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Iron (Fe) is a vital microelement required for the growth and development of plants. Hydrogen sulfide (H 2 S) and nitric oxide (NO), as messenger molecules, participated in the regulation of plant physiological processes. Here, we studied the interaction effects of H 2 S and NO on the adaptation to Fe deficiency in Glycine max L. Physiological, biochemical and molecular approaches were conducted to analyze the role of H 2 S and NO in regulating the adaptation to Fe deficiency in soybean. We found that H 2 S and NO had obvious rescuing function on the Fe deficiency-induced the plant growth inhibition, which was significantly correlated with the increase in Fe content in the leaves, stems, and roots of soybean. Meanwhile, H+-flux, ferric chelate reductase (FCR) activity, and root apoplast Fe content were significantly affected by H 2 S and NO. Under Fe deficiency conditions NO and H 2 S regulated the expression of genes related to Fe homeostasis. Moreover, photosynthesis (Pn) and photosystem II (PSII) efficiency were enhanced by H 2 S and NO, and thiol redox modification was important for regulating the adaptation of Fe deficiency. The aforementioned affirmative influences caused by H 2 S and NO were also totally reversed by cPTIO (a NO scavenger). Our results suggested that H 2 S might act upstream of NO in response to Fe deficiency by affecting the Fe homeostasis enzyme activities and gene expression, and by promoting Fe accumulation in plant tissues as well as by enhancing thiol redox modification and photosynthesis in soybean plants. • H 2 S and NO had significant rescuing effects on the Fe deficiency-induced inhibition of plant growth. • H+-flux, ferric chelate reductase (FCR) activity, and root apoplast Fe contents were significantly affected by H 2 S and NO. • H 2 S and NO regulated the gene expression of Fe homeostasis in soybean plants under Fe deficiency conditions. • H 2 S and NO regulated the adaptation of Fe deficiency by affecting thiol redox modification and photosynthesis. [ABSTRACT FROM AUTHOR]

Abstract Background Hydrogen sulphide (H2S) is involved in regulating physiological processes in plants. We investigated how H2S ameliorates iron (Fe) deficiency in soybean (Glycine max L.) seedlings. Multidisciplinary approaches including physiological, biochemical and molecular, and transcriptome methods were used to investigate the H2S role in regulating Fe availability in soybean seedlings. Results Our results showed that H2S completely prevented leaf interveinal chlorosis and caused an increase in soybean seedling biomass under Fe deficiency conditions. Moreover, H2S decreased the amount of root-bound apoplastic Fe and increased the Fe content in leaves and roots by regulating the ferric-chelate reductase (FCR) activities and Fe homeostasis- and sulphur metabolism-related gene expression levels, thereby promoting photosynthesis in soybean seedlings. In addition, H2S changed the plant hormone concentrations by modulating plant hormone-related gene expression abundances in soybean seedlings grown in Fe-deficient solution. Furthermore, organic acid biosynthesis and related genes expression also played a vital role in modulating the H2S-mediated alleviation of Fe deficiency in soybean seedlings. Conclusion Our results indicated that Fe deficiency was alleviated by H2S through enhancement of Fe acquisition and assimilation, thereby regulating plant hormones and organic acid synthesis in plants.

Abstract—Two Meyerozyma (Candida, Pichia) guilliermondii genes coding for homologs of transcriptional factor Sef1p of Candida famata and Tup1p of Candida albicans were identified, cloned, and deleted. Deletion of a homologue of Sef1p transcriptional factor in M.(P.) guilliermondii completely blocked over-synthesis of riboflavin under conditions of iron deficiency. The results of genetic complementation analysis suggest that previously reported rib83 mutants and newly constructed knock-out strains belong to the same complementation group and are defective in the same SEF1 gene. Inactivation of the identified homolog of the TUP1 gene in M.(P.) guilliermondii wild-type strain led to 1.5-fold increase in cellular iron content and 1.5–1.7-fold increase in riboflavin production. Introduction of a plasmid-borne copy of the TUP1 gene did not restore metabolic defects of the riboflavin overproduction and iron accumulation in mutant strain M. (P.) guilliermondii m3, bearing the hit1 mutation. The obtained results suggest that both transcription factors Sef1p and Tup1p are involved in the regulation of iron acquisition and riboflavin biosynthesis by yeast belonging to the CUG-clade. The molecular mechanism of action Tup1p on riboflavin biosynthesis in M.(P.) guilliermondii required further elucidation. [ABSTRACT FROM AUTHOR]

