tobacco and SsIRT9 did not affect plant growth. In hydroponic experiments, SsIRT9 lines displayed higher Cd in the shoots than the wild type. When grown in Cd-contaminated soils, Cd levels in transgenic tobacco increased by 152-364% in roots and by 135-444% in shoots, demonstrating significant superiority in Cd accumulation over other functional IRT/ZIP transporters. Moreover, expressing SsIRT9 in tobacco altered metal homeostasis, especially manganese and zinc. Taken together, we envision that SsIRT9 expression in plants is a promising strategy for upgrading extraction of Cd from soils.

More effective than direct contact: Nano hydroxyapatite pre-treatment regulates the growth and Cd uptake of rice (Oryza sativa L.) seedlings

Cd contamination in rice urgently needs to be addressed. Nano hydroxyapatite (n-HAP) is an eco-friendly material with excellent Cd fixation ability. However, due to its own high reactivity, innovative application of n-HAP in the treatment of Cd contamination in rice is needed. In this study, we proposed a new application, namely n-HAP pre-treatment, which can effectively reduce Cd accumulation in rice and alleviate Cd stress. The results showed that 80 mg/L n-HAP pre-treatment significantly reduced Cd content in rice shoot by 35.1%. Biochemical and combined transcriptomic-proteomic analysis revealed the possible molecular mechanisms by which n-HAP pre-treatment promoted rice growth and reduced Cd accumulation. (1) n-HAP pre-treatment regulated gibberellin and jasmonic acid synthesis-related pathways, increased gibberellin content and decreased jasmonic acid content in rice root, which promoted rice growth; (2) n-HAP pre-treatment up-regulated gene CATA1 expression and down-regulated gene OsGpx1 expression, which increased rice CAT activity and GSH content; (3) n-HAP pre-treatment up-regulated gene OsZIP1 expression and down-regulated gene OsNramp1 expression, which reduced Cd uptake, increased Cd efflux from rice root cells.

Natural resistance-associated macrophage proteins are involved in tolerance to heavy metal Cd2+ toxicity and resistance to bacterial wilt of peanut (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) is one of the most important oil and industrial crops. However, heavy-metal pollution and frequent soil diseases, poses a significant threat to the production of green and healthy peanuts. Herein, we investigated the effects of heavy metal Cd2+ toxicity to the peanuts, and screened out two peanut cultivars H108 and YZ 9102 with higher Cd2+-tolerance. RNA-seq revealed that Natural resistance-associated macrophage proteins (NRAMP)-like genes were involved in the Cd2+ stress tolerance in H108. Genome-wide identification revealed that 28, 13 and 9 Nramp-like genes existing in the A. hypogaea, A. duranensis and A. ipaensis, respectively. The 50 peanut NRAMP genes share conserved architectural characters, and they were classified into two groups. Expressions of AhNramps, particularly AhNramp4, AhNramp12, AhNramp19, and AhNramp25 could be greatly induced by not only cadmium toxicity, but also copper and zinc stresses. The expression profiles of AhNramp14, AhNramp16 and AhNramp25 showed significant differences in the H108 (resistance) and H107 (susceptible) under the infection of bacterial wilt. In addition, we found that the expression profiles of AhNramp14, AhNramp16, and AhNramp25 were greatly up- or down-regulated by the application of exogenous salicylic acid, methyl jasmonate, and abscisic acid. The AhNramp25, of which expression was affected by both heavy metal toxicity and bacterial wilt infection, were selected as strong candidate genes for peanut stress breeding. Our findings will provide an additional information required for further analysis of AhNramps involved in tolerance to heavy metal toxicity and resistance to bacterial wilt of peanut.

The Golgi-localized transporter OsPML4 contributes to manganese homeostasis in rice

