Transgenic Plants Model Answers

Transcription

1 Transgenic Plants Model Answers Compiled by Mr. Nitin Swamy Asst. Prof. Department of Biotechnology Page 1 of 7

2 Transgenic plants are the ones, whose DNA is modified using genetic engineering techniques. The aim is to introduce a new trait to the plant which does not occur naturally in the species. A transgenic plant contains a gene or genes that have been artificially inserted. The inserted gene sequence is known as the transgene, it may come from an unrelated plant or from a completely different species. The purpose of inserting a combination of genes in a plant, is to make it as useful and productive as possible. This process provides advantages like improving shelf life, higher yield, improved quality, pest resistance, tolerant to heat, cold and drought resistance, against a variety of biotic and abiotic stresses. Transgenic plants can also be produced in such a way that they express foreign proteins with industrial and pharmaceutical value. Plants made up of vaccines or antibodies (Plantibodies) are especially stricing as plants are free of human diseases, thus reducing screening costs for viruses and bacterial toxins. The first transgenic plants were reported in Since then, many recombinant proteins have been expressed in several important agronomic species of plants including tobacco, corn, tomato, potato, banana, alfalfa and canola. Tobacco plants were generally used, however potatoes and bananas are also considered, for the purpose of vaccines for human beings. Here, some of the traits improved through transgenic approach are being discussed. Page 2 of 7

3 Resistance to Biotic Stresses: a. Insect Resistance- Bacillus thuringiensis (Bt) encodes for the Bt toxin which are active against Lepidopteran insect has been introduced in many of the crop plants like rice, maize, fibre yielding plant cotton, vegetables like tomato and potato against many insects. Cowpea Trypsin Inhibitor (CpTi) from cowpea, α-amylase Inhibitor from Phaseolus vulgaris, Lectins from Galanthes nivalis (snowdrop) all these different kinds of proteinase inhibitor genes give resistance against some insect pests. Transgenic tobacco, pea and potato have been obtained carrying these genes show resistance against insects. b. Virus Resistance A number of coat protein genes from different virus groups have been found to provide resistance by inhibiting the virus replication of the challenge virus during the infection. Page 3 of 7

4 Many of the transgenic tobacco, potato, tomato, soya-bean, rice, maize have been produced using the coat protein gene of TMV (Tobacco Mosaic Virus), PVX (Potato Virus X), TYLCV (Tomato Yellow Leaf Curl Virus), BMV (Bean Mosaic Virus), RSV (Rice Strip Virus), MDMV (Maize Dwarf Mosaic Virus), etc. c. Disease Resistance A large number of plant defense response genes encoding antimicrobial proteins are now have been cloned. The products of these defense response genes may include (i) Chitinase and PR proteins, (ii) Ribosome inactivating proteins (RIPs), (iii) Antifungal proteins (AFPs), (iv) Enzyme for phytoalexin, (v) Phenolics, Lectins, etc. II. Resistance to Abiotic Stresses: Several abiotic stresses such as drought, salinity and extreme temperatures have a common consequence of causing cellular water deficit or osmotic stress. Some osmoprotectants within cells like proline, soluble carbohydrates like polyols and some ammo-nium compounds like glycine, betaine help to lower the osmotic potential and maintain-ing turgor within the cell. Here is a list of few transgenic plants derived against resistance to abiotic stresses: III. Resistance to Herbicide: Transgenic plants against various herbicides such as phosphinothricin (bialaphos), glyphosate, sulfonylurea, imidazolinones, bromoxynil, atrazine, 2, 4-D, etc. have been generated in different food crops, vegetables, horticultural Page 4 of 7

5 and ornamentals species. Herbicide resistant transgenic plants like cotton, flax, canola, corn and soya-bean have already released. IV. Transgenics for Quality: 1. Transgenic Flowers have Longer Shelf Life: Transgenic carnations expressing antisense ACC oxidase and producing flowers with little ethylene and marked delay in senescence. 2. Transgenic for Improved Storage: Transgenic tomato Flavr Savr with delayed ripening developed by Calgene, UBA using antisense RNA technology of ACC deaminase. Monsanto produced transgenic tomato to express a gene from Pseudomonas which produces metabolites other than ethylene from ACC. Another gene SAM hydrolase from bacteriophage T3 also reduced the ethylene production in tomato giving more shelf life Transgenics for Flower Color and Shape: Delphinidin is the compound responsible for blue colour in flower, the Flavonoid 3-5 hydroxylase (F 3-5 H) is the enzyme responsible for blue colour formation has been cloned and transgenic violet carnation Moon-dust is available. Modification of intensity of flower color from white to pink has been obtained by antisense RNA technology of chalcone synthase and trans-genics have been obtained in Petunia carnation, Gerbera, etc. Page 5 of 7

6 4. Transgenics for Nutritional Quality: Tailor made starch i.e. starch with reduced level of amylose and higher amount of starch have been developed in potato. Trehalose is an additive which improves the taste quality in processed food. Transgenic tobacco has been produced by Calgene producing trehalose. Overexpression SPS (Sucrose Phosphate Synthase) holds promise for achieving the sugar content increase, trans-genic tomato has been produced with over-expression of SPS. V. Transgenic Plants as Bioreactors: 1. Transgenic Plants for PHB Synthesis: Transgenic plants are also being produced to be used as bioreactors for synthesis of various types of chemicals; the technique is called as Molecular pharming. Polyhydroxy Butyrate (PHB), an polyester with thermoplastic property, is synthesized by transgenic Arabidopsis after introducing the transgene from Alcaligenes euthophus. 2. Transgenics for Production of Vaccines and other Peptides: The use of transgenic plants as the producer of many peptides of pharmaceutical use and the vaccines are becoming significant now-adays. Human Serum Albumin (HSA) is being success-fully produced in transgenic tobacco and potato plants. Transgenic maize plants have been produced capable of producing avidin. Potato tubers have also been used as the bioreactor for high level production of a recombinant single chain FV (SCFV) antibody. Disadvantages of transgenic crops The use of transgenic crops was an issue for many years. Many concerns have been raised and these are falling into two categories. 1. A concern, about what affect genetically modified material, could have on human health. For example, transgenic crops have been suggested to cause allergies in some people, although it is uncertain, whether transgenic crops are the source of this reaction.20 Furthermore, the antibiotic resistance genes, placed in these crops have been suggested to cause resistance to antibiotics, leading to super bugs, which cannot be killed with antibiotic treatments.21 The population being uncomfortable with ingesting DNA that originated from another source, like virus or bacteria. Page 6 of 7

7 2. A concern, about whether transgenic crops cause damage to the natural environment. One example that includes pollen from transgenic corn, which has capacity to kill the Monarch butterfly larvae. It has been shown that hybrid corn expresses a bacterial toxin in its pollen, which is then dispersed over 60 m by wind. In this range, the corn pollen is deposited on other plants near cornfields, where it can be ingested by non-target organisms including the monarch butterfly21 which leads to their death. The future Although genetically modified crops offer a potential solution to food shortages around the globe, the viability of their cultivation remains questionable. The enhanced production of GM crops to eliminate hunger carries hidden costs in environment and health concerns. The issue continues to be controversial and the future of genetically modified crops remains uncertain. Page 7 of 7