What is transgenic organism?
An organism in which a foreign gene has been artificially transferred is known as 'transgenic organism. A transgenic organism is also called genetically modified organism (GMO) or genetically engineered organism (GEO).
Transgene means a foreign gene artificially transferred into an organism. The transgene is constructed by ligating the foreign DNA into a vector or a carrier DNA which can then be incorporated into the host DNA and expressed correctly by the host cells. The vector DNA with the inserted DNA fragment is called recombinant DNA or, rDNA. A rDNA could also serve as a transgene. The inserted DNA is called cloned DNA and the process of preparing rDNA is called cloning the DNA.
What is Transgenic Plants?
When a foreign gene has been artificially transferred to the plants are called the Transgenic Plants. During the recent past, several transgenic plants have been produced which are resistant to herbicides, insects, viruses and a host of other stresses. Transgenic plants which are suitable for food processing have also been evolved. Transgenic plants are used as bioreactors or factories for production of special chemicals and Pharmaceuticals. They are also being used for identification of regulatory sequences for many genes, using gene constructs with overlapping deletions.
Transgenic plants used in crop improvement
Several transgenic plants of economic value are produced for various purposes. Here are some examples: -Nicotianatabacum(tobacco), Petunia hybrida(petunia), tersiconesculentum(tomato), Solanumtuberosum(potato), Lactuca saliva (lettuce), Apiumgraveolens'), Helianthus annuus(sunflower), Linumusitatissimum(flax), Gossypiumhirsutum(cotton), Glycine J(soybean), Beta vulgaris (sugarbeet), Daucuscarota(carrot), Oryza saliva (rice), Zea mays (maize), fie cereale(rye), etc.
Methods of generation
These transgenic plants have been generated by the introduction of genes which could make them resistant to diseases and herbicides, increase their nutritional value or increase their storage span. The Bttoxin genes of Bacillus thuringiensis (Bt) has been introduced into corn, cotton and potatoes to make them resistant to insect pests. They encode toxins which act as a pesticide and protect plants against worms. Tobacco plant is usually used as a bioreactor as it can be transformed by Ti plasmid carrying the gene of interest. A number of genes responsible for providing resistance against stresses such as heat, cold, salt, etc. have also been identified and incorporated into a number of plants.
A number of examples are available where transgenic plants suitable for food processing have been devoloped. As for instance, Bruise resistant tomatoes were developed which express antisense RNA against polygalacturonase (PG), which attacks pectin in the cell walls of ripening fruit and thus softens the skin \). Similarly, starch contents in potatoes could be increased by 20-40 per cent by using a bacterial ADP glucose prophosphorylasegeni (ADP GPPase).
Transgenic plants in monocotyledons
Production of transgenic plants in monocotyledons was initially not possible due to two major limitations : (i) monocotyledons are ordinarily not infected by Agrobacterium, which carry Ti plasmids for transformation, and (ii) the regeneration of plants from protoplasts or single cells, which are commonly used for transformation, was not possible. Both these limitations have been overcome, since alternative methods for DNA uptake have now been developed and regeneration protocols for crops like rice and maize have been successful during the last few years. In rice, transgenic ere produced which carried a functional gene for aminoglycoside phosphotransferase II. along with the reporter gene for neomycin phosphotransferase (NPT II). In the other case, the transgenic rice plants possessed a bacterial hph gene, encoding hygromycin B resistance (Hmr) alongwith the reporter gene encoding β-glucuronidase (GLJS).
Transgenic plants for molecular farming
Transgenic plants are also used as factories for manufacturing speciality chemicals and pharmaceutical . The genetic engineering has helped in increasing the contents of sugars, fatty acids, starches, celluloses, rubber and waxes obtained from plants.
Transgenic plants to study regulated gene expression
Transgenic plants have particularly been found useful in the study of development, since with their help gene expression can be studied in time and space. They facilitated the recognition of regulatory sequences involved in differential expression of gene activity.