Inhibition of geranylgeranyl diphosphate synthesis in in vitro systems

The incorporation of [¹⁴C]mevalonate and [¹⁴C]isopentenyl diphosphate into geranylgeranyl diphosphate was investigated in in vitro systems from Cucurbita pepo (pumpkin) endosperm and from Avena sativa etioplasts. Mevalonate incorporation was effectively inhibited in the pumpkin system by geranylgeranyl diphosphate and geranylgeranyl monophosphate but less effectively by phytyl diphosphate or inorganic diphosphate. Membrane lipids, geranyllinalool, or lecithin enhanced mevalonate incorporation in the Cucurbita system. Incorporation of isopentenyl diphosphate was also enhanced by lecithin and inhibited by geranylgeranyl diphosphate in the Cucurbita system. No lipid enhancement was found in the Avena system; inhibition by GGPP required a much higher GGPP concentration than in the Cucurbita system.     

A p38 MAPK-CREB pathway functions to pattern mesoderm in Xenopus

Dorsal-ventral patterning is specified by signaling centers secreting antagonizing morphogens that form a signaling gradient. Yet, how morphogen gradient is translated intracellularly into fate decisions remains largely unknown. Here, we report that p38 MAPK and CREB function along the dorsal-ventral axis in mesoderm patterning. We find that the phosphorylated form of CREB (S133) is distributed in a gradient along the dorsal-ventral mesoderm axis and that the p38 MAPK pathway mediates the phosphorylation of CREB. Knockdown of CREB prevents chordin expression and mesoderm dorsalization by the Spemann organizer, whereas ectopic expression of activated CREB-VP16 chimera induces chordin expression and dorsalizes mesoderm. Expression of high levels of p38 activator, MKK6E or CREB-VP16 in embryos converts ventral mesoderm into a dorsal organizing center. p38 MAPK and CREB function downstream of maternal Wnt/β-catenin and the organizer-specific genes siamois and goosecoid. At low expression levels, MKK6E induces expression of lateral genes without inducing the expression of dorsal genes. Loss of CREB or p38 MAPK activity enables the expansion of the ventral homeobox gene vent1 into the dorsal marginal region, preventing the lateral expression of Xmyf5. Overall, these data indicate that dorsal-ventral mesoderm patterning is regulated by differential p38/CREB activities along the axis.     

Efficient RNA polymerase II pause release requires U2 snRNP function

1. Download : Download high-res image (88KB)
2. Download : Download full-size image

     

p24 proteins play a role in peroxisome proliferation in yeast

Emp24 is a member of the p24 protein family, which was initially localized to the endoplasmic reticulum, Golgi and COP vesicles, but has recently shown to be associated with Saccharomyces cerevisiae peroxisomes as well. Using cell fractionation and electron- and fluorescence microscopy, we show that in the yeast Hansenula polymorpha, Emp24 also associates with peroxisomes. In addition, we show that peroxisome numbers are strongly decreased in H. polymorpha cells lacking two proteins of the p24 complex, Emp24 and Erp3. Detailed fluorescence microscopy analyses suggest that emp24.erp3 cells are disturbed in peroxisome fission and inheritance.     

A non-radiolabeled heme-GSH interaction test for the screening of antimalarial compounds

Intraerythrocytic Plasmodium produces large amounts of toxic heme during the digestion of hemoglobin, a parasite specific pathway. Heme is then partially biocristallized into hemozoin and mostly detoxified by reduced glutathione. We proposed an in vitro micro assay to test the ability of drugs to inhibit heme-glutathione dependent degradation. As glutathione and o-phthalaldehyde form a fluorescent adduct, we followed the extinction of the fluorescent signal when heme was added with or without antimalarial compounds. In this assay, 50 microM of amodiaquine, arthemether, chloroquine, methylene blue, mefloquine and quinine inhibited the interaction between glutathione (50 microM) and heme (50 microM), while atovaquone did not. Consequently, this test could detect drugs that can inhibit heme-GSH degradation in a fast, simple and specific way, making it suitable for high throughput screening of potential antimalarials.     

Structural conservation of the B subunit in the ammonia monooxygenase/particulate methane monooxygenase superfamily

The ammonia monooxygenase (AMO)/particulate methane monooxygenase (pMMO) superfamily is a diverse group of membrane‐bound enzymes of which only pMMO has been characterized on the molecular level. The pMMO active site is believed to reside in the soluble N‐terminal region of the pmoB subunit. To understand the degree of structural conservation within this superfamily, the crystal structure of the corresponding domain of an archaeal amoB subunit from Nitrosocaldus yellowstonii has been determined to 1.8 Å resolution. The structure reveals a remarkable conservation of overall fold and copper binding site location as well as several notable differences that may have implications for function and stability. Proteins 2014; 82:2263–2267. © 2014 Wiley Periodicals, Inc.     

