Production of Transgenic plant

Here gene transfer through Ti plasmid vector is taken as an example : Interspecific ge transfer are now possible through genetic engineering. Ti plasmid (tumour inducing) from the soil bacterium Agrobacterium tumefaciens is effectively used as vector for gene transfer to plant cells. This is, so called because in nature, it induces tumors in broad leaf plants such as tomato, tobacco and soybean. For using Ti plasmid as a vector, researchers have elimi- nated its tumor causing properties while keeping its ability to transfer DNA into plant cells. This bacterium is called natural genetic engineer because genes carried by its plasmid produce effect in several parts of the plant. Ri plasmid of A. rhizogenes is also being used as vector.

This bacterium infects all broad-leaved agricultural crops such as tomato sunflower and cotton etc. It does not infect cereals. It induces formation of can growth called a crown gall tumor. This transformation of plant cells is due to the effect of Ti plasmid carried by Agrobacterium strains are developed in which tumor-forming genes are deleted. These trans- formed bacteria can still infect plant cells. (ii) The part of Ti plasmid transferred into plant cell DNA, is called the T-DNA. This T-DNA with desired DNA spliced into it, is inserted into the chromosomes of the host plant where it produces copies of itself, by migrating from one chromosomal position to another at random. But it no longer produces tumors. (iii) Such plant cells are then cultured, induced to multiply and differentiate to form plantlets. (iv) Transferred into soil, the plantlets grow into mature plants, carrying the foreign gene, expressed throughout the new plant. the pathogenic bacterium.