Manganese (Mn), an indispensable plant micronutrient, functions as a vital enzyme co-factor in numerous biochemical reactions. In rice, the Golgi-localized PHOTOSYNTHESIS-AFFECTED MUTANT 71-LIKE 3 (OsPML3), a member of the UNCHARACTERIZED PROTEIN FAMILY (UPF0016), plays a pivotal role in Mn homeostasis, particularly in rapidly developing tissues. This study focused on the functional characterization of another UPF0016 family member in rice, OsPML4, to elucidate its involvement in Mn homeostasis. OsPML4 had a 73% sequence identity with OsPML3 and exhibited expression in both shoots and roots, albeit at a lower transcriptional level than OsPML3. Furthermore, subcellular localization studies confirmed that OsPML4 localizes in the Golgi apparatus. Notably, heterologous expression of OsPML4 restored growth in the Mn uptake-deficient yeast strain Δsmf1 under Mn-limited conditions. Under Mn-deficient conditions, OsPML4 knockout exacerbated the decline in shoot dry weight and intensified necrosis in young leaves of OsPML3 knockout lines, which displayed stunted growth. The Mn concentration in OsPML3PML4 double knockout lines was lower than in wild-type (WT) and OsPML3 knockout lines. At the reproductive phase, OsPML3PML4 double knockout lines exhibited reduced fertility and grain yield compared to WT and OsPML3 knockout lines. Notably, reductions were observed in the deposition of cell wall polysaccharides and the content of Lea (Lewis A structure)-containing N-glycans in the young leaves of OsPML3PML4 double knockout lines, surpassing the reductions in WT and OsPML3 knockout lines. These findings underscore the significance of OsPML4 in Mn homeostasis in the Golgi apparatus, where it co-functions with OsPML3 to regulate cell wall polysaccharide deposition and late-stage Golgi N-glycosylation.

Multi-omics analysis reveals differential molecular responses to cadmium toxicity in rice root tip and mature zone

Cadmium (Cd) is a highly toxic heavy metal that can be readily absorbed by plants and enriched in human body. Rice (Oryza sativa L.) yield and grain quality are affected by excessive Cd in the soil. Therefore, understanding the mechanisms of Cd absorption, accumulation and detoxification in the root apex is crucial for developing low-Cd rice cultivars. After Cd treatment, Cd concentration in rice root tips (RT) was 1.4 times higher than that in basal roots (BR). To uncover the distinct molecular responses to Cd toxicity, we conducted transcriptomic, proteomic, and metabolomic analyses on the two root sections. The results revealed that the RT exhibited 1.2-2.0 fold higher transcript or protein abundance of several Cd-related transporters than the BR, including Nramp1, Nramp5, IRT1, and HMA3, thereby contributing to more Cd accumulation in the RT. Furthermore, multi-omics analysis unveiled that the RT had enhanced activity in 'phenylpropanoid metabolism', 'AsA-GSH cycle' and 'tryptophan metabolism', conferring the stronger antioxidant system. While the BR showed higher activation in 'cell wall remodeling' and 'terpenoid biosynthesis'. This comprehensive study provides insights into the regulatory network of genes, proteins and metabolites involved in the differential responses to Cd toxicity between rice root tips and mature zones.

NRAMP gene family in Kandelia obovata: genome-wide identification, expression analysis, and response to five different copper stress conditions

Natural resistance-associated macrophage proteins (NRAMPs) are a class of metal transporters found in plants that exhibit diverse functions across different species. Transporter proteins facilitate the absorption, distribution, and sequestration of metallic elements within various plant tissues. Despite the extensive identification of NRAMP family genes in various species, a full analysis of these genes in tree species is still necessary. Genome-wide identification and bioinformatics analysis were performed to understand the roles of NRAMP genes in copper (CuCl2) stress in Kandelia obovata (Ko). In Arachis hypogaea L., Populus trichocarpa, Vitis vinifera, Phaseolus vulgaris L., Camellia sinensis, Spirodela polyrhiza, Glycine max L. and Solanum lycopersicum, a genome-wide study of the NRAMP gene family was performed earlier. The domain and 3D structural variation, phylogenetic tree, chromosomal distributions, gene structure, motif analysis, subcellular localization, cis-regulatory elements, synteny and duplication analysis, and expression profiles in leaves and CuCl2 were all investigated in this research. In order to comprehend the notable functions of the NRAMP gene family in Kandelia obovata, a comprehensive investigation was conducted at the genomic level. This study successfully found five NRAMP genes, encompassing one gene pair resulting from whole-genome duplication and a gene that had undergone segmental duplication. The examination of chromosomal position revealed an unequal distribution of the KoNRAMP genes across chromosomes 1, 2, 5, 7, and 18. The KoNRAMPs can be classified into three subgroups (I, II, and SLC) based on phylogeny and synteny analyses, similar to Solanum lycopersicum. Examining cis-regulatory elements in the promoters revealed five hormone-correlated responsive elements and four stress-related responsive elements. The genomic architecture and properties of 10 highly conserved motifs are similar among members of the NRAMP gene family. The conducted investigations demonstrated that the expression levels of all five genes exhibited alterations in response to different levels of CuCl2 stress. The results of this study offer crucial insights into the roles of KoNRAMPs in the response of Kandelia obovata to CuCl2 stress.

