Program Book - 27th Fungal Genetics Conference

FULL POSTER SESSION ABSTRACTSepigenetic and cytoplasmic element. In the wild-type strain, this element is produced during stationary phase and eliminated at growth renewal. However,in some particular growth conditions, the element is not eliminated in growing hyphae triggering CG. Previous results showed that CG is controlled by twoMAPK modules, the PaNox1 NADPH oxidase and IDC1, a protein with unknown activity. Here, we describe the identification and characterization of twonew partners involved in the control of CG, IDC2 and IDC3. Data show that IDC2 and IDC3 likely act downstream of PaNox1 to regulate the paMpk1 MAPK.We will present a thorough analysis of the phenotypic of the IDC2 and IDC3 mutants and the phylogenetic studies of the IDC2 and IDC3 proteins.158. Dynein drives oscillatory nuclear movements in the phytopathogenic fungus Ashbya gossypii and prevents nuclear clustering. S. Grava, M. Keller, S.Voegeli, S. Seger, C. Lang, P. Philippsen. Biozentrum, Molecular Microbiology, University of Basel, CH 4056 Basel, Switzerland.In the yeast Saccharomyces cerevisiae the dynein pathway has a specific cellular function. It acts together with the Kar9 pathway to position the nucleusat the bud neck and to direct the pulling of one daughter nucleus into the bud. Nuclei in the closely related multinucleated filamentous fungus Ashbyagossypii are in continuous motion and nuclear positioning or spindle orientation is not an issue. A. gossypii expresses homologues of all components of theKar9/Dyn1 pathway, which apparently have adapted novel functions. Previous studies with A. gossypii revealed autonomous nuclear divisions and,emanating from each MTOC, an autonomous cytoplasmic microtubule (cMT) cytoskeleton responsible for pulling of nuclei in both directions of the hyphalgrowth axis. We now show that dynein is the sole motor for bidirectional movements. Surprisingly, deletion of Kar9 shows no phenotype. Dyn1, thedynactin component Jnm1, the accessory proteins Dyn2 and Ndl1, and the potential dynein cortical anchor Num1 are involved in the dynamic distributionof nuclei. In their absence, nuclei aggregate to different degrees, whereby the mutants with dense nuclear clusters grow extremely long cMTs. Like inbudding yeast, we found that dynein is delivered to cMT +ends, and its activity or processivity is probably controlled by dynactin and Num1. Together withits role in powering nuclear movements, we propose that dynein also plays (directly or indirectly) a role in the control of cMT length. Those combineddynein actions prevent nuclear clustering in A. gossypii and thus reveal a novel cellular role for dynein.159. Quantification of the thigmotropic response of Neurospora crassa to microfabricated slides with ridges of defined height and topography. KarenStephenson 1 , Fordyce Davidson 2 , Neil Gow 3 , Geoffrey Gadd 1 . 1) Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee,United Kingdom; 2) Division of Mathematics, University of Dundee, Dundee, United Kingdom; 3) Institute of Medical Sciences, University of Aberdeen,Aberdee, United Kingdom.Thigmotropism is the ability of an organism to exhibit an orientation response to a mechanical stimulus. We have quantified the thigmotropic responseof Neurospora crassa to microfabricated slides with ridges of defined height and topography. We show that mutants that lack the formin BNI-1 and theRho-GTPase CDC-42, an activator of BNI-1, had an attenuated thigmotropic response. In contrast, null mutants that lacked cell end-marker protein TEA-1and KIP-A, the kinesin responsible for its localisation, exhibited significantly increased thigmotropism. These results indicate that vesicle delivery to thehyphal tip via the actin cytoskeleton is critical for thigmotropism. Disruption of actin in the region of the hyphal tip which contacts obstacles such as ridgeson microfabricated slides may lead to a bias in vesicle delivery to one area of the tip and therefore a change in hyphal growth orientation. This mechanismmay differ to that reported in Candida albicans in so far as it does not seem to be dependent on the mechanosensitive calcium channel protein Mid1. TheN. crassa Dmid-1 mutant was not affected in its thigmotropic response. Although it was found that depletion of exogenous calcium did not affect thethigmotropic response, deletion of the spray gene, which encodes an intracellular calcium channel with a role in maintenance of the tip-high calciumgradient, resulted in a decrease in the thigmotropic response of N. crassa. This predicts a role for calcium in the thigmotropic response. Our findingssuggest that thigmotropism in C. albicans and N. crassa are similar in being dependent on the regulation of the vectorial supply of secretory vesicles, butdifferent in the extent to which this process is dependent on local calcium-ion gradients.160. Specificity determinants of GTPase recognition by RhoGEFs in Ustilago maydis. Britta A.M. Tillmann 1 , Kay Oliver Schink 2 , Michael Bölker 1 . 1) Philipps-Universität Marburg FB Biologie, AG Bölker Karl-von-Frisch-Str. 8 35032 Marburg, Germany; 2) Department of Biochemistry, Institute for Cancer ResearchThe Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway.Small GTPases of the Rho family act as molecular switches and are involved in the regulation of many important cellular processes. They are activated byspecific guanine nucleotide exchange factors (Rho-GEFs). Rho-GTPases interact in their active, GTP-bound state with downstream effectors and triggervarious cellular events. The number of Rho-GEFs and downstream effectors exceeds the number of GTPases. This raises the question how signallingspecificity is achieved. In recent years it became evident that correct signalling depends on both the specificity of the activating Rho-GEF and on scaffoldingproteins that connect the activators with specific downstream effectors. Here, we analysed the Cdc42-specific U.maydis Rho-GEFs Don1, Its1 and Hot1andthe Rac1-specific Rho-GEF Cdc24 for their role in Cdc42 and Rac1 signalling both in vivo and in vitro. We observed that the recognition mechanisms forCdc42 differ between Hot1 and the other Cdc42-specific Rho-GEFs. While a single amino acid at position 56 of Cdc42 and Rac1 is critical for specificrecognition by Don1, Its1 and Cdc24, Hot1 is insensitive to changes at this position. Instead, Hot1 relies on a different set of amino acids to bind its specifictarget Cdc42. We could demonstrate that this unusual mechanism to discriminate between different Rho-type GTPases is also used by the mammalianorthologue of Hot1, TUBA1. These data allowed us to generate a chimeric Cdc42/Rac1 GTPase which can be activated by both Cdc42- and Rac1-specificRho-GEFs with comparable efficiency. Importantly, such a chimeric GTPase was able to complement the morphological phenotypes of Cdc42 and Rac1deletion mutants in vivo.161. Moisture dependencies of P. Rubens on a porous substrate. K.A. van Laarhoven 1 , F.J.J. Segers 2 , J. Dijksterhuis 2 , H.P. Huinink 1 , O.C.G. Adan 1 . 1)Eindhoven University of Technology, Eindhoven, Netherlands; 2) CBS - KNAW, Utrecht, Netherlands.Fungal growth indoors can lead to both disfigurement of the dwelling and medical problems such as asthma. It is generally accepted that the primarycause for mould growth is the presence of moisture. Strategies to prevent fungal growth are therefore often based on controlling indoor humidity. Still,mould is often encountered in ventilated buildings that are considered to be relatively dry. Preliminary experiments showed that fungi can survive onporous materials due to short intervals of favorable circumstances; even when - on average - conditions for growth are not met. This suggests that theinteractions between porous materials and the fluctuating indoor humidity play an important role in a colony’s survival. We study this interplay betweenindoor climate, substrate water household and fungal growth. A property of water that is crucial for fungal growth is water activity (a w). This propertydetermines a fungus’s ability to take up water. The effect of a w on fungal growth has been determined in the past by extensive growth experiments onagar, and many previous studies of growth on building materials take this parameter into account. Up till now, however, little attention has been paid tothe water content (q) of a substrate, which represents the amount of water that is physically present in a system. In most porous materials, even when awis relatively high, only little water is present. We suspect therefore that growth on porous substrates is limited by water content (whereas on agar, q isalways close to 100% and will therefore be of little concern). We performed growth experiments with P. rubens inoculated on gypsum while separatelycontrolling q and a w. Video microscopy was used to monitor the germination and subsequent growth of hyphae. The early development of the fungus was160