Characterization Of A Novel Effector From Blumeria Graminis F. Sp. Hordei That Suppress Host Cell Death
The interaction of barley, Hordeum vulgare L., with the powdery mildew fungus, Blumeria graminis f. sp. hordei, is a well-developed model to investigate resistance and susceptibility to obligate biotrophic pathogens. The 130-Mb Blumeria genome encodes ca. 540 predicted effectors, which are hypothesized to suppress or induce host processes to promote colonization. Blumeria effector candidate (BEC)1019, a singlecopy gene encoding a putative, secreted metalloprotease, is expressed in haustorial feeding structures, and Host-Induced-Gene-Silencing of BEC1019 restricts haustorial development in compatible interactions. Here we show that Barley stripe mosaic virusInduced Gene Silencing of BEC1019 significantly reduces fungal biomass in barley leaves, demonstrating that BEC1019 plays a central role in virulence. In addition, delivery of BEC1019 to the host cytoplasm via Xanthomonas type III secretion suppresses cultivar non-specific hypersensitive reaction (HR) induced by Xanthomonas oryzae pv. oryzicola, as well as cultivar specific HR induced by AvrPphB from Pseudomonas syringae pv. phaseolicola. BEC1019 homologs are present in 97 of 241 sequenced fungal genomes, including plant pathogens, human pathogens, and freeliving non-pathogens. Comparative analysis revealed variation at several amino acid positions that correlate with fungal lifestyle, and at least two highly conserved, noncorrelated motifs. Site-directed mutagenesis of one of these, ETVIC, compromises the HR suppressing activity of BEC1019. When mutating another conserved motif, HRxxH, and delivered by Xanthomonas campestris pv. vesicatoria translocation mutant strain, BEC1019 failed to suppress cell death caused by Xoc, indicating that HRxxH may play a role in effector translocation.
Blumeria graminis; effector; Type III secretion system
Bogdanove, Adam Joseph
Collmer, Alan Raymond; Turgeon, Barbara Gillian
M.S., Plant Pathology
Master of Science
dissertation or thesis