Mitigating cadmium accumulation in dicotyledonous vegetables by iron fertilizer through inhibiting Fe transporter IRT1-mediated Cd uptake

The solubility of cadmium (Cd) in soil and its transfer to plants are influenced by soil pH. While increasing soil pH reduces Cd solubility and accumulation in rice plants grown in acidic soils, its effect on Cd accumulation in vegetables remains inconclusive. Here, we investigated the impact of soil pH on Cd accumulation in dicotyledonous vegetables and elucidated the underlying molecular mechanisms. Soils collected from various locations were supplemented with varying quantities of lime to achieve soil pH values of around 5.0, 6.0, 7.0, and 8.0. Raising soil pH from around 5.0 to 8.0 markedly decreased extractable Cd. However, increasing soil pH tended to promote shoot Cd accumulation in dicotyledonous vegetable species including lettuce, pakchoi, and Chinese cabbage, and the model dicotyledonous plant Arabidopsis thaliana. Conversely, soil pH increase resulted in a monotonic decrease in rice Cd accumulation. In our hydroponic experiments, we discovered that iron (Fe) deficiency substantially increased Cd uptake and accumulation in dicotyledonous plants but not in rice. Increasing soil pH reduced soil Fe availability and induced the Fe transporter gene IRT1 expression in dicotyledonous vegetables roots, which led to an increase in IRT1-mediated Cd uptake and subsequently increased Cd accumulation as soil pH increases. A comprehensive model incorporating extractable Cd and root IRT1 expression better explained Cd accumulation in vegetable shoots. The application of 50 mg/kg of Fe fertilizer in neutral or alkaline soils resulted in a significant reduction in Cd accumulation by 34-58% in dicotyledonous vegetables. These findings reveal that increasing soil pH has two opposite effects, decreasing soil Cd availability while promoting Cd uptake through IRT1 upregulation, reconciling the inconsistency in its effect on Cd accumulation in dicotyledonous plants. Our findings provide important insights for understanding the factors affecting Cd uptake in plants and offer a practical solution to mitigate Cd contamination in vegetables.

IAR4 mutation enhances cadmium toxicity by disturbing auxin homeostasis in Arabidopsis thaliana

Cadmium (Cd) is highly toxic to plants, but the targets and modes of toxicity remain unclear. We isolated a Cd-hypersensitive mutant of Arabidopsis thaliana, Cd-induced short root 2 (cdsr2), in the background of the phytochelatin synthase-defective mutant cad1-3. Both cdsr2 and cdsr2 cad1-3 displayed shorter roots and were more sensitive to Cd than their respective wild type. Using genomic resequencing and complementation, IAR4 was identified as the causal gene, which encodes a putative mitochondrial pyruvate dehydrogenase E1α subunit. cdsr2 showed decreased pyruvate dehydrogenase activity and NADH content, but markedly increased concentrations of pyruvate and alanine in roots. Both Cd stress and IAR4 mutation decreased auxin level in the root tips, and the effect was additive. A higher growth temperature rescued the phenotypes in cdsr2. Exogenous alanine inhibited root growth and decreased auxin level in the wild type. Cadmium stress suppressed the expression of genes involved in auxin biosynthesis, hydrolysis of auxin-conjugates and auxin polar transport. Our results suggest that auxin homeostasis is a key target of Cd toxicity, which is aggravated by IAR4 mutation due to decreased pyruvate dehydrogenase activity. Decreased auxin level in cdsr2 is likely caused by increased auxin-alanine conjugation and decreased energy status in roots.

