The following points highlight the twelve main approaches to improve traits in transgenic plants. The approaches are: 1. Resistance against the Biotic Stresses Like Insects, Bacterial and Fungal Pathogens 2. Resistance against the Abiotic Stresses Like Cold, Drought, Heat, Acidity, Metal (Al, Hg), Toxicity, etc 3. Herbicide Resistance 4. Improvement in Vitamin Content 5. Improvement in Nutritional Quality and Others.
Approaches to Improve Traits in Transgenic Plants:
- Resistance against the Biotic Stresses Like Insects, Bacterial and Fungal Pathogens
- Resistance against the Abiotic Stresses Like Cold, Drought, Heat, Acidity, Metal (Al, Hg), Toxicity, etc
- Herbicide Resistance
- Improvement in Vitamin Content
- Improvement in Nutritional Quality
- Production of Edible Vaccines
- Production of Hybrid seed by Using Sterility-Fertility Restoration System
- Improvement of Fruit Quality by Delayed Ripening and Bruise Resistance
- Development of Seedless Fruit
- Molecular Pharming
- Improved Agricultural Traits
- Transgenic Plants for Other Different Traits
Approach # 1. Resistance against the Biotic Stresses Like Insects, Bacterial and Fungal Pathogens:
The use of transgenic with toxin genes of Bacillus thuringiensis (Bt. gene) in some of the plants has been successful, specially in tobacco and cotton. The use of proteinases against insects – digesting the insect protein, and chitinases against fungi like Rhizoctonia solani, has also met with success.
The scope of utilizing endogenous antibodies, effective against infection by pathogen – viral, bacterial or fungal, is also proving to be successful. Similarly, viral attack is repelled through the development of transgenic with coat protein genes of viruses, as in tobacco.
Approach # 2. Resistance against the Abiotic Stresses Like Cold, Drought, Heat, Acidity, Metal (Al, Hg), Toxicity, etc:
There are number of genes responsible for providing resistance against various types of stresses such as heat, cold, salt, heavy metals, have been identified.
A gene for production of glycerol-l-phosphate acyltransferase has been isolated from Arabidopsis and transferred to tobacco which imparts resistance against chilling; gene producing proline and betaine imparts drought tolerance in mustard; gene producing mannitol-phosphate dehydrogenase imparts salinity tolerance in tobacco.
Approach # 3. Herbicide Resistance:
Herbicides inhibit the plant growth by blocking the biosynthesis of essential amino acids, such as glyphosate which inhibits the synthesis of aromatic amino acids. Glyphosate resistant tobacco and wheat plants have been developed by isolating and introducing a resistance gene from Salmonella typhimurium.
Approach # 4. Improvement in Vitamin Content:
To save a large population of children from vitamin A deficiency (which causes night blindness), the improved variety of transgenic rice have been developed with 23 fold increase in β-carotene content in the seed. The rice is named as ‘Golden Rice’ due to golden colour of the grain.
Approach # 5. Improvement in Nutritional Quality:
In case of many cereals, legumes, the protein content is being altered through change in amino acid content like increase in lysine content, etc. In case of oil seed crop, the change in content and composition of fatty acids has been attempted through transgenic plant production. Improvement of starch quality and composition (relative proportion of amylase and amylopectin) in crops like potato has been achieved.
Approach # 6. Production of Edible Vaccines:
The gene for vaccine production has been introduced in some fruits (which can be eaten raw) which can be helpful for eradication of some of the diseases.
Approach # 7. Production of Hybrid seed by Using Sterility-Fertility Restoration System:
The character of male sterility has wide use in securing fertile hybrids in interspecific hybridization. This character has now been widely used for trans- genesis to secure male sterile transgenic plants. This method involves induction of male sterility – fertility restoration.
Bacterial coding sequence for ribonuclease (barnase) has been attached with anther specific promoter which will kill the pollen grain by production of cytotoxic element in tapetal cells. Another gene which is a ribonuclease inhibitor (barstar gene), has also been isolated from the same bacteria and used to produce transgenic plants that nullify the effect of barnase gene.
The transgenic plant with barstar gene was developed which was crossed with the male sterile transgenic plant (with barnase gene). The F1 progeny is restored due to suppression of cytotoxic ribonuclease activity in the anther. The extensive work on CMS (cytoplasmic male sterility) line has been carried out in India in species of Brassica.
Approach # 8. Improvement of Fruit Quality by Delayed Ripening and Bruise Resistance:
In tomato using antisense RNA technology, transgenic plants were produced which were either ‘bruise resistant’ (suitable for transport and storage) or exhibited ‘delayed ripening’ giving more time for ripening and sugar accumulation and also giving higher shelf-life. The tomato variety ‘Flavr-Savr’ is the transgenic for hard skin, improved flavour and higher shelf-life.
Approach # 9. Development of Seedless Fruit:
Transgenic approach has been taken to develop fruit without pollination (parthenocarpy), leads to seedless fruit development and high solidity in fruit pulp which helps in food processing industry.
Approach # 10. Molecular Pharming:
Transgenic plants are also proposed to be used as factories or bioreactors for manufacturing speciality chemicals and pharmaceuticals.
Sugars, fatty acids, starch, cellulose, rubber and wax are obtained from plants; transgenic are made to get more production. pHB (polyhydroxybutyrate), a biodegradable polymer can be produced in transgenic Arabidopsis plants; HSA (human serum albumin) could be successfully produced in transgenic tobacco and potato plants.
Approach # 11. Improved Agricultural Traits:
Improvement in phosphorus uptake through the use of phosphorus transporter genes has been achieved to reduce dependence on fertilizer application. Improvement in harvest index is attempted using phytochrome genes.
Approach # 12. Transgenic Plants for Other Different Traits:
Other traits are improvement in architecture, colour, fragrance and vase life of flowers of commercial value; development of caffeine-free transgenic coffee; improvement of iron content in the crop like rice, etc.