Program Book - 27th Fungal Genetics Conference

FULL POSTER SESSION ABSTRACTS588. Genomic approaches to understand pathogenesis in the basidiomycete pathogen of food and energy crops, Rhizoctonia solani. Jonathan P.Anderson 1,2 , James K. Hane 1 , Rhonda Foley 1 , Cynthia Gleason 1 , Karam B. Singh 1,2 . 1) Plant Industry, CSIRO, Floreat, West Australia, Australia; 2) The UWAInstitute of Agriculture, The University Of Western Australia, Crawley, West Australia.Rhizoctonia solani is a broad-host-range necrotising fungal pathogen that is responsible for significant diseases to diverse crops. In Australia, R. solanimost notably causes bare patch of cereals and costs $77 million pa in direct losses, while internationally it is a significant problem for global riceproduction. In the absence of strong host resistance, an understanding of fungus pathogenesis underpins alternative approaches to enhance resistance incrop plants. While the majority of phytopathogens sequenced to date belong to the Ascomycotina, R. solani is a basidiomycete with the closest sequencedrelatives being biotrophic rust and smut fungi and saprophytic mushrooms, each possessing a lifestyle vastly different from R. solani. We have over-comecomplications associated with the multinucleate, heterokaryotic nature of R. solani to assemble a high quality consensus haploid genome of an AG8isolate. Transcriptomics assisted with genome annotation and identified putative pathogenesis genes. Several of these genes display host-specificexpression, while others show consistent infection-related expression across different anastomosis groups on different hosts. LC-MS basedproteogenomics identified proteins from three fractions; soluble hyphal proteins, membrane localised proteins and secreted proteins, from R. solanigrowing in-vitro or in wheat infection mimicking conditions. QPCR confirmed up-regulation of some of the corresponding genes in infected wheat rootscompared to R. solani grown in vitro, providing further support for a pathogenesis-related role. Functional testing of the role of candidate pathogenesisgenes is on-going. On the plant side of the interaction, large scale gene expression and mutant analyses revealed the high degree of resistance inArabidopsis (unlike its’ susceptible relative, canola) was dependent on reactive oxygen species and not jasmonic acid, ethylene or salicylic acid. Bycontrast, moderate resistance in Medicago truncatula was dependent on ethylene mediated defences, which when over-activated, lead to enhancedresistance. These findings suggest that different plant species employ different defences with differing effectiveness against the same pathogen and acollective understanding of the interplay of host and fungal responses may facilitate novel strategies for enhancing resistance.589. The Cpc1 (CpcA/Gcn4) regulator of the cross-pathway control of amino acid biosynthesis is required for plant infection of the vascular pathogenVerticillium longisporum. Susanna A. Braus-Stromeyer, Christian Timpner, Van Tuan Tran, Gerhard H Braus. Molecular Microbiology and Genetics, Georg-August-University, Goettingen, Germany.The plant pathogenic fungus Verticillium longisporum is the causal agent of early senescence and ripening in Brassica napus (oilseed rape, Canola) andother cruciferous crops. Verticillium wilts have become serious agricultural threats during the last decades. Verticillia infect host-plants through the rootsand colonize xylem vessels of the host-plant, which provide an environment with limited carbon sources. V. longisporum induces the cross-pathwaycontrol in the xylem fluid to cope with an imbalanced amino acid supply.The transcriptional activator gene VlCPC1 (similar to CpcA/GCN4) was knock-downed via RNA-mediated gene silencing and the expression of the twoCPC1 isogenes (VlCPC1-1, VlCPC1-2) in V. longisporum could be reduced up to 85%. The resulting mutants were more sensitive to amino acid starvationinduced by 5-methyltryptophane (5-MT). In plant infection assays, the silenced mutant showed significantly less symptoms such as stunting and earlysenescence. Knockouts of CPC1 in the haploid V. dahliae were sensitive to amino acid starvation and strongly reduced in symptom formation in their hostSolanum lycopersicum (tomato).The hybrid V. longisporum and the haploid V. dahliae are the first phytopathogenic fungi, which were shown to require CPC1 for infection andcolonization of their respective host plants oilseed rape and tomato.590. Fungal-Specific Transcription Factor AbPf2 Activates Pathogenicity in Alternaria brassicicola . Yangrae Cho 1 , Robin Ohm 2 , Igor Grigoriev 2 , AkhilSrivastava 1 . 1) Plant and Environmental Protection Sciences, University of Hawaii at Manoa, Honolulu, HI; 2) United States Department of Energy JointGenome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598.Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen. Molecular determinants of its life style shift between saprophyte andpathogen, however, are unknown. To identify these determinants we studied nonpathogenic mutants of a transcription factor-coding gene, AbPf2.Frequency and timing of germination and appressorium formation on host plants were similar between the nonpathogenic Dabpf2 mutants and wild-typeA. brassicicola. The mutants were also similar in vitro to wild-type A. brassicicola in vegetative growth, conidium production, and responses to chemicalstressors, such as a phytoalexin, reactive oxygen species, and osmolites. The mutants, however, did not penetrate host plant tissues, though their hyphaecontinued to grow on the plant surface. Transcripts of the AbPf2 gene increased exponentially soon after wild-type conidia encountered their host plants.A small amount of AbPf2 protein, monitored by fused green fluorescent protein, was located in both the cytoplasm and nuclei of young, mature conidia.The protein level decreased during saprophytic growth but increased several-fold during pathogenesis. Levels of both the proteins and transcripts sharplydeclined following colonization of host tissues beyond the initial infection site. When the transcription factor was expressed at an induced level in the wildtype during early pathogenesis, the expression of 106 fungal genes was down-regulated in the Dabpf2 mutants. Notably, 33 of the 106 genes encodedsecreted proteins, including eight putative effector proteins. Plants inoculated with Dabpf2 mutants expressed higher levels of genes associated withphotosynthesis, the pentose phosphate pathway, and primary metabolism, but lower levels of defense-related genes. Our results suggest that conidia ofA. brassicicola are programmed as saprophytes, but become parasites upon contact with their hosts. AbPf2 coordinates this transformation by expressingpathogenesis-associated genes, including those coding for effectors.591. WITHDRAWN592. Host-to-pathogen gene transfer facilitated infection of insects by a pathogenic fungus. Weiguo Fang, Xiaoxuan Chen. College of Life Sciences,Zhejiang University, Hangzhou, Zhejiang, China.Inspite being of great concern to human health and the management of plants and animals, the mechanisms facilitating host switching of eukaryoticpathogens remain largely unknown. The endophytic insect-pathogenic fungus Metarhizium robertsii evolved directly from endophytes and itsentomopathogenicity is an evolutionarily acquired characteristic. We found that M.robertsii acquired a sterol carrier (Mr-NPC2a) from an insect byhorizontal gene transfer (HGT). Mr-NPC2a increased the amount of ergosterol in hyphal bodies by capturing sterol from insect hemolymph, and thusmaintained cell membrane integrity and improved fungal survival rate. On the other hand, the reduction in sterol (substrate for molting hormonesynthesis) in insect hemolymph elongated larval stage, which allows the fungus to fully exploit host tissues and produce more conidia. This is first report ofHGT from host to a eukaryotic pathogen, and the host gene ultimately improved the infectivity of the pathogen.266