IlNRAMP5 is required for cadmium accumulation and the growth in Iris lactea under cadmium exposures

Iris lactea is potentially applied for remediating Cd-contaminated soils due to the strong ability of Cd uptake and accumulation. However, its molecular mechanism underlying Cd uptake pathway remains unknown. Here, we report a member of NRAMP (Natural Resistance-Associated Macrophage Protein) family, IlNRAMP5, is involved in Cd/Mn uptake and the growth in I. lactea response to Cd. IlNRAMP5 was localized onto the plasma membrane, and was induced by Cd. It was expressed in the root cortex rather than the central vasculature, and in leaf vascular bundle and mesophyll cells. Heterologous expression in yeast showed that IlNRAMP5 could transport Cd and Mn, but not Fe. Knockdown of IlNRAMP5 triggered a significant reduction in Cd uptake, further diminishing the accumulation of Cd. In addition, silencing IlNRAMP5 disrupted Mn homeostasis by lowering Mn uptake and Mn allocation, accompanied by remarkably inhibiting photosynthesis under Cd conditions. Overall, the findings suggest that IlNRAMP5 plays versatile roles in Cd accumulation by mediating Cd uptake, and contributes to maintain the growth via modulating Mn homeostasis in I. lactea under Cd exposures. This would provide a mechanistic understanding Cd phytoremediation efficiency in planta.

Comprehensive Genomic Analysis of Trihelix Family in Tea Plant (Camellia sinensis) and Their Putative Roles in Osmotic Stress

In plants, Trihelix transcription factors are responsible for regulating growth, development, and reaction to various abiotic stresses. However, their functions in tea plants are not yet fully understood. This study identified a total of 40 complete Trihelix genes in the tea plant genome, which are classified into five clades: GT-1 (5 genes), GT-2 (8 genes), GTγ (2 genes), SH4 (7 genes), and SIP1 (18 genes). The same subfamily exhibits similar gene structures and functional domains. Chromosomal mapping analysis revealed that chromosome 2 has the most significant number of trihelix family members. Promoter analysis identified cis-acting elements in C. sinensis trihelix (CsTH), indicating their potential to respond to various phytohormones and stresses. The expression analysis of eight representative CsTH genes from four subfamilies showed that all CsTHs were expressed in more tissues, and three CsTHs were significantly induced under ABA, NaCl, and drought stress. This suggests that CsTHs plays an essential role in tea plant growth, development, and response to osmotic stress. Furthermore, yeast strains have preliminarily proven that CsTH28, CsTH36, and CsTH39 can confer salt and drought tolerance. Our study provides insights into the phylogenetic relationships and functions of the trihelix transcription factors in tea plants. It also presents new candidate genes for stress-tolerance breeding.

Phenotypic and Proteomic Insights into Differential Cadmium Accumulation in Maize Kernels

The contamination of agricultural soil with cadmium (Cd), a heavy metal, poses a significant environmental challenge, affecting crop growth, development, and human health. Previous studies have established the pivotal role of the ZmHMA3 gene, a P-type ATPase heavy metal transporter, in determining variable Cd accumulation in maize grains among 513 inbred lines. To decipher the molecular mechanism underlying mutation-induced phenotypic differences mediated by ZmHMA3, we conducted a quantitative tandem mass tag (TMT)-based proteomic analysis of immature maize kernels. This analysis aimed to identify differentially expressed proteins (DEPs) in wild-type B73 and ZmHMA3 null mutant under Cd stress. The findings demonstrated that ZmHMA3 accumulated higher levels of Cd compared to B73 when exposed to varying Cd concentrations in the soil. In comparison to soil with a low Cd concentration, B73 and ZmHMA3 exhibited 75 and 142 DEPs, respectively, with 24 common DEPs shared between them. ZmHMA3 showed a higher induction of upregulated genes related to Cd stress than B73. Amino sugar and nucleotide sugar metabolism was specifically enriched in B73, while phenylpropanoid biosynthesis, nitrogen metabolism, and glyoxylate and dicarboxylate metabolism appeared to play a more significant role in ZmHMA3. This study provides proteomics insights into unraveling the molecular mechanism underlying the differences in Cd accumulation in maize kernels.

Toxic effects of lead on plants: integrating multi-omics with bioinformatics to develop Pb-tolerant crops

