The Crotalaria juncea metal transporter CjNRAMP1 has a high Fe uptake activity, even in an environment with high Cd contamination

Ectopic expression of the yeast Mn2+ transporter SMF2 enhances tolerance and resistance to cadmium and arsenic in transgenic Arabidopsis

Vesicular sequestration is a potential strategy for enhancing plant tolerance to cadmium (Cd) and arsenic (As). In this study, the ectopic overexpression of yeast-derived ScSMF2 in Arabidopsis thaliana was found to enhance the accumulation and tolerance of Cd and As in transgenic plants. ScSMF2 was localized on vacuole membranes and formed puncta structures in plant cells when agro-infiltrated for transient expression. Transgenic Arabidopsis showed less retardation on root elongation and shoot weight and more accumulation of Cd, As (III) and As (V) when cultured on medium containing Cd or As. Overexpression of ScSMF2 promoted accumulation of Cd and arsenic in transgenic Arabidopsis, which were over twice higher than in WT plants when cultured in soil. This study provides insights into the mechanisms involved in the vesicular sequestration of heavy metals in plant and presents a potential strategy for enhancing the phytoremediation capacity of plants toward heavy metals.

Significance and genetic control of membrane transporters to improve phytoremediation and biofortification processes

Humans frequently consume plant-based foods in their daily life. Contamination of agricultural soils by heavy metals (HMs) is a major food and nutritional security issue. The crop plants grown in HM-contaminated agricultural soil may accumulate more HMs in their edible part, further transferring into the food chain. Consumption of HM-rich crops can cause severe health issues in humans. On the other hand, the low content of the essential HM in the edible part of the crop also causes health problems. Therefore, researchers must try to reduce the non-essential HM in the edible part of the crop plants and improve the essential HMs. Phytoremediation and biofortification are the two strategies for resolving this problem. The genetic component helps to improve the efficiency of phytoremediation and biofortification processes in plants. They help eliminate HMs from soil and improve essential HM content in crop plants. The membrane transporter genes (genetic components) are critical in these two strategies. Therefore, engineering membrane transporter genes may help reduce the non-essential HM content in the edible part of crop plants. Targeted gene editing by genome editing tools like CRISPR could help plants achieve efficient phytoremediation and biofortification. This article covers gene editing's scope, application, and implication to improve the phytoremediation and biofortification processes in non-crop and crop plants.

Biofortification of common bean (Phaseolus vulgaris L.) with iron and zinc: Achievements and challenges

Micronutrient deficiencies (hidden hunger), particularly in iron (Fe) and zinc (Zn), remain one of the most serious public health challenges, affecting more than three billion people globally. A number of strategies are used to ameliorate the problem of micronutrient deficiencies and to improve the nutritional profile of food products. These include (i) dietary diversification, (ii) industrial food fortification and supplements, (iii) agronomic approaches including soil mineral fertilisation, bioinoculants and crop rotations, and (iv) biofortification through the implementation of biotechnology including gene editing and plant breeding. These efforts must consider the dietary patterns and culinary preferences of the consumer and stakeholder acceptance of new biofortified varieties. Deficiencies in Zn and Fe are often linked to the poor nutritional status of agricultural soils, resulting in low amounts and/or poor availability of these nutrients in staple food crops such as common bean. This review describes the genes and processes associated with Fe and Zn accumulation in common bean, a significant food source in Africa that plays an important role in nutritional security. We discuss the conventional plant breeding, transgenic and gene editing approaches that are being deployed to improve Fe and Zn accumulation in beans. We also consider the requirements of successful bean biofortification programmes, highlighting gaps in current knowledge, possible solutions and future perspectives.

Citric acid assisted phytoextraction of nickle from soil helps to tolerate oxidative stress and expression profile of NRAMP genes in sunflower at different growth stages

INTRODUCTION

Soil polluted with Nickel (Ni) adversely affects sunflower growth resulting in reduced yield. Counterbalancing Ni toxicity requires complex molecular, biochemical, and physiological mechanisms at the cellular, tissue, and whole plant levels, which might improve crop productivity. One of the primary adaptations to tolerate Ni toxicity is the enhanced production of antioxidant enzymes and the elevated expression of Ni responsive genes.

