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Novel biosynthetic gene cluster in Pantoea ananatis is critical to foliar lesion development in center rot of onion

Jo Ann Asselin: Cornell University

<div>Center rot of onion, caused by the bacteria <em>Pantoea ananatis</em>, <em>P. allii</em>, and <em>P. agglomerans</em>, results in economic losses in many onion-growing areas worldwide. The disease is characterized by lesions on leaves and water soaking, discoloration, and scale shrinkage within onion bulbs. <em>P. ananatis</em> is arguably the best studied center rot pathogen. However, few pathogenicity or virulence factors have been identified and verified empirically. Also, pathogenicity to onion by <em>P. ananatis</em> is variable by strain. The goal of this work was to identify additional pathogenicity/virulence factors in <em>P. ananatis</em> towards onion. In this study, genome comparisons from two onion-pathogenic and two onion-non-pathogenic <em>P. ananatis </em>strains yielded a list of candidate genes that appeared well-conserved in onion-pathogenic strains, but absent or poorly-conserved in onion-non-pathogenic strains. Screening of additional strains with PCR primers designed to amplify some of these genes suggested the presence of a previously uncharacterized biosynthetic gene cluster present in only the onion-pathogenic strains. Preliminary results demonstrate that the gene cluster is necessary for <em>P. ananatis</em> to cause leaf lesions and water soaking in onion bulbs. Furthermore, genes from this cluster were detected in onion-pathogenic strains of <em>P. allii</em> and <em>P. agglomerans.</em> These results suggest that activity of this cluster is involved in center rot of onion.</div>