- Production of crops that are resistant to specific insect pests: Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces proteins that show specific toxicity to some insects. Bt has been used as an insecticide spray to protect crops from the European corn borer. The use of Bt in the form of a spray has been limited by the fact the bacteria are unable to survive for long on the surface of the crop. Another consideration is that for pests that start their life cycle inside the plant, Bt has limited effectiveness. Bt produces two classes of prions that show toxicity to specifc insects. Cytolysins (Cyt) are toxic to insect in the orders Coleoptera (i.e. beetles) and Diptera (i.e. flies). Crystal proteins (Cry) are toxic towards insects in the order Lepidopterans (moths and butterflies). Genes that code for various Cry proteins have been inserted into some crops to give them resistance to specific insect pests.
- Production of crops that are tolerant to herbicides: The broad spectrum herbicide glyphosate (Roundup) acts by blocking a step in the synthesis of some amino acids which are required for growth and development of the plant. Roundup acts by binding to the enzyme 5-enolpyruvyl-shikimate synthase (EPSPS) and thus blocks its action. Agrobacterium, another soil bacterium is not affected by Roundup because it uses a slightly different EPSPS and as a result, is not affected by Roundup. The gene that codes for EPSPS in Agrobacterium has been inserted into various crops to give them resistance to Roundup.
Liberty (Glufosinate ammonium) is another broad spectrum herbicide that has been used in a similar manner. Liberty acts by binding to the enzyme Glutamine synthetase which is involved in synthesis of some amino acids as well as recycling ammonium. A gene that codes for Phosphinothricin acetyl transferase (PAT) confers resistance. This enzyme destroys Liberty thus rendering it inactive.
- Manipulation of the breeding system: Modern biotechnology has also been used to insert genes that result in male sterility. For example, the barnase gene derived from Bacillus amyloliquefaciens has been inserted into plants. The gene codes for the barnase ribonuclease (RNAse) enzyme which interfers with Ribonucleotide (RNA) in the cells of the anthers causing sterility.
- Modification of product quality:
- Tolerance to specific diseases: :
- Tolerance to biotic stress: