The -689/+197 region of the maize protease inhibitor gene directs high level, wound-inducible expression of the cry1B gene which protects transgenic rice plants from stemborer attack

To investigate the activity of the regulatory region of the maize (Zea mays L.) proteinase inhibitor (mpi) gene, we transferred into rice (Oryza sativa L.) plants the -689/+197 (C1) fragment of the mpi genomic clone fused to either the uidA gene or a synthetic Bacillus thuringiensis cry1B gene. Although uidA and cry1B encode very different proteins consistent results were obtained from their respective histochemical and fluorometric and immunoblot detections in T3 transgenic rice lines. In response to mechanical wounding, a 4-5 fold increase in GUS activity and a Cry1B accumulation reaching 0. 1-0.2% of total soluble proteins were observed from basal and undetectable" levels respectively in leaf tissue. The establishment of the time-course of wound response in both systems revealed a maximum induction level 12-16h after treatment. From both systems we also deduced that the C1 region is not active in pollen and seed endosperm. Three independent transformation events expressing cry1B under the control of the C1 region exhibited protection against striped stem borer damage and showed 100% mortality of second instar larvae 8 days after release. These results illustrate the first evidence that wound-inducible expression of a Bacillus thuringiensis endotoxin gene affords full protection to transgenic rice plants. (Résumé d'auteur