Downloaded 65 times
More Related Content
Similar to insect resistance plant, bt gene
insect resistance plant, bt gene
- 1. Insect Resistance Plant By KAUSHALKUMAR SAHU Assistant Professor (Ad Hoc) Department of Biotechnology Govt. Digvijay Autonomous P. G. College Raj-Nandgaon ( C. G. )
- 2. SYNOPSIS Introduction Definitionof an Insect Resistant Plant What is the Bt gene? History The crystal ( cry)Proteins Definition of cry protein How does Bt work? Mechanism of Bt toxicity Mode of Action of Insecticidal Crystal Protein Bt Technology The Insect Resistance Problem Advantages Limitations Conclusion References
- 3. Introduction Insect attack isa serious agricultural problem leading to yield losses and reduced product quality. Insects can cause damage both in the field and during storage in soils. Insect resistant transgenic plants contain either a gene from the bacterium B.thuringiensis or some other gene. B.thuringiensis has been used since World War 1st,particularly in Europe,to control some insect pests.
- 4. Definition of anInsect-Resistant Plant In the broadest sense, plant resistance is defined as "the consequence of heritable plant qualities that result in a plant being relatively less damaged than a plant without the qualities." In practical agricultural terms, an insect-resistant crop cultivar is one that yields more than a susceptible cultivar when confronted with insect pest invasion. Resistance of plants is relative and is based on comparison with plants lacking the resistance characters, i.e., susceptible plants.
- 5. What is theBt gene? Bacillus thuringiensis, or Bt, is a type of bacterium found in soil. It is an aerobic, motile , gram-positive, endospore-forming bacillus . The soil bacterium produces a protein that is toxic to various herbivorous insects , including moths, beetles, mosquitoes, black flies, nematodes and flatworms. The protein, known as Bt toxin, is produced in an inactive, crystalline form. The Bt gene is a small stretch of DNA from the Bt chromosome that codes for the production of these protein crystals. When consumed by insects, the protein is converted to its active, toxic form (delta endotoxin), which in turn destroys the gut of the insect. Bt preparations are commonly used in organic agriculture to control insects, as Bt toxin occurs naturally and is completely safe for humans.
- 6. History B. thuringiensiswas first discovered in 1901 by Japanese biologist Shigetane Ishiwatari. In 1911, B. thuringiensis was rediscovered in Germany by Ernst Berliner, who isolated it as the cause of a disease called Schlaffsucht in flour moth caterpillars. In 1976, Robert A. Zakharyan reported the presence of a plasmid in a strain of B. thuringiensis and suggested the plasmid's involvement in endospore and crystal formation.
- 7. The crystal (cry)Proteins The cry gene of B.thuringiensis produces a protein, which forms crystalline inclusions in the bacterial spores. These crystal proteins are responsible for the insectisidal activities of the bacterial strains. Upon sporulation, B. thuringiensis forms crystals of proteinaceous insecticidal δ-endotoxins (called crystal proteins or Cry proteins), which are encoded by cry genes. In most strains of B. thuringiensis, the cry genes are located on the plasmid. Cry toxins have specific activities against insect species of the orders Lepidoptera (moths and butterflies), Diptera (flies and mosquitoes), Coleoptera (beetles), Hymenoptera (wasps, bees, ants and sawflies) and nematodes.
- 8. Thus, B.thuringiensis serves as an important reservoir of Cry toxins for production of biological insecticides and insect- resistant genetically modified crops. When insects ingest toxin crystals, the alkaline pH of their digestive tract activates the toxin. Cry toxin gets inserted into the insect gut cell membrane, forming a pore. The pore results in cell lysis and eventual death of the insect. Definition of cry protein Any of several proteins that comprise the crystal found in spores of Bacillus thuringiensis (Bt). Activated by enzymes in the insect's midgut, these proteins attack the cells lining the gut, cause gut paralysis and subsequently kill the insect that is known as cry protein.
