Genetic Engineering for crop improvement
Genetic engineering becomes a powerful technique that applicable for altering the genetic make up of the crop plants. It is achieved through transgenic or recombinant DNA technology. The crop plants having so many desired characters but due the presence of one or few unfavourable characters makes the crop to limit in its area and production. This makes the farmers to forcefully have to shift to other crops. And also to overcome the malnutritional problems facing a huge mass of the people of the world, transgenic technology helps in mitigating this problem in an effective manner. Recombinant technology is also helpful in solving the problems arising due to biotic and abiotic stresses. To over come all these problems, transgenic technology helps to transfer desired characters from various sources to required crop plants by identification and isolating the gene of our interest. The technology of genetic modification trough transgenic approach is more directed and the inserted genes can be easily followed. In contrast to green revolution that only emphasis on three main crops (rice, wheat and maize) and produced ambivalent results, the gene revolution represents a technical and ethical advance and can be use to improve the characteristics of all targeted plants with significantly enhanced social impacts. However, genetic engineering is not set to replace conventional plant breeding but is a modern tool for use of plant breeders to fasten the breeding programme.
The varieties of maize, tobacco, cotton etc., that are resistance to herbicide were developed by transformation of plants with glyphosate resistant gene through Agrobacterium mediated transformation. Transgenic technology yielded genetically modified (GM) crops having novel genes with favourable characteristics like higher yields, herbicide resistant, insect and disease resistant, drought resistant, salinity resistant, etc.
Depending upon their preference, there are three methods for transformation of the novel genes are as follows:
1. Biological method
2. Mechanical method
3. Chemical method
1. Biological method:
This method involves the use of biological systems for transformation of the desired gene or genes.
• Agrobacterium mediated transformation: Agrobacterium remains on the preferred mechanism to introduce exogenous genes into plant cells. One of the reasons for this is the wide spectrum of plants that are susceptible to transformation by this bacterium.
• A modified T- DNA region of the Ti (Tumor inducing) plasmid in which the genes responsible for tumor formation are removed and inserted the foreign novel gene by genetic engineering.
• Viruses: Phages (Viruses that infect bacteria) and Tobacco Mosaic virus can be used as vectors for transformation of genes into plant cells. The technique is still being developed.
2. Mechanical method:
It includes the use of equipments for transformation of gene is as follows;
• Electrophoration: Is a process whereby electric pulses of high field strength are used to reversibly permiabilise cell membranes to facilitate uptake of DNA. Electrophoration has been successfully used for transforming plants in which efficient regeneration of plants from protoplast is possible.
• Microinjection: In this case needles used for injecting DNA are with a diameter greater than cell diameter. DNA (0.3 ml) solution is injected with conventional syringe into region of plant which will develop into floral tillers fourteen days before meiosis.
• Biolistic or Microprojectile for DNA transfer: This method involves bombardment of particles carrying DNA or RNA of interest into target cells using high velocity transfer mechanism. This method can be used for any plant cells, leaves, root sections, embryo seeds and pollens.
3. Chemical method: This method using polyethylene glycol and calcium phosphate for gene transfer.
Applications of Genetic Engineering in crop improvement
Transgenic breeding enables the transfer of genes across taxonomic boundaries unlike conventional breeding where it is possible to transfer genes from closely related species only. It also offers new avenues of plant improvement in shorter period compared to conventional breeding and new possibility of incorporating new genes without problems incompatibility.
• Herbicide resistant: herbicides normally affect processes like photosynthesis or biosynthesis of essential amino acids. Transformation of cereal crops with Glyphosate resistant gene (Glyphosate = herbicide). Herbicide tolerant (HT) soybean and canola are released for commercial cultivation.
• Insect resistant: the genes which responsible for the production of delta-endotoxine in Bacillus thuringiensis is used as biological insecticide. The transgene Cry 1AC has been transferred to many crops for example looper resistance in soybean, pod borer resistance in groundnut, head borer resistance in sunflower, semi-looper resistance in castor etc. snowdrop lectin gene from snow drop (Galanthus nivalis) was transferred to brassica and safflower for aphid resistant.
• Resistance against viral infection: coat protein gene from Tobacco Mosaic Virus (TMV) was transferred to develop resistant varieties of crop plants. The resistant varieties developed in crop plants like soybean for resistant to yellow mosaic virus, groundnut for resistant to bud and stem necrosis, clump and stripe virus resistance, whereas in sunflower, resistance developed for bud necrosis.
• Resistance against bacterial and fungal pathogens: Chitinase genes was transferred to crops like Brassica, Soybean, Sunflower, Sesame etc for alternaria leaf spot disease, where as in case of groundnut which was introduced against leaf spot and alternaria blight and in castor for Botrytis resistance. Acetyl transferase gene was transferred for wildfire disease of tobacco caused by pseudomonas syringae.
• Improvement of the nutritional qualities in crop plants: The carotene gene has been transferred from daphoddils to rice grains (Golden Rice) for increasing Beta-carotene content in grains and for solving the blindness in childerns. Antisense Fae 1 gene transferred to Brassica napus and Brassica juncea for low erucic acid content and also for low linolenic acid content in case of linseed. Antisense ricin gene transferred to castor for reduction of ricin content and RCA endosperm in castor seeds. Antisense sterol desaturase/ + ac1 inserted into sunflower for developing high oleic acid containing types.
• Improvement of crop plants against abiotic stresses: transcription factor genes, structural genes, regulatory genes were introduced into the groundnut, soybean, Brassica juncea, B. napus to develop drought and salinity tolerant types.
• Development of transgenic male sterile lines: transgenic male sterile lines of safflower Brassica juncea were developed through the transfer of Barnase gene from Bacteria (Bacillus amyloliquefaciens).
• A long term goal in agriculture is to introduce the genes (Nif genes) for nitrogen fixation in crop plants.
There is a need to establish reliable protocols for genetic engineering of crop plants so that these crops also could be brought under the umbrella of crops amenable for genetic engineering. This technology also increased our capacity to reduce disease susceptible varieties and enhance the efficiency of production. The greatest challenge in agriculture is to improve food grain production and eradication of malnutritional problem in the developing countries and hopefully this technique will be applied to the regions where food shortage is greatest. By knowing the present problems of farmers and also health point of view, developing safe and efficient transgenic plants is needed. For achieving these, there is need of intensifying research at national and international levels to ensure that biotechnology leads to second revolution in agriculture, which both productive and sustainable. Synergy between GM breeding and traditional plant breeding needs to be further strengthened.
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