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1.

Background

Selenium (Se) is a micronutrient required for many life forms, but toxic at higher concentration. Plants do not have a Se requirement, but can benefit from Se via enhanced antioxidant activity. Some plant species can accumulate Se to concentrations above 0.1% of dry weight and seem to possess mechanisms that distinguish Se from its analog sulfur (S). Research on these so-called Se hyperaccumulators aims to identify key genes for this remarkable trait and to understand ecological implications.

Scope of review

This review gives a broad overview of the current knowledge about Se uptake and metabolism in plants, with a special emphasis on hypothesized mechanisms of Se hyperaccumulation. The role of Se in plant defense responses and the associated ecological implications are discussed.

Major conclusions

Hyperaccumulators have enhanced expression of S transport and assimilation genes, and may possess transporters with higher specificity for selenate over sulfate. Genes involved in antioxidant reactions and biotic stress resistance are also upregulated. Key regulators in these processes appear to be the growth regulators jasmonic acid, salicylic acid and ethylene. Hyperaccumulation may have evolved owing to associated ecological benefits, particularly protection against pathogens and herbivores, and as a form of elemental allelopathy.

General significance

Understanding plant Se uptake and metabolism in hyperaccumulators has broad relevance for the environment, agriculture and human and animal nutrition and may help generate crops with selenate-specific uptake and high capacity to convert selenate to less toxic, anticarcinogenic, organic Se compounds.  相似文献   

2.

Background

Selenium hyperaccumulation in plants often involves the synthesis of non-proteinaceous methylated selenoamino acids serving for the elimination of excess selenium from plant metabolism to protect plant homeostasis.

Methods

Our study aimed at the identification of the main selenium species of the selenium hyperaccumulator plant Cardamine violifolia (Brassicaceae) that grows in the wild in the seleniferous region of Enshi, China. A sample of this plant (3.7?g?Se?kg?1 d.w.) was prepared with several extraction methods and the extracted selenium species were identified and quantified with liquid chromatography mass spectrometry set-ups.

Results

The Cardamine violifolia sample did not contain in considerable amount any of the organic selenium species that are often formed in hyperaccumulator plants; the inorganic selenium content (mostly as elemental selenium) accounted only for <20% of total Se. The most abundant selenium compound, accounting for about 40% of total Se was proved to be selenolanthionine, a selenium species that has never been unambiguously identified before from any selenium containing sample. The identification process was completed with chemical synthesis too. The molar ratio of lanthionine:selenolanthionine in the water extract was ca. 1:8.

Conclusions

Finding selenolanthionine as the main organic selenium species in a plant possibly unearths a new way of selenium tolerance. This article is part of a Special Issue entitled Selenium research in biochemistry and biophysics - 200?year anniversary issue, edited by Dr. Elias Arnér and Dr. Regina Brigelius-Flohe.  相似文献   

3.

Background

Selenium (Se) is not an essential element for plants, although it can benefit their growth and survival in some envionments. Excess tissue Se concentrations are toxic. The ability to sequester Se in vacuoles, synthesise non-toxic Se metabolites, or volatilise Se compounds determines maximum tissue Se concentrations and the ability to colonise seleniferous soils.

Scope of review

This review first classifies plant species on their abilities to accumulate Se in their tissues and to colonise seleniferous soils. It then presents our knowledge of Se uptake by roots and its movement within the plant, the primary and secondary metabolism of Se in plants, effects of Se on sulfur and nitrogen metabolism, and the detoxification of excessive Se by plants. Finally, it presents a current hypothesis for the evolution of seleniferous flora.

Major conclusions

Selenium and sulfur share the same primary metabolism. When grown in the same environment, most plant species have similar tissue Se/S quotients. However, Se-hyperaccumulator species, which can have tissue Se concentrations >1?mg?g?1 dry matter, have larger Se/S quotients than other species. Secondary Se metabolism determines differences in tissue Se concentration among plant species. Among non-hyperaccumulator species, alliums and brassicas have particularly large tissue Se concentrations. Selenium hyperaccumulation results from the effective metabolic detoxification of Se in tissues.

