Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSSaturday, March 16 2:00 PM–5:00 PMNautilusDimorphic TransitionsCo-chairs: Anne Dranginis and Alex AndrianopoulosEpigenetic Switching Regulates the Yeast-Hyphal Transition in Candida albicans. Haoyu Si 1 , Allison Porman 1 , Matthew Hirakawa 1 , Stephen Jones 1 , AaronHernday 2 , Alexander Johnson 2 , Richard Bennett 1 . 1) Mol Microbiol & Immunology, Brown University, Providence, RI; 2) Mol Microbiol & Immunology,UCSF, San Francisco, CA.Candida albicans is a dimorphic yeast that is normally found as a commensal organism in the mammalian gastrointestinal tract. It is also a prevalentopportunistic pathogen able to infect multiple mucosal and internal sites in the human body. A principle feature of C. albicans biology is its ability to growin multiple phenotypic states, including both yeast and filamentous forms. Phenotypic plasticity is also exemplified by the “white-opaque switch”, in whichcells can reversibly transition between the white and opaque states. White and opaque forms differ in multiple aspects including their shape, theirinteraction with host immune cells, their mating competency, and their pathogenesis. Furthermore, white cells are induced to form hyphal filaments whengrown at 37°C, neutral pH, or in the presence of serum, whereas opaque cells do not form filaments in response to these conditions, and this differencecould explain the decreased virulence of opaque cells in models of systemic infection. In this study, we show that opaque cells can undergo the yeastfilamenttransition in response to environmental cues, but that these cues are distinct from those that induce the transition in white cells. For example,growth on low phosphate medium or medium containing the sugar sorbitol induced efficient filamentous growth in opaque cells, while these conditionsdid not induce filamentous growth in white cells. Genetic dissection of the regulation of opaque cell filamentation showed extensive overlap with theregulation of filamentation in white cells, including roles for the established transcriptional regulators Ume6, Efg1, and Tup1. However, genes induced byfilamentous growth in opaque cells showed only limited overlap with those induced during white cell filamentation. Together, these studies indicate thatC. albicans white and opaque cells are both capable of undergoing filamentation but do so in response to different environmental signals and generatedistinct transcriptional profiles, reflecting intrinsic differences in the programming of the two phenotypic states.Extracellular and intracellular signaling orchestrates morphotype-transition and virulence in human pathogen Cryptococcus neoformans. Linqi Wang,Xiuyun Tian, Rachana Gyawali, Xiaorong Lin. Biology, College Station, TX.Interactions with the environment and divergent species drive the evolution of microbes. To sense and rapidly respond to these dynamic interactions,“simple” microbes developed bet-hedging social behaviors, including the construction of heterogeneous biofilm communities and transition betweendifferent morphotypes. The human fungal pathogen Cryptococcus neoformans can undergo morphotype transition between the yeast and the filamentousform. Most recently, we demonstrated that the zinc-finger regulator Znf2 bridges the bi-direction yeast-hypha transition and virulence in this pathogen.One of Znf2 downstream targets is extracellular protein Cfl1. Cfl1 is a cell-wall bound adhesin and a signaling molecule when it is released. This matrixprotein Cfl1 plays a similar but less prominent role than Znf2 in orchestrating morphogenesis and virulence in C. neoformans. Through transcriptomeanalyses and screening Znf2 downstream targets by overexpression, we identified an additional player in the control of morphogenesis and biofilmformation. This factor is an intracellular RNA-binding protein Pum1. As expected, Pum1 affects filamentation in a Znf2 dependent manner. However, theeffect of Pum1 on morphogenesis is independent of Cfl1. The pum1D cfl1D double mutant shows a more severe defect in filamentation than either of thesingle mutant, indicating that Pum1 and Cfl1 act in two parallel pathways. Two of Pum1’s targets, Fad1 and Fad2, form a Cryptococcus-specific adhesinfamily. Like Cfl1, these two extracellular adhesins show regulatory roles in conducting morphogenesis and virulence in C. neoformans and thus may beinvolved in extracellular signaling transduction. Our results indicate that complex regulatory cascades composed of extracellular and intracellular circuitsmay be responsible for mediating morphological transition in response to the cues in the environments and the host.Histoplasma strain variations and differences in pathogenic-phase transcriptomes. Jessica A. Edwards 1 , Chenxi Chen 2 , Megan M. Kemski 1 , Thomas K.Mitchell 2 , Chad A. Rappleye 1 . 1) Microbiology, Ohio State University, Columbus, OH; 2) Plant Pathology, Ohio State University, Columbus, OH.The morphological dimorphism of Histoplasma capsulatum reflects an underlying change in gene expression that is essential for pathogenesis. In theyeast-phase, Histoplasma infects the mammalian lung and proliferates within phagocytic cells. Geographically distinct strains of Histoplasma exhibitdifferences in their relative virulence and in their pathogenic mechanisms. The close similarity in the genome sequences of these diverse strains suggeststhat phenotypic variations result from gene expression differences rather than gene content. To better understand how the transcriptional programtranslates into morphological and pathogenic differences between strains, we profiled the yeast-phase transcriptomes of two Histoplasma strains byRNAseq methodology. For both strains, about 50% of sequence reads align to the genome providing evidence for approximately 9000 genes. Quantitativecomparisons reveal about 200 genes are at least 10-fold differentially expressed between strains, and these include genes related to Histoplasmapathogenesis (SOD3, YPS3, AGS1). The genes encoding the secreted calcium-binding protein (CBP1), histone proteins (H2B, H3, and H4) and an ammoniumtransporter are among the most highly expressed genes overall. Using GFP-transcriptional fusions and their introduction into both strain backgrounds, wedemonstrate that dissimilarity in the transcriptional activity of individual genes reflects variations in the trans-acting factors between strains rather thanthe sequence of the promoters, themselves. These studies lay an essential foundation to facilitate discovery of the factors that contribute to strain-specificvirulence differences of Histoplasma.27th Fungal Genetics Conference | 97