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  • 1
    Publication Date: 2011-10-07
    Description: Maize smut caused by the fungus Ustilago maydis is a widespread disease characterized by the development of large plant tumours. U. maydis is a biotrophic pathogen that requires living plant tissue for its development and establishes an intimate interaction zone between fungal hyphae and the plant plasma membrane. U. maydis actively suppresses plant defence responses by secreted protein effectors. Its effector repertoire comprises at least 386 genes mostly encoding proteins of unknown function and expressed exclusively during the biotrophic stage. The U. maydis secretome also contains about 150 proteins with probable roles in fungal nutrition, fungal cell wall modification and host penetration as well as proteins unlikely to act in the fungal-host interface like a chorismate mutase. Chorismate mutases are key enzymes of the shikimate pathway and catalyse the conversion of chorismate to prephenate, the precursor for tyrosine and phenylalanine synthesis. Root-knot nematodes inject a secreted chorismate mutase into plant cells likely to affect development. Here we show that the chorismate mutase Cmu1 secreted by U. maydis is a virulence factor. The enzyme is taken up by plant cells, can spread to neighbouring cells and changes the metabolic status of these cells through metabolic priming. Secreted chorismate mutases are found in many plant-associated microbes and might serve as general tools for host manipulation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Djamei, Armin -- Schipper, Kerstin -- Rabe, Franziska -- Ghosh, Anupama -- Vincon, Volker -- Kahnt, Jorg -- Osorio, Sonia -- Tohge, Takayuki -- Fernie, Alisdair R -- Feussner, Ivo -- Feussner, Kirstin -- Meinicke, Peter -- Stierhof, York-Dieter -- Schwarz, Heinz -- Macek, Boris -- Mann, Matthias -- Kahmann, Regine -- England -- Nature. 2011 Oct 5;478(7369):395-8. doi: 10.1038/nature10454.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Strasse 10, D-35043 Marburg, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21976020" target="_blank"〉PubMed〈/a〉
    Keywords: Chorismate Mutase/*metabolism ; Cytoplasm/enzymology ; Gene Expression Regulation, Plant ; Genetic Complementation Test ; Host-Pathogen Interactions ; Metabolome ; Models, Biological ; Plant Proteins/metabolism ; Plastids/enzymology ; Protein Multimerization ; Saccharomyces cerevisiae/genetics ; Salicylic Acid/metabolism ; Two-Hybrid System Techniques ; Ustilago/*enzymology/*pathogenicity ; Virulence Factors/genetics/*metabolism ; Zea mays/*metabolism/*microbiology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2011-05-13
    Description: Diatoms dominate the biomass of phytoplankton in nutrient-rich conditions and form the basis of some of the world's most productive marine food webs. The diatom nuclear genome contains genes with bacterial and plastid origins as well as genes of the secondary endosymbiotic host (the exosymbiont), yet little is known about the relative contribution of each gene group to diatom metabolism. Here we show that the exosymbiont-derived ornithine-urea cycle, which is similar to that of metazoans but is absent in green algae and plants, facilitates rapid recovery from prolonged nitrogen limitation. RNA-interference-mediated knockdown of a mitochondrial carbamoyl phosphate synthase impairs the response of nitrogen-limited diatoms to nitrogen addition. Metabolomic analyses indicate that intermediates in the ornithine-urea cycle are particularly depleted and that both the tricarboxylic acid cycle and the glutamine synthetase/glutamate synthase cycles are linked directly with the ornithine-urea cycle. Several other depleted metabolites are generated from ornithine-urea cycle intermediates by the products of genes laterally acquired from bacteria. This metabolic coupling of bacterial- and exosymbiont-derived proteins seems to be fundamental to diatom physiology because the compounds affected include the major diatom osmolyte proline and the precursors for long-chain polyamines required for silica precipitation during cell wall formation. So far, the ornithine-urea cycle is only known for its essential role in the removal of fixed nitrogen in metazoans. In diatoms, this cycle serves as a distribution and repackaging hub for inorganic carbon and nitrogen and contributes significantly to the metabolic response of diatoms to episodic nitrogen availability. The diatom ornithine-urea cycle therefore represents a key pathway for anaplerotic carbon fixation into nitrogenous compounds that are essential for diatom growth and for the contribution of diatoms to marine productivity.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Allen, Andrew E -- Dupont, Christopher L -- Obornik, Miroslav -- Horak, Ales -- Nunes-Nesi, Adriano -- McCrow, John P -- Zheng, Hong -- Johnson, Daniel A -- Hu, Hanhua -- Fernie, Alisdair R -- Bowler, Chris -- England -- Nature. 2011 May 12;473(7346):203-7. doi: 10.1038/nature10074.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉J. Craig Venter Institute, San Diego, California 92121, USA. aallen@jcvi.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21562560" target="_blank"〉PubMed〈/a〉
    Keywords: Carbamoyl-Phosphate Synthase (Ammonia)/metabolism ; Diatoms/*classification/enzymology/genetics/growth & development/*metabolism ; Gene Expression Regulation ; Gene Knockdown Techniques ; Nitrates/metabolism ; *Photosynthesis ; *Phylogeny ; RNA Interference ; Urea/*metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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