General significance

Differences in Se metabolism determine the maximum Se concentrations in plant tissues, which is important for the delivery of Se to diets of herbivores and for the evolution of plant species to colonise seleniferous soils.  相似文献   

4.
5.

Background

Selenophosphate, the key selenium donor for the synthesis of selenoprotein and selenium-modified tRNA, is produced by selenophosphate synthetase (SPS) from ATP, selenide, and H2O. Although free selenide can be used as the in vitro selenium substrate for selenophosphate synthesis, the precise physiological system that donates in vivo selenium substrate to SPS has not yet been characterized completely.

Scope of review

In this review, we discuss selenium metabolism with respect to the delivery of selenium to SPS in selenoprotein biosynthesis.

Major conclusions

Glutathione, selenocysteine lyase, cysteine desulfurase, and selenium-binding proteins are the candidates of selenium delivery system to SPS. The thioredoxin system is also implicated in the selenium delivery to SPS in Escherichia coli.

General significance

Selenium delivered via a protein-bound selenopersulfide intermediate emerges as a central element not only in achieving specific selenoprotein biosynthesis but also in preventing the occurrence of toxic free selenide in the cell. This article is part of a Special Issue entitled “Selenium research in biochemistry and biophysics – 200 year anniversary”.  相似文献   

6.

Background

Selenium (Se) is an essential micronutrient required by avian species. Dietary Se/vitamin E deficiency induces three classical diseases in chicks: exudative diathesis, nutritional pancreatic atrophy, and nutritional muscular dystrophy.

Scope of review

This review is to summarize and analyze the evolution, regulation, and function of avian selenogenome and selenoproteome and their relationship with the three classical Se/vitamin E deficiency diseases.

Major conclusions

There are 24 selenoproteins confirmed in chicks, with two avian-specific members (SELENOU and SELENOP2) and two missing mammalian members (GPX6 and SELENOV). There are two forms of SELENOP containing 1 or 13 selenocysteine residues. In addition, a Gallus gallus gene was conjectured to be the counterpart of the human SEPHS2. Expression of selenoprotein genes in the liver, pancreas, and muscle of chicks seemed to be highly responsive to dietary Se changes. Pathogeneses of the Se/vitamin E deficient diseases in the chicks were likely produced by missing functions of selected selenoproteins in regulating cellular and tissue redox balance and inhibiting oxidative/reductive stress-induced cell death.

General significance

Gene knockout models, similar to those of rodents, will help characterize the precise functions of avian selenoproteins and their comparisons with those of mammalian species.  相似文献   

7.

Background

Selenium is an essential element with a rich and varied chemistry in living organisms. It plays a variety of important roles ranging from being essential in enzymes that are critical for redox homeostasis to acting as a deterrent for herbivory in hyperaccumulating plants. Despite its importance there are many open questions, especially related to its chemistry in situ within living organisms.

Scope of review

This review discusses X-ray spectroscopy and imaging of selenium in biological samples, with an emphasis on the methods, and in particular the techniques of X-ray absorption spectroscopy (XAS) and X-ray fluorescence imaging (XFI). We discuss the experimental methods and capabilities of XAS and XFI, and review their advantages and their limitations. A perspective on future possibilities and next-generation of experiments is also provided.

Major conclusions

XAS and XFI provide powerful probes of selenium chemistry, together with unique in situ capabilities. The opportunities and capabilities of the next generation of advanced X-ray spectroscopy experiments are particularly exciting.

