ARS | Publication request: A Bacterial Pathogen uses Distinct Type III Secretion Systems to Alternate between Host Kingdom

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2010
Publication Date: August 1, 2010
Citation: Correa, V.R., Majerczak, D.R., Pratt, R.C., Redinbaugh, M.G., Coplin, D.L., Hogenhout, S.A. 2010. A Bacterial Pathogen uses Distinct Type III Secretion Systems to Alternate between Host Kingdom. Phytopathology. 100:S27.

Technical Abstract: Gram-negative bacterial pathogens of eukaryotes often secrete proteins directly into host cells via a needle-like protein channel called a ‘type III secretion system’ (T3SS). Bacteria that are adapted to either animal or plant hosts use phylogenetically distinct T3SSs for secreting proteins. Here, we report that Pantoea stewartii subsp. stewartii (Pnss), the causative agent of Stewart’s wilt in maize, carries phylogenetically distinct T3SSs that enable it to invade its insect and plant hosts. In addition to a Hrp-type T3SS, known to be essential for maize pathogenesis, Pnss has a second T3SS (PSI-2) that is required for persistence in its flea beetle vector, Chaetocnema pulicaria. PSI-2 belongs to the Inv-Mxi-Spa T3SS family typically found in animal pathogens. Mutagenesis of the PSI-2 psaN gene, which encodes an ATPase essential for building the structural components of T3SS and secretion of T3SS effectors, greatly reduced both the persistence of Pnss in flea beetle guts and its transmission to maize. Ectopic expression of the psaN gene complemented these phenotypes. In addition, the relative expression level of the PSI-2 psaN gene was higher in insects compared to maize tissues. When mechanically inoculated, the Pnss psaN mutant was fully virulent on sweet maize, indicating that PSI-2 is not required for plant pathogenicity. Our findings demonstrate that the two T3SS in Pnss play different roles in the life cycle of this bacterium as it alternates between insects and plants.