Transgenic plants, generally modified organisms (GMOs), living modified organisms (LMOs) and generally Engineering Organism (GEOs) are synonyms and represents products of the process of transgenesis. In literary terms transgenic (trans+genic), as the word denotes, means transfer of genetic material (DNA fragment carrying known gene/s) from across the biological systems, i.e. from viruses to man (donors) into plants cells (recipients), through in-vitro techniques. The plants derived from these cells are termed as genetically transformed plants or transgenic plants. These plants transmit and express the introduced traits in successive generations.
IMPORTANCE OF TRANSENICS IN AGRICULTURE
Biotechnology, based on recombinant DNA technology, is being advocated as an important adjunct to conventional plant breeding for sustainable development in agriculture. The tools and techniques of recombinant DNA technology have widened the definition of gene pool in plant breeding because it is possible to mobilize candidate gene of interest into plants from hitherto inaccessible bioresources. Encouraged by these developments, a wider role of biotechnology in ecotechnology based precision farming of future, especially for developing countries like India has been envisaged. There should be a judicious integration of biotechnological approaches in each of the following major components of conventional crop improvement, programs, viz (i) integrated (ii) integrated nutrients management, (iii) integrated pest management, (iv) water management,(v) soil health care, and (vi) post-harvest management. The development of genetically tailored plants of tomorrow endowed with attributes enumerated above is a distinct possibility through the application of recombinant DNA technologies. In recent years, the practical utility of alien gene through transgenesis has been extensively demonstrated and transgenic plants harboring genes for insect pest, herbicide tolerance, improved post harvest shelf life, and for quality have been developed in a number of crop plants and are being grown commercially in both developed and developing countries.
LANDMARK DISCOVERIES LEADING TO DEVELOPMENT OF TRANSGENICS.
The 20th century began with the rediscovery of Mendel's Law of inheritance and ended with full genome sequence of a number of organisms, including Arabidopsis among plants and human being among animals. The hundred years are dotted with revolutionizing scientific discoveries Which led to the development of recombinant DNA technology and in turns to transgenics. These discoveries established that all the characters in living beings are governed by genes: each gene with a well defined nucleotide sequence in DNA occupy a pre-determined location in the chromosome: there is site specific cleavage of DNA by registration enzymes: restricted DNA fragments cab be cloned into appropriate vectors: these vectors mediate the mobilization of cloned into recipients: the expression of the introduced gene in the recipient plant cell can be manipulated: and transformed plant cell can be regenerated into a transgenic plant.
The recombinant DNA technology developed so far permits only random insertion of foreign DNA in the chromosomes and therefore, the level of expression of the inserted gene and its stability is greatly influenced by the neighbouring DNA sequences in the chromosome.
Potential to developed into a full and that they can be transformed with foreign DNA has paved the way for genetic engineering of plants for desires traits. A large number of methos of gene transfer in plant cell been tried over the years, and are discussed here.
Year of Discovery
1900 De vries, Carl correns, and Enrich von Tschermak--Rediscovered Mendel's of inheritance
1902 Walter Sutton and T.Boveri--proposed chromosome theory of heredity
1909 Wihelm Johannsen--Coined the term 'Gene'
1910 Thomos Hunt Morgan--Demostrated linkage between genes
1941 G.Beadle and E. Tatum--proposed One gene one enzyme hypothesis
1944 Avery, Macleod and Mc Carty--Demonstrated DNA as the genetic material
1953 Francis Crick and James Watson--Discovered Double helical structure of DNA
1954 Skoog and Miller---plant regeneration from cell cultures
1961 S.Brenner, F.Jacob, and M,Meselson--Discovered m RNA
1966 Nirenberg, Khorana and Ochoa--Cracked the Genetic code
1968 M.Meselson and H.C.Smith, K.W.Wilcox and T.J.kelley--Described first restriction enzyme
1972 Stanely cohen and H,Boyer---produced first recombinant DNA molecule
1973 Stanley cohen cloned first animal gene--in to E.coli
1975-77 Sanger, maxam and Gillbert--Developed DNA sequencing methods
1976 Genentech--first genetic engineering Company established
1983 E.L.Herrera-Estella, A.Depicker,M. Van Montagu J.SCHEL--Demonstrated Agrobacterium mediated transformation in plants
1987 Burke et al--Developed yeast Atificial Chromosome (YAC) as vectors in plants
1990 N.Sternberg--Developed Bacterial Artificial Chromosome (BAC) as vector in plants
1994 Calgene--Developed FLAVR SAVR,the first transgenic tomato showing extended shelf life.
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