MAIN CONCLUSION

Lead disrupts plant metabolic homeostasis and key structural elements. Utilizing modern biotechnology tools, it's feasible to develop Pb-tolerant varieties by discovering biological players regulating plant metabolic pathways under stress. Lead (Pb) has been used for a variety of purposes since antiquity despite its toxic nature. After arsenic, lead is the most hazardous heavy metal without any known beneficial role in the biological system. It is a crucial inorganic pollutant that affects plant biochemical and morpho-physiological attributes. Lead toxicity harms plants throughout their life cycle and the extent of damage depends on the concentration and duration of exposure. Higher levels of lead exposure disrupt numerous key metabolic activities of plants including oxygen-evolving complex, organelles integrity, photosystem II connectivity, and electron transport chain. This review summarizes the detrimental effects of lead toxicity on seed germination, crop growth, and yield, oxidative and ultra-structural alterations, as well as nutrient absorption, transport, and assimilation. Further, it discusses the Pb-induced toxic modulation of stomatal conductance, photosynthesis, respiration, metabolic-enzymatic activity, osmolytes accumulation, and antioxidant activity. It is a comprehensive review that reports on omics-based studies along with morpho-physiological and biochemical modifications caused by lead stress. With advances in DNA sequencing technologies, genomics and transcriptomics are gradually becoming popular for studying Pb stress effects in plants. Proteomics and metabolomics are still underrated and there is a scarcity of published data, and this review highlights both their technical and research gaps. Besides, there is also a discussion on how the integration of omics with bioinformatics and the use of the latest biotechnological tools can aid in developing Pb-tolerant crops. The review concludes with core challenges and research directions that need to be addressed soon.

RsPDR8, a member of ABCG subfamily, plays a positive role in regulating cadmium efflux and tolerance in radish (Raphanus sativus L.)

Radish (Raphanus sativus L.) is one of the most vital root vegetable crops worldwide. Cadmium (Cd), a non-essential and toxic heavy metal, can dramatically restrict radish taproot quality and safety. Although the Peiotrpic Drug Resistance (PDR) genes play crucial roles in heavy metal accumulation and transport in plants, the systematic identification and functional characterization of RsPDRs remain largely unexplored in radish. Herein, a total of 19 RsPDR genes were identified from the radish genome. A few RsPDRs, including RsPDR1, RsPDR8 and RsPDR12, showed significant differential expression under Cd and lead (Pb) stress in the 'NAU-YH' genotype. Interestingly, the plasma membrane-localized RsPDR8 exhibited significantly up-regulated expression and enhanced promoter activity under Cd exposure. Ectopic expression of RsPDR8 conferred Cd tolerance via reducing Cd accumulation in yeast cells. Moreover, the transient transformation of RsPDR8 revealed that it positively regulated Cd tolerance by promoting ROS scavenging and enhancing membrane permeability in radish. In addition, overexpression of RsPDR8 increased root elongation but deceased Cd accumulation compared with the WT plants in Arabidopsis, demonstrating that it could play a positive role in mediating Cd efflux and tolerance in plants. Together, these results would facilitate deciphering the molecular mechanism underlying RsPDR8-mediated Cd tolerance and detoxification in radish.

Dissecting the promotional effect of zinc on cadmium translocation from roots to shoots in rice

It is often expected that Zn decreases Cd accumulation in plants due to competition for the same transporters. Here, we found that increasing Zn supply markedly increased the root-to-shoot translocation of Cd in rice. RNA sequencing showed that high Zn up-regulated expression of genes involved in glutathione biosynthesis and metabolism and the Zn/Cd transporter gene OsHMA2, but down-regulated expression of genes related to Zn uptake. Knockout of the iron or Zn transporter genes OsIRT1, OsIRT2, or OsZIP9 did not affect the Zn promotional effect on Cd translocation. Knockout of the manganese/Cd transporter gene OsNRAMP5 greatly reduced Cd uptake but did not affect the Zn promotional effect. Variation in the tonoplast transporter gene OsHMA3 affected Cd translocation but did not change the Zn promotional effect. Knockout of the Zn/Cd transporter gene OsHMA2 not only decreased Cd and Zn translocation, but also abolished the Zn promotional effect. Increased expression of OsHMA2 under high Zn conditions supports the hypothesis that this transporter participates in the promotional effect of Zn on Cd translocation. The results also show that OsIRT1, OsIRT2, and OsZIP9 made only small contributions to Cd uptake under low Zn conditions but not under high Zn conditions, whereas the dominant role of OsNRAMP5 in Cd uptake diminished under low Zn conditions.

