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Expression of an Engineered Cecropin Gene Cassette in Transgenic Tobacco Plants Confers Disease Resistance to Pseudomonas syringae pv. tabaci

A chimeric gene fusion cassette, consisting of a secretory sequence from barley α-amylase joined to a modified cecropin (MB39) coding sequence and placed under control of the promoter and terminator from the potato proteinase inhibitor II (PiII) gene, was introduced into tobacco by Agrobacterium-mediated transformation. Transgenic and control plants reacted differently when inoculated with tobacco wildfire pathogen Pseudomonas syringae pv. tabaci at various cell concentrations. With control plants (transformed with a PiII-GUS [β-D-glucuronidase] gene fusion), necrosis was clearly visible in leaf tissue infiltrated with bacterial inoculum levels of 10², 10³, 10⁴, 10⁵, and 10⁶ CFU/ml. With MB39-transgenic plants, however, necrosis was observed only in the areas infiltrated with the two highest levels (10⁵ and 10⁶ CFU/ml). No necrosis was evident in areas infiltrated with bacterial concentrations of 10⁴ CFU/ml or less. Bacterial multiplication in leaves of MB39-transgenic plants was suppressed more than 10-fold compared to control plants, and absence of disease symptom development was associated with this growth suppression. We conclude that the pathogen-induced promoter and the secretory sequence were competent elements for transforming a cecropin gene into an effective disease-control gene for plants.