Infection and Stress Activation of Bean Chalcone Synthase Promoters in Transgenic Tobacco. Bruce A. Stermer. Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73402. Jürg Schmid(2), Christopher J. Lamb(2), and Richard A. Dixon(1). (1)Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73402; (2)Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037 U.S.A. MPMI 3:381-388. Accepted 20 June 1990. Copyright 1990 The American Phytopathological Society.

Chalcone synthase (CHS) catalyzes a key regulatory step in the synthesis of pterocarpan phytoalexins that is characteristic of many legumes. The 5'-flanking sequences from two bean CHS genes, CHS8 and CHS15, were each fused upstream of the coding region of the β-glucuronidase (GUS) reporter gene and transformed into tobacco. Shortwave UV light or 1 mM HgCl₂ induced the expression of both gene fusions in transgenic tobacco leaves. The response to UV irradiation occurred within 6 hr and was more rapid than the response to Hg. Increased GUS activity was restricted to tissue in the immediate vicinity of localized treatments with these inducers. Application of 100 mM oxalate, a treatment that induces disease resistance in cucumbers, or infiltration of an incompatible isolate of Pseudomonas syringae pv. syringae induced the expression of the CHS8-GUS, but not the CHS15-GUS gene fusion. Both oxalate and P. s. pv. syringae induced the CHS8 promoter in tissues 30-40 mm from localized sites of application, indicating the involvement of a secondary signal. These data imply the operation of several distinct mechanisms for stress activation of defense genes. These mechanisms are conserved between tobacco and bean such that the bean CHS promoters are induced even though CHS plays no role in phytoalexin biosynthesis in tobacco.