Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSSaturday, March 16 2:00 PM–5:00 PMHeatherLight Sensing and Circadian RhythmsCo-chairs: Luis Larrondo and Reinhard FischerCircadian rhythms in gene expression in Aspergillus nidulans. Maria Olmedo 1,2 , Julio Rodriguez-Romero 3,4 , Julian Röhrig 3 , Martha W. Merrow 1,2 , ReinhardFischer 3 . 1) Institute for Medical Psychology, Ludwig-Maximilians-Universität-München, München, Bavaria, Germany; 2) Department of MolecularChronobiology, University of Groningen, The Netherlands; 3) Institute for Applied Biosciences, Karlsruhe Institute of Technology, Germany; 4) Centre forPlant Biotechnology and Genomics Universidad Politécnica de Madrid(UPM) Campus de Montegancedo Autopista M-40 (Km 38) 28223-Pozuelo de Alarcón(Madrid).The circadian clock is an endogenous timekeeper that allows organisms to predict cyclic changes in their environment derived from the rotationalmovement of the Earth. The fungus Neurospora crassa has substantially contributed to the understanding of the mechanism of the circadian clock, mainlydue to the presence of an easily assayable rhythm in conidiation. Our understanding of circadian rhythms tells us that they are present in most organisms(from bacteria to humans), yet they have been difficult to detect in other fungal species, likely due to the absence of a clear readout. To circumvent thisproblem, we have adopted a tool developed for the study of the clock in Neurospora and other model organism, namely bioluminescent reporter proteins,to study circadian rhythms in Aspergillus nidulans, where a previous report has suggested a circadian clock (Greene et al. 2003). The characterization of theAspergillus clock represents a further step in the understanding of the biology of this fungal genus, which is of great importance for medical, industrial andagricultural reasons. We have produced strains with the promoters of Neurospora clock controlled gene homologs conJ, ccgA and gpdA fused to the (A.nidulans optimized) firefly luciferase ORF. We observe an oscillation in the bioluminescence signal in these strains in constant conditions, implying thepresence of an endogenous oscillator. This free running rhythm is detectable in both constant light and darkness and is entrained by environmentalsignals. Using these reporters we are studying the contribution of the wc (white collar) homologs and other photoreceptors to the Aspergillus clock. Theprotein WC-1 is a central molecule of the best-studied Neurospora oscillator, which also comprises the protein FRQ (FREQUENCY). The absence of a FRQhomolog in Aspergillus implies that the characterization of its clockwork may unveil new components of additional Neurospora oscillators.Circadian clock-gated cell division cycles in Neurospora crassa. C. Hong 1 , J. Zamborszky 1 , M. Baek 1 , K. Ju 1 , H. Lee 1 , L. Larrondo 2 , A. Goity 2 , A. Csikasz-Nagy 3 .1) Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, OH; 2) Departamento de Genética Molecular y Microbiología, Facultad deCiencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile; 3) Randall Division of Cell and Molecular Biophysics, andInstitute for Mathematical and Molecular Biomedicine, King’s College London, London, SE1 UL, UK.Asynchronous nuclear divisions are readily observed in filamentous fungi such as Ashbya gossypii and Neurospora crassa. Our computational simulations,however, predict synchronous circadian clock-gated mitotic divisions if the division cycles of such multinucleated organisms are coupled with circadianrhythms. Based on this hypothesis, we investigate the coupling between the cell cycle and the circadian clock in Neurospora crassa. First, we show WC-1-dependent light-induced expression of stk-29 mRNA (homolog of wee1), which suggests that there exists a conserved coupling between the clock and thecell cycle via STK-29 in Neurospora as in mammals. Second, we demonstrate that G1 and G2 cyclins, CLN-1 and CLB-1, respectively, show circadianoscillations with luciferase bioluminescence reporters. Moreover, clb-1 and stk-29 gene expressions show circadian clock-dependent light-induced phaseshifts, which may alter the timing of divisions. Third, we show circadian clock-dependent synchronized nuclear divisions by tracking nuclear morphologywith histone hH1-GFP reporter. Synchronized divisions occur late in the evening, and they are abolished in the absence of circadian rhythms (frq KO ). Ourfindings demonstrate the importance of circadian rhythms for synchronized mitotic cycles and establish Neurospora crassa as an ideal model system toinvestigate mechanisms that couple the cell cycle and the circadian clock.Light regulates growth, stress resistance and metabolism in the fungal pathogen Aspergillus fumigatus. Kevin K. Fuller, Carol S. Ringleberg, Jennifer J.Loros, Jay C. Dunlap. Genetics, Geisel School of Medicine at Darmouth, Hanover, NH.Light serves as an important environmental cue that influences developmental and metabolic pathways in a variety of fungi. Interestingly, orthologs of aconserved blue light receptor, WC-1, promote virulence in two divergently related pathogenic species, Cryptococcus neoformans and Fusarium oxysporum,suggesting that photosensory systems may be conservatively linked to fungal pathogenesis. Aspergillus fumigatus is the predominant mold pathogen ofimmunocompromised patients, but if and how the organism responds to light has not been described. In this report, we demonstrate that the fungus canindeed sense and distinctly respond to both blue and red portions of the visible spectrum. Included in the A. fumigatus photoresponse is a reduction inconidial germination kinetics, increased hyphal pigmentation, enhanced resistance to acute ultra-violet and oxidative stresses, and an increasedsusceptibility to cell wall perturbation. Through gene deletion analysis we have found that the WC-1 ortholog, LreA, is a bone fide blue light receptor in A.fumigatus that is required for the photopigmentation response. However, the DlreA mutant retains several blue light mediated responses, including thegermination and stress resistance phenotypes , suggesting other blue light receptors are operative in this fungus. We also show that the putative red lightsensing phytochrome, FphA, is involved with some, but not all, blue light specific phenotypes, indicating a complex interaction between red and blue lightphotosystems in A. fumigatus. Finally, whole genome microarray analysis has revealed that A. fumigatus displays broad patterns of gene induction andrepression upon exposure to light. Affected genes are largely metabolic and include those involved in lipid and sterol synthesis, respiration, carbohydratecatabolism, amino acid metabolism and metal ion homeostasis. Taken together, these data demonstrate the importance of the photic environment on thephysiology of A. fumigatus and provide a foundation for future studies into an unexplored area of this important pathogen.90