GENETIC-ENGINEERING OF INSECT-RESISTANT CROP PLANTS WITH BACILLUS-THURINGIENSIS CRYSTAL PROTEIN GENES

Bacillus thuringiensis a soil bacterium, produces crystalline proteins which are toxic to the insect larvae. The toxicity Is brought about b y the protein fragments released due to the action of mid-gut protease s, and their binding to the receptors on the epithelial membrane, whic h in turn loses its selective permeability. The genes (cry) coding for these insecticidal crystal proteins have been cloned, characterized a nd mobilized into a number of crop plants. Such transgenic plants were shown to be resistant to insects. However, the expression of these ba cterial genes in higher plants has been limited because of differentia l codon usage. Various strategies for maximizing the expression of the se genes in transgenic plants have been described. In addition, altern ative approaches have been suggested for circumventing the development of resistance in insects to the crystal proteins.