Cd isotope fractionation in a soil-rice system: Roles of pH and mineral transformation during Cd immobilization and migration processes

Cd speciation in soil and its transport to rice roots are influenced by the soil pH, oxidation-reduction potential, and mineral transformation; however, the immobilization and migration of Cd in soil-rice systems with different pH values under distinct water regimes remain unclear. This study used Cd isotope fractionation, soil physical analysis, and root gene quantification to elucidate the immobilization and transport of Cd in different soil-rice systems. In drainage soils, the high soil pH enhanced the transformation and magnitude of negative fractionation of Cd from MgCl2 extract to FeMn oxide-bound pool; however, it favored Cd uptake and root-to-grain transport. Compared with drainage regimes, the flooding regimes shifted fractionation toward heavy isotopes from MgCl2-extracted Cd to FeMn oxide-bound Cd in acidic soils (∆114/110CdMgCl2 extract - FeMn oxide-bound Cd = -0.09 ± 0.03 ‰) and to light isotopes from MgCl2-extracted Cd to carbonate-bound Cd in neutral and alkaline soils (∆114/110CdMgCl2 extract - carbonate-bound Cd = 0.29-0.40 ‰). The submerged soils facilitated the forming of carbonate and poorly crystalline minerals (such as ferrihydrite), which were transformed into highly crystalline forms (such as goethite). These results demonstrated that the dissolution-precipitation process of iron oxides was essential for controlling soil Cd availability under flooding regimes, and the relative contribution of carbonate minerals to Cd immobilization was promoted by a high soil pH. Flooding regimes induced lower expressions of OsNRAMP1 and OsNRAMP5 to limit the uptake of light Cd isotopes from MgCl2-extract pool, whereas a teeter-totter effect on gene expression patterns in roots (including those of OsHMA3 and OsHMA2) limited the transport of heavy Cd isotopes from root to grain. These findings demonstrate that flooding regimes could exert multiple effects on soil Cd immobilization and Cd transport to grain. Moreover, alkaline soil was conducive to forming carbonate minerals to sequester Cd.

Advancements and prospects of CRISPR/Cas9 technologies for abiotic and biotic stresses in sugar beet

Sugar beet is a crop with high sucrose content, known for sugar production and recently being considered as an emerging raw material for bioethanol production. This crop is also utilized as cattle feed, mainly when animal green fodder is scarce. Bioethanol and hydrogen gas production from this crop is an essential source of clean energy. Environmental stresses (abiotic/biotic) severely affect the productivity of this crop. Over the past few decades, the molecular mechanisms of biotic and abiotic stress responses in sugar beet have been investigated using next-generation sequencing, gene editing/silencing, and over-expression approaches. This information can be efficiently utilized through CRISPR/Cas 9 technology to mitigate the effects of abiotic and biotic stresses in sugar beet cultivation. This review highlights the potential use of CRISPR/Cas 9 technology for abiotic and biotic stress management in sugar beet. Beet genes known to be involved in response to alkaline, cold, and heavy metal stresses can be precisely modified via CRISPR/Cas 9 technology for enhancing sugar beet's resilience to abiotic stresses with minimal off-target effects. Similarly, CRISPR/Cas 9 technology can help generate insect-resistant sugar beet varieties by targeting susceptibility-related genes, whereas incorporating Cry1Ab and Cry1C genes may provide defense against lepidopteron insects. Overall, CRISPR/Cas 9 technology may help enhance sugar beet's adaptability to challenging environments, ensuring sustainable, high-yield production.

Molecular-Assisted Breeding of Cadmium Pollution-Safe Cultivars

Cadmium (Cd) contamination in edible agricultural products, especially in crops intended for consumption, has raised worldwide concerns regarding food safety. Breeding of Cd pollution-safe cultivars (Cd-PSCs) is an effective solution to preventing the entry of Cd into the food chain from contaminated agricultural soil. Molecular-assisted breeding methods, based on molecular mechanisms for cultivar-dependent Cd accumulation and bioinformatic tools, have been developed to accelerate and facilitate the breeding of Cd-PSCs. This review summarizes the recent progress in the research of the low Cd accumulation traits of Cd-PSCs in different crops. Furthermore, the application of molecular-assisted breeding methods, including transgenic approaches, genome editing, marker-assisted selection, whole genome-wide association analysis, and transcriptome, has been highlighted to outline the breeding of Cd-PSCs by identifying critical genes and molecular biomarkers. This review provides a comprehensive overview of the development of Cd-PSCs and the potential future for breeding Cd-PSC using modern molecular technologies.