- 9. How does Btwork? Bt has to be eaten to cause mortality. The Bt toxin dissolve in the high pH insect gut and become active. The toxins then attack the gut cells of the insect, punching holes in the lining. The Bt spores spills out of the gut and germinate in the insect causing death within a couple days.
- 10. 1. Insecteats Bt crystals and spores. 2. The toxin binds to specific receptors in the gut and the insects stops eating. 3. The crystals cause the gut wall to break down, allowing spores and normal gut bacteria to enter the body. 4. The insect dies as spores and gut bacteria proliferate in the body.
- 11. Bt actionis very specific. Different strains of Bt are specific to different receptors in insect gut wall. Bt toxicity depends on recognizing receptors, damage to the gut by the toxin occurs upon binding to a receptor. Each insect species possesses different types of receptors that will match only certain toxin proteins, like a lock to a key.
- 12. Mode of actionof insecticidal crystal proteins The insecticidal crystals are composed of a large protein that is essentially inactive. When a caterpillar ingests some of the insecticidal crystals, the alkaline reducing conditions of the insects midgut cause the crystals to dissociate and release the crystal protein. At this stage the protein toxin is inactive, but specific proteases within the gastric juices of the insect chop the protein down to its protease resistant core that is now fully active. This activated insecticidal protein then binds to a specific receptor on the brush border membranes of the cells lining the midgut and inserts itself into the cells membrane.
- 13. When abouteight of these aggregate together, they form a pore or channel through the membrane, and allow the cell contents to leak out causing the death of the cells essential for nutrient absorption. rapidly stop feeding and The insects eventually starve to death or die from secondary bacterial infections within about 24 hours.
- 14. FIG:- mode ofaction of BT in killing insects.
- 15. Bt Technology DNAtechnology makes it possible to locate the gene that produces Bt proteins lethal to insects and transfer the gene into crop plants. First, scientists identify a strain of Bt that kills the targeted insect. Then they isolate the gene that produces the lethal protein. That gene is removed from the Bt bacterium and a gene conferring resistance to a chemical (usually antibiotic or herbicide) is attached that will prove useful in a later step. The Bt gene with the resistance gene attached is inserted into plant cells. At this point, scientists must determine which plant cells have successfully received the Bt gene and are now transformed. Any plant cell that has the Bt gene must also have the resistance gene that was attached to it.
- 16. Researchers growthe plant cells in the presence of the antibiotic or herbicide and select the plant cells that are unaffected by it. These genetically transformed plant cells are then grown into whole plants by a process called tissue culture. The modified plants produce the same lethal Bt protein produced by Bt bacteria because the plants now have the same gene.
- 18. Advantages There are severaladvantages in expressing Bt toxins in transgenic Bt crops: The level of toxin expression can be very high, thus delivering sufficient dosage to the pest. The toxin expression is contained within the plant system, hence only those insects that feed on the crop perish. Bt crops can also kill insects even after they have invaded the plant tissues. The toxin expression can be modulated by using tissue-specific promoters, and replaces the use of synthetic pesticides in the environment. Bt is washed away from plants with water or rain, and it is broken down by sunlight. These properties convey an environmental benefit.
- 19. LIMITATIONS Constant exposureto a toxin creates evolutionary pressure for pests resistant to that toxin. Already, a diamondback moth population is known to have acquired resistance to Bt in spray form (i.e., not engineered) when used in organic agriculture. High levels of transgene expression, nearly all of the heterozygotes (S/s), i.e., the largest segment of the pest population carrying a resistance allele, will be killed before they reach maturity, thus preventing transmission of the resistance gene to their progeny.
- 20. Conclusion Insect attackis a serious agricultural problem leading to yield losses and reduced product quality. Insects can cause damage both in the field and during storage in soils. Each year, insects destroy about 25 percent of food crops worldwide. The larvae of Ostrinia nubilalis, the European corn borer, can destroy up to 20 percent of a maize crop.
- 21. References 1 .U.Satyanarayan- Biotechnology 2. B.D.Singh - Biotechnology Website: www.google.co.in