Lecture 11/12 - Applications of transgenic plant technology Flashcards
What are 4 examples of current applications of Transgenic technology?
1-herbicide tolerance e.g. introduction of tolerance to broad-spectrum herbicide Glyphosphate, ‘round-up ready’ crops
2-Pest resistance e.g. synthesis of insecticidal proteins in cotton and maize, ‘Bt crops’
3-Virus resistance e.g. using RNAi to supress viral accumulation, ‘Rainbow papaya’
4-Nutritional enhancement e.g. alteration of composition of food to increase nutritional value e.g. ‘Golden Rice’
Why create crops with herbicide resistance?
-weed control one of the biggest problems in crop production and is controlled by weeding/herbicides
What is Glyphosate?
a broad spectrum systemic herbicide
- does not bio-accumulate
- breaks down rapidly
What is the process of Glyphosate treatment?
1) Glyphosate is added to Shikimic acid and Phosphoenol pyruvate, Plant EPSP sunthase converts to EPSP
2) forms aromatia amino acids
How are GM Glyphosate tolerant crops ‘round up ready?
survive after round up treatment
-contain EBBP synthase gene from bacteria resistant to glyphosate
What is 2,4 Dichlorophenoxyacetic acid? (2,4 D) And how is it used for herbicide resistance?
- synthetic auxin herbicide
- acts on auxin receptors (essential for normal plant growth)
- bacterial AAD enzyme class cleaves 2,4D
- soybeans carrying AAD transgene are resistant to 2,4 D herbicide
What is an USA and Canadian major corn pests and what is its economical effects?
European corn borer (US & Canada)
-damage and control costs >$1 billion yearly
What is Bt?
Bacillus thuringiensis, a soil bacterium, spores contain toxic crystalline (Cry) protein
Insecticide
How does Bt insecticide work?
1) Insect eats Bt crystals and spores
2) Toxin binds to specific receptors in gut and the insect stops eating
3) gut wall breaks down allowing spores and normal bacteria to enter the body
4) Insect dies as spores and gut bacteria proliferate within the body
Why create transgenic Bt crops?
Performance of Bt insecticides not consistent
-toxin is sensitive to UV, heat, dessication
-incomplete coverage of feeding sites
-reduced toxicity against older larvae
Bt crops overcome these limitations
-protein is protected from rapid environmental degredation
-plants produce protein in tissues where insects feed so coverage not an issue
-protein is present whenever newly hatched larvae emerge so timing not a problem
What are the pros and cons of Bt crops?
Reduced pesticide use
-2004 farmers used 77 million kg less pesticides on Bt cotton and 6.3 million less on Bt corn than in 1993
Lowered risk of poisoning
Less danger to wildlife and environment, fewer beneficial insects harmed
Lowered costs as fewer pesticide applications may be needes
CONS
Continued exposure to insecticide can lead to insecticide resistance
Risk of losing the use of a relatively safe insecticide
What are two examples of cotton pests?
Cotton bollworn
Pink Bollworm
What is insect resistance management (IRM)?
Strategies to delay the development of insect resistance to Bt
What is the most widely used IRM strategy?
The use of refuges
Strip of non Bt corn next to field of Bt corn
How can refuges prolong the usefulness of Bt crops?
Maintains a population of insect pests not resistance to Bt proteins, allowing non resistant pests to mate with any resistance pests that might emerge
What technique is an alternative IRM strategy to refuges?
Sterile Insect Technique
What is sterile insect technique?
Release of sterile insects along with presence of Bt cotton to reduced the level of damage and reduce chance of moth resistance
How has Sterile Insect technique been shown to be effective?
Three conditions
1) Bt cotton begins with low damage level but high resistance in absence of refuges -> emergence of resistance alleles -> severe damage from resistant insects
2) Non Bt cotton has severe damage from wild insects -> release large amount of sterile moths -> low level of damage but costly release of large numbers of sterile moths
3) Bt cotton and release of some sterile moths -> v low chance of damage with reduced change of resistance and less extensive release of sterile insects
How is virus resistance generated in Papaya?
Use RNAi to supress papaya ringspot virus
What is the push-pull system?
Main crop and trap crop
Main crop attracts natural enemies, moths are pushed away from the main crop
-Trap crop attracts moths
Why is Golden Rice beneficial?
-worldwide, 3 billion people depend on rice as major staple
BUT rice lacks beta-carotene which can be converted to vitamin A when digested
Vitamin A deficiency major health problem
-WHO 100-140 million children are vitamin A deficient
-leading cause in preventable blindness in children
-implicated in >1million deaths yearly
What is golden rice?
Rice that has been genetically engineered so that the endosperm (edible part) contain beta-carotene
What is the B carotene pathway?
1) IPP converted to Geranylgeranyl diphosphate
2) Phytoene synthase converts Geranylgeranyl diphosphate to Phytoene
3) Phytoene desaturase and Carotene desaturase convert Phytoene to Lycopene
4) Lycopene-cyclase converts Lycopene to B carotene (vitamin A precursor)
What enzymes does rice lack for making beta carotene?
- Phytiene synthase
- Phytodene desaturase
- Carotene desaturase
- Lycopene-cyclase