Application of CRISPR/Cas9-based genome editing in ecotoxicology

Chemicals are widely used and released into the environment, and their degradation, accumulation, migration, and transformation processes in the environment can pose a threat to the ecosystem. The advancement in analytical methods with high-throughput screening of biomolecules has revolutionized the way toxicologists used to explore the effects of chemicals on organisms. CRISPR/Cas is a newly developed tool, widely used in the exploration of basic science and biologically engineered products given its high efficiency and low cost. For example, it can edit target genes efficiently, and save loss of the crop yield caused by environmental pollution as well as gain a better understanding of the toxicity mechanisms from various chemicals. This review briefly introduces the development history of CRISPR/Cas and summarizes the current application of CRISPR/Cas in ecotoxicology, including its application on improving crop yield and drug resistance towards agricultural pollution, antibiotic pollution and other threats. The benefits by applying the CRISPR/Cas9 system in conventional toxicity mechanism studies are fully demonstrated here together with its foreseeable expansions in other area of ecotoxicology. Finally, the prospects and disadvantages of CRISPR/Cas system in the field of ecotoxicology are also discussed.

Exploring the mechanism of Cd uptake and translocation in rice: Future perspectives of rice safety

Cadmium (Cd) contamination in rice fields has been recognized as a severe global agro-environmental issue. To reach the goal of controlling Cd risk, we must pay more attention and obtain an in-depth understanding of the environmental behavior, uptake and translocation of Cd in soil-rice systems. However, to date, these aspects still lack sufficient exploration and summary. Here, we critically reviewed (i) the processes and transfer proteins of Cd uptake/transport in the soil-rice system, (ii) a series of soil and other environmental factors affecting the bioavailability of Cd in paddies, and (iii) the latest advances in regard to remediation strategies while producing rice. We propose that the correlation between the bioavailability of Cd and environmental factors must be further explored to develop low Cd accumulation and efficient remediation strategies in the future. Second, the mechanism of Cd uptake in rice mediated by elevated CO2 also needs to be given more attention. Meanwhile, more scientific planting methods (direct seeding and intercropping) and suitable rice with low Cd accumulation are important measures to ensure the safety of rice consumption. In addition, the relevant Cd efflux transporters in rice have yet to be revealed, which will promote molecular breeding techniques to address the current Cd-contaminated soil-rice system. The potential for efficient, durable, and low-cost soil remediation technologies and foliar amendments to limit Cd uptake by rice needs to be examined in the future. Conventional breeding procedures combined with molecular marker techniques for screening rice varieties with low Cd accumulation could be a more practical approach to select for desirable agronomic traits with low risk.

Transcriptome analysis reveals the molecular mechanism of different forms of selenium in reducing cadmium uptake and accumulation in wheat seedlings

Selenium (Se) can counteract cadmium (Cd) toxicity in wheat, but the molecular mechanism of different Se forms reducing Cd uptake and accumulation in wheat seedlings remain unclear. Here, a hydroponic experiment was conducted to investigate the effects of three Se forms (selenite (Se(IV)), selenate (Se(VI)) and seleno-L-methionine (SeMet)) on Cd2+ influx, Cd subcellular distribution, and Cd accumulation in wheat seedlings, and the underlying molecular mechanisms were investigated through transcriptome analysis. Consequently, Se(IV) and Se(VI) addition significantly reduced root Cd concentration by 74.3% and 80.8%, respectively, and all Se treatments significantly decreased shoot Cd concentration by approximately 34.2%-74.9%, with Se(IV) addition having the most pronounced reducing effect. Transcriptome analysis showed the reduction of Cd accumulation after Se(IV) addition was mainly due to the downregulation of Cd uptake genes. The inhibition of Cd accumulation after Se(VI) addition was not only associated with the downregulation of Cd uptake genes, but also related to the sequestration of Cd in vacuole. For SeMet addition, the reduction of Cd accumulation was mainly related to the sequestration of Cd in vacuole as GSH-Cd. The above findings provide novel insights to understand the effects of different forms of Se on Cd uptake and accumulation and tolerance in wheat.

An intracellular transporter OsNRAMP7 is required for distribution and accumulation of iron into rice grains

Iron (Fe) is an essential micronutrient for plant growth and human health. Plants have evolved an efficient transport system for absorbing and redistributing Fe from the soil to other organs; however, the molecular mechanisms underlying Fe loading into grains are poorly understood. Our study shows that OsNRAMP7, a member of the natural resistance-associated macrophage protein (NRAMP) family, is a rice Fe transporter that localizes to the Golgi and trans-Golgi network (TGN). OsNRAMP7 was highly expressed in leaf blade, node I, pollen, and vascular tissues of almost tissues at the rice flowering stage. OsNRAMP7 knockdown by RNA interference (RNAi) increased Fe accumulation in the flag leaf blade, but decreased the Fe concentration in node I and rice grains. In addition, the knockdown of OsNRAMP7 also reduced grain fertility, pollen viability, and grain Fe concentration in the paddy fields; OsNRAMP7 overexpression significantly promoted Fe accumulation in the grains. Thus, our results suggest that OsNRAMP7 is required for the distribution and accumulation of Fe in rice grains and its overexpression could be a novel strategy for Fe biofortification in staple food crops.

