Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSSpecific Structural Features of Sterols Affect Cell-Cell Signaling and Fusion in Neurospora crassa. Martin Weichert 1 , Ewald Priegnitz 1 , Raphael Brandt 1 ,Thorben Nawrath 2 , Stefan Schulz 2 , André Fleissner 1 . 1) Institut für Genetik, Technische Universität Braunschweig, Spielmannstrasse 7, 38106Braunschweig, Germany; 2) Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.Sterols are major constituents in the plasma membrane of eukaryotic cells. They modulate the physical properties of the lipid bilayer, e.g. fluidity. Byinteracting with certain lipids and proteins in the plasma membrane, sterols cluster into microdomains which might act as platforms for many biologicalfunctions, such as signal transduction. In the early stages of colony formation in Neurospora crassa, germinating spores direct their growth towards eachother, establish physical contact, and fuse. Cell-to-cell signaling requires the coordinated dynamic recruitment of the MAP kinase MAK-2 and thecytoplasmic protein SO to the tips of interacting cells. Subsequent plasma membrane fusion is facilitated by the transmembrane protein PRM1. Here, wereport that mutants affected in the biosynthesis of ergosterol, the major sterol in most fungal species, show distinct defects during germling fusion.Deletion of erg-2, which encodes an enzyme mediating the last step in the pathway, strongly impairs both directed growth and cell fusion. Interestingly,both MAK-2 and SO mislocalize at the tips of interacting Derg-2 germlings. In contrast, the absence of ERG-10a and ERG-10b, two enzymes with redundantfunction that act upstream of ERG-2, does not affect cell-to-cell communication. However, Derg-10a Derg-10b germling pairs show DPrm1-like deficienciesin plasma membrane merger. By relating the sterol composition and fusion competence of several erg mutants, we find that not the absence of ergosterolbut the accumulation of sterol intermediates specifically impairs distinct steps of germling fusion. While the presence of two double bonds in the sterolside chain provokes Derg-2-like deficiencies, an altered double bond arrangement in the sterol ring system causes DPrm1-like defects. During sexualdevelopment, cell fusion precedes the fertilization of fruiting bodies. Unlike the defects during germling fusion, female and male mating partners of Derg-2and Derg-10a Derg-10b efficiently fuse, suggesting that alterations in the sterol composition specifically impair signaling mechanisms mediating vegetativecell fusion. These data suggest that specific structural features of sterols differentially affect membrane properties and functions, such as the membranerecruitment of proteins, the assembly of signaling complexes, and plasma membrane fusion.Co-option of a sex pheromone receptor and MAPK signalling pathway for chemotropism of Fusarium oxysporum towards plant host compounds. DavidTurra, Federico Rossi, Antonio Di Pietro. Departamento de Genética, Universidad de Córdoba, 14071 Córdoba, Spain.Fungal hyphae explore the surrounding environment in search of nutrient sources, mating partners or host organisms by sensing gradients of tropicallyactive cues. Chemotropism is crucial for fungal development and virulence, but the underlying mechanisms are poorly understood. Here we followed agenetic approach to dissect chemotropism in the soilborne plant pathogen Fusarium oxysporum. A plate assay was used to measure directed growth ofgerm tubes towards different classes of compounds, including carbon and nitrogen sources, sex pheromones, plant secondary metabolites and tomatoroot exudate. F. oxysporum mutants lacking the mitogen activated protein kinase (MAPK) Fmk1 or the transcription factor Ste12, two components of theconserved Pathogenicity MAPK cascade, were impaired in chemotropism towards nutrients, but fully responsive to a-pheromone and root exudate. Bycontrast, Rho1 and Mpk1, two components of the cell integrity MAPK cascade, were specifically required for directed growth towards a-pheromone androot exudate. Deletion of the seven transmembrane G protein coupled receptor Ste2 abolished the chemotropic response to a-pheromone and,unexpectedly, also to tomato root exudate. Our results provide evidence for co-option of a cognate sex pheromone receptor and a conserved MAPKsignalling pathway for chemotropism of F. oxysporum towards plant host compounds.Characterization of new STRIPAK complex interaction partners in the filamentous ascomycete Sordaria macrospora. Britta Herzog, Yasmine Bernhards,Berit Habing, Eva Reschka, Sabine Riedel, Stefanie Pöggeler. Institute of Microbiology and Genetics, Department of Genetics of EurkaryoticMicroorganisms, Georg-August-University Göttingen, Germany.Using Sordaria macrospora as model organism we investigate the complex process of fruiting-body development and involved proteins in thisfilamentous ascomycete. This differentiation process is regulated by more than 100 developmental genes. Recently, we have shown that a homologue ofthe human STRIPAK (striatin-interacting phosphatase and kinase) complex engages a crucial role in sexual development in fungi. The S. macrospora striatinhomologue PRO11 and its interaction partner SmMOB3 are key components of this complex (Bloemendal et al., 2012). PRO11 contains a conserved WD40repeat domain and is supposed to function as scaffolding protein linking signaling and eukaryotic endocytosis (Pöggeler and Kück, 2004). SmMOB3(phocein) is a member of the MOB family (Bernhards and Pöggeler, 2011). Beside their important role in multicellular development and hyphal fusion bothproteins seem to be involved in vesicular trafficking and endocytosis.By means of yeast two-hybrid screens and GFP-Trap analysis we identified several new interaction partners of PRO11 and SmMOB3. Similar to PRO11and SmMOB3, a multitude of them are predicted to be involved in vesicular trafficking and are localized to the ER or to the Golgi. Here, we show theresults of a detailed analysis of the new STRIPAK complex interaction partners. Initially, we isolated the cDNA of the genes and confirmed the interactionby yeast two-hybrid. For further characterization and to get knowledge about their cellular functions we created knock-out strains and analyzed theirmorphological phenotypes. For localization and expression studies we constructed EGFP-tagged fusion proteins and expressed them in S. macrospora.Bernhards and Pöggeler, 2011; Curr Genet 57 (2): 133-49.Bloemendal et al., 2012; Mol Microbiol 84 (2): 310-23.Pöggeler and Kück, 2004; Eukaryot Cell 3 (1): 232-40.27th Fungal Genetics Conference | 101