The plants which are genetically engineered to carry desirable traits like disease resistance, insect resistance, herbicide resistance are called as transgenic plants.
Examples: Bt cotton, Golden rice, Flavr Savr tomato
a. Bacillus thuringiensis (Bt) is a soil bacterium that produces a protein with insecticidal property.
Bt toxin proteins occur as inactive protoxin.
The ‘cry’ gene codes for this inactive protoxin.
Crops have now been genetically engineered using rDNA technology, by inserting the ‘cry’ gene in plants.
After the insects ingest the transgenic crops, they are killed because the inactive protoxin is converted into the active form due to alkaline pH of the insect gut.
Bt toxin gene has been cloned and introduced in many plants to provide resistance to insects without the need of insecticides.
Bt cotton is commercially available to control the disease affecting the cotton balls.
b. Golden rice is genetically engineered rice with greater pro-vitamin A [β – carotene] content.
c. In Flavr Savr variety of tomato, the expression of a native gene that codes for the enzyme polygalacturonase, has been blocked. The enzyme is responsible for degradation of pectin during fruit ripening.
In the absence of this enzyme, the fruit ripening or softening is delayed and hence, the fruit remains fresh for longer periods and flavour is saved.
