Chapter 20 Flashcards
How can plants be genetically manipulated to produce flowers with unusual colours?
Manipulate genes for enzymes in anthocyanin biosynthesis pathways to produce different colours. Plants can also contain combination of flavonoids and carotenoids for more different colours.
How can soybeans be genetically manipulated to increase lysine content?
Increase lysine content of seeds by deregulating lysine biosynthetic pathway. Both AK and DHDPS are feedback inhibited by lysine. Therefore, feedback inhibition must be removed in order to overproduce lysine.
Process of genetic manipulation: cloning naturally lysine feedback-insensitive genes for DHDPS and AK. Genes were fused to chloroplast transit peptide gene under the control of seed-specific promoter; and introduced onto Ti plasmid binary vector into the plants.
This resulted in a five-fold increase in total lysine content in soybean.
How can vitamins be overproduced in rice plants?
Introduce beta-carotene biosynthetic pathway into rice.
How does an antigen expressed in a transgenic plant act as an edible vaccine
The ingested antigen, which is expressed as part of a plant, binds to and is taken up by M cells present in the lining of the intestine and is then passed to other cells in the immune system, including macrophages and B cells. The macrophages display portions of the antigen to the helper T cells, which in turn respond by secreting small molecules that activate B cells to synthesize and release antibodies that can neutralize the antigen.
How would you engineer an edible vaccine directed against chloerae-caused diarrhea?
Cholera toxin subunit B and A2 are fused to different antigen genes and transformed into transgenic potato plants. Without toxin subunit A, the vaccine is non-toxic.
How would you engineer rice plants to overproduce tetrahydrofolate? Why would you do this?
Genes in chloroplastic and cytosolic pathway (rate-limiting) introduced from A. thanliana into plant and over expressed. Tetrafolate is vitamin B9 which is a necessary component of human diet.
Why is it necessary to genetically engineer soybean plants to have a small amount of phytate in their seeds when low phytate mutants may be selected following conventional mutagenesis
Phytate cannot be digested by nonruminant animals. So it runs through the gastrointestinal tract and elevates the amount of phosphorus in manure. High phosphorus levels can lead to environmental consequences.
Low-phytate mutants were isolated and the enzyme involved in one of the steps was identified. This enzyme was altered so the amount of phytate in the seed was reduced by 50-90% which lead to an increase in inorganic phosphate. However, extensive reduction of phytate has negative effects on whole plant (decrase in seed germination, emergence, stress tolerance, and seed filling. Therefore, a mutant of soybean was constructed so that the transport of phytate to seeds was defected by silencing the ATP binding cassette (ABC) transporter.
Briefly describe a vector system that may be used to engineer plants to produce large amounts of full size IgG molecules?
Coinfect plant cells with two separate plant virus vectors that can coexist in the plant. One vector will produce the heavy chain and the other produces the light chain of the IgG molecules.
Why are plants an attractive host system compared to bacteria and animal cells in culture for the production of human therapeutic proteins?
Plants are easy to grow and can generate considerable biomass. Crops can also be grown inexpensively. There is a reduced risk of mammalian virus contamination from when proteins are produced in animal cells.
What is phytate? How can the levels of phytate in seeds be modulated? Why would you want to do this?
Phytate is a form of phosphorous found in cereals and legumes. Construct mutants that are defective in transport of phytate to seed by silencing ATP-binding cassette (ABC) transporter in a seed specific manner. Cannot reduce phytate in plant (negative impact without it) but excretion of phytate by animals is bad for the environment.
Describe a strategy for developing a plant vaccine against type 2 shiga toxin
Isolate the genes encoding for Shiga toxin A and B subunits. Inactivate the A subunit and modify the two subunits to eliminate sequences on both genes that might adversely affect their transcription in plants. Insert sequences into T-DNA of binary Ti plasmid vector under the control of cailiflower mosaic virus 35s promoter. Transform into tobacco plant.
How can the lignin content of trees be decreased? What is the benefit of this type of genetic manipulation?
Create antisense gene for skimiate hydroxycinnmoyl transferase gene. This decrease in lignin can change treatment of tree using mild treatment before enzymatic digestion which is cheaper and more environmentally friendly. Cell walls can more easily be treated by cellulose and hemicelluloses enzymes.
