Gene transfer in plants is the process of introducing foreign DNA (a desired gene) into a plant’s genome so that the plant can express a new trait, such as pest resistance, drought tolerance, or enhanced nutrition. This process is a key part of plant genetic engineering and can be done using several physical, chemical, or biological methods.
Here’s a clear explanation of how gene transfer is performed in plants:
1. Identification and Isolation of the Desired Gene
The first step is to identify and isolate a gene responsible for a specific trait — for example, a bacterial gene for insect resistance or a gene for salt tolerance. This gene is then copied and prepared for insertion into the plant.
2. Insertion of the Gene into a Vector
The desired gene is inserted into a vector, which acts as a carrier to deliver the gene into the plant.
Common vectors include:
- Plasmids (circular DNA molecules) from Agrobacterium tumefaciens.
- Viral vectors in some cases.
The vector is modified to include:
- The desired gene.
- A promoter to control expression.
- A marker gene to identify successfully transformed cells (for example, antibiotic resistance).
3. Gene Transfer Methods
There are two main categories of gene transfer methods:
A. Biological Methods
These use living organisms to deliver genes.
- Agrobacterium-mediated transformation:
- Uses Agrobacterium tumefaciens, a bacterium that naturally transfers DNA into plant cells.
- The desired gene replaces the tumor-inducing genes in the bacterium’s Ti plasmid.
- The bacterium infects plant cells, transferring the new DNA into the plant genome.
- Commonly used in dicots such as tobacco, tomato, and soybean.
- Viral-mediated transfer:
- Modified plant viruses can deliver genes into plant cells without causing disease.
B. Direct (Physical or Chemical) Methods
These do not rely on biological vectors.
- Biolistics or Gene Gun Method:
- Tiny metal particles (usually gold or tungsten) coated with DNA are shot into plant cells using high pressure.
- The DNA penetrates the cell wall and integrates into the plant’s DNA.
- Useful for monocots like rice, maize, and wheat.
- Electroporation:
- Plant cells are exposed to an electric field that creates temporary pores in the cell membrane, allowing DNA to enter.
- Microinjection:
- DNA is directly injected into the plant cell nucleus using a fine glass needle.
- Highly precise but technically demanding.
- PEG (Polyethylene Glycol)–Mediated Transformation:
- Used with protoplasts (plant cells without cell walls).
- PEG makes the cell membrane permeable to DNA molecules.
4. Selection and Regeneration
After gene transfer, only some cells successfully integrate the new DNA.
- Marker genes help identify transformed cells (for example, those that survive on antibiotic-containing media).
- The selected transformed cells are cultured in a nutrient medium and regenerated into whole plants through tissue culture techniques.
5. Confirmation of Gene Integration
Molecular tests such as PCR (Polymerase Chain Reaction), Southern blotting, or gene expression analysis are performed to confirm that the new gene is integrated and functioning correctly.
6. Development of Transgenic Plants
The transformed plants that express the desired trait are called transgenic plants. These plants are tested for stability, performance, and safety before being used for cultivation.
In summary:
Gene transfer in plants involves introducing a specific gene into plant cells using biological or physical methods, followed by selection and regeneration of the modified cells into new plants. This process allows scientists to develop plants with improved traits that are difficult or impossible to achieve through traditional breeding.