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Genetic modification of plants


Genetically modified plants are plants whose genetic program has been altered as a result of the introduction of a foreign gene into their genetic material; which allows these plants to acquire a new character: it is transgenesis.

The natural genetic modification of plants

Crown gall; natural hereditary tumor

Crown gall; natural tumor:
 -The drop in temperature causes some plants lesions that can later give rise to tumors (Anarchic proliferation of cells) localized to the
collar level (Between root and stem).
 -Bacteria; a natural carrier:
Studies have shown that the tumor is due to a bacterium that lives in the soil, called Agrobacterium tumefaciens (A.T).
After the injury of the plant, the bacterium A.T comes into contact with a plant cell and injects a portion of its genetic material which is incorporated into the material of plant genetics. Thus the infected cells are changed and develop, therefore, tumors.
 -The plant, therefore, acquires a new character, it is that it releases composites (Les opines) which are used by the bacterium for its growth and its multiplication. The plant is genetically modified.
Deduce from the analysis of these data the notion of natural genetic modification.

 -The bacterium Agrobacterium tumefaciens can come into contact with a cell plant, and inject it with part of its genetic material, which is incorporated with that of this plant. Thus the infected cells are genetically modified. The transfer of genetic material from one species to another can be done naturally, we speak of natural genetic modification or natural transgenesis.

Role of the Ti plasmid in this transgenesis

The bacterium A.T has a special chromosome and Ti plasmids (Les
plasmids are circular DNA fragments). Experiments have shown
that the destruction of plasmids in the bacterium A.T, makes the latter unable to induce tumors in plants.

The bacterium A.T devoid of its Ti plasmid does not cause the appearance of crown gall. We then conclude that the training manager of tumors is the Ti (tumor-inducing) plasmid.

 -When the bacterium comes into contact with a plant cell, part of the Ti plasmid (T-DNA) becomes incorporated into the genetic material of that cell. The plant cell thus acquires a new character, which is the ability to multiply in an anarchic way; resulting in a tumor. The cell is genetically modified, and the plant resulting from this cell is called a genetically modified organism (GMO).

 -A transgenic organism is an organism whose genome has been modified by the introduction of a gene often coming from a different species, a gene that brings a new hereditary character.

Role of the Ti plasmid in this transgenesis

image 1: Role of the Ti plasmid in this transgenesis

The techniques of transgenesis

Transgenesis using a biological vector

To genetically modify plants, researchers use a variety of tools,
the most important are:
 -A biological vector such as the bacterium Agrobacterium tumefaciens has a great power of multiplication, and simplicity of culture and has plasmids.
 -Specific enzymes are cleavage or restriction enzymes,
which cut the DNA molecule at specific locations. And the enzymes of welding or ligases, bind the DNA molecule to specific places.

- Transgenesis using a biological vector requires several steps which are :

- Identify the gene of interest from the genetic material of another organism (plant or bacteria);

- Isolate the gene of interest (DNA segment) from the donor cell, at

using restriction enzyme;

- Prepare a vector, for example, a plasmid extracted from a bacterium: open the plasmid with the same restriction enzymes, then integrate the gene of interest in the vector with ligases;

- Transfer of the genetically modified plasmid to a bacterium that can inject genes into the cells of the plant;

- Select the plant cells that have integrated the gene of interest;

- Multiply the modified plant cells in a culture medium;

- Regenerate genetically modified seedlings from the cells


Transgenesis using a biological vector
image 2: Transgenesis using a biological vector

Transgenesis by biolistics or DNA gun method

Genetic material is integrated through very fine particles (0.5μm).
These particles carrying the gene, are sent from a particle cannon, they cause temporary perforations of the cellulosic membrane without killing the plant cells, which allows the penetration of the gene and its integration into the genetic material of the target cell. Thus, each genetically modified cell gives a genetically modified whole plant.

Transgenesis by biolistics or DNA gun method
image 3: Transgenesis by biolistics or DNA gun method

Transgenesis; advantages and disadvantages

The benefits of transgenesis

PGMs synthesize toxic proteins

Thanks to transgenesis, a gene of interest can be isolated, such as the gene coding for a toxin. The gene is transferred to a plant such as maize, via the Ti plasmid. This makes it possible to obtain a genetically modified plant, resistant to the corn borer, hence the protection of the plant and the improvement of corn production.

PGMs synthesize toxic proteins
image 4:PGMs synthesize toxic proteins

PGMs synthesize vitamin A

Plants can appropriate, following transgenesis, new properties, as the synthesis of a chemical substance useful for the consumer. Transgenesis of rice makes this plant capable of synthesizing ß-carotene, a precursor of vitamin A, an essential element for health. This rice could contribute to curbing health problems resulting from dietary vitamin A deficiency.

The disadvantages of transgenesis

Among the problems posed by genetically modified plants are:
- The use, in transgenic processes, of marker genes for resistance to antibiotics poses the problem of the risks of a transfer of genes to bacteria in the digestive system, or to pathogenic bacteria, to become resistant in turn.
- The allergic risk may be due to the fact that the transferred genes may code for allergens not present in the original plant;
- Herbicide resistance can be manifested by:
- PGMs can become invasive plants,
- The resistance of GMPs to herbicides can be transmitted to weeds and give hybrids capable of resisting the herbicide in question.
- The toxins produced by transgenic plants to fight against
certain insects, can destroy beneficial insects such as bees and the ladybug. Based on the use of the data in this document, specify the adverse effects possibilities of transgenic plants.