METHODS

In this study, biochemical parameters, production of ROS, antioxidants regulation, and expression of NRAMP metal transporter genes were studied under Ni stress in sunflower. There were four soil Ni treatments (0, 50, 100, and 200 mg kg^-1 soil), while citric acid (CA, 5 mM kg^-1 soil) was applied on the 28^th and 58^th days of plant growth. The samples for all analyses were obtained on the 30^th and 60^th day of plant growth, respectively.

RESULTS AND DISCUSSION

The results indicated that the concentrations of Ni in roots and shoots were increased with increasing concentrations of Ni at both time intervals. Proline contents, ascorbic acid, protein, and total phenolics were reduced under Ni-stress, but with the application of CA, improvement was witnessed in their contents. The levels of malondialdehyde and hydrogen peroxide were enhanced with the increasing concentration of Ni, and after applying CA, they were reduced. The contents of antioxidants, i.e., catalase, peroxidase, superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase, were increased at 50 ppm Ni concentration and decreased at higher concentrations of Ni. The application of CA significantly improved antioxidants at all concentrations of Ni. The enhanced expression of NRAMP1 (4, 51 and 81 folds) and NRAMP3 (1.05, 4 and 6 folds) was found at 50, 100 and 200ppm Ni-stress, respectively in 30 days old plants and the same pattern of expression was recorded in 60 days old plants. CA further enhanced the expression at both developmental stages.

CONCLUSION

In conclusion, CA enhances Ni phytoextraction efficiency as well as protect plant against oxidative stress caused by Ni in sunflower.

Cadmium-resistant Streptomyces stimulates phytoextraction potential of Crotalaria juncea L. in cadmium-polluted soil

This work evaluated the competence of two strains of cadmium (Cd)-resistant Streptomyces, namely Streptomyces rapamycinicus K5PN1, an indole-3-acetic acid (IAA) producer, and Streptomyces cyaneus 11-10SHTh, a siderophore producer on promoting Cd phytoextraction by sunn hemp. The results showed that S. rapamycinicus improved root elongation of sunn hemp seedlings under Cd stress conditions. S. rapamycinicus and S. cyaneus were colonized on the root surface of sunn hemp at concentrations of 2.3 × 10⁴ and 6.4 × 10³ CFU g^-1 root fresh weight, respectively. The results of pot-culture experiments showed that S. rapamycinicus increased the root and shoot lengths, and dry biomass of sunn hemp planted in high Cd-contaminated soil. The Cd concentration in the leaves of sunn hemp inoculated with S. cyaneus (73.82 ± 2.20 mg kg^-1 plant dry wt) was higher than that of plants with S. rapamycinicus inoculation and the uninoculated control. The phytoextraction of Cd by sunn hemp was significantly increased with Cd-resistant Streptomyces inoculation. In conclusion, both strains of Cd-resistant Streptomyces had potential on enhancing Cd phytoextraction efficiency of sunn hemp. Our study suggests the application of Cd-resistant Streptomyces can improve Cd phytoextraction by sunn hemp for restoration of Cd-polluted sites.

Advances in Genes-Encoding Transporters for Cadmium Uptake, Translocation, and Accumulation in Plants

Cadmium (Cd) is a heavy metal that is highly toxic for plants, animals, and human beings. A better understanding of the mechanisms involved in Cd accumulation in plants is beneficial for developing strategies for either the remediation of Cd-polluted soils using hyperaccumulator plants or preventing excess Cd accumulation in the edible parts of crops and vegetables. As a ubiquitous heavy metal, the transport of Cd in plant cells is suggested to be mediated by transporters for essential elements such as Ca, Zn, K, and Mn. Identification of the genes encoding Cd transporters is important for understanding the mechanisms underlying Cd uptake, translocation, and accumulation in either crop or hyperaccumulator plants. Recent studies have shown that the transporters that mediate the uptake, transport, and accumulation of Cd in plants mainly include members of the natural resistance-associated macrophage protein (Nramp), heavy metal-transporting ATPase (HMA), zinc and iron regulated transporter protein (ZIP), ATP-binding cassette (ABC), and yellow stripe-like (YSL) families. Here, we review the latest advances in the research of these Cd transporters and lay the foundation for a systematic understanding underlying the molecular mechanisms of Cd uptake, transport, and accumulation in plants.

