8 Biotechnology- Biology for Human Welfare
8.2 Transgenic plants
Transgenic plants
Dr V Malathi
Transgenic plants are genetically modified organisms (GMOs). These plants carry foreign genes introduced through genetic engineering. These plants can take up desirable traits such as pest resistance, enhanced nutrition, and tolerance to environmental stress and thus have revolutionized agriculture, medicine, and environmental science.Bt cotton, Bt corn, Bt potato, and Bt tobacco are a few types of transgenic plants. Endotoxin, which is present in these genetically modified plants, inhibits the activity of a variety of pests that are members of the order Lepidoptera, Coleoptera, Hymenoptera, Diptera, and Nematoda.
Development of Transgenic Plants
Genetic engineering techniques are used to create transgenic plants. These plants are produced by inserting foreign genes into a plant’s genome.These genes provide the plant additional features or attributes, such enhanced nutritional value or resistance to pests, herbicides, or environmental stressors.
The following steps are typically included in the process
- Gene Identification and Isolation:
- The first step involves the identification of the gene of interest from another organism that confers a desirable trait (e.g., pest resistance or drought tolerance).
- The donor organism—such as a bacteria, mammal, or other plant—has the desired gene has to be identified
- This gene is then isolated using molecular biology techniques.
- Gene Cloning:
- The isolated gene is then cloned using vectors such as plasmids or viral genomes.
- This is done by inserting the desired gene into a suitable vector (a carrier DNA molecule, such as a plasmid or a virus).
- To make sure the gene works correctly in the target plant, a promoter sequence—which regulates gene expression—is attached to it.
- Gene Insertion into Plant Cells:
- The next steps involves the introduction of the transgene into plant cells .
- This is done by using methods such as:
- Agrobacterium-mediated transformation: The gene is inserted into the plant genome by use of Agrobacterium tumefaciens, a naturally occurring soil bacterium.
Gene gun (Biolistics): tiny particles coated in DNA are injected into plant cells.
Electroporation: The process of making holes in the cell membrane for DNA entrance using electric pulses.
Microinjection : This is direct injection of DNA into the nucleus of plant cells .
- Selection and Regeneration:
- Selectable indicators, such as resistance to antibiotics or herbicides, are used to identify plant cells that have successfully incorporated the transgene.
- Using tissue culture techniques, the transformed cells are cultivated in hormone-rich, nutrient-rich conditions to grow back into complete plants.
- Screening and Verification:
- Transgenic plants are examined using methods such as PCR, Southern blotting, or protein assays to verify the introduced gene’s existence, expression, and stability.
6. Commercialization and Field Testing :
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- The performance of the transgenic plants is evaluated in the field. Prior to commercial cultivation, regulatory approval is sought to guarantee safety.
Agrobacterium-mediated plant transformation
One popular technique for transferring foreign genes into plants is agrobacterium-mediated gene transfer. This method takes advantage of the soil bacterium Agrobacterium tumefaciens‘ innate capacity to introduce DNA into plant cells. Crown gall disease in plants is caused by the bacterium Agrobacterium tumefaciens.
It causes tumors by transferring a portion of its DNA, known as T-DNA, from the Ti (tumor-inducing) plasmid into the plant genome.
Ti Plasmid
The size of the Ti plasmid is considerable, usually between 200 and 800 kilobases.T-DNA (Transfer DNA) Region which is between 10 and 30 kilobases long, gets incorporated into the plant’s DNA during infection.
The Ti plasmid contains the following genes /regions
T-DNA : this region contains genes responsible for Tumor formation: These genes cause unchecked cell division, which results in the creation of a crown gall and tumor and Opine synthesis: The bacterium uses the opines produced by the enzymes encoded by these genes as a source of nutrition.
Border Sequences : The left border (LB) and right border (RB) are two brief (about 25 base pairs) direct repeat sequences that flank the T-DNA. The removal and integration of T-DNA into the plant genome depend on these sequences.
Vir (Virulence) Region : This area, which lies outside the T-DNA, is home to genes that facilitate the transfer process. Proteins that excise the T-DNA are encoded by the Vir genes. These Deliver the T-DNA to the nucleus of the plant cell and aid in its incorporation in the plant’s genome.
Origin of Replication : permits independent replication of the Ti plasmid in the Agrobacterium.
Opine Catabolism Genes :Opines, which are formed by infected plant cells, can be used by Agrobacterium as a source of carbon and nitrogen
Steps involved in Agrobacterium mediated gene transfer in plants
The following crucial steps are involved in the process:
Engineering the Ti Plasmid ( disarmed Ti plasmids ): To stop tumor formation, the T-DNA’s tumor-inducing genes are eliminated. The desired gene and a selectable marker gene (such as tolerance to antibiotics or herbicides) are added to the T-DNA region.
Preparation of the Vector : A non-tumorigenic, disarmed form of the bacteria is employed.The modified Ti plasmid carrying the desired gene is introduced into Agrobacterium tumefaciens.
