Program Book - 27th Fungal Genetics Conference

FULL POSTER SESSION ABSTRACTS170. Sex determination directs uniparental mitochondrial inheritance in Phycomyces blakesleeanus. Viplendra P.S. Shakya, Alexander Idnurm. School ofBiological Sciences, University of Missouri-Kansas City, MO.Uniparental inheritance (UPI) of mitochondria is common among eukaryotes. Various mechanisms have been suggested for UPI, but the underlyingmolecular basis is yet to be fully explained. We used a series of genetic crosses to establish that the sexM and sexP genes in the mating type locus controlthe UPI of mitochondria in the Mucoromycotina fungus Phycomyces blakesleeanus. Inheritance is from the (+) sex type, and is associated with degradationof the mitochondrial DNA from the (-) parent in the developing zygospore. Hence, the UPI of mitochondria in Phycomyces shows that this process can bedirectly controlled by genes that determine sex identity, independent of cell size or the complexity of the genetic composition of a sex chromosome.171. Exploring the role of a highly expressed, secreted tyrosinase in Histoplasma capsulatum mycelia. Christopher F. Villalta 1 , Dana Gebhart 2 , Anita Sil 1 .1) Microbiology and Immunology, UCSF, San Francisco, CA; 2) AvidBiotics Corporation, South San Francisco, California, United States of America.The human pathogen Histoplasma capsulatum is a dimorphic ascomycete that resides in the soil at ambient temperature as a mycelium. Infection ofimmunocompetent individuals with H. capsulatum occurs when mycelial fragments and associated conidia are inhaled. These fungal cells undergo aconversion to a budding-yeast form in response to mammalian body temperature. We are interested in genes that specify the biological attributes ofeither the infectious form (mycelia or conidia) or the parasitic form (yeast). Previous work from our lab compared the gene expression profiles of mycelia,conidia, and yeast cells to determine genes that were preferentially expressed in each developmental form. We determined that the TYR1 gene, whichencodes a putative polyphenol oxidase, or “tyrosinase”, is highly differentially expressed in the mycelial form of H. capsulatum. Notably, the H. capsulatumgenome contains seven tyrosinases, all of which are more highly expressed in mycelia and conidia compared to yeast. These enzymes contain a conservedtyrosinase domain, but their function in pathogenic fungi has not been investigated. Our expression data suggest that tyrosinases play a specific role in thebiology of H. capsulatum filaments and spores. Strains that either lack TYR1 or express deregulated TYR1 display altered growth properties during themycelial phase. Interestingly, our preliminary results indicate that Tyr1 is secreted into the media during mycelial-phase growth. We are currentlyinvestigating whether Tyr1 affects mycelial growth by modifying a cell-surface or secreted molecule. Additionally, we are determining if Tyr1 is importantin the production of infectious spores.172. Hypobranching induced by both anti-oxidants and ROS control gene knockouts in Neurospora crassa. Michael K. Watters, Jacob Yablonowski, TaylerGrashel, Hamzah Abduljabar. Dept Biol, Valparaiso Univ, Valparaiso, IN.Wild-type Neurospora grows with the same branch density (statistical distribution of physical distances between branch points along a growing hypha) ata wide range of incubation temperatures. Previous work highlighted the impact of reactive oxygen species (ROS) control on branch density. Here we reportthe branching effects of selected ROS control gene knockout mutants; the impact of exogenously added anti-oxidants. In all ROS control mutants tested,growth was shown to branch tighter when grown at higher temperatures and looser when grown at lower temperatures. The branch density displayed bythe ROS mutants at low temperature is measurably hypobranched. In tests on wild type Neurospora, added Ascorbic Acid and Glutathione producedunusual branching patterns. Hypha exposed to Ascorbic Acid or Glutathione display a distribution of branching with two distinct maxima. They show anincrease in both very closely spaced branching as well as an increase in more distantly spaced branching. At lower doses however, hypobranching, again, isobserved with average branch density being linearly related to the dose of added anti-oxidants. We also report on the interaction between ROS mutantsand added anti-oxidants.173. Septum formation starts with the establishment of a septal actin tangle (SAT) at future septation sites. Diego Delgado-Álvarez 1 , S. Seiler 2 , S.Bartnicki-García 1 , R. Mouriño-Pérez 1 . 