Program Book - 27th Fungal Genetics Conference

FULL POSTER SESSION ABSTRACTSMicrobiology, Marburg, Hessen, Germany; 2) Heinrich Heine University Düsseldorf, Institute for Microbiology, Universitätsstrabe 1, 40225 Düsseldorf; 3)Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.Secreted fungal proteins play a crucial role during the biotrophic interaction between the smut fungus Ustilago maydis and its host plant Zea mays. Inthe last decade it has been well established that proteins without a signal peptide can also be targeted to the outside of the cell in an ER/ Golgiindependent manner. We want to identify such unconventionally secreted proteins in U. maydis and investigate their potential function as pathogenicityfactors. Our approach is based on affinity purification of tagged candidate proteins, detected in the apoplastic fluid of infected maize leaves. Four oftwelve candidate proteins tested so far could be detected in culture supernatants. One candidate protein, Um11938, displays 55 % amino acid similarity tothe human sterol carrier protein 2 (SCP2) and we were able to demonstrate that it co-localizes intracellularly with peroxisomes. Mammalian SCP2 isdetected in peroxisomes but also found in the cytoplasm. It interacts with a variety of phospholipids as well as cholesterol and has been implicated in nonvesicular cholesterol transport and in regulating lipid rafts (Schroeder et al., 2007). um11938 deletion strains of U. maydis are severely compromised invirulence and peroxisomal localization of Um11938 is required to fulfill its function as a pathogenicity factor. um11938 deletion strains display no growthdefect on minimal media supplemented with different fatty acids as sole carbon source, suggesting that the Um11938 protein is not involved in bona fideb-oxidation. The results of ongoing experiments aimed to differentiate whether the pathogenicity relevant function of Um11938 is performedextracellularly or within the fungal peroxisomes will also be presented.Schroeder F., Atshaves B.P., McIntosh A.L., Gallegos M., Storey S.M., Parr R.D., Jefferson J.R., Ball J.M. and Kier A.B. Sterol carrier protein-2: New roles inregulating lipid rafts and signaling, Biochim. Biophys. Acta 1771 (2007) 700-718.626. Identification of a key regulator for the developmental switch leading to sporogenesis in Ustilago maydis. Marie Tollot, Regine Kahmann.Organismic Interactions, MPI Marburg, Marburg, Hessen, Germany.Ustilago maydis is a biotrophic pathogen of maize. Its life cycle begins with the mating of two compatible haploid sporidia to form a dikaryotic infectiousfilament. After penetrating the plant cuticle, the dikaryon spreads inside the plant tissues and induces the formation of tumors. At a defined time ofdevelopment, the sporogenesis program begins in tumor tissue: the hyphae start to fragment into individual cells that eventually differentiate into matureteliospores. The isolation of several mutants affected in spore formation has shown that a tight regulation of the cAMP signaling pathway and the activityof two transcriptional regulators Hda1 and Rum1, potentially functioning in the same chromatin modifying complex, are required. We have identified anew regulator for the sporogenesis program of U. maydis. It belongs to a family of transcriptional regulators that are characterized by the presence of aWOPR DNA binding domain. The best studied member of this family is Wor1 from Candida albicans which plays a key role in the switch from the nonpathogenicto the pathogenic form of the fungus. The U. maydis wor1 homologue um05853, was deleted in the compatible haploid strains FB1 and FB2.The deletion mutants were able to mate and to infect maize as efficiently as the wild-type. However, although the tumor rate was similar, no spores couldbe detected in plants infected by the deletion mutants. Confocal microscopy of the mutant dikaryon revealed that hyphal fragmentation and consequentlyspore maturation were not occurring. The hyphae were still spreading at a time when the wild type dikaryon had already formed mature spores. To furtherinvestigate the role of um05853, we expressed the gene in a haploid strain where the filamentous program can be induced in axenic culture via expressionof a functional b-heterodimer. The cells failed to switch to filaments, started to enlarge and showed septation, with each section containing one nucleus.This result suggests that Um05853 is able to counteract the b function and trigger fragmentation. Preliminary results show that Um05853 mightdownregulate several b-dependent genes including the gene encoding the master regulator Rbf1. We are currently identifying targets of Um05853 using amicroarray approach and expect that these results will highlight how Um05853 controls spore formation.627. Genetic characterization of virulence in the Pyrenophora teres f. teres - barley pathosystem. Timothy L. Friesen 1,2 , Rachel A. Shjerve 2 , Justin D. Faris 1 ,Robert S. Brueggeman 2 . 1) Cereal Crops Research Unit, USDA-ARS, Fargo, ND; 2) Department of Plant Pathology, North Dakota State University, Fargo, ND.Pyrenophora teres f. teres is a necrotrophic fungal pathogen that causes net form net blotch (NFNB) on barley throughout the world. Several resistancesources have been identified but few are effective against all P. teres f. teres pathotypes, indicating that the pathogen has an arsenal of effectors that areinvolved in disease induction. Genetic analysis identified two barley genotypes, Rika and Kombar, that each harbor unique dominant susceptibility geneslocated at the centromeric region of barley chromosome 6H. P. teres f. teres isolate 15A is virulent on Kombar but avirulent on Rika whereas P. teres f.teres isolate 6A is virulent on Rika but avirulent on Kombar. Based on the necrotrophic effector model, 15A and 6A each secrete unique effectors that aredirectly or indirectly interacting with genes on chromosome 6H in Kombar and Rika, respectively. A linkage map was generated using a mappingpopulation developed from a sexual cross between 15A and 6A, and 118 progeny were phenotyped on barley genotypes Rika and Kombar. Two majorvirulence QTL derived from 15A contributed to virulence on Kombar, and two additional unique virulence QTL derived from 6A contributed to virulence onRika. All susceptibility loci in the host mapped to the same region on barley chromosome 6H. Therefore, it is likely that at least four necrotrophic effectorspresent throughout the P. teres f. teres genome are interacting with host susceptibility genes located in one region of barley chromosome 6H. Theseresults strongly indicate that the NFNB-barley compatibility is at least partially due to necrotrophic effector-host susceptibility gene interactions that resultin disease induction. Currently, we are using a genotype by sequencing (GBS) approach to generate a saturated map to identify candidate genes in the QTLregions in order to clone and characterize the effector genes involved in the NFNB interaction.27th Fungal Genetics Conference | 275