Characterization of a cell death suppressing effector broadly conserved across the fungal kingdom

Whigham, Ehren
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The proteins used by pathogens to modify, suppress or evade host defenses (called effectors) are fascinating probes into plant defense pathways and are changing the way scientists think about host/pathogen interactions. Blumeria graminis f. sp. hordei, causal agent of barley powdery mildew disease, is a model system to study the nature of obligate biotrophy. In addition to the nearly 500 predicted effector candidates unique to the mildews, this pathogen contains at least one that is broadly conserved across the fungal kingdom. Understanding the functions and targets of both the unique and conserved effectors has the potential to reveal new mechanisms of resistance. The development of RNAi-mediated gene silencing assays and the use of bacterial secretion based delivery systems has enabled the functional characterization of effectors in ways that were impossible until now.

Silencing an effector candidate from B. graminis by Barley Stripe Mosaic Virus -Induced Gene Silencing is shown to significantly reduce accumulation of fungal biomass. When delivered to barley cells via the Xanthomonas bacterial type III secretion system, this effector is able to suppress host cell death. Conservation of this protein in 96 of 240 surveyed fungal genomes is presented. Notably, orthologs of this gene are present in non-pathogens as well as major pathogens of both plants and animals. Site-directed mutagenesis revealed two amino acids that are required for the cell death suppression phenotype. Taken together, this evidence supports reclassification of this gene from candidate effector to bona fide effector.

Biological research and bioinformatic analysis are meaningful only to the extent that scientists can communicate value to stakeholders and the public. Through collaboration with high school science teachers, a curriculum was developed to expose students to plant biology and illustrate that an organism's DNA (genotype) has a direct influence on its traits (phenotype). Students plant seeds, extract DNA from leaf tissue, amplify genes through polymerase chain reactions, and screen plant phenotypes. They learn to use pipets, how to conduct PCR and gel electrophoresis, and spend time determining relevant traits of their plants. The goal is to equip teachers to train and excite students about the field of plant biology.

fungal effector