Isolation and Characterization of a Pseudomonas syringae pv. syringae Mutant Deficient in Lesion Formation on Bean. David K. Willis. ARS/USDA Plant Disease Resistance Research Unit and Department of Plant Pathology, University of Wisconsin, Madison 53706. Estelle M. Hrabak(2), Jessica J. Rich(2), Terese M. Barta(2), Steven E. Lindow(3), and Nickolas J. Panopoulos(3). (1)ARS/USDA Plant Disease Resistance Research Unit and (2)Department of Plant Pathology, University of Wisconsin, Madison 53706; and (3)Department of Plant Pathology, University of California, Berkeley 94720 U.S.A. MPMI 3:149-156. Accepted 30 November 1989. 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, 1990.

The lesion-forming ability of Pseudomonas syringae pv. syringae was found to be genetically separable from other in planta phenotypes. We identified a Tn5 mutant, derived from the pathogenic strain B728a, that had lost the ability to form lesions on either the pods or leaves of bean (Phaseolus vulgaris). The mutant, designated as NPS3136, was prototrophic, retained the ability to elicit a hypersensitive reaction on the nonhost tobacco, and attained levels of growth similar to the parental strain on bean. NPS3136 was shown to contain a single Tn5 insertion within a 6.1-kb EcoRI fragment. We showed that the transposon insertion was causal to the mutant phenotype by marker exchange mutagenesis of B728a using a clone containing the Tn5-disrupted EcoRI fragment from NPS3136. We have designated the DNA region affected by the Tn5 insertion in NPS3136 as the lemA locus. Eight overlapping cosmid clones that restored lesion formation to NPS3136 were isolated from a B728a genomic library. By restriction analysis of these cosmids and the original Tn5 insertion, we have localized the lemA locus within a 6.7-kb region of the B728a chromosome.