Pseudomonas solanacearum: Plasmid pJTPS1 Mediates a Shift from the Pathogenic to Nonpathogenic Phenotype. Hideaki Negishi. Japan Tobacco Inc., Applied Plant Research Laboratory, Yokohama Center, 6-2 Umegaoka, Midori-ku, Yokohama 227, Japan. Tetsuji Yamada(2), Tomonori Shiraishi(2), Hachiro Oku(2), and Hiroshi Tanaka(1). (1)Japan Tobacco Inc., Applied Plant Research Laboratory, Yokohama Center, 6-2 Umegaoka, Midori-ku, Yokohama 227, Japan; (2)Laboratory of Plant Pathology, College of Agriculture, Okayama University, 1-1-1 Tsushimanaka, Okayama 700, Japan.. MPMI 6:203-209. Accepted 17 December 1992. Copyright 1993 The American Phytopathological Society.

To elucidate the role of a small plasmid, pJTPS1, harbored by a spontaneous nonpathogenic mutant (M4S) of Pseudo-monas solanacearum (U-7), a recombinant plasmid pJTPS2, expressing a hygromycin resistance gene inserted in pJTPS1, was transformed into the parental pathogenic strain, U-7. The hygromycin-resistant transformant (U-7T1) formed nonfluidal colonies similar to M4S and lost pathogenicity on tobacco and tomato. Moreover, the amount of extracellular polysaccharide (EPS) production and the level of endoglucanase (EG) activity in U-7T1 were decreased to levels lower than those of M4S. Furthermore, a pJTPS2-cured mutant isolated from U-7T1 formed fluidal colonies with high EPS production and EG activity and regained pathogenicity. These data suggest that pJTPS1 reduces or eliminates pathogenicity of the bacterium upon tobacco and tomato.