Das Cellobioselipid Ustilaginsäure aus Ustilago maydis: Biosynthese und transkriptionelleRegulation

Der Brandpilz Ustilago maydis produziert unter Stickstoffmangelbedingungen zwei Arten von extrazellulären Glycolipiden, Ustilaginsäure und Mannosylerythritollipide. In dieser Arbeit konnte der Biosyntheseweg für die Ustilaginsäure aufgeklärt werden. Sämtliche Gene, die an der Biosynthese dieses Cellobioselipids beteiligt sind, liegen in einem Gencluster angeordnet, das von einem eigenen Transkriptionsfaktor reguliert wird. An der Biosynthese der Ustilaginsäure sind zwei Cytochrom P450 Monooxygenasen, eine Fettsäuresynthase, eine Glycosyltransferase, eine Acyl- und eine Acetyltransferase sowie zwei Hydrogenasen beteiligt. Durch Deletionsanalysen der einzelnen Gene, sowie massenspektrometrische Analyse der Substanzen, die von den Deletionsstämmen synthetisiert wurden, konnten die Enzyme charakterisiert und ihre Funktion den einzelnen Schritten während der Biosynthese zugeordnet werden. Des weiteren wurde der Transkriptionsfaktor Rua1 näher untersucht. Er gehört zur Familie der Cys2His2 Zinkfingerproteine und ist für die Regulation des Ustilaginsäuregenclusters verantwortlich. Über die C-terminal gelegene Zinkfingerdomäne bindet Rua1 an ein konserviertes DNA-Motiv innerhalb der Promotorregion der einzelnen Clustergene und aktiviert dadurch deren Transkription. Die Ustilaginsäure weist antibiotische Wirksamkeit gegenüber pro- und eukaryotischen Mikroorganismen auf. So konnte in dieser Arbeit durch Inkubation von S. cerevisiae Zellen mit Ustilaginsäurederivaten, die von den verschiedenen Mutantenstämmen produziert wurden, bestimmt werden, welche Gruppen des Moleküls essentiell für die antibiotische Wirkung sind. Darüberhinaus weist U. maydis Biocontrolaktivität gegenüber dem pflanzen-pathogenen Pilz Botrytis cinerea auf. B. cinerea verursacht Grauschimmelfäule z.B. auf Tomatenpflanzen. Eine Inkubation von U. maydis Zellen mit B. cinerea Sporen auf Tomatenblättern konnte eine Infektion durch B. cinerea verhindern. Verantwortlich für diese antagonistische Wirksamkeit ist die Ustilaginsäure, denn Deletionsstämme, die keine Ustilaginsäure produzieren können, sind nicht in der Lage, eine Infektion durch B. cinerea zu verhindern. U. maydis eignet sich damit für den Einsatz in der Natur, da er auf natürliche Weise Pflanzenschädlinge eliminieren kann

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

Wünsch M, Schröder DC, Fröhr T, et al. Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics. Beilstein Journal of Organic Chemistry. 2017;13:2428-2441.The amide moiety of peptides can be replaced for example by a triazole moiety, which is considered to be bioisosteric. Therefore, the carbonyl moiety of an amino acid has to be replaced by an alkyne in order to provide a precursor of such peptidomimetics. As most amino acids have a chiral center at C-alpha, such amide bond surrogates need a chiral moiety. Here the asymmetric synthesis of a set of 24 N-sulfinyl propargylamines is presented. The condensation of various aldehydes with Ellman's chiral sulfinamide provides chiral N-sulfinylimines, which were reacted with (trimethylsilyl) ethynyllithium to afford diastereomerically pure N-sulfinyl propargylamines. Diverse functional groups present in the propargylic position resemble the side chain present at the Ca of amino acids. Whereas propargylamines with (cyclo) alkyl substituents can be prepared in a direct manner, residues with polar functional groups require suitable protective groups. The presence of particular functional groups in the side chain in some cases leads to remarkable side reactions of the alkyne moiety. Thus, electron-withdrawing substituents in the C-alpha-position facilitate a base induced rearrangement to alpha, beta-unsaturated imines, while azide-substituted propargylamines form triazoles under surprisingly mild conditions. A panel of propargylamines bearing fluoro or chloro substituents, polar functional groups, or basic and acidic functional groups is accessible for the use as precursors of peptidomimetics

Global exposure of population and land‐use to meteorological droughts under different warming levels and SSPs: a CORDEX‐based study

