Insect Resistance in Transgenic Plants - Bt Cotton | NEET BIOLOGY STUDY MATERIAL

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Insect Resistance in Transgenic Plants - Bt Cotton

• Bt Cotton. Soil bacterium Bacillus thuringiensis (Bt for short) produces proteins that kill certain insects like lepidopterans (tobacco budworm, armywor), coleopterans (beetles) and dipterans (flies, mosquitoes).
• Bacillus 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 solublizes 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 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.
• There are number of genes.
• Two cry genes, cry IAc and cry II Ab have been incorporated in cotton.
• The genetically modified crop is called Bt cotton as it contains Bt toxin genes.
• The genes cry I Ac and cry II Ab control cotton bollworms.
• Similarly, cry I Ab has been introduced in Bt corn to protect the same from corn borer.
• Gene symbol usually has small letters and is invariably in italics, e.g. , cry.
• The first letter of the protein symbol, on the other hand, is always capital and the symbol is always written in roman letters, e.g. , Cry.
• The Government has agreed to allow cultivation of genetically modified Bt Cotton.
• Bt cotton farming has shown good results in Malwa region of Punjab.
• The government should encourage such farming.
• It will save water starved Malwa region from turning into desert as cotton which needs much less water, will replace paddy.

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