A Genome-Wide Association Study of the Maize Hypersensitive Defense Response Identifies Genes That Cluster in Related Pathways

Much remains unknown of molecular events controlling the plant hypersensitive defense response (HR), a rapid localized cell death that limits pathogen spread and is mediated by resistance (R-) genes. Genetic control of the HR is hard to quantify due to its microscopic and rapid nature. Natural modifiers of the ectopic HR phenotype induced by an aberrant auto-active R-gene (Rp1-D21), were mapped in a population of 3,381 recombinant inbred lines from the maize nested association mapping population. Joint linkage analysis was conducted to identify 32 additive but no epistatic quantitative trait loci (QTL) using a linkage map based on more than 7000 single nucleotide polymorphisms (SNPs). Genome-wide association (GWA) analysis of 26.5 million SNPs was conducted after adjusting for background QTL. GWA identified associated SNPs that colocalized with 44 candidate genes. Thirty-six of these genes colocalized within 23 of the 32 QTL identified by joint linkage analysis. The candidate genes included genes predicted to be in involved programmed cell death, defense response, ubiquitination, redox homeostasis, autophagy, calcium signalling, lignin biosynthesis and cell wall modification. Twelve of the candidate genes showed significant differential expression between isogenic lines differing for the presence of Rp1-D21. Low but significant correlations between HR-related traits and several previously-measured disease resistance traits suggested that the genetic control of these traits was substantially, though not entirely, independent. This study provides the first system-wide analysis of natural variation that modulates the HR response in plants.     

Exogenous supply of pantoyl lactone to excised leaves increases their pantothenate levels

BACKGROUND AND AIMS: All plants synthesize pantothenate but its synthesis and regulation are not well understood. The aim of this work is to study the effect of exogenous supply of precursor compounds on pantothenate levels in leaves. METHODS: Precursor compounds were supplied in solution to excised leaves and the pantothenate content was measured using a microbial method. KEY RESULTS: Pantothenate levels in excised leaves of Limonium latifolium, tomato (Lycopersicon esculentum), bean (Phaseolus vulgaris) and grapefruit (Citrus x paradisi) were examined following an exogenous supply of the precursor compounds pantoyl lactone or beta-alanine. Significantly higher levels of extractable pantothenate were found when pantoyl lactone was supplied, but not when beta-alanine was supplied despite a measurable uptake of beta-alanine into the leaf. CONCLUSIONS: The results suggested that the pantoate supply may be rate-limiting or regulating pantothenate synthesis in leaves.     

Effects of the new adiponectin paralogous protein CTRP-3 and of LPS on cytokine release from monocytes of patients with type 2 diabetes mellitus

Aims/Hypothesis: It was the aim to investigate the hypothesis that the new C1q/TNF-family member CTRP-3 (C1q/TNF-related protein-3) acts anti-inflammatory in human monocytes from healthy controls and patients with type 2 diabetes mellitus (T2D). Methods: Monocytes were isolated from 20 healthy controls and 30 patients with T2D. IL-6 and TNF concentrations were measured by ELISA. CTRP-3 was expressed in insect cells and used for stimulation experiments. Results: Basal IL-6 and TNF were not different in control and in T2D monocytes. LPS-stimulation (1 μg/ml) significantly (p < 0.001) increased IL-6 and TNF in the supernatants of control and in T2D monocytes to a similar extent. CTRP-3 (1 μg/ml) significantly (p = 0.03) inhibited LPS-induced IL-6 in control monocytes but not in T2D monocytes. TNF upon co-stimulation with LPS and CTRP-3 was significantly (p = 0.012) lower in control than in T2D monocytes. LPS-induced TNF concentration was significantly and positively correlated with serum total cholesterol and LDL cholesterol in T2D patients. Conclusions: CTRP-3 inhibits LPS-induced IL-6 and TNF release. This anti-inflammatory effect is lost in T2D. Serum cholesterol concentration affects the pro-inflammatory potential of LPS to induce TNF release from T2D monocytes in the presence or absence of CTRP-3. CTRP-3 might partly account for the pro-inflammatory state in T2D.     

