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Uses of Transgenic plants Transgenic plants for Molecular Farming Many plant products useful for humans such as sugars, fatty acids, starches, celluloses, rubber, and wax are obtained by using the traditional methods. The efforts are going on to use genetic engineering to increase their production. In this regard, the transgenic plants can play an important role as ‘factories’ for manufacturing specialty chemicals and pharmaceuticals. Some of the examples are: increase in the level of mannitol in transgenic tobacco plants following the transfer of the gene for mannitol dehydrgenase from E.Coli to tobacco. Similarly Chimeric genes having CaMV promoter and encoding human serum albumin (HSA) were transferred and transgenic potato and tobacco plants were obtained. The secretion of protein was achieved by using either the human preprosequence or the signal sequence from extra cellular PR-S protein from tobacco. HSA was secreted in transgenic leaf tissue. Transgenic plants to study regulated gene expression Transgenic plants have been used to study the expression of genes in different environmental conditions or at different stages of development which can lead to induction or suppression of gene expression. Using transgenic plants it was possible to recognize the regulatory sequences involved in differential expression of gene activity. The regulatory sequences of a number of structural genes was studied using this method. E.g. In order to study heat shock genes which start transcription under thermal stress and reduces the expression of many other vital genes, a gene construct, carrying NPT II reporter gene was fused with upstream region of heat shock gene hsp70 from Drosophila. This was then introduced into Tobacco. The expression of NPT II due to heat shock was comparable to that of endogenous plant heat shock genes. Similarly when hsp 70 gene of maize, with 1.1 kilobases of upstream sequence was introduced in petunia, it exhibited heat inducibility. Similar studies were carried out using different systems such as the gene for small subunit of ribulose bisphosphate carboxylase (rbcS) was transferred from pea plant to petunia and tobacco plants and the soybean rbcS gene was transferred to petunia. The gene expressed itself in transgenic plants. The gene for chlorophyll a/b binding protein (Cab gene) was transferred from pea plant and wheat to tobacco. Transgenic plants suitable for food processing Transgenic plants suitable for food processing have also been developed. Tomatoes showing ‘delayed ripening’ were developed either by using antisense RNA against enzymes involved in ethylene production (e.g. ACC synthase) or by using gene for ACC deaminase, which degrades 1 aminocyclopropane-1 carboxylic acid (ACC) which is an immediate precursor to ethylene. This not only increases the shelf life of tomato but also the tomatoes can stay longer on the plant which gives more time for accumulation of sugars and acids for improving flavour. Therefore they are described as ‘Flavr Savr. Another example is the development of bruise resistant tomatoes which express antisense RNA against polygalacturonase (PG), which attacks pectin in the cell walls of ripening fruit and softens the skin. Some pathogens for which resistance has been transferred in some crop plants
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