General significance

XAS and XFI provide versatile tools that are generally applicable to any element with a convenient X-ray absorption edge, suitable for investigating complex systems essentially without pre-treatment.  相似文献   

8.
Hyperaccumulators are plants that accumulate toxic elements to extraordinary levels. Selenium (Se) hyperaccumulators can contain 0.1-1.5% of their dry weight as Se, levels toxic to most other organisms. In this review we summarise what is known about the ecological functions and implications of Se (hyper)accumulation by plants. Selenium promotes hyperaccumulator growth and also offers a plant several ecological advantages through negative effects on Se-sensitive partners. High tissue Se levels reduce herbivory and pathogen infection, and high-Se litter deposition can inhibit neighbouring plants. There is no evidence for a cost of hyperaccumulation in terms of reproductive functions or pollinator visitation. Hyperaccumulators offer a niche for Se-tolerant herbivores, pollinators, microbes and neighbouring plants. They may even facilitate these partners through Se enrichment: neighbouring plants with elevated Se levels enjoy enhanced growth and reduced herbivory. Through combined negative and positive effects on ecological partners, Se hyperaccumulators likely affect local plant, microbial and animal species composition and richness, favouring Se-tolerant species at different trophic levels. By locally concentrating Se and altering its chemical form, Se hyperaccumulators likely play an important role in Se entry into, and Se cycling through, seleniferous ecosystems. These findings are of significance since they provide insight into the ecological reverberations of Se hyperaccumulation, and shed light on the possible selection pressures that have led to the evolution of this fascinating phenomenon. Better ecological insight will also help in the management of seleniferous areas and the agricultural production of Se-rich crops for phytoremediation or biofortification.  相似文献   

9.

Aims

The study aimed to find soil parameters that are best related to Se plant uptake for low Se soils with predominantly organic Se, and to explore the mechanisms that control Se bioavailability in the soils under study.

Methods

A pot experiment using nineteen soil samples taken from different fields of arable land (potato fields) in the Netherlands was conducted on summer wheat (Triticum aestivum L.). Selenium in wheat shoots and soil parameters, including basic soil properties, C:N ratio, inorganic selenite content, and Se and organic C in different soil extractions (0.01 M CaCl2, 0.43 M HNO3, hot water, ammonium oxalate, aqua regia) were analysed. Regression analysis was performed to identify soil parameters that determine Se content in wheat shoots.

Results

The regression model shows that Se:DOC ratio in 0.01 M CaCl2 soil extraction explained about 88 % of the variability of Se uptake in wheat shoots. Selenium uptake increased with Se:DOC ratio in CaCl2 extraction, which can be interpreted as a measure of the content of soluble Se-rich organic molecules. Selenium:DOC ratio in CaCl2 extraction and Se uptake increased towards higher soil pH and lower soil C:N ratio. The soil C:N ratio is also negatively correlated to Se:organic C ratio in other extractions (0.43 M HNO3, hot water, ammonium oxalate, aqua regia), indicating that at low soil C:N ratio soil organic matter is richer in Se. Contrarily, the soil pH is positively and strongly correlated to Se:organic C ratio in CaCl2 and hot water extractions, but only weakly correlated to Se:organic C ratio in other extractions.

Conclusions

Selenium-rich dissolved organic matter is the source of bioavailable Se in low Se soils with predominantly organic Se. The soil pH and quality of soil organic matter (i.e. soil C:N ratio) are the main soil properties determining Se bioavailability in these soil types.
  相似文献   

10.

Background

It remains an open question whether plant phloem sap proteins are functionally involved in plant defense mechanisms.

Methods

The antifungal effects of two profilin proteins from Arabidopsis thaliana, AtPFN1 and AtPFN2, were tested against 11 molds and 4 yeast fungal strains. Fluorescence profiling, biophysical, and biochemical analyses were employed to investigate their antifungal mechanism.

Results

Recombinant AtPFN1 and AtPFN2 proteins, expressed in Escherichia coli, inhibited the cell growth of various pathogenic fungal strains at concentrations ranging from 10 to 160?μg/mL. The proteins showed significant intracellular accumulation and cell-binding affinity for fungal cells. Interestingly, the AtPFN proteins could penetrate the fungal cell wall and membrane and act as inhibitors of fungal growth via generation of cellular reactive oxygen species and mitochondrial superoxide. This triggered the AtPFN variant-induced cell apoptosis, resulting in morphological changes in the cells.