1) CICESE, Ensenada, Mexico; 2) Georg August University, Göttingen, Germany.The machinery responsible for cytokinesis and septum formation is well conserved among eukaryotes. Its main components are actin and myosins, whichform a contractile actomyosin ring (CAR). The constriction of the CAR is coupled to the centripetal growth of plasma membrane and deposition of cell wall.In filamentous fungi, such as Neurospora crassa, cytokinesis in vegetative hyphae is incomplete and results in the formation of a centrally perforatedseptum. We have followed the molecular events that precede formation of septa and constructed a timeline that shows that a tangle of actin filaments isthe first element to conspicuously localize at future septation sites. We named this structure the SAT for septal actin tangle. SAT formation seems to bethe first event in CAR formation and precedes the recruitment of the anillin Bud-4, and the formin Bni-1, known to be essential for septum formation.During the transition from SAT to CAR, tropomyosin is recruited to the actin cables. . Constriction of the CAR occurs simultaneously with membraneinternalization and synthesis of the septal cell wall.174. Characterization of the Neurospora crassa STRIPAK complex. Anne Dettmann 1 , Yvonne Heilig 1 , Sarah Ludwig 1 , Julia Illgen 2 , Andre Fleissner 2 , StephanSeiler 1 . 1) Institute for Biology II, Molecular Plant Physiology, Freiburg, Germany; 2) Biozentrum, Technische Universität Braunschweig,Germany.The majority of fungi grow by polar tip extension, branching and intercellular fusion to generate a supra-cellular, syncitial mycelium. This hyphal networkformation increases the fitness of the organisms and is central to the organization and function of the fungal colony. Multiple mutants deficient in hyphalfusion and/or intercellular signaling were characterized in Neurospora crassa, the currently best understood model for interhyphal signaling. Among themare components of the two MAK1 and MAK2 MAP kinase cascades and a cell fusion-specific phosphatase 2A termed the STRIPAK complex. While theMAK2 cascade is central for signaling through oscillatory recruitment of the MAK2 module to opposing tips of communicating cells, the MAK1 cell wallintegrity pathway is assumed to play a critical role in the cell wall rearrangement after the physical contact of the two partner cells. The mechanisticfunction of the STRIPAK complex and the functional relationship of the three modules is not resolved. By a combination of genetic, biochemical and life cellimaging techniques, we present the characterization of the STRIPAK complex of N. crassa that consists of HAM2/STRIP, HAM3/striatin, HAM4/SLMAP,MOB3/phocein, PPG1/PP2AC and PP2AA. We further describe that the fungal STRIPAK complex localizes to the nuclear envelope and regulates the nuclearaccumulation of the MAP kinase MAK1 in a MAK2-dependent manner.175. Does the CENP-T-W-S-X tetramer link centromeres to kinetochores? Jonathan Galazka, Mu Feng, Michael Freitag. Biochemistry and Biophysics,Oregon State University, Corvallis, OR.In vertebrates, the centromeric proteins, CENP-T, -W, -S and -X, form a tetramer (CENP-T-W-S-X) in vitro that binds DNA [1]. Furthermore, theunstructured N-terminus of CENP-T interacts with the Ndc80 complex at kinetochores [2]. This suggests that CENP-T-W-S-X has a central role in linkingcentromeric DNA to kinetochores. Despite the appeal of this model, there is no evidence that this complex forms in vivo, no information of the DNAsequences it may bind at centromeres and little understanding of how it interacts with canonical nucleosomes. CENP-T, -W, -S, and -X are conserved infungi, including Neurospora [1-3]. Neurospora is an attractive model in which to understand the function of the CENP-T-W-S-X complex as its centromeric27th Fungal Genetics Conference | 163