Characterization of a DNA Region Required for Production of the Phytotoxin Coronatine by Pseudomonas syringae pv. tomato. S. -W. Ma. Agriculture Canada Research Center, London, Ontario, Canada, N6G 2V4. V. L. Morris(2), and D. A. Cuppels(1). (1)Agriculture Canada Research Center, London, Ontario, Canada, N6G 2V4; and (2)Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, Canada, N6A 5C1.. MPMI 4:69-74. Accepted 26 September 1990. Copyright 1991 Department of Agriculture, Government of Canada.

Pseudomonas syringae pv. tomato DC3000, a tomato pathogen, produces the chlorosis-inducing phytotoxin coronatine. A 30-kilobase fragment of chromosomal DNA containing genes that control coronatine synthesis (cor) was characterized using saturation mutagenesis with the transposons Tn3-Spice and TnphoA and functional complementation analysis. The data indicated that the cor genes distributed across this 30-kilobase fragment are tightly clustered and fall into six distinct complementation groups, designated CorI to CorVI. Lack of alkaline phosphatase activity by TnphoA-induced Cor‾ mutants suggested that the cor loci containing these insertion mutations do not code for secreted or membrane proteins. Cor‾ mutants induced by Tn3-Spice, which generates transcriptional gene fusions with the ice nucleation gene inaZ, expressed ice nucleation activity both in vitro and in planta. Growth on tomato plants increased expression of the gene(s) present in the CorII region 370-fold over that observed in vitro.