Involvement of the lemA Gene in Production of Syringomycin and Protease by Pseudomonas syringae pv. syringae. Estelle M. Hrabak. Department of Plant Pathology University of Wisconsin, Madison 53706 U.S.A. David K. Willis(1,2). (1)Department of Plant Pathology and (2)USDA/ARS Plant Disease Resistance Unit, University of Wisconsin, Madison 53706 U.S.A. . MPMI 6:368-375. Accepted 8 March 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993.

The lemA gene of Pseudomonas syringae pv. syringae has been proposed to encode a transmembrane protein related to a large family of bacterial regulatory proteins. A lemA mutation in P. s. pv. syringae isolate B728a eliminates lesion development in brown spot disease of bean. In this study, we report that the lemA gene is also required for P. s. pv. syringae to produce normal levels of extracellular protease and of the toxin, syringomycin, but not for motility or the production of pyoverdin or bacteriocin. The role of protease and syringomycin in lesion development was investigated after isolation of mutants affected in production of either activity. One class of syringomycin mutants was identified that produced no syringomycin as measured by in vitro bioassay, but retained wild-type levels of pathogenicity on bean. In addition, protease mutants were isolated that had lost most of their proteolytic activity and remained pathogenic on bean. These results suggest that protease or syringomycin production by P. s. pv. syringae does not play a major role in the process of lesion formation on bean.