How does the insecticidal protein encoded by cry gene in Bt cotton kill the cotton ball worms? OR  Bt toxin gene has been cloned from bacteria and expressed in plants like cotton . This provides the plant resistance to insects without using insecticides. Explain how the plants kill the insects.

 Bt toxin is produced by a bacterium called Bacillus thuringiensis. Bt toxin gene has been cloned from the bacteria and been expressed in plants to provide resistance to insects without the need for insecticides. Eg. the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms. Bt cotton produces proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein Bt toxin as inactive protoxins which when ingested by insect larvae is converted into an active form due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect.