Genetic organization of the Pantoea stewartii subsp stewartii hrp gene cluster and sequence analysis of the hrpA, hrpC, hrpN, and wtsE operons

The hrp/wts gene cluster of Pantoea stewartii subsp. stewartii is required for pathogenicity on sweet corn and the ability to elicit a hypersensitive response (HR) in tobacco. Site-directed transposon mutagenesis and nucleoti de sequencing were used to identify hrp/wts genes within the left 20 kb of this cluster. Seventeen open reading frames (ORFs) comprise seven genetic c omplementation groups. These ORFs share homology with hrp and dsp genes fro m Erwinia amylovora, Erwinia chrysanthemi, and Pseudomonas syringae pathova rs and have been designated, in map order, wtsF, wtsE, hrpN, hrpV, hrpT, hr cC, hrpG, hrpF, hrpE, hrpD, hrcJ, hrpB, hrpA, hrpS, hrpY, hrpX, and hrpL. P utative hrp consensus promoter sequences were identified upstream of hrpA, hrpF, hrpN, and wtsE. Expression of the hrpA, hrpC, and wtsE operons was re gulated by HrpS. Transposon mutations in all of the hrp operons abolished p athogenicity and HR elicitation, except for the hrpN and hrpV mutants, whic h were still pathogenic. hrpS, hrpXY, and hrpL regulatory mutations abolish ed HrpN synthesis, whereas secretory mutations in the hrpC, hrpA, and hrpJ operons permitted intracellular HrpN synthesis. wtsEF mutants were not path ogenic but still produced HrpN and elicited the HPL wtsE encodes a 201-kDa protein that is similar to DspE in E. amylovora and AvrE in P. syringae pv. tomato, suggesting that this protein is a major virulence factor involved In the elicitation of water-soaked lesions.