Amplification of a chimeric Bacillus gene in chloroplasts leads to an extraordinary level of an insecticidal protein in tobacco.

The Bacillus thuringiensis (Bt) crystal toxins are safe biological insecticides, but have short persistance and are poorly effective against pests that feed inside plant tissues. Production of effective levels of these proteins in plants has required resynthesis of the genes encoding them. We report that amplification of an unmodified crylA(c) coding sequence in chloroplasts up to approximately 10,000 copies per cell resulted in the accumulation of an unprecedented 3-5% of the soluble protein in tobacco leaves as protoxin. The plants were extremely toxic to larvae of Heliothis virescens, Helicoverpa zea, and Spodoptera exigua. Since the plastid transgenes are not transmitted by pollen, this report has implications for containment of Bt genes in crop plants. Furthermore, accumulation of insecticidal protein at a high level will facilitate improvement in the management of Bt resistant insect populations.