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Evolution of necrotrophic phytopathogenic bacteria in the Enterobacteriaceae

R. McNally: Colorado State University

<div>The emergence of plant pathogenesis by bacteria is the product of convergent evolution. Within the Enterobacteriaceae alone, two groups of bacteria have independently evolved the ability to cause plant disease. Soft rot Enterobacteria (SRE) represent one of these groups and include three genera: <em>Pectobacterium</em>, <em>Dickeya</em>, and <em>Brennaria</em>. While much research has focused on biotrophic bacterial plant pathogens, SRE pathogenicity is characterized by necrotrophy and the production of cell wall-degrading enzymes. Here we report a comparative genomic analysis of the Enterobacteriaceae to elucidate the evolution of necrotrophy in SRE. In total, 307 Enterobacteriaceae genomes were analyzed including 20 genomes from <em>Pectobacterium</em>, <em>Dickeya</em> and <em>Brennaria</em>. Predicted proteins were grouped according to orthology and phylogenetically evaluated. Genes gained or lost in SRE bacteria were determined via thresholded RAxML analysis (≥ 0.75) and represent putative evolutionary adaptions for plant necrotrophy. In total, 195 genes were acquired by SRE bacteria while 253 were lost. 7% of acquired genes represent predicted virulence factors while 53% are involved in metabolism, signal transduction or transport. Our results indicate that the evolution of necrotrophy in the Enterobacteriaceae required extensive acquisition of methyl-accepting chemotaxis proteins and ATP-binding cassette transporters in addition to a small number of cell-wall degrading enzymes.</div>