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A genetic locus determining pathogenicity of Pantoea ananatis

Yuichi Takikawa: Shizuoka University

<div><em>Pantoea ananatis </em>(<em>Pa</em>) is a gram-negative plant pathogenic bacterium. <em>Pa</em> strains are divided into three groups (Group I, II and III) depending on their pathogenicity on rice, onion and melon and ability to induce hypersensitive response (HR)-like reaction in tobacco (Kido et al. 2010). The whole genome analysis and transposon-tagging analysis on one rice isolate SUPP2219 (Group I) suggested that a genetic region spanning ca. 19 kb in length existed exclusively in the known genomes of plant pathogenic <em>Pa</em> strains but not in saprophytic <em>Pa</em>. Tn-<em>5</em> insertion in some genes of this region abolished the virulence of the isolate. This genetic region was tentatively named as PASVIL (<em><u>P</u>antoea <u>a</u>nanatis</em> <u>s</u>pecific <u>vi</u>rulence <u>l</u>ocus). PCR and Southern-hybridization tests revealed that PASVIL existed in all of Group I strains examined but not in Group II and III strains. In complementation tests, one large clone (pL422), spanning nearly entire region of PASVIL (ca. 18 kb), not only restored the virulence of the mutants, but also turned non-pathogenic Group III strains virulent. PASVIL contains at least 19 ORFs, coding membrane proteins, proteins for amino-acid transport and metabolism, and transposases, adjacent to tRNA-Phe gene at one border. The GC content of PASVIL was ca. 39%, significantly lower than that of whole genome average 53%. It was deduced that PASVIL might constitute a pathogenicity island, encoding pathogenicity determinant(s) not described before in <em>Pantoea </em>spp.</div>