Genetic Engineering of the Cry Gene as a Source of Resistance to Insect Pest of Some Major Crops

In recent times, genetic engineering has become a source of agriculture innovations, providing a new solution to the age of old problems. Transfers of genes between plant species have played an important role in crop development for many decades. Advancement field of genetic engineering have provided new technologies for gene identification and gene transfer into plants has provided the opportunity for genetically engineering insect pest resistance into agriculturally desirable cultivars without altering critical quality traits. Bt toxin gene the source of the insecticidal toxins produced in commercial transgenic plants is the soil bacterium Bacillus thuringiensis (Bt). Bacillus thuringiensis synthesizes crystalline proteins during sporulation. These crystalline proteins are highly insecticidal at very low concentrations. With the advent of molecular biology and genetic engineering, it has become possible to use Bt more effectively and rationally by introducing the cry genes of Bt in crop plants. The bacterium produces an insecticidal crystal protein (ICP: also called Cry proteins, encoded by cry genes). The toxin protein binds to specific receptors present in the midgut epithelial membranes. The disturbances in osmotic equilibrium and cell lysis lead to insect paralysis and death. Scientists have mitigated this risk through stacking or pyramiding different genes such as multiple but different Cry genes and Cry genes combined with other insecticidal proteins, which target different receptors in insect pests but also provide resistance to a wider range of pests. Alternatively, synthetic variants of Cry genes has been employed as in the case of MON863 which expresses a synthetic Bt kumamotoensis Cry3Bb1 gene against maize rootworm, which is eight times more effective than the native, non-modified version. The success of the transgenic approach led to the development of Bt crops, transgenic crops are used worldwide to control major pests of rice, cotton, maize and soybean. Rice effective against lepidopteron pests, Cotton (Gossypium hirsutum) tolerant to lepidopteran larvae (caterpillars), maize (Zea mays) tolerant to both lepidopteran and coleopteran larvae (rootworms) and soya bean (Glycine max) both lepidopteran and coleopteran larvae have become widely used in global agriculture and have led to reductions in pesticide usage and lower production costs. To overcome resistance acquired by insects against Cry toxins different strategies were employed to modify Cry functional domains to improve their toxicity. Therefore, multiple mutations/adaptations need to be made by target pests in order to develop resistance to this robust new generation of insect resistant crops. Keywords: Cry gene, Genetic engineering, Source of resistance to insect pest DOI: 10.7176/JBAH/11-7-04 Publication date: April 30th 202