The following points highlight the eight achievements in Bio technology. Some of the achievements are: 1. Herbicide Tolerant Crop Plants 2. Engineering for Virus Resistance 3. Crop plants Resistant to Insect Attack 4. Resistance to Pathogenic Fungi and Bacteria.
Crop Biotechnology Achievement # 1. Herbicide Tolerant Crop Plants:
Development of herbicide tolerant plants was the first major achievement in crop biotechnology employing the genetic transformation techniques. Transgenic plants resistant to a number of herbicides like Glyphosate, Imidazoline, Sulphonylurea, Triazine, Gluphosinate, etc. have been successfully developed.
Herbicides are used in agriculture for controlling the unwanted plants i.e., weeds. Attention has been given during the recent years for production of safe and biodegradable herbicides which do not cause much harm to the environment.
Such new herbicides may affect the crop plants by disturbing the processes like biosynthesis of amino acids or photosynthesis, etc. Therefore it has become necessary to produce such plants which can tolerate and/or resist the herbicidal effects.
Mainly three types of approaches are followed for production of herbicide resistant plants:
(a) Modifying the target protein to make it insensitive to the herbicide
(b) Excessive production of the herbicide-sensitive target protein,
(c) Introduction of a pathway which degrades the herbicide. So far, the herbicide resistant plants have been produced in a number of crops, out of which, cotton, soybean, maize, etc. are already being cultivated commercially.
Crop Biotechnology Achievement # 2. Engineering for Virus Resistance:
Various biotechnological attempts have been made to achieve resistance for pathogenic viruses in plants.
Transgenic tobacco and tomato plants have been obtained using the coat protein (CP) approach, which are resistant to the Tobacco Mosaic Virus (TMV) and Tomato Mosaic Virus (ToMV), respectively. Similarly, other transgenic plants have also been achieved having resistance against Alfalfa mosaic virus (ALMV), Potexvirus (PVX), Cucumovirus (CMV), etc.
Crop Biotechnology Achievement # 3. Crop plants Resistant to Insect Attack:
Insect resistant transgenic varieties of several crops have already been developed. Bt-cotton is the most common and prominent example which contains the insecticidal property of cry gene of a gram-positive bacterium Bacillus thuringiensis. Similarly, proteinase inhibitor gene from tomato is inserted to produce the transgenic insect-resistant tobacco plants.
Crop Biotechnology Achievement # 4. Resistance to Pathogenic Fungi and Bacteria:
The genetic transformation techniques are also being used to produce transgenic crop plants showing resistance to various fungal and bacterial diseases. The losses in agriculture due to reduction in crop-yield can be prevented to some extent by cross protection of plants from pathogenic fungi or bacteria.
Crop Biotechnology Achievement # 5. Engineering for Tolerance Against Abiotic Stresses:
The abiotic stresses like drought, flood, salinity, heat-shock etc. can also be resisted by the transgenic plants. All these abiotic stresses adversely affect the growth of plants and thus cause a major loss in agriculture.
To prevent such losses, genetic engineers have developed the stress tolerant plants of a number of crops. For this purpose, several plant genes have been cloned which encode for enzymes that are important for avoiding loss due to different stresses.
Tolerance to salinity, drought, chilling, etc. has been induced successfully in tobacco plants. Other major plant species in which the transgenic with improved drought resistance or other abiotic stress resistance has been achieved are rice and Arabidopsis.
Crop Biotechnology Achievement # 6. Introduction of Nuclear Male Sterility:
Male sterile plants are an advantage for the plant breeders in case of many plants e.g., in cereals.
Some male sterility-causing genes have been transferred to the plant cells to engineer the male sterility in plants like oil-seeds, tomato, maize, cotton, etc.
Gene barnase from Bacillus amyloliquefaciens and genes rol B, rol C from A. rhizogenes are used to induce male sterility in plants.
Another gene barstar from B. amyloliquefaciens is an intracellular inhibitor of barnase and thus it is an effective fertility restoration gene.
Crop Biotechnology Achievement # 7. Development of Transgenic Plants with Quality Modifications:
The genetic transformation has enabled the development of crop plants having improved quality like the modification of protein quality, oil or starch quality. Successful attempts have been made in case of rice, sweet potato, maize and wheat for modifying their protein quality.
A common example is a transgenic rice popularly known as Golden Rice which contains the transgenes transferred into rice by using Agrobacterium. Golden rice contains high content of pro-vitamin A i.e., (β-carotene which imparts the rice, a golden colour.
Crop Biotechnology Achievement # 8. Improved Nitrogen Fixing Ability:
Leguminous roots bear nitrogen-fixing nodules induced by some bacterial strains. Most important bacteria in this respect is Rhizobium. Some other bacterial strains like Klebsiella, Azotobacter and Cyanobacteria (Blue Green Algae) like Anabaena also fix nitrogen. The nitrogen fixing ability of these microbes is due to the presence of a cluster of genes called as nif-genes.
It is believed that if these nif-genes can be cloned in crop plants, the need to use fertilizers for enriching soil with nitrogen can be eliminated. Efforts are being made in this direction to transfer nif-genes cluster from bacterial or cyanobacterial strains to plants. So far, success has been achieved in improvement of sugarcane and wheat, while research is being carried on for other plant species.
Opines:
These are the unique nitrogenous compounds which are produced by the plant cells which have been transformed by Agrobacterium. They are unusual amino acid or sugar derivatives which act as the nutrition source for Agrobacterium cells. The genes responsible for opine synthesis are present in the T-DNA region of Ti-plasmid in Agrobacterium.
Most common opines are Nopaline, Octopine and Agropine. Based on the type of opines produced, the Ti-plasmid may be of different kinds like nopaline-type—Ti-plasmid, octopine-type-Ti-plasmid and Agropine-type- Ti-plasmid. Opines are utilized by the bacterium as a source of carbon and nitrogen after their catabolism. The genes for opine catabolism are present in Ti-plasmid outside T-DNA region.
Agro-infection:
This strategy involves the viral infection of plant cell by using Agrobacterium cells (Fig. II).
First of all, the viral genome is placed within the T-DNA region of Ti-plasmid of Agrobacterium. Now this Agrobacterium cell containing the viral genome is co-cultured with the plant cells. This results into the introduction of viral genome (within the T-DNA) into the plant cell.
In this way, virus infects the host plant cell as a part of T-DNA carried by Agrobacterium and this phenomenon is called as Agro infection. Agro infection with MSV (maize streak virus) has been demonstrated successfully in maize. It has great potential for the production of transgenic plants especially the cereals.
Ri-plasmid:
It is the root inducing plasmid which is present in A. rhizogenes. It is responsible for causing ‘hairy root disease’ in plants. On infection, a segment of Ri-plasmid is transferred to the plant cell genome and causes excessive proliferation of the branched root system.
General functional features of Ri-plasmid are similar to that of Ti-plasmid. however, there is no high sequence homology between the two. Like Ti-plasmid, the Ri-plasmids are capable of infecting di-cotyledons and do not infect monocot plants usually under natural conditions.
However modern artificial techniques have been achieved for the same.
Ri-plasmids also contain few genes in its I-DNA which can De expressed only when they are transferred into the plant cell i.e., those genes have the capability to be expressed only within the plant cells and not in the bacterium. Any A. rhizogenes e which doesn’t contain PRi is non-virulent and it cannot induce hairy root disease in the plant cell on infection.
It can be rightly said that Ri-plasmid is very much similar to pTi, but main difference between the two is that T-DNA transferred from R,-plasmid does not cause crown gall disease of stem; instead it causes a massive proliferation of the highly branched root system resulting into a disease called as Hairy Root Disease.