Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSThursday, March 14 3:00 PM–6:00 PMHeatherCytoskeleton, Motors, and Intracellular TransportCo-chairs: Samara Reck-Peterson and Ping WangThe molecular basis of extended dynein run-length. Sreedhar Kilaru, Martin Schuster, Gero Steinberg. School of Bioscinces, Univ Exeter, EX4 4QD Exeter,UK.Dynein is a minus-end directed motor that utilises ATP to transport organelles along microtubules. In fungi, a major "cargo" of dynein are earlyendosomes that are taken over long distance from the plus-ends near the growing apex to the central part of the hyphal cell. In cell-free assays it wasshown that single dynein motors can only overcome 1 micrometer, and long-distance motility of organelles requires binding of several dynein motors thatcooperate to extend the transport distance. We recently showed that this does not apply to the fungus Ustilago maydis. Here, single dynein motors moveover 30 micrometers, raising the question of the underlying molecular mechanism for this extraordinary motor performance. This talk will provide acomprehensive explanation for this phenomenon.The role of microtubule-based motors in the spatiotemporal control of autophagy. Martin Egan, Mark McClintock, Samara Reck-Peterson. Cell Biology,Harvard Medical School, Boston, MA.Autophagy is a highly conserved eukaryotic process in which components of the cytoplasm, including damaged organelles and misfolded proteins, aresequestered into double membrane-bound vesicles called autophagosomes that are subsequently delivered to the vacuole for recycling. In fungi,autophagy is linked to cellular remodeling and differentiation, while in mammals dysfunction in the autophagy pathway has been implicated in cancer andneurodegenerative diseases. Here we explore the role of microtubule-based motors in the spatiotemporal control of autophagy in the model filamentousfungus Aspergillus nidulans. Using a molecular genetic and live-cell imaging approach, we identify the motors responsible for autophagosome motility, anddissect their role in the delivery and fusion of autophagic vesicles with the vacuolar system. Furthermore, we examine the role of microtubule-basedmotors in the clearance of aggregation-prone proteins associated with motor neuron disease, and determine the effect of these aggregates on normalmicrotubule-based transport processes.Microtubule-dependent co-transport of mRNPs and endosomes. Sebastian Baumann 1,2 , Thomas Pohlmann 1,2 , Andreas Brachmann 2,3 , MichaelFeldbrügge 1,2 . 1) Heinrich-Heine University Düsseldorf, Institute for Microbiology, 40204 Düsseldorf, Germany; 2) Max Planck Institute for TerrestrialMicrobiolgy, Department of Organismic Interactions, Karl-von-Frisch-Str. 10, 45043 Marburg, Germany; 3) Biocenter of the Ludwigs Maximilians UniversityMunich, Genetics Section, Grosshaderner Str. 2-4, 82152 Planegg-Martinsried, Germany.Long-distance transport of mRNAs is important in determining polarity in eukaryotes. Molecular motors shuttle large messenger ribonucleoproteincomplexes (mRNPs) containing mRNAs, RNA-binding proteins and associated factors along microtubules. However, precise mechanisms including theinterplay of molecular motors and a potential connection to membrane trafficking remain elusive. In recent studies we identified the RNA-binding proteinRrm4 as the key player in microtubule-dependent mRNA transport in Ustilago maydis. Combining in vivo CLIP and RNA-live imaging revealed a subset ofmRNAs that are bound by Rrm4 and transported processively throughout the hyphae. Studying the molecular motors revealed that shuttling is mediatedby Kin3 and Dyn1/2. The same set of motors acts in endosome trafficking and indeed, studying the SNARE Yup1 and the small GTPase Rab5 we found cotransportwith endosomes as a novel mechanism for mRNP transport. Currently, we address the link between mRNAs and endosomes.Role of tea1 and tea4 homologs in cell morphogenesis in Ustilago maydis. Flora Banuett, Woraratanadharm Tad, Lu Ching-yu, Valinluck Michael.Biological Sciences, California State University, Long Beach, CA.We are interested in understanding the molecular mechanisms that govern cell morphogenesis in Ustilago maydis. This fungus is a member of theBasidiomycota and exhibits a yeast-like and a filamentous form. The latter induces tumor formation in maize (Zea mays) and teosinte (Zea mays subsp.parviglumis and subsp. mexicana). We used a genetic screen to isolate mutants with altered cell morphology and defects in nuclear position. One of themutants led to identification of tea4. Tea4 was first identified in Schizosaccharomyces pombe, where it interacts with Tea1 and other proteins thatdetermine the axis of polarized growth. Tea4 recruits a formin (For3), which nucleates actin cables towards the site of growth, and thus, polarizessecretion (Martin et al., 2005). Tea1 and Tea4 have been characterized in Aspergillus nidulans and Magnaporthe oryzae (Higashitsuji et al., 2009; Patkar etal., 2010; Takeshita et al., 2008; Yasin et al., 2012). Here we report the characterization for the first time of the Tea4 and Tea1 homologs in theBasidiomycota. The U. maydis tea4 ORF has coding information for a protein of 1684 amino acid residues that contains a Src homology (SH3) domain, aRAS-associating domain, a phosphatase binding domain, a putative NLS, and a conserved domain of unknown function. All Tea4 homologs in theBasidiomycota contain a RA domain. This domain is absent in Tea4 homologs in the Ascomycota, suggesting that Tea4 performs additional functions in theBasidiomycota. We also identified the Umtea1 homolog, which codes for a putative protein of 1698 amino acid residues. It contains three Kelch repeats.The Tea1 homologs in the Ascomycota and Basidiomycota contain variable numbers of Kelch repeats. The Kelch repeat is a protein domain involved inprotein-protein interactions. The tea1 gene was first identified in S. pombe and is a key determinant of directionality of polarized growth (Mata and Nurse,1997). To understand the function of tea1 and tea4 in several cellular processes in U. maydis, we generated null mutations. We demonstrate that tea4 andtea1 are necessary for the axis of polarized growth, cell polarity, normal septum positioning, and organization of the microbutubule cytoskeleton. We alsodetermined the subcellular localization of Tea1::GFP and Tea4::GFP in the yeast-like and filamentous forms.27th Fungal Genetics Conference | 51