Program Book - 27th Fungal Genetics Conference

FULL POSTER SESSION ABSTRACTS531. Identification and functional assay of Phytophthora sojae avirulence effectors. Yuanchao Wang, Suomeng Dong, Weixiao Yin. Plant Pathology Dept,Nanjing Agri Univ, Nanjing, China.Phytophthora sojae is a notorious oomycete pathogen producing a great loss on global soybean production annually. The disease outcome betweensoybean and P. sojae depends on whether hosts could recognize pathogen avirulence effectors. Recently identified oomycete avirulence effectors arecharacterized by N-terminal host entry motif (RxLR motif), sequence and transcriptional polymorphisms between virulent and avirulent strains. Benefitfrom 454 genome sequencing and solexa transcriptome sequencing of P. sojae strains, eight RxLR effectors are bioinformatically identified, geneticmapping suggested that two of them perfectly matched Avr3b and Avr1d phenotype respectively. Transient expression of the ORF from avirulence strainon soybean specifically triggered Rps3b and Rps1d mediated program cell death, respectively. confirming that they encodes avirulence effector Avr3b andAvr1d. Transient expression of Avr3b and Avr1d on Nicotiana benthamiana could promote the infection of Phytophthora capasici, suggesting bothavirulence effectors could suppress plant immunity and contribute to pathogen infection. Silencing of Avr3b impaired the virulence of Phytophthora sojae.Our progress in elucidating the mechanism under the inhibiting plant immunity by these effectors will be presented.532. Evaluating the translocation- and phospholipid binding abilities of the Phytophthora infestans AVR3a and Phytophthora sojae Avr1b RxLR-leaders.Stephan Wawra 1 , Armin Djamei 2 , Isabell Küfner 3 , Thorsten Nürnberger 3 , Justin A. Boddey 4 , Stephen C. Whisson 5 , Paul R.J. Birch 5 , Regine Kahmann 2 , Pietervan West 1 . 1) Sch Med Sci, Univ Aberdeen, Aberdeen, United Kingdom; 2) Department of Organismic Interactions, Max Planck Institute for TerrestrialMicrobiology, Germany; 3) Department of Plant Biochemistry, University Tübingen, Germany; 4) Department of Medical Biology, University of Melbourne,Australia; 5) Cell and Molecular Sciences, James Hutton Institute, Dundee, UK.Plant pathogenic oomycetes have a large set of secreted effectors that are directed into their host cells during infection. One group of these effectors arethe RxLR-effectors found in plant pathogenic oomycetes. These RxLR-effectors are defined as putative secreted proteins that contained a conservedtetrameric amino acid sequence motif, Arg-Xaa-Leu-Arg. This motif has to be within 40 amino acids C-terminal of the predicted cleavage sites of canonicalsignal peptides. Often this sequence is followed by a Glu-Glu-Arg (EER) motif. It has been shown, in a few cases, that the RxLR-motif is important for thedelivery of these proteins into host cells. However, how these proteins translocate into the cytoplasm of their host is currently the object of intenseresearch activity and debate. One model suggests that the RxLR-leader sequences of these effectors are sufficient to translocate the respective effectorsinto eukaryotic cells through binding to surface exposed phosphoinositol-3-phosphate. However, analysing the translocation behaviour of the RxLR-leadersfrom Phytophthora infestans avirulence protein 3a (AVR3a) and Phytophthora sojae avirulence protein 1b (Avr1b) we were unable to obtain conclusiveevidence for specific RxLR-mediated translocation. Importantly, we confirm that the reported phospholipid binding properties of AVR3a and Avr1b are notmediated by their RxLR-leaders. In addition, we will present data showing that the observed phospholipid interaction of the AVR3a effector domain isattributable to a weak association with denatured protein molecules, and is therefore most likely physiologically irrelevant.533. Identifying essential effectors from the soybean pathogen Phytophthora sojae. Hua Z. Wise 1,2 , Ryan G. Anderson 3 , John M. McDowell 3 , Brett M.Tyler 1,2 . 