Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSUnravelling the GTPase polarity complex in Claviceps purpurea. Andrea Herrmann 1 , Janine Schürmann 1 , Britta Tillmann 2 , Michael Bölker 2 , Paul Tudzynski 1 .1) IBBP, WWU Muenster, Schlossplatz 8, 48143 Muenster, Germany; 2) Philipps-Universität, Karl-von-Frisch-Strasse 8, 35032 Marburg, Germany.Claviceps purpurea is a plant pathogen infamous for its production of toxic alkaloids on infected host plants like barley. Consumption of infected grainsleads to severe symptoms up to the death of the patient. Infection patterns are complex and the topic of intensive research. One interesting aspect is thestrict polarity of the hyphal growth during the first infection stage which seems to be crucial for the non-recognition of C. purpurea as a pathogen by thehost. To address the question of the importance of polarity the structure and dynamics of the polarity complex are the focus of this work. The guaninenucleotide exchange factors (GEFs) Cdc24 and Dock180 belong to different families, Cdc24 being a member of the Dbl GEF family and Dock180 a CZH GEF.Cdc24-GFP localises cytosolically and to hyphal tips whereas Dock180-GFP is present in small vesicles in the hypha, though concentrated at the tip region,too. Cdc24 DHPH domains are able to activate the small GTPases Rac and Cdc42 of C. purpurea and U. maydis In vitro, whereas the catalytic domain ofDock180 only activates Rac in both organisms. Despite the proven activation Cdc24 does not interact with any GTPase in yeast two hybrid assays. Dock180shows a weak interaction with Rac and the two p21-activated kinases (PAKs) Ste20 and Cla4. Thus, both GEFs do not share many characteristics apart fromtheir GEF activity. The PAKs Ste20 and Cla4 and the scaffold protein Bem1 are involved in the polarity complex, too. Ste20 localises to hyphal tips andinteracts with Cdc42 in a loading status dependent manner, whereas Cla4 is the main partner of Rac. Other interactions of Ste20 with Dock180 and Cla4could also be shown. Bem1 is present in the cytosol - concentrated at the hyphal tip - and links most of the proteins of the polarity complex as interactionswith Cdc24, Cla4, Ste20 and Dock180 have been detected. Taken together we postulate at least two different polarity complexes, the Rac complex and theCdc42 complex. Both are gathered by Bem1, but Cla4 is the main partner of Rac, whereas Ste20 plays a similar role for Cdc42. Dock180 is mainly linked toRac, Cdc24 can be active in both complexes. We are interested in the spatial and temporal formation and regulation of these complexes and its influenceon polarity and virulence which will be the subject of further studies.27th Fungal Genetics Conference | 31