Triiron Tetrairon Phosphate (Fe7(PO4)6) Nanomaterials Enhanced Flavonoid Accumulation in Tomato Fruits

Flavonoids contribute to fruit sensorial and nutritional quality. They are also highly beneficial for human health and can effectively prevent several chronic diseases. There is increasing interest in developing alternative food sources rich in flavonoids, and nano-enabled agriculture provides the prospect for solving this action. In this study, triiron tetrairon phosphate (Fe₇(PO₄)₆) nanomaterials (NMs) were synthesized and amended in soils to enhance flavonoids accumulation in tomato fruits. 50 mg kg⁻¹ of Fe₇(PO₄)₆ NMs was the optimal dose based on its outstanding performance on promoting tomato fruit flavonoids accumulation. After entering tomato roots, Fe₇(PO₄)₆ NMs promoted auxin (IAA) level by 70.75 and 164.21% over Fe-EDTA and control, and then up-regulated the expression of genes related to PM H⁺ ATPase, leading to root proton ef-flux at 5.87 pmol cm⁻² s⁻¹ and rhizosphere acidification. More Mg, Fe, and Mn were thus taken up into plants. Subsequently, photosynthate was synthesized, and transported into fruits more rapidly to increase flavonoid synthesis potential. The metabolomic and transcriptomic profile in fruits further revealed that Fe₇(PO₄)₆ NMs regulated sucrose metabolism, shi-kimic acid pathway, phenylalanine synthesis, and finally enhanced flavonoid biosynthesis. This study implies the potential of NMs to improve fruit quality by enhancing flavonoids synthesis and accumulation.

The Mechanism of Metal Homeostasis in Plants: A New View on the Synergistic Regulation Pathway of Membrane Proteins, Lipids and Metal Ions

Heavy metal stress (HMS) is one of the most destructive abiotic stresses which seriously affects the growth and development of plants. Recent studies have shown significant progress in understanding the molecular mechanisms underlying plant tolerance to HMS. In general, three core signals are involved in plants' responses to HMS; these are mitogen-activated protein kinase (MAPK), calcium, and hormonal (abscisic acid) signals. In addition to these signal components, other regulatory factors, such as microRNAs and membrane proteins, also play an important role in regulating HMS responses in plants. Membrane proteins interact with the highly complex and heterogeneous lipids in the plant cell environment. The function of membrane proteins is affected by the interactions between lipids and lipid-membrane proteins. Our review findings also indicate the possibility of membrane protein-lipid-metal ion interactions in regulating metal homeostasis in plant cells. In this review, we investigated the role of membrane proteins with specific substrate recognition in regulating cell metal homeostasis. The understanding of the possible interaction networks and upstream and downstream pathways is developed. In addition, possible interactions between membrane proteins, metal ions, and lipids are discussed to provide new ideas for studying metal homeostasis in plant cells.

Kosteletzkya pentacarpos: A Potential Halophyte Candidate for Phytoremediation in the Meta(loid)s Polluted Saline Soils

Kosteletzkya pentacarpos (L.) Ledebour is a perennial facultative halophyte species from the Malvacea family that grows in coastal areas with high amounts of salt. The tolerance of K. pentacarpos to the high concentration of salt (0.5–1.5% salinity range of coastal saline land) has been widely studied for decades. Nowadays, with the dramatic development of the economy and urbanization, in addition to the salt, the accumulation of mate(loid)s in coastal soil is increasing, which is threatening the survival of halophyte species as well as the balance of wetland ecosystems. Recently, the capacity of K. pentacarpos to cope with either single heavy metal stress or a combination of multiple meta(loid) toxicities was studied. Hence, this review focused on summarizing the physiological and biochemical behaviors of K. pentacarpos that has been simultaneously exposed to the combination of several meta(loid) toxicities. How the salt accumulated by K. pentacarpos impacts the response to meta(loid) stress was discussed. We conclude that as a potential candidate for phytoremediation, K. pentacarpos was able to cope with various environmental constrains such as multiple meta(loid) stresses due to its relative tolerance to meta(loid) toxicity.

