Altered gene expression in plants with constitutive expression of a mitochondrial small heat shock protein suggests the involvement of retrograde regulation in the heat stress response

Heat stress can negatively affect crop productivity. One way in which plants attempt to alleviate the effects of heat stress is to induce the expression of genes encoding heat shock proteins (HSPs), including small HSPs (sHSPs). We produced transgenic lines of Arabidopsis thaliana expressing a transgene encoding a maize mitochondrial sHSP, ZmHSP22. The transgene, under the control of the cauliflower mosaic virus 35S promoter, is constitutively highly expressed in these lines. As demonstrated by confocal immunofluorescence microscopy and analyses of isolated mitochondria, ZmHSP22 is directed to the mitochondria of Arabidopsis and is processed into the mature form. These transgenic lines demonstrated altered expression of nuclear genes encoding the endogenous mitochondrial sHSP, AtHSP23.6, chloroplast localized AtHSP25.3, class I cytosolic AtHSP17.4, cytosolic AtHSP70-1 and chloroplast localized AtHSP70-6, but not cytosolic AtHSP70-15, following exposure to heat stress. This suggests that the expression of HSPs can be affected by heat-induced mitochondrial retrograde regulation. Three-week-old plants from the transgenic Arabidopsis lines expressing ZmHSP22 have increased thermotolerance, as measured by the maintenance of higher leaf mass following successive days with short periods of heat stress.     

Acquisition of ionic copper by the bacterial outer membrane protein OprC through a novel binding site

Copper, while toxic in excess, is an essential micronutrient in all kingdoms of life due to its essential role in the structure and function of many proteins. Proteins mediating ionic copper import have been characterised in detail for eukaryotes, but much less so for prokaryotes. In particular, it is still unclear whether and how gram-negative bacteria acquire ionic copper. Here, we show that Pseudomonas aeruginosa OprC is an outer membrane, TonB-dependent transporter that is conserved in many Proteobacteria and which mediates acquisition of both reduced and oxidised ionic copper via an unprecedented CxxxM-HxM metal binding site. Crystal structures of wild-type and mutant OprC variants with silver and copper suggest that acquisition of Cu(I) occurs via a surface-exposed “methionine track” leading towards the principal metal binding site. Together with whole-cell copper quantitation and quantitative proteomics in a murine lung infection model, our data identify OprC as an abundant component of bacterial copper biology that may enable copper acquisition under a wide range of conditions.

How do Gram-negative bacteria acquire copper? This study shows that the outer membrane protein OprC from Pseudomonas aeruginosa is abundant during infection and mediates highly selective acquisition of both copper redox states via an extracellular "methionine track" and an unprecedented near-irreversible binding site.     

Assessment of in vitro effects of metyrapone on Leydig cell steroidogenesis

Metyrapone, a specific inhibitor of 11beta-hydroxylase inhibits glucocorticoid production and it is used in the diagnosis/treatment of hypercortisolism and also to test the functional integrity of hypothalamo-pituitary-adrenal axis. To assess the impact of glucocorticoid deficiency, this drug is preferred over adrenalectomy, which eliminates all the hormonal secretions of the adrenal cortex and medulla. However, whether metyrapone has any direct effect on the extra-adrenocortical cellular or tissue functions remains to be resolved. Our previous study showed a depressed testicular Leydig cell testosterone production in rats treated with metyrapone. Therefore, the present study was designed to examine the possible direct effect of metyrapone on testicular Leydig cell steroidogenesis in vitro. Leydig cell viability and the reactive oxygen species (ROS) concentration were not altered by any of the concentration of metyrapone tested. The efficacy of Leydig cell testosterone production under basal as well as LH-stimulated condition was not altered by metyrapone treatment. Further, Leydig cellular (14)C-glucose oxidation, the activity and mRNA levels of cytochrome side chain cleavage (P(450)scc), 3beta- and 17beta-hydroxysteroid dehydrogenase (3beta-HSD and 17beta-HSD) were not altered in metyrapone-treated cells. Therefore, it is concluded from the present study that metyrapone has no direct effect on Leydig cell testosterone production and, therefore, changes recorded in the in vivo studies are exclusively due to corticosterone deficiency.     

