Plant Biotechnology. Chapter 6. Motivation for genetically engineered crops. Agriculture is the biggest industrial sector in the world $1.3 trillion of products/year Over past 40 years, world population has doubled while agricultural land area has increased by only 10%. Plant transgenics.
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Motivation for genetically engineered crops
- Agriculture is the biggest industrial sector in the world
- $1.3 trillion of products/year
- Over past 40 years, world population has doubled while agricultural land area has increased by only 10%
- Transfer of genes to plants directly accelerates selective breeding practices used in the past.
- Cotton fiber strength
- increased 1.5% per year through conventional breeding
- Increased 60% by inserting a single gene into the plant
- Corn and soybean have been targets of much genetic engineering
Genetic engineering techniques applied to plants
- Many types of plants can regenerate from a single cell, similar to a bacterium.
- The resulting plant is a clone or replica of plant from which original cell was taken.
- Protoplast fusion
- Introducing a gene into a “denuded” plant cell and generating a new plant
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This bacterium naturally infects plant cells causing cancerous growths - crown gall disease
Infection (vir) genes carried on Ti plasmid
Agrobacterium tumefaciens as a vector for transferring foreign genes into plant chromosome
Vir genes copy T-DNA
Open channel in bacterial cell membrane for T-DNA to pass through
T-DNA enters plant through wound, integrates itself into plant chromosome
Leaf fragment technique used to introduce foreign genes into plant
- Small discs are cut from plant leaf
- Discs are cultured to start a new plant
- Early in the regeneration process, the bacterium Agrobacterium tumefaciens carrying a Ti plasmid is introduced into the culture
- The plasmid DNA combines with the plant chromosome
- Discs are treated with hormones to encourage shoot and root development and then the new plant is planted in the soil
Leaf fragment technique
Make leaf discs
Transfer to shoot stimulating medium
with Ti plasmid
with foreign gene
Transfer to filter
paper over nurse
Culture 2-3 days
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- Used to produce the Flavr-Savr tomato in 1994.
- Enzyme polygalacturonase breaks down structural polysaccharide pectin in wall of a plant.
- This is part of the natural decay process in a plant
- Monsanto identified the gene than encodes the enzyme and made another gene that blocked the production of the enzyme.
- Plants are susceptible to diseases caused by viruses (tobacco mosaic virus)
- Virus surface protein induces an immune response in the plant against the protein/virus
- Researchers inserted the virus protein into the plant genome using the Ti plasmid/ Agrobacter vector for insertion and expression in the plant
Concerns about genetically modified foods
- Human health
- Unsuspected allergens
- What other issues are there?
- Messing up the gene pool of non-target species in the environment
- Lateral gene transfer
- Still poorly understood in nature
- Variety of techniques are available to introduce genes into plants and have the plants express the gene
- Such genetic engineering is used to
- Improve disease resistance
- Flavor of product
- Nutrition of product
- Shelf life of product
- Any other property of plant that improves its value