Synthesis and characterization of potent inhibitors of Trypanosoma cruzi dihydrofolate reductase

Dihydrofolate reductase (DHFR) of the parasite Trypanosoma cruzi (T. cruzi) is a potential target for developing drugs to treat Chagas’ disease. We have undertaken a detailed structure–activity study of this enzyme. We report here synthesis and characterization of six potent inhibitors of the parasitic enzyme. Inhibitory activity of each compound was determined against T. cruzi and human DHFR. One of these compounds, ethyl 4-(5-[(2,4-diamino-6-quinazolinyl)methyl]amino-2-methoxyphenoxy)butanoate (6b) was co-crystallized with the bifunctional dihydrofolate reductase-thymidylate synthase enzyme of T. cruzi and the crystal structure of the ternary enzyme:cofactor:inhibitor complex was determined. Molecular docking was used to analyze the potential interactions of all inhibitors with T. cruzi DHFR and human DHFR. Inhibitory activities of these compounds are discussed in the light of enzyme–ligand interactions. Binding affinities of each inhibitor for the respective enzymes were calculated based on the experimental or docked binding mode. An estimated 60–70% of the total binding energy is contributed by the 2,4-diaminoquinazoline scaffold.     

Up-regulation of microRNA-155 in macrophages contributes to increased tumor necrosis factor {alpha} (TNF{alpha}) production via increased mRNA half-life in alcoholic liver disease

Activation of Kupffer cells (KCs) by gut-derived lipopolysaccharide (LPS) and Toll-Like Receptors 4 (TLR4)-LPS-mediated increase in TNFα production has a central role in the pathogenesis of alcoholic liver disease. Micro-RNA (miR)-125b, miR-146a, and miR-155 can regulate inflammatory responses to LPS. Here we evaluated the involvement of miRs in alcohol-induced macrophage activation. Chronic alcohol treatment in vitro resulted in a time-dependent increase in miR-155 but not miR-125b or miR-146a levels in RAW 264.7 macrophages. Furthermore, alcohol pretreatment augmented LPS-induced miR-155 expression in macrophages. We found a linear correlation between alcohol-induced increase in miR-155 and TNFα induction. In a mouse model of alcoholic liver disease, we found a significant increase in both miR-155 levels and TNFα production in isolated KCs when compared with pair-fed controls. The mechanistic role of miR-155 in TNFα regulation was indicated by decreased TNFα levels in alcohol-treated macrophages after inhibition of miR-155 and by increased TNFα production after miR-155 overexpression, respectively. We found that miR-155 affected TNFα mRNA stability because miR-155 inhibition decreased whereas miR-155 overexpression increased TNFα mRNA half-life. Using the NF-κB inhibitors, MG-132 or Bay11-7082, we demonstrated that NF-κB activation mediated the up-regulation of miR-155 by alcohol in KCs. In conclusion, our novel data demonstrate that chronic alcohol consumption increases miR-155 in macrophages via NF-κB and the increased miR-155 contributes to alcohol-induced elevation in TNFα production via increased mRNA stability.     

Inactivation of Cyanobacterial Nitrogenase After Exposure to Ultraviolet-B Radiation

Exposure of the N₂-fixing cyanobacterium Anabaena BT2 to ultraviolet-B radiation (2.5 W m⁻²) for 30 min resulted in complete loss of nitrogenase activity but 100% cell killing occurred only after a 90-min exposure. Inactivation of nitrogenase activity was not specific to Anabaena BT2; other species also showed a similar effect. The time required for 100% killing and inactivation of nitrogenase activity differed in various species, and this difference may be ascribed to the presence of different levels of UV-B protection mechanisms in individual species. Inhibition of nitrogenase activity was immediate, since exposure of cultures to UV-B for as little as 5 min elicited some inhibition of activity. The activity of UV-B-inhibited nitrogenase did not recover upon transfer of exposed cells to fluorescent light, suggesting that the inhibition may be due to specific inactivation of the enzyme. By employment of inhibitors of protein synthesis and PS-II activity, it was demonstrated that restoration of nitrogenase activity in a UV-B-treated culture occurred by fresh synthesis of nitrogenase polypeptide. Our findings suggest that estimation of nitrogenase activity in diazotrophic species may be used as a marker enzyme for assessing the impact of UV-B radiation. Received: 13 June 2002 / Accepted: 22 July 2002     