Conclusion

PFNs may play a critical role as antifungal proteins in the Arabidopsis defense system against fungal pathogen attacks.

General significance

The present study indicates that two profilin proteins, AtPFN1 and AtPFN2, can act as natural antimicrobial agents in the plant defense system.  相似文献   

11.
12.

Background

Selenium, an essential dietary micronutrient, is incorporated into proteins as the amino acid selenocysteine (Sec) in response to in-frame UGA codons. Complex machinery ensures accurate recoding of Sec codons in higher organisms. A specialized elongation factor eEFSec is central to the process.

Scope of review

Selenoprotein synthesis relies on selenocysteinyl-tRNASec (Sec-tRNASec), selenocysteine inserting sequence (SECIS) and other selenoprotein mRNA elements, an in-trans SECIS binding protein 2 (SBP2) protein factor, and eEFSec. The exact mechanisms of discrete steps of the Sec UGA recoding are not well understood. However, recent studies on mammalian model systems have revealed the first insights into these mechanisms. Herein, we summarize the current knowledge about the structure and role of mammalian eEFSec.

Major conclusions

eEFSec folds into a chalice-like structure resembling that of the archaeal and bacterial orthologues SelB and the initiation protein factor IF2/eIF5B. The three N-terminal domains harbor major functional sites and adopt an EF-Tu-like fold. The C-terminal domain 4 binds to Sec-tRNASec and SBP2, senses distinct binding domains, and modulates the GTPase activity. Remarkably, GTP hydrolysis does not induce a canonical conformational change in eEFSec, but instead promotes a slight ratchet of domains 1 and 2 and a lever-like movement of domain 4, which may be critical for the release of Sec-tRNASec on the ribosome.

General significance

Based on current findings, a non-canonical mechanism for elongation of selenoprotein synthesis at the Sec UGA codon is proposed. Although incomplete, our understanding of this fundamental biological process is significantly improved, and it is being harnessed for biomedical and synthetic biology initiatives. This article is part of a Special Issue entitled “Selenium research” in celebration of 200 years of selenium discovery, edited by Dr. Elias Arnér and Dr. Regina Brigelius-Flohe.  相似文献   

13.

Background

Methylmercury (CH3Hg+) toxicity is characterized by challenging conundrums: 1) “selenium (Se)-protective” effects, 2) undefined biochemical mechanism/s of toxicity, 3) brain-specific oxidative damage, 4) fetal vulnerability, and 5) its latency effect. The “protective effects of Se” against CH3Hg+ toxicity were first recognized >50?years ago, but awareness of Se's vital functions in the brain has transformed understanding of CH3Hg+ biochemical mechanisms. Mercury's affinity for Se is ~1 million times greater than its affinity for sulfur, revealing it as the primary target of CH3Hg+ toxicity.

Scope of review

This focused review examined research literature regarding distinctive characteristics of CH3Hg+ toxicity to identify Se-dependent aspects of its biochemical mechanisms and effects.

Conclusions

Research indicates that CH3Hg+ irreversibly inhibits the selenoenzymes that normally prevent/reverse oxidative damage in the brain. Unless supplemental Se is provided, consequences increase as CH3Hg+ approaches/exceeds equimolar stoichiometries with Se, thus forming HgSe and inducing a conditioned Se deficiency. As the biochemical target of CH3Hg+ toxicity, Se-physiology provides perspectives on the brain specificity of its oxidative damage, accentuated fetal vulnerability, and latency. This review reconsiders the concept that Se is a “tonic” that protects against CH3Hg+ toxicity and recognizes Se's role as Hg's molecular “target”. As the most potent intracellular nucleophile, the selenoenzyme inhibition paradigm has broad implications in toxicology, including resolution of conundrums of CH3Hg+ toxicity.

General significance

Mercury-dependent sequestration of selenium and the irreversible inhibition of selenoenzymes, especially those required to prevent and reverse oxidative damage in the brain, are primarily responsible for the characteristic effects of mercury toxicity.  相似文献   

14.

