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Genetic Organization of the Pantoea stewartii subsp. stewartii hrp Gene Cluster and Sequence Analysis of the hrpA, hrpC, hrpN, and wtsE Operons

October 2001 , Volume 14 , Number  10
Pages  1,213 - 1,222

Reid D. Frederick , 1 Musharaf Ahmad , 1 Doris R. Majerczak , 1 Angel S. Arroyo-Rodríguez , 1 Shulamit Manulis , 2 and David L. Coplin 1

1Department of Plant Pathology, The Ohio State University, Columbus 43210-1087, U.S.A.; 2Department of Plant Pathology, The Volcani Center, Bet Dagan 50250, Israel

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Accepted 25 June 2001.

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 nucleotide sequencing were used to identify hrp/wts genes within the left 20 kb of this cluster. Seventeen open reading frames (ORFs) comprise seven genetic complementation groups. These ORFs share homology with hrp and dsp genes from Erwinia amylovora, Erwinia chrysanthemi, and Pseudomonas syringae pathovars and have been designated, in map order, wtsF, wtsE, hrpN, hrpV, hrpT, hrcC, hrpG, hrpF, hrpE, hrpD, hrcJ, hrpB, hrpA, hrpS, hrpY, hrpX, and hrpL. Putative hrp consensus promoter sequences were identified upstream of hrpA, hrpF, hrpN, and wtsE. Expression of the hrpA, hrpC, and wtsE operons was regulated by HrpS. Transposon mutations in all of the hrp operons abolished pathogenicity and HR elicitation, except for the hrpN and hrpV mutants, which were still pathogenic. hrpS, hrpXY, and hrpL regulatory mutations abolished HrpN synthesis, whereas secretory mutations in the hrpC, hrpA, and hrpJ operons permitted intracellular HrpN synthesis. wtsEF mutants were not pathogenic but still produced HrpN and elicited the HR. 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.

Additional keywords: Erwinia stewartii , Stewart's wilt, type III secretion.

© 2001 The American Phytopathological Society