Global warming is likely to cause a progressive drought increase in some regions, but how population and natural resources will be affected is still underexplored. This study focuses on global population, forests, croplands and pastures exposure to meteorological drought hazard in the 21st century, expressed as frequency and severity of drought events. As input, we use a large ensemble of climate simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), population projections from the NASA-SEDAC dataset and land-use projections from the Land-Use Harmonization 2 project for 1981–2100. The exposure to drought hazard is presented for five Shared Socioeconomic Pathways (SSP1-SSP5) at four Global Warming Levels (GWLs: 1.5°C to 4°C). Results show that considering only Standardized Precipitation Index (SPI; based on precipitation), the SSP3 at GWL4 projects the largest fraction of the global population (14%) to experience an increase in drought frequency and severity (versus 1981–2010), with this value increasing to 60% if temperature is considered (indirectly included in the Standardized Precipitation-Evapotranspiration Index, SPEI). With SPEI, considering the highest GWL for each SSP, 8 (for SSP2, SSP4, SSP5) and 11 (SSP3) billion people, that is, more than 90%, will be affected by at least one unprecedented drought. For SSP5 at GWL4, approximately 2 × 10$^{6}$ km$^{2}$ of forests and croplands (respectively, 6% and 11%) and 1.5 × 10$^{6}$ km$^{2}$ of pastures (19%) will be exposed to increased drought frequency and severity according to SPI, but for SPEI this extent will rise to 17 × 10$^{6}$ km$^{2}$ of forests (49%), 6 × 10$^{6}$ km$^{2}$ of pastures (78%) and 12 × 10$^{6}$ km$^{2}$ of croplands (67%), being mid-latitudes the most affected. The projected likely increase of drought frequency and severity significantly increases population and land-use exposure to drought, even at low GWLs, thus extensive mitigation and adaptation efforts are needed to avoid the most severe impacts of climate change

Activation of the Ustilagic Acid Biosynthesis Gene Cluster in Ustilago maydis by the C2H2 Zinc Finger Transcription Factor Rua1▿

The phytopathogenic basidiomycetous fungus Ustilago maydis secretes, under conditions of nitrogen starvation, large amounts of the biosurfactant ustilagic acid (UA). This secreted cellobiose glycolipid is toxic for many microorganisms and confers biocontrol activity to U. maydis. Recently, a large gene cluster that is responsible for UA biosynthesis was identified. Here, we show that expression of all cluster genes depends on Rua1, a nuclear protein of the C2H2 zinc finger family, whose gene is located within the gene cluster. While deletion of rua1 results in complete loss of UA production, overexpression of rua1 promotes increased UA synthesis even in the presence of a good nitrogen source. Bioinformatic analysis allowed us to identify a conserved sequence element that is present in the promoters of all structural genes involved in UA biosynthesis. Deletion analysis of several promoters within the cluster revealed that this DNA element serves as an upstream activating sequence (UAS) and mediates Rua1-dependent expression. We used the yeast one-hybrid system to demonstrate specific recognition of this DNA element by Rua1. Introduction of nucleotide exchanges into the consensus sequence interfered with Rua1-dependent activation, suggesting that this sequence element acts as a direct binding site for Rua1

Centrohexaindane: six benzene rings mutually fixed in three dimensions - solid-state structure and six-fold nitration

Kuck D, Linke J, Teichmann LC, et al. Centrohexaindane: six benzene rings mutually fixed in three dimensions - solid-state structure and six-fold nitration. PHYSICAL CHEMISTRY CHEMICAL PHYSICS. 2016;18(17):11722-11737.The solid-state molecular structure of centrohexaindane (1), a unique hydrocarbon comprising six benzene rings clamped to each other in three dimensions around a neopentane core, and the molecular packing in crystals of 1 center dot CHCl3 are reported. The molecular T-d-symmetry and the Cartesian orientation of the six indane wings of 1 in the solid state have been confirmed. The course and limitation of electrophilic aromatic substitution of 1 are demonstrated for the case of nitration. Based on nitration experiments of a lower congener of 1, tribenzotriquinacene 5, the six-fold nitrofunctionalisation of 1 has been achieved in excellent yield, giving four constitutional isomers, two nonsymmetrical (14 and 17) and two C-3-symmetrical ones (15 and 16), all of which contain one single nitro group in each of the six benzene rings. The relative yields of the four isomers (similar to 3 : 1 : 1 : 3) point to a random electrophilic attack of the electrophiles at the twelve formally equivalent outer positions of the aromatic periphery of 1, suggesting electronic independence of its six aromatic pi-electron systems. In turn, the pronounced conformational rigidity of the centrohexacyclic framework of 1 enables the unequivocal structural identification of the isomeric hexanitrocentrohexaindanes 14-17 by H-1 NMR spectroscopy

Global exposure of population and land‐use to meteorological droughts under different Warming Levels and Shared Socioeconomic Pathways: A Coordinated Regional Climate Downscaling Experiment‐based study