Preparing Plant Cells : In order to expose cells for infection, plant tissues or explants (such as leaf discs) are injured. Agrobacterium infection susceptibility is increased by wounding.
Co-Cultivation : The explants are incubated with Agrobacterium tumefaciens.The T-DNA containing the desired gene is then transferred by the bacterium into the plant cell’s genome through the following steps:
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- Attachment: Agrobacterium attaches to the plant cell wall.
- T-DNA Transfer: T-DNA is excised from the plasmid and transported into the plant cell nucleus . The bacterium’s Vir (virulence) proteins mediates this transport.
- Integration: The T-DNA then integrates randomly into the plant’s chromosomal DNA.
Selection and Regeneration : A selectable marker, such as resistance to antibiotics or herbicides, is used to identify plant cells that have the transgene. To grow into whole plants, the chosen cells are cultivated in a nutritional medium with plant hormones.
Confirmation of Transformation : Successful integration and expression of the transgene are verified by molecular methods (such as Southern blot, PCR, or reporter genes like GUS).
A.Agrobacterium cell, B. Agrobacterium DNA, C. Ti Plasmid
a.T-DNA ; b.vir genes ; c.replication origin; d.opines catabolism D. Plant cell ; E. Plant mitochondria ; F.Plant chloroplast ; G.Plant nucleus
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VirA recognition
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VirA phosphorylates VirG
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VirG causes transcription of Vir genes
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Vir genes cut out T-DNA and form nucleoprotein complex ("T-complex")
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T-complex enters plant cytoplasm through T-pilus
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T-DNA enters into plant nucleus through nuclear pore
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T-DNA achieves integration
“Transfection by Agrobacterium” by Chandres is licensed under CC BY-SA 3.0
“Mango (Mangifera indica) Probably crown gall caused by Agrobacterium tumefaciens” by Scot Nelson Via Wikimedia commons is in the Public Domain, CC0
Applications of transgenic plants
Agricultural Applications
Production of Pest and Disease Resistance crops
For instance, genes from the bacteria Bacillus thuringiensis are present in Bt crops (such as Bt cotton and Bt maize), which reduce the need for pesticides by creating a protein that is harmful to particular pests.
Crop losses are reduced by plants that have been genetically modified to be resistant to bacterial, viral, or fungal diseases.
Resistance to Herbicides
Certain pesticides are tolerated by transgenic plants, enabling effective weed management without endangering crops.
For instance, roundup Glyphosate tolerance in ready soybeans makes controlling weeds easier.
Stress Tolerance
Abiotic stressors such as drought, salt, high temperatures, and unfavorable soil conditions are things that plants are designed to survive.
For instance, rice cultivars that can withstand salt on saline soils.
Increased Production and Development
Increased productivity results from genetic alterations that enhance growth rates, nutrient intake, and photosynthetic efficiency.
Nutritional Improvements
Biofortification
In order to combat malnutrition, transgenic plants are created to increase the nutritional value of food.
For instance, provitamin A (beta-carotene)-enriched golden rice helps people who are vitamin A deficient.
Improved Quality
Features like improved shelf life, taste, or texture are added. For instance, Flavr Savr tomatoes have a longer shelf life since they don’t rot.
Applications in Medicine and Pharmacy
Manufacturing Biopharmaceuticals
Plants serve as biofactories that produce medicinal proteins, antibodies, and vaccines. For instance, tobacco plants were modified to yield the ZMapp medication, which is used to treat Ebola.
Edible Vaccines
Antigens produced by transgenic plants boost immunity when ingested. Hepatitis B vaccination antigen-expressing potatoes are an example.
Reduction of Allergens
It is possible to reduce or completely eradicate allergenic substances in crops such as wheat and peanuts.
Industrial Applications
Biofuel Production
Transgenic plants with altered lignin or increased cellulose content increase biomass for the manufacture of biofuel.
For instance, switchgrass that has been genetically modified to produce ethanol.
Bioplastics
Biodegradable plastics are made from modified plants.
Transgenic corn that produces polyhydroxyalkanoates (PHAs) is one example.
Phytoremediation
Toxins, hydrocarbons, and heavy metals are among the contaminants that are cleaned up by transgenic plants.
For instance, plants designed to take up mercury or arsenic from polluted soil.
Environmental Applications
Decreased Use of Chemicals
Crops that are resistant to pests and herbicides reduce the need for chemical pesticides and herbicides, which in turn lessens pollution in the environment.
Sequestration of Carbon
Climate change can be lessened by producing plants that have improved carbon fixation.
Examples of Transgenic Crops and Their Traits
| Crop | Trait | Purpose |
|---|---|---|
| Bt cotton | Insect resistance | minimizes damage from pests |
| Golden rice | Vitamin A enrichment | Prevents malnutrition |
| Herbicide-tolerant soybean | Herbicide resistance | Makes weed control easier |
| Virus-resistant papaya | Resistance to Papaya Ring Spot Virus | Prevents viral diseases |
| Arctic apple | Non-browning | enhanced appearance and shelf life |