The Complete hrp Gene Cluster of Pseudomonas syringae pv. syringae 61 Includes Two Blocks of Genes Required for HarpinPss Secretion that Are Arranged Colinearly with Yersinia ysc Homologs. Hsiou- Chen Huang. Agricultural Biotechnology Laboratories, National Chung-Hsing University, Taichung, Taiwan 40227 R.O.C. Rong-Hwa Lin(1), Chun-Jung Chang(1), Alan Collmer(2), and Wen-Ling Deng(1). (1)Agricultural Biotechnology Laboratories, National Chung-Hsing University, Taichung, Taiwan 40227 R.O.C. (2) Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. MPMI 8:733-746. Accepted 18 May 1995. Copyright 1995 The American Phytopathological Society.

Pseudomonas syringae pv. syringae 61 contains a 25-kb hrp cluster that is sufficient to elicit the hypersensitive response (HR) in nonhost plants. Previous studies have shown that mutations in complementation groups VIII, IX, and XI in the hrp cluster abolished the ability of the bacterium to cause the HR. The sequence of a 3.7-kb Smal-SstI fragment covering groups VIII and IX now reveals five open reading frames (ORFs) in the same transcript, designated as hrpU, hrpW, hrpO, hrpX, and hrpY, and predicted to encode proteins of 14,795, 23,211, 9,381, 28,489, and 39,957 Da, respectively. The hrpU, hrpW, hrpO, hrpX, and hrpY genes are homologous and arranged colinearly with the yscQ/spa33/spaO, yscR/spa24/spaP, yscS/spa9/spaQ, yscT/spa29/spaR, and yscU/spa40/spaS genes of Yersinia spp., Shigella flexneri, and Salmonella ty-phimurium, respectively. These proteins also show similarity to Fli/Flh proteins of Bacillus and enteric bacteria. The Ysc and Spa proteins are involved in the secretion of virulence factors, like the Yop and Ipa proteins. Fli/FIh proteins are involved in flagellar biogenesis. The sequence of a 2.9-kb EcoKV-EcoRl DNA fragment containing mainly group XI revealed five ORFs, designated hrpC, hrpD, hrpE, hrpF, and hrpG, predicted to encode proteins of 29,096,15,184, 21,525, 7,959, and 13,919 Da, respectively. The first three genes belong to an operon conaining hrpZ, which encodes an extracellular protein that elicits the HR. hrpE and hrpG are two potential ORFs upstream of hrpH in the hrpH operon. HrpC is homologous to Yersinia Yscj, Pseudomonas solanacearum HrpI, Xanthomonas campestris pv. vesicatoria HrpB3, and Rhizobium fredii NolT. HrpE is similar to YscL of Yersinia spp. P. s. pv. syringae 61 Hrp proteins are most similar to Ysc proteins among those homologs. TnphoA insertions in hrpC, hrpE, hrpW, hrpX, and hrpY abolished the ability of P. s. pv. syringae 61 to secrete HrpZ (harpinPss), as determined by immunoblot analysis of cell-bound and culture supernatant fractions. Thus, many of the proteins required for flagellar biogenesis and virulence protein secretion in plant and animal pathogens may have a common ancestry.