The Interactions of Pseudomonas Syringae Harpins, HRP Secretion Proteins, and AVR Proteins in Eliciting Either theHypersensitive Response or Pathogenesis in Higher Plants

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9305178 Collmer The hypersensitive response (HR) of higher plants is characterized by the rapid, localized death of plant cells at the site of invasion by an "incompatible" pathogen (a microorganism that causes disease only in another plant) and is associated with resistance against many nematodes, fungi viruses and bacteria. Elicitation of the HR by Pseudomonas syringae and other plant pathogenic bacteria is controlled by hrp genes, which are also required for the multiplication and pathogenicity of these bacteria in their respective host plants. The overall goal of the research is to use two recent advances to dissect the functions of the hrp genes and to determine the general basis for the phenotypic dependence of avr genes on hrp genes. We expect that (i) harpins are needed for P. syringae strains to initiate a metabolically active interaction with the plant, (ii) HrpH and several other Hrp proteins are needed for the secretion of harpin, (iii) harpin production must be carefully regulated for successful pathogenesis, and (iv) Avr proteins depend on the Hrp secretion system and/or harpin to produce their phenotypes. The work will involve potentially three strains of P. syringae: (i) P.s. syringae 61, whose cloned cluster of hrp genes has been extensively characterized and is unique in that, it functions in nonpathogens like E. coli. (ii) P.s. glycinea race 4, which becomes incompatible with Rpg1 soybean cultivars upon acquisition of the cloned avrB gene, and (iii) P.s. tomato DC3000, whose compatibility with Arabidopsis thaliana is reversed by acquisition of avrB. Early work on the project will determine whether P.s. glycinea race 4 or P.s. tomato DC3000 will be the focus of work on Avr protein function. We intend to (1) Characterize the P.s. syringae 61 hrpZ gene and the encoded harpin with respect to primary sequence, elicitor-active domains, and subcellular location. (2) Determine the relative effects of hrpH and hrpZ mutations on the initial interac tion of P.s. syringae 61 with bean and tobacco (or of P.s. tomato DC3000 with A. thaliana or of P.s. glycinea race 4 with soybean). (3) Clone and characterize the P.s. glycinea race 4 (or P.s. tomato DC3000) hrpZ gene, construct derivatives that are deficient in harpin overproduce harpin produce harpin instead of harpin or contain a hrpZ promoter- uida fusion in trans; determine the phenotype of these derivatives (with or without an avrB+ plasmid) on tobacco and differential host cultivars. %%% Because homologs of Hrp secretion proteins are present in some animal pathogens, successful testing of these hypothesis should have a broad impact on research addressing bacterial pathogenicity. ***