APS Abstract of Presentation

Characterization of a Pantoea stewartii TTSS gene required for persistence in its flea beetle vector
V. R. CORREA (3), D. R. Majerczak (5), E. Ammar (2), M. Merighi (5), D. L. Coplin (5), R. C. Pratt (3), M. G. Redinbaugh (4), S. A. Hogenhout (1)
(1) Dept. of Entomology, OARDC/The Ohio State University, USA & Dept. of Disease and Stress Biology, John Innes Centre, Norwich, UK; (2) Dept. of Entomology, OARDC/The Ohio State University, USA; (3) Dept. of Horticulture and Crop Science, OARDC/The Ohio State University, USA; (4) Dept. of Plant Pathology, OARDC/The Ohio State University & USDA, ARS Corn and Soybean Research, Wooster, OH, USA; (5) Dept. of Plant Pathology, OARDC/The Ohio State University, USA
Phytopathology 98:S41

Stewart’s wilt and leaf blight disease of sweet corn and maize is caused by Pantoea stewartii subsp. stewartii (Pnss), a bacterium that is transmitted by the flea beetle, Chaetocnema pulicaria. Few studies have focused on the molecular basis of the interactions of Pnss with its vector. Genome analyses indicated that Pnss carries gene clusters for two type III secretion systems (TTSS). The first (TTSS-1) encodes hrp genes for secretion of effector proteins into plant cells. TTSS-1 effectors are required for plant infection, but no function has been assigned to TTSS-2. The purpose of this study was to determine if TTSS-2 is involved in Pnss colonization and persistence in its vector. Two Pnss wild-type strains (DM283 and DM440) and transposon insertion mutants of a ysaN homolog in TTSS-2 and a sapD homolog were tested for persistence in flea beetles after feeding on infected plant. ysaN is a structural gene of the TTSS and sapD is an ABC transporter involved with antimicrobial peptide resistance. Immunofluorescence microscopy of dissected insect organs revealed that the wild-type and sapD strains persisted in the beetles for at least 12 days, whereas the ysaN mutant strain was significantly lower at 8 to 12 days post acquisition. Bacteria persisted primarily in the lumen of the midgut and hindgut of the beetles. Viable cell counts of Pnss present in beetle extracts were significantly lower for the ysaN mutant at 8 to 10 days post acquisition relative to wild-type and the sapD mutants. The lack of persistence of the ysaN mutant suggests that TTSS-2 is involved in Pnss persistence in its flea beetle vector. The relative expression levels of TTSS-1 and TTSS-2 genes in plants and in insects are currently being assessed by semi-quantitative RT-PCR.

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