Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSCommon strategies in plant and human "necrotrophic" pathogens: role of PCD. N. Shlezinger 1 , H. Irme 2 , G. Braus 2 , A. Sharon 1 . 1) Tel Aviv University, TelAviv, Israel; 2) Georg-August University Goettingen, 37077 Goettingen, Germany.Botrytis cinerea is a model system to study pathogenicity of necrotrophic fungi. As inferred by the term "necrotrophic", such pathogens must first killhost cells before they can use them as a source of nutrients. To achieve this, B. cinerea promotes apoptotic cell death in infected plants, which facilitateslesion spreading during late infection stage. How the fungus survives the first encounter with living plant tissue remained unclear. We found that hyphaeof B. cinerea undergo massive PCD during early stages of infection, but fully recover upon transition to second phase of infection. Further studies using thefungal and plant mutants showed that survival, and hence pathogenicity of the fungus depended on anti-apoptotic machinery; fungal mutants bearingdefects in the anti-apoptotic gene BcBIR1 had reduced virulence whereas strains over-expressing this gene were hypovirulent. A similar phenomenon wasobserved with another necrotrophic plant pathogen, but not with two hemi-biotrophic pathogens. These results showed that the anti-PCD machinery isessential for pathogenic development necrotrophic plant pathogens. In order to extend these finding to other systems, we generated transgenic strains ofthe human pathogen Aspergillus fumigatus. This fungus shares common stages of infection with B. cinerea and hence might also need the anti-PCDmachinery for infection. Indeed, when conidia of A. fumigates are inoculated on a sensitive tissue, the developing hyphae undergo massive cell death, andsimilar to B. cinerea they fully recover later. Collectively, our results show that certain plant and human fungal pathogen share common strategies andmechanisms when infecting their host. One such mechanism is control of host-induced cell death, through conserved anti-apoptotic machinery.Septin-mediated plant tissue invasion by the rice blast fungus Magnaporthe oryzae. Yasin Dagdas, Lauren Ryder, Michael Kershaw, Nick J. Talbot. DeptBiological Sci, Univ Exeter, Exeter, United Kingdom.Magnaporthe oryzae is the causal agent of rice blast, one of the most serious economic problems affecting rice production. During plant infection, M.oryzae develops a differentiated infection structure called an appressorium. This unicellular, dome-shaped structure generates cellular turgor, that istranslated into mechanical force to cause rupture of the rice cuticle and entry into plant tissue. Development of a functional appressorium requirescompletion of a single round of mitosis shortly after conidial germination, which also leads to initiation of autophagic recycling of the contents of thefungal spore to the appressorium. We have recently shown that a hetero-oligomeric septin GTPase complex is necessary for re-organisation of a toroidal F-actin network at the base of the appressorium which allows re-establishment of polarised fungal growth. Septins scaffold F-actin, via the ezrin-radixinmoesin(ERM) protein, Tea1, and phosphatidylinositide interactions at the appressorium plasma membrane. The septin ring assembles in a Cdc42 andChm1-dependent manner and forms a diffusion barrier to localize the Inverse-Bin-Amphiphysin-RVS (I-BAR)-domain protein, Rvs167, and Wiskott-AldrichSyndrome protein (WASP), Las17 at the point of penetration. This leads to formation of a penetration hyphae that breaches the host cuticle and leads toplant tissue colonization. We present evidence that septin-mediated plant infection is regulated by a specialised NADPH oxidase-tetraspanin complexnecessary for control of F-actin dynamics. We also describe the potential operation of a pressure-mediated checkpoint pathway that leads to initial septinassembly and activation and the re-orientation of the cortical F-actin cytoskeleton to facilitate plant tissue invasion.Components of the urease complex govern virulence of Fusarium oxysporum on plant and animal hosts. Katja Schaefer, Elena Pérez-Nadales, Antonio DiPietro. Departamento de Genética, Universidad de Córdoba, 14071 Cordoba, Spain.In the soilborne pathogen Fusarium oxysporum, a mitogen-activated protein kinase (MAPK) cascade homologous to the yeast filamentous growthpathway controls invasive growth and virulence on tomato plants. Full phosphorylation of Fmk1 requires the transmembrane protein Msb2, a member ofthe family of signalling mucins that have emerged as novel virulence factors in fungal plant pathogens. A yeast two-hybrid screen for proteins interactingwith the Msb2 cytoplasmic tail identified UreG, a component of the urease enzymatic complex. UreG belongs to a set of accessory proteins needed toactivate Apo- urease, which converts urea to yield ammonia and carbon dioxide. The F. oxysporum genome contains two structural urease genes, ure1 andure2. Mutants in ureG or ure1 showed reduced growth on urea as the sole carbon and nitrogen source. Lack of urease activity in the mutants resulted infailure to secrete ammonia and to increase the extracellular pH. The DureG mutants caused significantly reduced mortality on tomato plants and on theanimal model host Galleria melonella, while Dure1 mutants only showed reduced virulence on tomato plants. Real-time qPCR analysis of key genesinvolved in nitrogen uptake and assimilation, as well as in the urea cycle, during infectious growth of F. oxysporum in G. melonella revealed increasedtranscript levels of arginase, which converts arginine to urea. Our results suggest a role for the urease accessory protein UreG in fungal virulence on plantand animal hosts.The role of LysM effectors in fungal fitness. Anja Kombrink 1 , Jason Rudd 2 , Dirk-Jan Valkenburg 1 , Bart Thomma 1 . 1) Phytopathology, WageningenUniversity, Wageningen, Netherlands; 2) Department of Plant Pathology and Microbiology, Rothamsted Research, Harpenden, Hertfordshire, UnitedKingdom.LysM effector genes are found in the genomes of a wide range of fungal species. The encoded LysM effectors are secreted proteins that contain a varyingnumber of LysM domains, which are carbohydrate-binding modules. Ecp6, secreted by tomato leaf mould fungus Cladosporium fulvum, is the firstcharacterized LysM effector. We demonstrated that Ecp6 specifically binds chitin, the major constituent of fungal cell walls that acts as a microbialassociatedmolecular pattern (MAMP) and triggers immune responses upon recognition by the host. Ecp6 outcompetes plant receptors for chitin binding,and thus prevents the activation of immune responses. Many fungal genomes, including saprophytes, carry multiple LysM effector genes that share onlylow sequence conservation and encode a varying number of LysM domains. We speculate that fungal LysM effectors might bind different carbohydratesand exert various functions in fungal fitness. In the fungal wheat pathogen Mycosphaerella graminicola, two LysM effectors were identified. Mg3LysM, butnot Mg1LysM, suppresses chitin-induced immune responses in a similar fashion as Ecp6. Interestingly, unlike Ecp6, both Mg1LysM and Mg3LysM inhibitdegradation of fungal hyphae by plant chitinases, revealing an additional function for LysM effectors in pathogen virulence. We recently observed thatMg1LysM binds to the bacterial cell wall constituent peptidoglycan. Similarly, a LysM effector from the saprophytic fungus Neurospora crassa showedpeptidoglycan binding. We hypothesize that peptidoglycan binding by LysM effectors plays a role in the interaction of fungal species with bacterialcompetitors. The soil-borne fungal pathogen Verticillium dahliae contains seven LysM effectors genes of which one (Vd2LysM) is induced during tomatoinfection. Inoculation with two independent knock-out mutants revealed that Vd2LysM is required for full virulence of V. dahliae. However, Vd2LysM doesnot specifically bind chitin and does not function in a similar fashion as previous characterized LysM effectors. Thus, its function in virulence remainsunclear.27th Fungal Genetics Conference | 85