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Cecropin B is a naturally-occurring lytic peptide found in Hyalophora cecropia, the Giant Silk Moth. It is thought to comprise part of an inducible humoral defense system that combats infection in the insect. Two 38 amino acid peptides, SB-37 and Shiva-1, were produced as substitution analogs of Cecropin B. SB-37 is 95% homologous to Cecropin B while Shiva-1 retains only 46% homology to the natural molecule. However, hydrophobic properties and charge density of the native structure were conserved at 100% in the synthetic peptides. The genes for both peptides were chemically synthesized and cloned into the binary vector pBI121 under the control of a constitutive or wound-inducible plant promoter. Transgenic tobacco plants (RO) were subsequently obtained via Agrobacterium transformation. Bioassays to test disease resistance of R1 progeny indicate that, compared to transgenic control and SB-37 plants, Shiva-1 seedlings exhibited delayed wilt symptoms and reduced disease severity and mortality after infection with a highly virulent strain of Pseudomonas solanacearum. © 1993. Agricultural Experiment Station, New Mexico State University The authors wish to acknowledge the expert technical assistance in peptide synthesis and purification provided by Martha Juban. This research was supported, in part, by funds from the Louisiana State University Agricultural Experiment Station.

The lethal concentration of cecropin SB37 was determined for protoplasts from 11 plant cultivars or experimental lines representing 7 plant species and for 9 bacterial species that are pathogens of these plants. Lethal concentrations ranged from 4.5 μM for tomato ( Lycopersicon esculentum cv Red Cherry) to 41 μM for sugarbeet ( Beta vulgaris REL 1). Cecropin SB37 exhibited potent antibacterial activity against all of the bacterial pathogens tested. Lethal concentrations ranged from 0.1–4.5 μM. The difference between the lethal concentrations of cecropin SB37 for protoplasts from certain plants and their respective bacterial pathogens suggests it may be feasible to protect against these pathogens by introducing a modified cecropin gene into the plant.