What are Cry proteins? Name an organism that produce it. How has man exploited this protein to his benefit?

Explanation

Cry proteins are insecticidal toxic protein produced by cry genes of Bacillus thuringiensis. It is also called Bt-toxin.
Man has explorted this protein to make insect resistant plants by introducing genes of bacteria into them using Agrobacterium tumefaciens having Ti plasmid. Bt toxin genes are 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 encoded by the genes cry I c and cry II Ab control the cotton bollworms that of cry IAD controls corn borer.
The part of Tiplasmid with desired Bt-toxin gene spliced into it, is inserted into the chromosomes of the host plant where it produces copies of itself, by migrating from one chromosomal position to another at random. But it no longer produces tumours.
Such plant cells are then cultured, induced to multiply and differentiate to form plantlets.
Transferred into soil, the plantlets grow into mature plants, carrying the Bt toxin gene, expressed throughout the new plant.
Bt toxin gene forms some protein crystals. These crystals contain a toxic insecticidal protein. 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 solubilizes 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 bollworm insect.