Program Book - 27th Fungal Genetics Conference

FULL POSTER SESSION ABSTRACTSpotential application in biomass bioconversion to e.g. higher value chemicals or biofuels.698. Antioxidant adaptation by Eugenol and its derivatives and their affect on the expression of virulence in candida species. Aijaz Ahmad, NikhatManzoor. Bioscience, Jamia Millia Islamia, New Delhi, Delhi, India.Present work investigates the antifungal activity and mode of action of eugenol (EUG), and its three derivatives- methyl eugenol, thymol and carvacrol.EUG and its derivatives were tested for antifungal activity by standard methods of CLSI. These varied in their mechanism of action depending upon theperiod of exposure. Short exposures of 5-15 minutes resulted in reduced H+ efflux by the H+-pump. From our studies we conclude that EUG and itsderivatives induce production of free radicals which stimulates the enzyme SOD. An increased SOD activity resulted in an increase in the concentration ofH2O2 which further stimulates the peroxide eliminating enzyme, primarily GPx. It is noteworthy that the levels of GSH an essential substrate of GPx weredrastically reduced by the test compounds and this reduction gets even greater as increased levels of H2O2 decrease the activity of G6PDH which providesreducing equivalents to GR, an enzyme that recycles GSH from GSSG. Decreased G6PDH activity aids further in the reduction of GSH. Again, reducedavailability of GSH explains decreased GPx activity. Another enzyme to eliminate H2O2 is catalase, which triggers a cellular response leading to an increasein its activity. Hence increase in the activity of two important antioxidant enzymes SOD and catalase, clearly demonstrates an increase in the concentrationof ROS when the Candida were exposed to the EUG and derivatives. These enzymatic responses were not enough to defend the cell completely against ahigh rise in ROS and therefore did not meet the required cellular antioxidant demand. Ultimately, the outburst of free radical production led to severe lipidperoxidation. Cell death on exposure to EUG and its derivatives hence may be due to (i) decrease in the rate of H+efflux (ii) reduced ergosterol content (iii)Induction of oxidative stress in the cell (iv) These processes impair membrane structure and function which form lesions. Infection process of Candida ischaracterized by crucial pathogenicity markers. The process of germ tube induction followed by the secretion of hydrolytic enzymes help in the invasion ofthe host cells. The expression profile of selected genes associated with Candida virulence by RT-PCR showed a reduced expression of HWP1, SAP1 andPLB2 genes in Candida treated with EUG and its derivatives.699. Elevation of chitin is linked with multiparallel mechanisms in response to C. albicans cell wall stress. F. Nogueira, L. Walker, C. Munro, N. Gow.Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom.The role of the MAPK, Ca 2+ /calcineurin and cAMP/PKA signal transduction pathways in regulating the Candida albicans cell wall stress response wasinvestigated. A library of mutants lacking receptors, signalling elements and transcription factors were screened for alterations in the ability to respond toa range of cell wall stressing agents, including CaCl 2, Calcofluor White and caspofungin. Pre-treatment of wild-type cells with CaCl 2 and CFW, activates theCa 2+ /calcineurin and PKC pathways, leading to an increase in chitin content, and reduced susceptibility to caspofungin. Although elevation of cell wall chitincontent often resulted in decreased sensitivity to caspofungin, we show here that some strains with increased chitin levels remained sensitive tocaspofungin. The results show that elevation of chitin is a common property of a range of mutants that are affected in coordinating cell wall stresspathways, but that multiple mechanisms are likely to operate in maintaining the robustness of the C. albicans cell wall.700. Prezygotic and postzygotic control of uniparental mitochondrial DNA inheritance in Cryptococcus neoformans. Rachana Gyawali, Xiaorong Lin.Biology, Texas A&M University, College Station, TX.Uniparental inheritance of mitochondrial DNA is pervasive in non-isogamic higher eukaryotes during sexual reproduction and postzygotic and/orprezygotic factors are shown to be important in