Salylic acid minimize cadmium accumulation in rice through regulating the fixation capacity of the cell wall to cadmium

Although salylic acid (SA) has been linked to how plants react to cadmium (Cd) stress, the exact mechanism is still unknown. The endogenous SA concentration in the rice (Oryza sativa L.) roots was enhanced by Cd stress in the current investigation, and exogenous SA reduced the hemicellulose content in root cell wall, which in turn inhibited its Cd binding capacity. What's more, exogenous SA also decreased the transcription level of genes such as Natural Resistance-Associated Macrophage Protein 5 (OsNRAMP5) and a major facilitator superfamily gene-OsCd1 that responsible for root Cd absorption. Finally, less Cd was accumulated in the rice as a result of the higher expression of Heavy Metal ATPase 3 (OsHMA3), Cation/Ca exchanger 2 (OsCCX2) and Pleiotropic Drug Resistance 9 (OsPDR9/OsABCG36) that were responsible for separating Cd into vacuole and getting Cd out of cells, respectively. In contrast, mutant with low SA level accumulated more Cd. Additionally, SA enhanced endogenous nitric oxide (NO) levels, and its alleviatory effects were mimicked by a NO donor, sodium nitroprusside (SNP). In conclusion, SA enhanced rice's Cd resistance through regulating the binding capacity of the cell wall to Cd, a pathway that might dependent on the NO accumulation.

Metabolic Responses to Manganese Toxicity in Soybean Roots and Leaves

Soybean is one of the most crucial beans in the world. Although Mn (manganese) is a kind of important nutritive element helpful to plant growth and health, excess Mn is harmful to crops. Nevertheless, the effect of Mn toxicity on soybean roots and leaves metabolism is still not clear. To explore this, water culture experiments were conducted on the development, activity of enzyme, and metabolic process of soybeans under varying levels of Mn treatment (5 and 100 μM). Compared with the control, the soybeans under Mn stress showed inhibited growth and development. Moreover, the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and the soluble protein content in leaves and roots of soybean were all increased. However, soluble sugar and proline contents in soybean roots and leaves showed the opposite trend. In addition, the Mg (magnesium) and Fe (iron) ion contents in soybean leaves significantly decreased, and the Mn ion content greatly increased. In roots, the Mn and Fe ion content increased, whereas the Mg ion content decreased. Furthermore, the metabolomic analysis based on nontargeted liquid chromatography-mass spectrometry identified 136 and 164 differential metabolites (DMs) that responded to Mn toxicity in roots and leaves of soybean, respectively. These DMs might participate in five different primary metabolic pathways in soybean leaves and roots, suggesting that soybean leaves and roots demonstrate different kinds of reactions in response to Mn toxicity. These findings indicate that Mn toxicity will result in enzymes activity being changed and the metabolic pathway being seriously affected, hence inhibiting the development of soybean.

Expression in A. thaliana and cellular localization reveal involvement of BjNRAMP1 in cadmium uptake

Although Brassica juncea has demonstrated potential as a hyperaccumulator crop, it was not entirely clear how cadmium (Cd) accumulates in plants. Here, we found that BjNRAMP1 (Natural Resistance-Associated Macrophage Protein 1) plays a crucial role in the accumulation of Cd and manganese (Mn) through its expression in yeast and Arabidopsis thaliana. The high concentration of Cd exposure could induce the expression of BjNRAMP1. The ectopic expression of BjNRAMP1 in yeast led to higher accumulation of Cd and Mn compared to the vector control. BjNARAMP1 was localized to the plasma membrane and expressed in the vascular system of roots, leaves, and flowers. The overexpression of BjNRAMP1 in A. thaliana resulted in an increased accumulation of Cd in both roots and shoots, which inhibited the normal growth of transgenic lines. Moreover, Mn uptake in roots was activated by the increase in Cd stress. Together, our results indicated that BjNRAMP1 significantly contributes to the uptake of Mn and Cd in B. juncea.