Aims

The objectives of this study were to determine the valence state of Se and major components in Se ore powder, examine its effect on Se enrichment in crops under different cultivation patterns, and assess the safety of edible parts of crops.

Methods

Se ore powder from Enshi was subjected to compositional analysis by X-ray photoelectron spectroscopy and applied to rice (wetland) and soybean (dryland) fields before planting.

Results

Se was mainly present in tetravalent and zero-valent forms at a 4:6 ratio in Se ore powder. Following soil application of Se ore powder, concentrations of As, Hg, Cr, and Pb in brown rice and soybean seed were below the limit of detection, and the Cd concentration was below the European Union food regulation limit. Organic Se accounted for more than 96% of total Se in both crops, including >91% Se-methionine. Compared with dryland, the flooded environment facilitated residual Se transformation into Fe/Mn oxide-bound Se, and thus increased the potential activity of Se in the soil.

Conclusions

Se ore powder can be applied for the production of Se-rich agricultural products in the short-term, and possibilities of upgrading the Se ore product should be considered in the future.
  相似文献   

15.

Background

Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that is currently investigated as an important target to extend lifespan and health span. Age-related NAD+ depletion due to the accumulation of oxidative stress is associated with reduced energy production, impaired DNA repair and genomic instability.

Scope of review

NAD+ levels can be elevated therapeutically using NAD+ precursors or through lifestyle modifications including exercise and caloric restriction. However, high amounts of NAD+ may be detrimental in cancer progression and may have deleterious immunogenic roles.

Major conclusions

Standardized quantitation of NAD+ and related metabolites may therefore represent an important component of NAD+ therapy.

General significance

Quantitation of NAD+ may serve dual roles not only as an ageing biomarker, but also as a diagnostic tool for the prevention of malignant disorders.  相似文献   

16.

Background

Methylation driven by thiopurine S-methylatransferase (TPMT) is crucial for deactivation of cytostatic and immunosuppressant thiopurines. Despite its remarkable integration into clinical practice, the endogenous function of TPMT is unknown.

Methods

To address the role of TPMT in methylation of selenium compounds, we established the research on saturation transfer difference (STD) and 77Se NMR spectroscopy, fluorescence measurements, as well as computational molecular docking simulations.

Results

Using STD NMR spectroscopy and fluorescence measurements of tryptophan residues in TPMT, we determined the binding of selenocysteine (Sec) to human recombinant TPMT. By comparing binding characteristics of Sec in the absence and in the presence of methyl donor, we confirmed S-adenosylmethionine (SAM)-induced conformational changes in TPMT. Molecular docking analysis positioned Sec into the active site of TPMT with orientation relevant for methylation reaction. Se-methylselenocysteine (MeSec), produced in the enzymatic reaction, was detected by 77Se NMR spectroscopy. A direct interaction between Sec and SAM in the active site of rTPMT and the formation of both products, MeSec and S-adenosylhomocysteine, was demonstrated using NMR spectroscopy.

Conclusions

The present study provides evidence on in vitro methylation of Sec by rTPMT in a SAM-dependant manner.

General significance

Our results suggest novel role of TPMT and demonstrate new insights into enzymatic modifications of the 21st amino acid.  相似文献   

17.

Background

Selenoproteins (25 genes in human) co-translationally incorporate selenocysteine using a UGA codon, normally used as a stop signal. The human selenoproteome is primarily regulated by selenium bioavailability with a tissue-specific hierarchy.

Methods

We investigated the hierarchy of selenoprotein expression in response to selenium concentration variation in four cell lines originating from kidney (HEK293, immortalized), prostate (LNCaP, cancer), skin (HaCaT, immortalized) and liver (HepG2, cancer), using complementary analytical methods. We performed (i) enzymatic activity, (ii) RT-qPCR, (iii) immuno-detection, (iv) selenium-specific mass spectrometric detection after non-radioactive 76Se labeling of selenoproteins, and (v) luciferase-based reporter constructs in various cell extracts.