Hepatoprotective activity of bacoside A against <Emphasis Type="Italic">N</Emphasis>-nitrosodiethylamine-induced liver toxicity in adult rats

N-Nitrosodiethylamine (DEN) is a notorious carcinogen, present in many environmental factors. DEN induces oxidative stress and cellular injury due to enhanced generation of reactive oxygen species; free radical scavengers protect the membranes from DEN-induced damage. The present study was designed to evaluate the protective effect of bacoside A (the active principle isolated from Bacopa monniera Linn.) on carcinogen-induced damage in rat liver. Adult male albino rats were pretreated with 15 mg/kg body weight/day of bacoside A orally (for 14 days) and then intoxicated with single necrogenic dose of N-nitrosodiethylamine (200 mg/kg bodyweight, intraperitonially) and maintained for 7 days. The liver weight, lipid peroxidation (LPO), and activity of serum marker enzymes (aspartate transaminases, alanine transaminases, lactate dehydrogenase, alkaline phosphatase, and γ-glutamyl transpeptidase) were markedly increased in carcinogen-administered rats, whereas the activities of marker enzymes were near normal in bacoside A-pretreated rats. Activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutatione-S-transferase, and reduced glutathione) in liver also decreased in carcinogen-administered rats, which were significantly elevated in bacoside A-pretreated rats. It is concluded that pretreatment of bacoside A prevents the elevation of LPO and activity of serum marker enzymes and maintains the antioxidant system and thus protects the rats from DEN-induced hepatotoxicity.     

Regioselective synthesis and biological evaluation of bis(indolyl)methane derivatized 1,4-disubstituted 1,2,3-bistriazoles as anti-infective agents

The regioselective synthesis of 1,4-disubstituted 1,2,3-bistriazoles from a variety of N-propargyl bis(indolyl)methanes with sodium azide using CuI as the catalyst in polyethyleneglycol-400 is reported. This process is of considerable synthetic advantages in terms of high atom economy, low environmental impact, mild reaction condition and good yields. The synthesized compounds have also been screened for their biological activity.     

Glucose-stimulated translation regulation of insulin by the 5' UTR-binding proteins

Insulin is the key regulator of glucose homeostasis in mammals, and glucose-stimulated insulin biosynthesis is essential for maintaining glucose levels in a narrow range in mammals. Glucose specifically promotes the translation of insulin in pancreatic β-islet, and the untranslated regions of insulin mRNA play a role in such regulation. Specific factors in the β-islets bind to the insulin 5' UTR and regulate its translation. In the present study we identify protein-disulfide isomerase (PDI) as a key regulator of glucose-stimulated insulin biosynthesis. We show that both in vitro and in vivo PDI can specifically associate with the 5' UTR of insulin mRNA. Immunodepletion of PDI from the islet extract results in loss of glucose-stimulated translation indicating a critical role for PDI in insulin biosynthesis. Similarly, transient overexpression of PDI resulted in specific translation activation by glucose. We show that the RNA binding activity of PDI is mediated through PABP. PDI catalyzes the reduction of the PABP disulfide bond resulting in specific binding of PABP to the insulin 5' UTR. We also show that glucose stimulation of the islets results in activation of a specific kinase that can phosphorylate PDI. These findings identify PDI and PABP as important players in glucose homeostasis.     

Different mechanisms for Arabidopsis thaliana hybrid necrosis cases inferred from temperature responses

Temperature is a major determinant of plant growth, development and success. Understanding how plants respond to temperature is particularly relevant in a warming climate. Plant immune responses are often suppressed above species‐specific critical temperatures. This is also true for intraspecific hybrids of Arabidopsis thaliana that express hybrid necrosis due to inappropriate activation of the immune system caused by epistatic interactions between alleles from different genomes. The relationship between temperature and defence is unclear, largely due to a lack of studies that assess immune activation over a wide range of temperatures. To test whether the temperature‐based suppression of ectopic immune activation in hybrids exhibits a linear or non‐linear relationship, we characterised the molecular and morphological phenotypes of two different necrotic A. thaliana hybrids over a range of ecologically relevant temperatures. We found both linear and non‐linear responses for expression of immunity markers and for morphological defects depending on the underlying genetic cause. This suggests that the influence of temperature on the trade‐off between immunity and growth depends on the specific defence components involved.     

Exploring bacterial diversity from contaminated soil samples from river Yamuna

The Yamuna is the source of key water supply in the national capital region of India. Due to its immense importance, the pollution of Yamuna has become an imperative issue of study. Various initiatives have been taken by the Indian Government to decontaminate this river, but so far no possible outcome has been obtained. Therefore bioremediation may seem to be a promising approach. To assess the bioremediation potential of the microbes at river Yamuna, study of microbial diversity was carried out. Escherichia, Pseudomonas, Bacillus, Thermomicrobium, Azoarcus, Nitrosomonas and Shigella were the dominant genera present at the contaminated river coastal zone. The presence of Escherichia and Shigella indicated the sewage contamination in the river. On the other hand, the presence of Pseudomonas and Bacillus indicated the existence of indigenous bacterial communities capable of de-polluting the river, thus providing a promising approach to decontaminate Yamuna by natural means.