A paradigm shift towards low-nitrifying production systems: the role of biological nitrification inhibition (BNI)

Background

Agriculture is the single largest geo-engineering initiative that humans have initiated on planet Earth, largely through the introduction of unprecedented amounts of reactive nitrogen (N) into ecosystems. A major portion of this reactive N applied as fertilizer leaks into the environment in massive amounts, with cascading negative effects on ecosystem health and function. Natural ecosystems utilize many of the multiple pathways in the N cycle to regulate N flow. In contrast, the massive amounts of N currently applied to agricultural systems cycle primarily through the nitrification pathway, a single inefficient route that channels much of this reactive N into the environment. This is largely due to the rapid nitrifying soil environment of present-day agricultural systems.

Scope

In this Viewpoint paper, the importance of regulating nitrification as a strategy to minimize N leakage and to improve N-use efficiency (NUE) in agricultural systems is highlighted. The ability to suppress soil nitrification by the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI), an active plant-mediated natural function that can limit the amount of N cycling via the nitrification pathway. The development of a bioassay using luminescent Nitrosomonas to quantify nitrification inhibitory activity from roots has facilitated the characterization of BNI function. Release of BNIs from roots is a tightly regulated physiological process, with extensive genetic variability found in selected crops and pasture grasses. Here, the current status of understanding of the BNI function is reviewed using Brachiaria forage grasses, wheat and sorghum to illustrate how BNI function can be utilized for achieving low-nitrifying agricultural systems. A fundamental shift towards ammonium (NH₄⁺)-dominated agricultural systems could be achieved by using crops and pastures with high BNI capacities. When viewed from an agricultural and environmental perspective, the BNI function in plants could potentially have a large influence on biogeochemical cycling and closure of the N loop in crop–livestock systems.     

Endomitosis and the effect of gibberellic acid in different Pisum sativum L. cultivars

The evolution of the total amount of DNA in epicotyls and of the amount of DNA per cell nucleus in epicotyl cortex cells during germination was followed in two closely related pea varieties, Pisum sativum cv. Finale and Pisum sativum cv. Rondo. Under etiolating conditions, growth of the cv. Rondo occurs only by cell elongation which is preceded by endomitotic DNA synthesis, while in the cv. Finale growth is the result of cell elongation accompanied by endomitotic DNA synthesis and cell division. The maximum C-level attained in both cultivars under etiolating conditions is 8 C (C=haploid amount of DNA in a gamete cell). Both the maximum C-level reached and the percentage of cells reaching this C-level seem to be under strict genetic control. In both cultivars, light inhibits the endomitotic DNA replication.Neither gibberellic acid (GA₃), nor AMO 1618 alter the maximum C-level or the percentage distribution of the C-classes. Both growth regulators are effective, although in an opposite way, only in tissues where cell division occurs or where endomitotic DNA synthesis is blocked, as in light-grown pea epicotyls.     

A 382-year reconstruction of August mean minimum temperature from tree-ring maximum latewood density on the southeastern Tibetan Plateau,China

Long-term summer temperature records are important for climate studies on the Tibetan Plateau (TP). Here, we used tree-ring maximum latewood density (MXD) to develop a well-replicated regional chronology back to the year 1630 for the southeastern TP. The MXD chronology is positively related to the observed August mean minimum temperatures (AMMT) in the period 1961–2011. Therefore, the AMMT was reconstructed from the MXD chronology. The reconstruction explained 42.6% of the total variance in the observed AMMT. During the past 382 years, warm periods were found during 1646–1694, 1770–1805, 1930–1971 and 1992–2011, and cold periods were found during 1630–1645, 1695–1749, 1806–1825, 1889–1929 and 1972–1991. Extreme cold summers (≤mean − 2 SD) occurred in the years 1701, 1777, 1810, 1817, 1835, 1843, 1857, 1871, 1911, 1914, 1915, 1939, 1983 and 1984, whereas the warm summers (≥mean + 2 SD) occurred in the years 1786, 1788, 2003, 2004 and 2005. A comparison with temperature records in surrounding regions showed general agreements, indicating the fidelity of our reconstruction and its ability to represent summer temperature variations over a broad geographic extent. Conspicuous in-phase relationships between our reconstruction and the Atlantic Multidecadal Oscillation (AMO) indicated a strongly positive association between large-scale climate circulations and summer temperature variability on the southeastern TP at multidecadal scales.