Results

We characterized cell-line specific alterations of the selenoproteome in response to selenium variation that, in most of the cases, resulted from a translational control of gene expression. We established that UGA-selenocysteine recoding efficiency, which depends on the nature of the SECIS element, dictates the response to selenium variation.

Conclusions

We characterized that selenoprotein hierarchy is cell-line specific with conserved features. This analysis should be done prior to any experiments in a novel cell line.

General significance

We reported a strategy based on complementary methods to evaluate selenoproteome regulation in human cells in culture.  相似文献   

18.

Background and aims

As an essential mineral element, selenium (Se) plays a critical role in human health. Given the low concentrations (<100 mg Se kg–1) of Se in staple crops, the identification of genetic resources with enriched Se, as well as the genes controlling Se concentration, is valuable for the marker-assisted selection of Se-rich varieties.

Methods

We determined the chromosomal quantitative trait (QTL) for Se concentration over two consecutive plant growth cycles using recombinant inbred lines (RILs) treated with two different concentrations of Se under both field-grown and hydroponic conditions.

Results

Several QTL for Se concentration were detected across the different treatments. Significant genotypic variation in the tissues of the RIL was found at Se-deficicencycondition. Notably, a QTL located on 3D (interval 214.00–218.00, Qse.sau-3D) affected root length and Se concentration in the leaves and grains, suggesting the existence of the same allele with distinctly different functions. However, the QTL for the agronomic traits measured (plant height, flowering time, and tillering number) and Se concentration were not found to be located on the same chromosomal regions, suggesting that marker-assisted selection for both traits is feasible. Se concentrations in the grains were primarily determined by the mineral transport efficiency of the lines, and the line with the highest Se concentration in the grains always possessed larger, more fibrous root systems. The concentrations of Se in the plant tissues were in the order of: root > stem > grain.

Conclusions

This is the first study to document a Se-rich synthetic wheat line, and root structure and Se grain concentration was strongly affected by QTL located on 3D.
  相似文献   

19.

Background

Selenoprotein synthesis requires the reinterpretation of a UGA stop codon as one that encodes selenocysteine (Sec), a process that requires a set of dedicated translation factors. Among the mammalian selenoproteins, Selenoprotein P (SELENOP) is unique as it contains a selenocysteine-rich domain that requires multiple Sec incorporation events.

Scope of review

In this review we elaborate on new data and current models that provide insight into how SELENOP is made.

Major conclusions

SELENOP synthesis requires a specific set of factors and conditions.

General significance

As the key protein required for proper selenium distribution, SELENOP stands out as a lynchpin selenoprotein that is essential for male fertility, proper neurologic function and selenium metabolism.  相似文献   

20.

Background

Spontaneous intracranial hypotension (SIH) is caused by cerebrospinal fluid (CSF) leakage. Definitive diagnosis can be difficult by clinical examinations and imaging studies.

Methods

SIH was diagnosed with the following criteria: (i) evidence of CSF leakage by cranial magnetic resonance imaging (MRI) findings of intracranial hypotension and/or low CSF opening pressure; (ii) no recent history of dural puncture. We quantified CSF proteins by ELISA or Western blotting.

Results

Comparing with non-SIH patients, SIH patients showed significant increase of brain-derived CSF glycoproteins such as lipocalin-type prostaglandin D synthase (L-PGDS), soluble protein fragments generated from amyloid precursor protein (sAPP) and “brain-type” transferrin (Tf). Serum-derived proteins such as albumin, immunoglobulin G, and serum Tf were also increased. A combination of L-PGDS and brain-type Tf differentiated SIH from non-SIH with sensitivity 94.7% and specificity 72.6%.

Conclusion

L-PGDS and brain-type Tf can be biomarkers for diagnosing SIH.

General significance

L-PGDS and brain-type Tf biosynthesized in the brain appears to be markers for abnormal metabolism of CSF.  相似文献   

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