Program Book - 27th Fungal Genetics Conference

FULL POSTER SESSION ABSTRACTS96. Cellular morphogenesis of Aspergillus nidulans conidiophores: a systematic survey of protein kinase and phosphatase function. Lakshmi PreethiYerra, Steven Harris. University of Nebraska-Lincoln, Lincoln, NE.In the filamentous fungus Aspergillus nidulans, the transition from hyphal growth to asexual development is associated with dramatic changes inpatterns of cellular morphogenesis and division. These changes enable the formation of airborne conidiophores that culminate in chains of sporesgenerated by repeated budding of phialides. Our objective is to characterize the regulatory modules that mediate these changes and to determine howthey are integrated with the well-characterized network of transcription factors that regulate conidiation in A. nidulans. Because protein phosphorylationis likely to be a key component of these regulatory modules, we have exploited the availability of A. nidulans post-genomic resources to investigate theroles of protein kinases and phosphatases in developmental morphogenesis. We have used the protein kinase and phosphatase deletion mutant librariesmade available by the Fungal Genetics Stock Center to systematically screen for defects in conidiophore morphology and division patterns. Our initialresults implicate ANID_11101.1 (=yeast Hsl1/Gin4) in phialide morphogenesis, and also reveal the importance of ANID_07104.1 (=yeast Yak1) in themaintenance of cell integrity during asexual development. Additional deletion mutants with reproducible defects have been identified and will bedescribed in detail. We will also summarize initial results from double mutant analyses that attempt to place specific protein kinase deletions within theregulatory network that controls conidiation.97. The Putative Guanine Nucleotide Exchange Factor RicA Mediates Upstream Signaling for Growth and Development in Aspergillus. Nak-Jung Kwon 1 ,Hee Soo Park 2 , Seunho Jung 3 , Sun Chang Kim 4 , Jae-Hyuk Yu 1,2 . 1) Dept Bacteriology, University of Wisconsin, Madison, WI. USA; 2) Molecular andEnvironmental Toxicology Center, University of Wisconsin, Madison, WI, USA,; 3) Department of Bioscience and Biotechnology, and Center forBiotechnology Research in UBITA, Konkuk University, Seoul, Republic of Korea; 4) Department of Biological Sciences, Korea Advanced Institute of Scienceand Technology, Dae-Jon, Republic of Korea.Heterotrimeric G proteins (G proteins) govern growth, development, and secondary metabolism in various fungi. Here, we characterized ricA, whichencodes a putative GDP/GTP exchange factor for G proteins in the model fungus Aspergillus nidulans and the opportunistic human pathogen Aspergillusfumigatus. In both species, ricA mRNA accumulates during vegetative growth and early developmental phases, but it is not present in spores. The deletionof ricA results in severely impaired colony growth and the total (for A. nidulans) or near (for A. fumigatus) absence of asexual sporulation (conidiation). Theoverexpression (OE) of the A. fumigatus ricA gene (AfricA) restores growth and conidiation in the DAnricA mutant to some extent, indicating partialconservation of RicA function in Aspergillus. A series of double mutant analyses revealed that the removal of RgsA (an RGS protein of the GanB Gasubunit), but not sfgA, flbA, rgsB, or rgsC, restored vegetative growth and conidiation in AnricA. Furthermore, we found that RicA can physically interactwith GanB in yeast and in vitro. Moreover, the presence of two copies or OE of pkaA suppresses the profound defects caused by DAnricA, indicating thatRicA-mediated growth and developmental signaling is primarily through GanB and PkaA in A. nidulans. Despite the lack of conidiation, brlA and vosAmRNAs accumulated to normal levels in the ricA mutant. In addition, mutants overexpressing fluG or brlA (OEfluG or OEbrlA) failed to restore developmentin the AnricA mutant. These findings suggest that the commencement of asexual development requires unknown RicA-mediated signaling input in A.nidulans.98. Evidence for a role of peroxisomes in microtubule organization. Ying