Identification of Pseudomonas syringae Genes Required for Initiating Type III Secretion in Response to Host Plant-derived Metabolite Signals
Jeff Anderson: Department of Botany and Plant Pathology, Oregon State University
<div><em>Pseudomonas syringae</em> is a bacterial pathogen that relies on a type III secretion system (T3SS) to inject immune-suppressing effector proteins into host cells during infection of plants. Although critical for virulence, the genes encoding the T3SS are not constitutively expressed and must be induced during infection. Recently, several plant-derived metabolites were identified as signals that increase expression of T3SS-associated genes in the model strain <em>P. syringae</em> pv tomato DC3000. To investigate how these chemical signals regulate the T3SS, we performed a large-scale <em>Tn</em>5 transposon mutagenesis of DC3000 to identify mutants with decreased response to the bioactive metabolites. We identified 200 <em>Tn5</em><sup>+</sup> strains with confirmed loss-of-response phenotypes. Using a whole genome Illumina sequencing strategy, we identified essentially all <em>Tn5</em> insertion sites within our collection of 200 mutants in less than one month’s time. Within this set of mutants we found <em>Tn5</em> insertions in all genes that encode known positive regulators of T3SS signaling in <em>P. syringae</em>, thus validating our screening method. Furthermore, we identified <em>Tn5</em> insertions in several previously uncharacterized genes predicted to encode two-component systems, membrane transporters and transcriptional regulators, suggesting a role for these genes as positive regulators of T3SS expression. These results, as well as our efforts to functionally characterize how these genes regulate the T3SS, will be presented.</div>
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