Bacillus thuringiensis, a soil bacterium, produces crystalline proteins which are toxic to the insect larvae. The toxicity is brought about by the protein fragments released due to the action of mid-gut proteases and their binding to the receptors on the epithelial membrane, which in turn loses its selective permeability. The genes (cry) coding for these insecticidal crystal proteins have been cloned, characterized and mobilized Into a number of crop plants. Such transgenic plants were shown to be resistant to insects. However, the expression of these bacterial genes in higher plants has been limited because of differential codon usage. Various strategies for maximizing the expression of these genes in transgenic plants have been described. In addition, alternative approaches have been suggested for circumventing the development of resistance in insects to the crystal proteins.
Bacillus thuringiensis, crystal protein genes, genetic engineering, transgenic plants