Innovative strategies are needed to address the current lack of clinically available antifungal drugs and for diagnostic techniques. ‘Repurposing’ of antifungal drugs, similar to techniques currently being utilized with ‘older’ antibacterial drugs in order to combat widespread resistance in the face of a dearth of new drugs, could prove beneficial. Although as yet very limited for fungi, a siderophore-based ‘Trojan Horse’ strategy, in the form of siderophore–antibiotic conjugates, siderophore–fluorescent probe conjugates, or Ga(III)–siderophore complexes, reveals potential clinical relevance and provides a strategy for targeting fungal infections through drug delivery, imaging, and in diagnostics. The application of siderophores against pathogenic fungi is evolving but is still far from its full potential, and further studies are needed to demonstrate their advantages and limitations. One of the biggest obstacles in developing fungus-specific diagnostics and side-effects-free therapeutics is that apart from the fungal cell wall, fungi are metabolically similar to mammalian cells; thus, pathogen-specific targets are extremely limited. One of the few fundamental differences between fungal and mammalian cells lies in the iron acquisition system. The most common mechanism is mediated by small organic chelators – siderophores, often essential for fungal virulence and pathogenicity. Fungi synthesize mainly hydroxamate-type siderophores, which are excreted into the environment, and bind ferric ions with high affinity and selectivity. Delivery of iron-loaded siderophores back to the pathogen occurs via specific membrane receptors and transport proteins. Natural siderophores are generally not species-specific; they exhibit broad-spectrum activity and can be recognized by various types of microorganisms. Moreover, they generally miss proper sites for incorporating additional functionalities; e.g. fluorescent probes, surface-adhesive moieties or drug molecules, to be used for imaging and/or as therapeutic conjugates smuggled into microbial species via siderophore recognition and a ‘Trojan Horse’ strategy. Biomimetic analogues can overcome both these limitations and offer novel tools for both diagnostics and therapeutics. Siderophore mimics with a narrow spectrum of activity offer the possibility of developing selective diagnostic tools, while those with broad-spectrum activity may find therapeutic applications as antifungal drug delivery tools. [ABSTRACT FROM AUTHOR]

Siderophores are structurally diverse, complex natural products that bind metals with extraordinary specificity and affinity. The acquisition of iron is critical for the survival and virulence of many pathogenic microbes and diverse strategies have evolved to synthesize, import and utilize iron. There has been a substantial increase of known siderophore scaffolds isolated and characterized in the past decade and the corresponding biosynthetic gene clusters have provided insight into the varied pathways involved in siderophore biosynthesis, delivery and utilization. Additionally, therapeutic applications of siderophores and related compounds are actively being developed. The study of biosynthetic pathways to natural siderophores augments the understanding of the complex mechanisms of bacterial iron acquisition, and enables a complimentary approach to address virulence through the interruption of siderophore biosynthesis or utilization by targeting the key enzymes to the siderophore pathways. [ABSTRACT FROM AUTHOR]

Preliminary Fe transmission Mössbauer spectroscopic data were obtained for the first time for live cells of the plant-growth-promoting rhizobacterium Azospirillum brasilense (wild-type strain Sp245) grown aerobically with Fe-nitrilotriacetate (NTA) complex as a sole source of iron. The results obtained have shown that live cells actively reduce part of the assimilated iron(III) to iron(II), the latter amounting up to 33 % of total cellular iron after 18 h of growth, and 48 % after additional 3 days of storage of the dense wet cell suspension in nutrient-free saline solution in air at room temperature (measured at 80 K). The cellular iron(II) was found to be represented by two quadrupole doublets of different high-spin forms, while the parameters of the cellular iron(III) were close to those typical for bacterioferritins. [ABSTRACT FROM AUTHOR]

Iron homeostasis is vital for many cellular processes and requires a precise regulation. Several iron efficient plants respond to iron starvation with the excretion of riboflavin and other flavins. Basic helix–loop–helix transcription factors (TF) are involved in the regulation of many developmental processes, including iron assimilation. Here we describe the isolation and characterisation of two Arabidopsis bHLH TF genes, which are strongly induced under iron starvation. Their heterologous ectopic expression causes constitutive, iron starvation independent excretion of riboflavin. The results show that both bHLH TFs represent an essential component of the regulatory pathway connecting iron deficiency perception and riboflavin excretion and might act as integrators of various stress reactions. [ABSTRACT FROM AUTHOR]

Using DNA microarray analysis, mRNA levels from wild-type Yersinia pestis cells treated with the iron chelator 2,2′-dipyridyl were compared with those supplemented with excessive iron, and subsequent to this, gene expression in the fur mutant was compared with that in the wild-type strain under iron rich conditions. The microarray analysis revealed many iron transport or storage systems that had been induced in response to the iron starvation, which is mediated by the Fur protein, using the iron as a co-repressor. The iron–Fur complex also affected some genes involved in various non-iron functions (ribonucleoside-diphosphate reductase, membrane proteins, electron transport and oxidative defense, etc.). The Fur protein still participated in the regulation of genes involved in broad cellular processes (virulence factors, pesticin activity, haemin storage and many proteins with unknown functions) that were not affected by iron depletion conditions. In addition to its classical negative regulatory activities, the Fur protein activates gene transcription. Using bioinformatics tools, we were able to predict the Y. pestis Fur box sequence that was clearly the over-presented motif in the promoter regions of members of the iron–Fur modulon. [ABSTRACT FROM AUTHOR]