ensuring such inheritance pattern. Although the fungus Cryptococcus neoformans undergoes sexualproduction with isogamic partners of opposite mating types a and a, most progeny derived from such mating events inherit the mitochondrial DNA fromthe a parent. The homeodomain protein complex Sxi1a/Sxi2a, formed in the zygote after a-a cell fusion, was previously shown to play a role in thisuniparental mtDNA inheritance. Here, we defined the timing of the establishment of the mtDNA inheritance pattern during the mating process anddemonstrated a critical role in determining the mtDNA inheritance pattern by a prezygotic factor Mat2. Mat2 is the key transcription factor that governsthe pheromone sensing and response pathway, and it is critical for the early mating events that lead to cell fusion and zygote formation. We show thatMat2 governs mtDNA inheritance independent of the postzygotic factors Sxi1a/Sxi2a, and the cooperation between these prezygotic and postzygoticfactors help achieve stricter uniparental mitochondrial inheritance in this eukaryotic microbe.701. SIS, a sex genome defense mechanism operating in Cryptococcus neoformans. Xuying Wang, Sabrina Darwiche, Joseph Heitman. Department ofMolecular Genetics and Microbiology, Duke University Medical Center, Durham, NC.Cryptococcus neoformans is a human fungal pathogen that undergoes a dimorphic transition from yeast to hyphae during a-a opposite-sex mating and a-a unisexual reproduction (same-sex mating). Infectious spores are generated during both processes. We previously identified a sex induced silencing (SIS)pathway in the C. neoformans serotype A var. grubii lineage, in which tandem transgene arrays trigger RNAi-dependent gene silencing at a high frequencyduring a-a opposite-sex mating, but at an ~250-fold lower frequency during asexual mitotic vegetative growth. Here we report that SIS also operatesduring a-a unisexual reproduction. A self-fertile strain containing either SXI2a-URA5 or NEO-URA5 transgene arrays exhibited an elevated silencingfrequency during solo and unisexual mating compared with mitotic vegetative growth. We also found that SIS operates at a similar efficiency on transgenearrays of the same copy number during either a-a unisexual reproduction or a-a opposite-sex mating. URA5-derived small RNAs were detected in thesilenced progeny of a-a unisexual reproduction and RNAi core components were required, providing evidence that SIS induced by same-sex mating is alsomediated by RNAi via sequence-specific small RNAs. This study, together with our previous finding of SIS in a-a opposite-sex mating of the C. neoformansserotype A var. grubii lineage, demonstrates that SIS is a conserved process between the divergent C. neoformans serotype A and serotype D siblingspecies. In each case, our data show that the SIS RNAi pathway operates to defend the genome via squelching transposon activity during the sexual cycles.Thus, our discovery of SIS brings a fresh perspective to meiotic silencing involving the upregulation of RNAi pathways as a strategy to guard genomicintegrity during sex. More importantly, the presence of SIS in both a-a unisexual reproduction and a-a opposite-sex mating indicate that SIS may betriggered by the shared pheromone sensing Cpk1 MAPK signal transduction cascade. Ongoing studies focus on defining at a mechanistic level how the SISRNAi pathway is initiated, including identifying new components involved in SIS.702. Effects of the use of biocontrol agent (Phlebiopsis gigantea) on fungal communities of Picea abies stumps. E. Terhonen 1 , H. Sun 1 , M. Buée 2 , R.Kasanen 1 , L. Paulin 3 , F. Asiegbu 1 . 1) University of Helsinki, Department of Forest Sciences, P.O.Box 27, FIN-00014, University of Helsinki, Finland; 2) INRA,UMR 1136 INRA/Nancy Université Interactions Arbres/Microorganismes, INRA-Nancy, 54280 Champenoux, France; 3) DNA Sequencing and Genomics Lab,Institute of Biotechnology, University of Helsinki, P.O. Box 56, FIN-00014 Helsinki, Finland.The saprotrophic fungus Phlebiopsis gigantea has for several years been used as a biocontrol agent against pathogen Heterobasidion annosum. Thispathogen is the major cause of root rot disease in conifers that results in economic losses estimated at 50 million euros to Finnish forestry. A major27th Fungal Genetics Conference | 293