Zhang, Andreas Herr, Reinhard Fischer. Karlsruhe Institute of Technology,Karlsruhe, Germany.In Aspergillus nidulans spindle pole bodies (SPBs) and septum-associated microtubule-organizing centres (sMTOCs) polymerize cytoplasmic microtubules.Previously, we identified a novel MTOC-associated protein, ApsB (Schizosaccharomyces pombe mto1), whose absence affected MT formation fromsMTOCs more than from SPBs, suggesting that the two protein complexes are organized differently (Suelmann et al., 1998; Veith et al., 2005). In addition,we discovered that ApsB localizes to a subclass of peroxisomes apparently without a peroxisomal targeting motif. However, we found that ApsB interactswith the Woronin body protein HexA, which has a PTS1 motif at the C-terminus (Zekert er al., 2010). Our hypothesis is that ApsB is imported toperoxisomes by a piggyback import mechanism along with HexA. To further investigate the role of peroxisomes in microtubule orgnization, We created adeletion mutant of pexC. PexC is an essential protein for peroxisomal biogenesis (Heiland & Erdmann, 2005). The pexC mutant partially phenocopied theapsB mutant, which shows reduced sporulation and nuclear migration defects in comparison to wild type. The number of astral and cytoplasmicmicrotubules and the activities of sMTOCs and SPBs was reduced in the pexC mutant in comparison to wild type. sMTOC activity was more affected thanthe SPB activity, which again resembles the phenotype of the apsB mutant. In conclusion, peroxisomes play a role in microtubule organization throughApsB.99. Autophagy promotes survival in aging submerged cultures of the filamentous fungus Aspergillus niger. Maria A. Burggraaf 1,2 , Benjamin M. Nitsche 1,2 ,Gerda Lamers 1 , Vera Meyer 2,3 , Arthur F.J. Ram 1,2 . 1) Institute of Biology Leiden, Molecular Microbiology and Biotechnology, Leiden, The Netherlands; 2)Kluyver Centre for Genomics of Industrial Fermentation, Delft, The Netherlands; 3) Institute of Biotechnology, Applied and Molecular Microbiology, BerlinUniversity of Technology, Berlin, Germany.The filamentous fungus Aspergillus niger is an important and versatile cell factory commonly exploited for the industrial-scale production of a wide rangeof enzymes and organic acids. Although numerous studies have been conducted aiming at improving our knowledge of degradative cellular activities thatdetermine product yields in A. niger including secretion of proteases and the unfolded protein response, there is a catabolic pathway that has yet not beenstudied in this industrially exploited fungus, namely Autophagy. Autophagy is a well conserved catabolic process constitutively active in eukaryotes that isinvolved in cellular homeostasis by targeting of cytoplasmic content and organelles to vacuoles. Autophagy is strongly induced by limitation of nutrientsincluding carbon, nitrogen and oxygen and is clearly associated with cell death. We previously demonstrated that the accumulation of empty hyphalcompartments and secondary regrowth in carbon starved submerged batch cultures of A. niger were accompanied by a joint transcriptional induction ofautophagy genes. In this study we examined the role of autophagy by deleting the atg1, atg8 and atg17 orthologues in A. niger and phenotypicallyanalyzing the deletion strains in surface and submerged cultures. Our results indicate that atg1 and atg8 are essential for efficient autophagy whereasdeletion of atg17 has little to no effect on autophagy. Depending on the stressor, autophagy deficiency renders A. niger both more resistant and moresensitive to oxidative stress. Fluorescence microscopy showed that mitochondrial turnover upon carbon depletion in submerged cultures is severelyblocked in autophagy impaired mutants. Furthermore, automated image analysis demonstrated that autophagy promotes survival in maintained carbonstarved cultures of A. niger. Taken together, our results suggest that besides its function in nutrient recycling, autophagy plays important roles inphysiological adaptation by organelle turnover and protection against cell death upon carbon depletion in submerged cultures.27th Fungal Genetics Conference | 145