Natural Genetic Engineer

A soil-inhabiting, plant pathogenic bac­terium, Agrobacterium tumefaciens, infects broad-leaved crops including tomato, soyabean, sunflower and cotton, but not the cereals. It causes tumours called crown galls. Tumour formation is induced by its plasmid, which is, therefore, called Ti plasmid (Ti for tumour inducing). The Ti plasmid integrates a segment of its DNA, termed T DNA, into the chromosomal DNA of its host plant cells. The T DNA causes tumours. As gene transfer occurs without human effort, the bacterium is known as "natural genetic engineer" of plants. Plant molecular biologists have started using Ti plasmids as vectors to transfer foreign genes of interest into the target plant cells. They use a version of theplasmid from which tumour-forming gene has been eliminated. The transformed bac­teria do not cause disease.

Genetic Engineering in Plants

Many plants can be regenerated from a single somatic cell grown in culture. These in­clude tomatoes, potatoes, tobac­co, cabbage, carrot, citrus plants. In these cases, genetic manipulation can be performed on a single cell, which can then be cultured to produce a new plant with a new trait. The usual DNA vector for moving genes into plant cells is a plasmid of the bacterium, Agrobacterium tumefaciens. The DNA seg­ment of this plasmid that integrates into the chromosomal DNA of its plant host cell is called T DNA. The uptake of genes by microbial and plant cells is called transfor­mation. The main steps in plant genetic engineering are given below:

1) Agronomically important gene is identified and isolated.

2) Plasmid is isolated from the bac­terium, Agrobacterium tumefaciens.

3) Plant DNA containing the gene of interest is integrated into the T DNA of the plasmid by using restriction endonuclease and ligase enzymes.

4) Recombinant plasmid is introduced into the cultured plant cells.

5) T DNA integrates into the plant cell's chromosomal DNA.

6) As the plant cells divide, each daughter cell receives a copy of T DNA and the gene of interest it carries.

7) The cells give rise to a plantlet, which, when transferred into soil, grows into a new plant that may express the new gene.

Applications of Plant Genetic Engineering

Some commercially important plants have developed pest resistance and some other useful features through genetic engineering. Many crop plants may be made more productive by genetic engineering in the near future.

Potential Applications of Plant Genetic Engineering

Plant genetic engineering may produce trans­genic plants that

1. are resistant to (a) diseases resulting from viral, bacterial and fungal infections; (b) pests, such as nematodes and insects; and (c) pesticides.

2. can tolerate adverse environmental condi­tions such as drought, high temperature, frost, salinity, heavy metals, etc.

3. can produce pharmaceutically important compounds such as human insulin, interferons, hormones, blood-clotting factors, etc,

4. can synthesize antibodies and vaccines and their fruits, when eaten, may give immunity against diseases in children.

5. can fix atmospheric nitrogen and exclude the need for using costly fertilizers.

6. may bear flowers with new colours and long life for better ornamental prospects.

7. may yield slow ripening fruits for longer shelf life.