Almost all organisms require iron for enzymes involved in essential cellular reactions. Aerobic microbes living at neutral or alkaline pH encounter poor iron availability due to the insolubility of ferric iron. Assimilatory ferric reductases are essential components of the iron assimilatory pathway that generate the more soluble ferrous iron, which is then incorporated into cellular proteins. Dissimilatory ferric reductases are essential terminal reductases of the iron respiratory pathway in iron-reducing bacteria. While our understanding of dissimilatory ferric reductases is still limited, it is clear that these enzymes are distinct from the assimilatory-type ferric reductases. Research over the last 10 years has revealed that most bacterial assimilatory ferric reductases are flavin reductases, which can serve several physiological roles. This article reviews the physiological function and structure of assimilatory and dissimilatory ferric reductases present in the Bacteria, Archaea and Yeast. Ferric reductases do not form a single family, but appear to be distinct enzymes suggesting that several independent strategies for iron reduction may have evolved. [Copyright &y& Elsevier]

Vibrio vulnificus strain L-180, a clinical isolate, can obtain iron from a synthetic heme, iron–tetra(4-sulfonatophenyl)porphyrin (Fe–TPPS), as well as from a natural heme, protoheme. This assimilation of iron bound to TPPS was demonstrated to be a common property of V. vulnificus by testing a total of 27 strains isolated from both clinical and environmental sources. Strain L-180 could also utilize Fe–TCPP, but not Fe–TMPyP, as a sole iron source. TPPS or its complex with a metal ion reduced bacterial multiplication in the broth containing a minimum dose of Fe–TPPS. When inoculated into human serum supplemented with Fe–TCPP, L-180 could grow only in the presence of a protease from the same bacterium. In both TPPS and TCPP, each side chain of a porphyrin ring has a negative charge. Therefore, this negative charge may be important for interaction with an outer membrane receptor involving in a heme-assimilating system of V. vulnificus. [Copyright &y& Elsevier]

Although iron deficiency poses severe nutritional problems to crop plants, to date iron transporters have only been characterized from the model plant Arabidopsis thaliana. To extend our molecular knowledge of Fe transport in crop plants, we have isolated two cDNAs ( LeIRT1 and LeIRT2) from a library constructed from roots of iron-deficient tomato ( Lycopersicon esculentum) plants, using the Arabidopsis iron transporter cDNA, IRT1, as a probe. Their deduced polypeptides display 64% and 62% identical amino acid residues to the IRT1 protein, respectively. Transcript level analyses revealed that both genes were predominantly expressed in roots. Transcription of LeIRT2 was unaffected by the iron status of the plant, while expression of LeIRT1 was strongly enhanced by iron limitation. The growth defect of an iron uptake-deficient yeast ( Saccharomyces cerevisiae) mutant was complemented by LeIRT1 and LeIRT2 when ligated to a yeast expression plasmid. Transport assays revealed that iron uptake was restored in the transformed yeast cells. This uptake was temperature-dependent and saturable, and Fe2+ rather than Fe3+ was the preferred substrate. A number of divalent metal ions inhibited Fe2+ uptake when supplied at 100-fold or 10-fold excess. Manganese, zinc and copper uptake-deficient yeast mutants were also rescued by the two tomato cDNAs, suggesting that their gene products have a broad substrate range. The gene structure was determined by polymerase chain reaction experiments and, surprisingly, both genes are arranged in tandem with a tail-to-tail orientation. [ABSTRACT FROM AUTHOR]

NADH:nitrate reductase (EC 1.6.6.1) from squash ( Cucurbita maxima Duch., cv. Buttercup) can catalyze the reduction of a ferriphytosiderophore from barley ( Hordeum vulgare L. cv. Europa). Maximal activity occurs at pH 6, with an apparent K and V of 76 μM and 21 nmol·min·(mg protein), respectively. The ferriphytosiderophore strongly inhibits nitrate reduction catalyzed by nitrate reductase at the optimal pH for nitrate reduction, i.e. 7.5. On the contrary, nitrate is a poor inhibitor of ferriphytosiderophore reduction catalyzed by nitrate reductase at the optimal pH for this reaction, pH 6.0. Thus, squash has the potential to assimilate the iron from a ferriphytosiderophore synthesized by another plant. [ABSTRACT FROM AUTHOR]