International audienceGlobal warming is likely to cause a progressive drought increase in some regions, but how population and natural resources will be affected is still underexplored. This study focuses on global population and land-use (forests, croplands, pastures) exposure to meteorological drought hazard in the 21st century, expressed as frequency and severity of drought events. As input, we use a large ensemble of climate simulations from the Coordinated Regional Climate Downscaling Experiment, population projections from the NASA-SEDAC dataset, and land-use projections from the Land-Use Harmonization 2 project for 1981–2100. The exposure to drought hazard is presented for five SSPs (SSP1-SSP5) at four Global Warming Levels (GWLs, from 1.5 to 4°C). Results show that considering only Standardized Precipitation Index (SPI; based on precipitation), the combination SSP3-GWL4 projects the largest fraction of the global population (14%) to experience an increase in drought frequency and severity (vs. 1981–2010), with this value increasing to 60% if temperature is considered (indirectly included in the Standardized Precipitation-Evapotranspiration Index, SPEI). With SPEI, considering the highest GWL for each SSP, 8 (for SSP2, SSP4, and SSP5) and 11 (SSP3) billion people, that is, more than 90%, will be affected by at least one unprecedented drought. For SSP5 (fossil-fuelled development) at GWL 4°C, approximately 2·106 km2 of forests and croplands (respectively, 6 and 11%) and 1.5·106 km2 of pastures (19%) will be exposed to increased drought frequency and severity according to SPI, but for SPEI, this extent will rise to 17·106 km2 of forests (49%), 6·106 km2 of pastures (78%), and 12·106 km2 of croplands (67%), with mid-latitudes being the most affected areas. The projected likely increase of drought frequency and severity significantly increases population and land-use exposure to drought, even at low GWLs, thus extensive mitigation and adaptation efforts are needed to avoid the most severe impacts of climate change.w

Global exposure of population and land-use to meteorological droughts under different warming levels and SSPs: A CORDEX-based study

Global warming is likely to cause a progressive drought increase in some regions, but how population and natural resources will be affected is still underexplored. This study focuses on global population, forests, croplands and pastures exposure to meteorological drought hazard in the 21st century, expressed as frequency and severity of drought events. As input, we use a large ensemble of climate simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), population projections from the NASA-SEDAC dataset and land-use projections from the Land-Use Harmonization 2 project for 1981–2100. The exposure to drought hazard is presented for five Shared Socioeconomic Pathways (SSP1-SSP5) at four Global Warming Levels (GWLs: 1.5°C to 4°C). Results show that considering only Standardized Precipitation Index (SPI; based on precipitation), the SSP3 at GWL4 projects the largest fraction of the global population (14%) to experience an increase in drought frequency and severity (versus 1981–2010), with this value increasing to 60% if temperature is considered (indirectly included in the Standardized Precipitation-Evapotranspiration Index, SPEI). With SPEI, considering the highest GWL for each SSP, 8 (for SSP2, SSP4, SSP5) and 11 (SSP3) billion people, that is, more than 90%, will be affected by at least one unprecedented drought. For SSP5 at GWL4, approximately 2 × 106 km2 of forests and croplands (respectively, 6% and 11%) and 1.5 × 106 km2 of pastures (19%) will be exposed to increased drought frequency and severity according to SPI, but for SPEI this extent will rise to 17 × 106 km2 of forests (49%), 6 × 106 km2 of pastures (78%) and 12 × 106 km2 of croplands (67%), being mid-latitudes the most affected. The projected likely increase of drought frequency and severity significantly increases population and land-use exposure to drought, even at low GWLs, thus extensive mitigation and adaptation efforts are needed to avoid the most severe impacts of climate change

Future Global Meteorological Drought Hot Spots : A Study Based on CORDEX Data

Two questions motivated this study: 1) Will meteorological droughts become more frequent and severe during the twenty-first century? 2) Given the projected global temperature rise, to what extent does the inclusion of temperature (in addition to precipitation) in drought indicators play a role in future meteorological droughts? To answer, we analyzed the changes in drought frequency, severity, and historically undocumented extreme droughts over 1981–2100, using the standardized precipitation index (SPI; including precipitation only) and standardized precipitation-evapotranspiration index (SPEI; indirectly including temperature), and under two representative concentration pathways (RCP4.5 and RCP8.5). As input data, we employed 103 high-resolution (0.448) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), based on a combination of 16 global circulation models (GCMs) and 20 regional circulation models (RCMs). This is the first study on global drought projections including RCMs based on such a large ensemble of RCMs. Based on precipitation only,;15% of the global land is likely to experience more frequent and severe droughts during 2071–2100 versus 1981–2010 for both scenarios. This increase is larger (;47% under RCP4.5,;49% under RCP8.5) when precipitation and temperature are used. Both SPI and SPEI project more frequent and severe droughts, especially under RCP8.5, over southern South America, the Mediterranean region, southern Africa, southeastern China, Japan, and southern Australia. A decrease in drought is projected for high latitudes in Northern Hemisphere and Southeast Asia. If temperature is included, drought characteristics are projected to increase over North America, Amazonia, central Europe and Asia, the Horn of Africa, India, and central Australia; if only precipitation is considered, they are found to decrease over those areas