Fe toxicity in plants: Impacts and remediation

Fe is the fourth abundant element in the earth crust. Fe toxicity is not often discussed in plant science though it causes severe morphological and physiological disorders, including reduced germination percentage, interferes with enzymatic activities, nutritional imbalance, membrane damage, and chloroplast ultrastructure. It also causes severe toxicity to important biomolecules, which leads to ferroptotic cell death and induces structural changes in the photosynthetic apparatus, which results in retardation of carbon metabolism. However, some agronomic practices like soil remediation through chemicals, nutrients, and organic amendments and some breeding and genetic approaches can provide fruitful results in enhancing crop production in Fe-contaminated soils. Some quantitative trait loci have been reported for Fe tolerance in plants but the function of underlying genes is just emerging. Physiological and molecular mechanism of Fe uptake, translocation, toxicity, and remediation techniques are still under experimentation. In this review, the toxic effects of Fe on seed germination, carbon assimilation, water relations, nutrient uptake, oxidative damages, enzymatic activities, and overall plant growth and development have been discussed. The Fe dynamics in soil rhizosphere and role of remediation strategies, that is, biological, physical, and chemical, have also been described. Use of organic amendments, microbe, phytoremediation, and biological strategies is considered to be both cost and environment friendly for the purification of Fe-contaminated soil, while to ensure better crop yield and quality the manipulation of agronomic practices are suggested.

Genome-Wide Identification of the Nramp Gene Family in Spirodela polyrhiza and Expression Analysis under Cadmium Stress

Natural resistance-associated macrophage proteins (Nramps) are specific metal transporters in plants with different functions among various species. The evolutionary and functional information of the Nramp gene family in Spirodela polyrhiza has not been previously reported in detail. To identify the Nramp genes in S. polyrhiza, we performed genome-wide identification, characterization, classification, and cis-elements analysis among 22 species with 138 amino acid sequences. We also conducted chromosomal localization and analyzed the synteny relationship, promoter, subcellular localization, and expression patterns in S. polyrhiza. β-Glucuronidase staining indicated that SpNramp1 and SpNramp3 mainly accumulated in the root and joint between mother and daughter frond. Moreover, SpNramp1 was also widely displayed in the frond. SpNramp2 was intensively distributed in the root and frond. Quantitative real-time PCR results proved that the SpNramp gene expression level was influenced by Cd stress, especially in response to Fe or Mn deficiency. The study provides detailed information on the SpNramp gene family and their distribution and expression, laying a beneficial foundation for functional research.

Genome-wide analysis of the NRAMP gene family in potato (Solanum tuberosum): Identification, expression analysis and response to five heavy metals stress

NRAMP family genes participate in the absorption and transport of heavy metals such as cadmium (Cd), zinc (Zn), copper (Cu), lead (Pb), iron (Fe) and manganese (Mn) and play an important role in the response to heavy metal stress. There is an abundance of research on these genes in bacteria, plants and fungi, although not in S. tuberosum. A total of 48 members(potato(5), Arabidopsis(7), Tomato(9), pepper(9), rice(12) and tobacco(6)) were identified from 6 species (potato (Solanum tuberosum), Arabidopsis thaliana, Tomato (Solanum lycopersicum), pepper (Capsicum annuum), rice (Oryza sativa) and tobacco (Nicotiana attenuate)) and were classified into four subgroups. Across NRAMP gene family members, there are 15 highly conserved motifs that have similar genetic structures and characteristics. In addition, a total of 16 pairs of colinear genes were found in eight species. Analysis of cis-elements indicated that, in response to abiotic stress, NRAMPs are mainly regulated by phytohormones and transcription factors. In addition, analysis of expression profiles indicated that StNRAMP4 is mainly expressed in the roots. According to a qRT-PCR-based analysis of the StNRAMP family, with the exception of Pb²⁺ stress, StNRAMPs positively responded to stress from Cu²⁺, Cd²⁺, Zn²⁺ and Ni²⁺ and The expression patterns is similar of StNRAMP2, under Pb²⁺, and Cu²⁺ treatment, the relative expression peaked at 24 h. the relative expression peaked at 12 h and was upregulated 428-fold in the roots under Ni²⁺ stress. Under Cd²⁺ stress, StNRAMP3 was upregulated 28-fold in the leaves. StNRAMP1, StNRAMP4 and StNRAMP5 showed significant upregulation under Cu²⁺, Cd²⁺ and Zn²⁺ stress, respectively. Expression of StNRAMPs could be specifically induced by heavy metals, implying their possible role in the transport and absorption of heavy metals. This research explains the colinear characteristics of NRAMPs in several food crop species, which is useful for providing important genetic resources for cultivating food crop that accumulate low amounts of heavy metals and for explaining the biological functions of NRAMPs in plants.