Write a detailed note on Bt. Cotton.

Explanation

Bacillusthuringiensis produces proteins that kill certain insects like lepi-dopterans (tobaccco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forms some protein crystals. These crystals contain a toxic Insecticidal protein. Why does this toxin not kill the Bacillus (bacterium) ? The Bt toxin proteins exist as inactive protoxins but once an insect ingests the inactive toxin it is converted into an active form of toxin due to the alkaline pH of the alimentary canal that solublize the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores which cause cell swelling and lysis and finally cause death of the insect.
Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton. The choice of genes depends upon the crop and targeted pest, as most Bt toxins are insect-group specific. The toxin is coded by a gene named cry. These are numerous genes. For example, the proteins eincoded by the genes cry IAc and cry ITAb control the cotton bollworms that of cry IAD controls corn borer.