Explain the production of Bt-cotton.

Explanation

Bt-cotton. Some strains of Bacillus thuringiensis produce toxic proteins that kill the insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forma protein crystals containing a toxic insecticidal protein during a particular phase of their growth. Bt-toxin occurs as an inactive protoxin and it is converted into an active toxin due to alkaline pH of the gut which solubilise the crystals. The activated toxin creates pores in the midout epithelial cells by lysing that causes death of the insect.
Specific Bt-toxin genes called cry genes were isolated from B. thuringiensis and incorporated into several crop plants such as cotton. It is done with the help of part of Ti plasmid called T-plasmid found in soil bacterium Agrobacterium tumefaciens. Ti-plasmid with desired Bt-toxin gene is inserted into chromosomes of cotton plant, where it produces copies of itself but not producing tumor. Such plant cells are then cultured and form plantlets, which are grown in soil to form Bt-cotton plants, which are resistant against attack by Bollworms. The choice of genes depends upon the crop and the target pest, as most Bt-toxins are insect-group specific.
There are a number of types of cry genes and cry I Ac and cry II Ab controls the cotton bollworms, while cry I Ab controls corn borer.