Disposable immunosensor for the determination of domoic acid in shellfish

The construction of an electrochemical immunosensor coupled to differential pulse voltammetry (DPV) for the detection of domoic acid (DA), a neurotoxic aminoacid responsible for the human syndrome known as "Amnesic Shellfish Poisoning" (ASP), is proposed here. The method involves the use of disposable screen-printed electrodes (SPEs) for the immunosensor development based on a "competitive indirect test". Domoic acid conjugated to bovine serum albumin (BSA-DA) was coated onto the working electrode of the SPE, followed by incubation with sample (or standard toxin) and anti-DA antibody. An anti-goat IgG-alkaline phosphatase (AP) conjugate was used for signal generation. A spectrophotometric enzyme-linked immunosorbent assay (ELISA) was used in a preliminary phase of development, prior to transferring the assay to the SPEs. Results showed a detection limit equal to 5 ng/ml of toxin. The electrochemical system is simple and cost-effective due to the disposable nature of the SPEs, and the analysis time is 150 min, shorter than that for the spectrophotometric method. The suitability of the assay for DA quantification in mussels was also evaluated. Samples were spiked with DA before and after the sample treatment to study the extraction efficiency and the matrix effect, respectively. After treatment, samples were analysed using a 1:250 v/v dilution in PBS-M (phosphate saline buffer pH 7.4 + CH3OH 10%) to minimise the matrix effect and allow for the detection of 20 microg/g of DA in mussel tissue. This represents the maximum acceptable limit defined by the Food and Drug Administration [Compliance Programme 7303.842. Guidance Levels, Table 3, p. 248, http://www.fda.org]. The optimised ELISA systems were then used, in parallel with a conventional HPLC method, to detect and confirm DA in shellfish extract in order to verify the performance of the electrochemical system. Very good recoveries were obtained, demonstrating the suitability of the proposed assay for accurate determination of the DA concentration in mussel samples.     

Leishmania (Viannia) panamensis: An in vitro assay using the expression of GFP for screening of antileishmanial drug

Promastigotes of Leishmania (Viannia) panamensis were successfully transfected with p6.5-egfp to express green fluorescent protein. The transfectants remained infective to macrophages, providing an in vitro model for screening antileishmanial drugs. This was demonstrated by flow cytometry of macrophage-associated GFP after exposure of infected cultures to known antileishmanial drugs, i.e. amphotericin B and glucantime^®. Fluorescence of GFP diminished progressively from infected cells with increasing drug concentrations used in both cases. The availability of this fluorescent assay for infection of macrophages by L. (V.) panamensis facilitates drug discovery program for the Viannia species, which differ significantly from those of the Leishmania subgenus.     

Adipocyte/macrophage fatty acid binding proteins control integrated metabolic responses in obesity and diabetes

Fatty acid binding proteins (FABPs) are cytosolic fatty acid chaperones whose biological role and mechanisms of action are not well understood. Here, we developed mice with targeted mutations in two related adipocyte FABPs, aP2 and mal1, to resolve their role in systemic lipid, glucose, and energy metabolism. Mice lacking aP2 and mal1 exhibited a striking phenotype with strong protection from diet-induced obesity, insulin resistance, type 2 diabetes, and fatty liver disease. These mice have altered cellular and systemic lipid transport and composition, leading to enhanced insulin receptor signaling, enhanced muscle AMP-activated kinase (AMP-K) activity, and dramatically reduced liver stearoyl-CoA desaturase-1 (SCD-1) activity underlying their phenotype. Taken together with the previously reported strong protection against atherosclerosis, these results demonstrate that adipocyte/macrophage FABPs have a robust impact on multiple components of metabolic syndrome, integrating metabolic and inflammatory responses in mice and constituting a powerful target for the treatment of these diseases.