Lecture 11/12 - Applications of transgenic plant technology Flashcards Preview

Molecular Biotechnology > Lecture 11/12 - Applications of transgenic plant technology > Flashcards

Flashcards in Lecture 11/12 - Applications of transgenic plant technology Deck (37):

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


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
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


How was golden rice created?

B-carotene pathway genes added
-Phytiene synthase - Daffodil gene
-Phytodene desaturase and Carotene desaturase - single bacterial gene
-Lycopene-cyclase - daffodil gene


What is Golden Rice 2?

New strain of golden rice provides the daily recommended Vitamin A allowance with 70g portion rice, by using Maize Psy instead of Dafodill Psy


Who owns golden rice?

-70 intellectual propery rights (32 companies)
-Humanitarian Use license issued
-as long as farmer makes less than $10,000 no royalties paid
-farmer can save seeds for replanting


What are 3 controversies of transgenic plants?

-Risk to human health e.g. antibiotic resistance genes
-Unfavourable to small farmers e.g. Terminator technology
-Risk to the environemtn e.g. monach butterfly


How might the antibiotic resistance gene be removed from transgenic plants?

the Cre-lox system


What are cre and loxP in the cre-lox system and what do they do?

Cre:cyclization recombination encodes a site specific recombinase
loxP: P1 bacteriophage sequence (34bp) not found in plants or animals

3)Cre catalyses recombination between loxP sites flanking selectable marker gene
1)Create transgenic plant expressing gene of interest
2)Cross plant expressing Cre recombinase
3)Cre catalyses recombination between loxP sites flanking selectable marker gene
4)Intervening DNA is excised, removing selectable marker


How are transgenic plants unfavourable to small farmers?

Through use of terminator technology
(Genetic Use Restriction Technology, GURT)


What is terminator technology?

-plant encorperates a trait (toxin) that kills developing embryos late in development
-expression of toxin is induced by a chemical applied to seed of the parent plant
-seed cannot be saved and planted next year
-prevents spread of transgenes


How is production of the toxin prevented in seeds that have no had the chemical inducer applied? (terminator technology)

1) Repressor is expressed
2)repressor binds to gene binding site and prevents recombinase expression
3)blocker consequently prevents production of the toxin


How is the toxin expressed in seeds that have had the chemical inducer applied? (terminator technology)

1)Repressor is expressed
2)Chemical inducer applied by seed company prevents repressor binding
3)recombinase is produced and excises the blocker
4) Toxin is available to be produced after late promotor


Does the Bt toxin endanger pollinator species?

-Dusted Bt corn pollen onto milkweed leaves and fed to Monarch larvae
-Larvae ate less and grew more slowly
-over four days nearly half larvae died compared with none in the control groups
Bt 176 produces pollen that is highly toxic to Monarch larvae


Why does Bt 176 produce a pollen that is highly toxic to Monarch larvae?

promotor is very efficient at producing Bt in pollen


How has damage to Monarch butterflies been reduced from Bt corn?

Bt 176 (highly toxic) transgene used in <2% corn acreage
More commonly grown Bt varieties do not produce much of the toxic Bt protein in pollen
-larvae can eat 1600 grains of pollen per cm2 of leaf surface without any ill effects