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Transgenic Plants / Genetically Modified Crops | In-Depth Analysis
This is post no. 1 under the main topic.
The best outcome of the Recombinant DNA Technology is Transgene. The Transgenic Plants or Genetically Modified Crops are the plants produced by having certain genes transferred from another species into that particular plant through various natural or artificial insertion techniques. This conventional technique goes handy and very precise in comparison to time consuming classical methods of breeding. The noble causes for producing transgenic plants are many; like enhancing the agricultural values (quality), for higher yields, for manufacturing certain commercially important products like pharmaceutical products, proteins; and also importantly to carry out the detailed study about various physiological and biological processes during the plant’s development. Tobacco was the first transgenic crop, in 1983, expressing the Kanamycin resistance. Well known Flavr Savr tomato was the transgenic plant to be first commercially launched in the market. Then started the never ending research and production of various transgenic plants and crops’ line expressing various biotic and abiotic stresses resistances and more.

Transgenic plants have both the commercial and applied benefits, which includes introduction of herbicide resistant gene, virus resistant genes, genes for self-incompatibility, pigmentation in floral products and tolerance to biotic and abiotic stress. Also as vaccines for immunization against various pathogens. As tools for studying plant molecular biology, mutations, etc. these GM plants have been aiming to produce various immunoglobulin, interferon and some useful polymers as well. The applications and the methods goes hand in hand to understand the GM plants. We shall discuss it in the paragraphs below. The method plays a very significant role in producing the transgenic plants and the foremost crucial part for production of the transgenes are construction of the gene and the gene transfer method. Plant gene in general comprises of regions: promoter, enhancer, cap site, leader sequence, initiation codon and a stop codon, exons and introns, an untranslated region and poly A tail. Each of these regions have different role and these specification signifies the assembly of DNA sequence designing and its expression in the transgenes.

The methods for gene transfer are categorized into two types: Vector Mediated gene transfer and Direct Transfer i.e., vector-less gene transfer method.

First one, Vector Mediated, as the name suggests is carried out by plant viruses being the vector or by Agrobacterium mediated transformation. Agrobacterium tumefaciens are considered the natural genetic engineer which conveniently infects any plant tissue or organ ensuring the large fragments of DNA with reasonably good stability and effective regeneration capability. Plant viruses are natural vector for genetic engineering and they can efficiently introduce the desirable genes into almost all plant cells systematically. The plant viruses are majorly inserted into a plant chromosome.

Second one i.e., Direct (vector-less) DNA transfer allows the foreign DNA to directly insert into the plant genome. These methods are more simple and effective. These methods includes: DNA absorption by cells/ tissues, physical gene transfer method and chemical gene transfer method. DNA absorption has very little or no success rate, but it is believed that the DNA gets absorbed and the cells get transformed in the cells suspensions. The physical gene transfer method includes: electroporation technique, gene gun (particle bombardment), microinjection, liposome fusion and silicon carbide fibres. The chemical gene transfer method includes: polyethylene glycol mediated and diethylaminoethyl dextran mediated transfer method. In addition to methods described here, there is one more new transformation technique known as chloroplast transformation which is in the developing stages and it holds efficiently promising future in plant biotechnology.

After the transformation of plants is accomplished, they need to be confirmed for being transgene by various selecting tools. These tools are set of genes referred as marker genes: selectable marker genes (eg. Bleomycin resistance genes, β-glucoronidase, Acetolactase synthase) and reporter genes (eg. Greeen fluorescent protein, Luciferase). Further step is to study and ensure the expression of genes which is carried out by promoters and terminators. Next step involves confirmation of integration of transgenes with the targeted plant genome; this is confirmed by techniques- southern hybridization and polymerase chain reaction. Later comes ensuring of transgene being stable in terms to avoid gene silencing followed by regeneration of the transformed plants which are transgenic plants.

These all genetic manipulations are done with the aim of improving crops with desired traits such as biotic and abiotic stress resistant, quality and yield, enhancing the nutrition and use of genetically modified plants as bioreactors. Biotic stress resistant crops include:

(i) Pest resistance by the use of Bacillus thuringieneses (Bt) toxins producing wide range of cry proteins; protease, lectins, etc. (Bt crops includes Bt cotton, rice, maize, tobacco, tomato, potato, cowpea and soybeans),

(ii) Virus resistance by incorporating virus coat proteins, antisense RNA technology, ribosome, etc. and

(iii) Fungal and bacterial disease resistance by incorporating pathogenesis related proteins, phytoalexins. While, abiotic stress resistant plants includes: herbicide resistant, drought and soil salinity resistant, freeze resistant, etc. Genetic modification however has contributed tremendously in the crop yield and quality; such as extended shelf life, slow ripening, and preventing discoloration in flowers, fruits and vegetables. Transgenic plants with improved nutrition have been engineered for human health improvement, e.g. Golden rice which is enriched with provitamin A, potato with increased protein and methionine levels, canola with cis-Stearates-lowering the risk of heart diseases, sugar beet with fructans-low calorie alternatives to sucrose. Also, transgenic have been engineered for allergen absence. Most importantly, transgenic plants as bioreactors have created boom in commercial aspect for manufacturing hemoglobin, monoclonal antibodies, interferons, serum albumin, proinsulin, edible vaccines, etc.

Despite of all these advantages the GM crops/ plants have been much controversial from ethical point of view. Nevertheless, GM crops have been potentially engineered in an eco-friendly way causing improvement to human health and environment.

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