1) Center for Genome Research and Biocomputing and Department of Botany and Plant Pathology, Oregon State University; 2) VirginiaBioinformatics Institute, Virginia Tech; 3) Department of Plant Pathology, Physiology and Weed Science, Virginia Tech.Breeding for resistance to plant pathogens is one of the most effective means of disease control. However, the ability of plant pathogens evolve newpathogenicity factors and evade host defense mechanisms drives the continual necessity to identify new resistance genes. We are exploiting genomictechnologies in an effector-directed breeding approach that augments traditional breeding efforts against Phytophthora sojae, the causal agent of soybeanroot and seedling rot. This approach is founded on identifying monomorphic P. sojae effector genes that are essential for virulence, and using these genesas probes to identify new sources of resistance in soybean and related legumes. These essential effectors will make excellent candidates for screening fornew, durable resistance to P. sojae, as these genes presumably cannot be mutated or deleted without a significant fitness penalty. The majority ofpredicted P. sojae RXLR effector genes are polymorphic amongst sequenced isolates of P. sojae, however, a subset of P. sojae RXLR effectors displays littleor no allelic diversity. We have established a workflow for transient gene silencing and quantitative virulence assays. To date, we have silenced andassessed the virulence contribution of 17 PsAvh genes. Silencing of 13 of these effectors produced reduced virulence. Among these effectors, Avh16,Avh180 and Avh240 showed substantially reduced pathogen growth at early stages of host colonization and reduced disease symptoms at later stages ofinfection. We are currently using these three effectors as candidates in a high throughput screen system utilizing Pseudomonas Type III secretion system toscreen for new resistance genes against P. sojae.534. The LysM effector, Ecp6, is a virulence factor in the interaction of the hemibiotroph, Setosphaeria turcica, but not the necrotroph, Cochliobolusheterostrophus, with their common host, maize. Dongliang Wu 1 , Qing Bi 2 , Gillian Turgeon 1 . 1) Department of Plant Pathology & Plant-Microbe Biology,Cornell University, Ithaca, NY 14853, USA; 2) State Key Program of Microbiology and Department of Microbiology, College of Life Sciences, NankaiUniversity, Tianjin, China, 300071.Fungal phytopathogens are characterized as biotrophs, which derive nutrients from living cells, and necrotrophs, which kill host cells and retrievenutrients from dead tissue. Hemibiotrophs are intermediate in that they initially establish themselves in living host tissue, then undergo rapid killing ofplant cells later on. Hemi- and bio-trophic fungi utilize specialized effectors to prevent host recognition triggered by pathogen associated molecularpatterns (PAMPs), whereas necrotrophs often produce toxins that induce programmed cell death. Chitin, a signature component of fungal cell walls, is onetype of PAMPs known to trigger the plant resistance response. Several fungal chitin-binding LysM effectors have been identified that broker counterdefenseagainst chitin-triggered immunity, including the first characterized one, Ecp6, from the tomato biotroph, Cladosporium fulvum, Mg3LysM, fromthe wheat hemibiotroph, Mycosphaerella graminicola, and Slp1, from the rice hemibiotroph, Magnaporthe oryzae. In this study, Ecp6 homologs wereidentified and deleted from the genomes of two maize pathogens which differ in pathogenic lifestyle, Setosphaeria turcica (hemibiotroph), causal agent ofNorthern Leaf Blight and Cochliobolus heterostrophus (necrotroph), causal agent of Southern Corn Leaf Blight. Deletion of StECP6 caused reducedvirulence, whereas absence of ChECP6 did not alter virulence to the host. Real time RT-PCR demonstrated that expression of pathogenesis related maizegenes, PR1 gene and a chitinase gene was increased in Stecp6 mutants compared to wild type at 4 days post inoculation. Additional in planta geneexpression analyses are underway to compare host responses to these two fungi differing in pathogenic lifestyle on the same host.535. Nematode-trapping fungi eavesdrop on nematode pheromones. Yen-Ping Hsueh 1 , Parag Mahanti 2 , Frank Schroeder 2 , Paul Sternberg 1 . 1) HowardHughes Medical Institute and Division of Biology, California Inst of Technology, Pasadena, CA; 2) Boyce Thompson Institute and Department of Chemistryand Chemical Biology, Cornell University, Ithaca, NY.The recognition of molecular patterns associated with specific pathogens or food sources is fundamental to ecology and plays a major role in theevolution of predator-prey relationships. Recent studies showed that nematodes produce an evolutionarily highly conserved family of small molecules, the252