Investigation and Development of Bacillus thuringiensis Insecticidal Proteins for Expression in Transgenic Plants

Abstract

In 1901 Ishiwata reported that the spore-forming bacterium Bacillus thuringiensis (Bt), caused death of the silkworm (Bombyx mori) (DuImage and Aizawa, 1982). Subsequently Bt has been found to produce three groups of novel protein toxins that are specific for a large number insect crop pests and some nematodes (de Maagd et al., 2001). The Cry and Cyt toxins (δ-endotoxins) are produced as cytoplasmic inclusions during sporulation and the Vip toxins (Vegetative Insecticidal Proteins) are secreted from the cells during vegetative growth. In vivo the Cry and Cyt toxins bind to insect-specific receptors on the surface of gut epithelial cells and in a second, irreversible step insert into the cell membrane to form leakage channels that result in cell death by colloid osmotic lysis (Knowles and Ellar, 1987). The receptors for some Cry toxins have been shown to be aminopeptidase-N and cadherin-like proteins exposed on the gut epithelial cell surface. Much less is known about the mechanism of the secreted Vip proteins and their receptors, but a recent report (Estruch et al US patent 5,877,012) claims that Vip3a (89kDa) binds to the epithelial cell surface protein Tenascin-X and causes cell lysis by triggering apoptosis. Vipl and Vip2 are binary toxins.