The following points highlight the top four methods of inserting foreign DNA into crop plants. The methods are: 1. Plasmid Method 2. Particle Bombardment Method 3. Direct DNA Transfer Method 4. Micro-Injection Method.
1. Plasmid Method:
This is agrobacterium mediated technique of foreign gene transfer and is also known as biological method of gene transfer.
Main features of this method are presented below:
(i) It is used with cell culture or protoplast culture, hence regeneration from cells or protoplasts is a basic requirement.
(ii) This is a cheaper method of transformation than gene gun method.
(iii) It has some control over the copy number and site of integration of transgenes.
(iv) Main drawbacks of this method are host specificity, somaclonal variation and slow regeneration.
2. Particle Bombardment Method:
In this method, foreign DNA is inserted into plant cells through gene gun using gold or tungsten coated DNA particles. It is also known as biolistic method, particle acceleration and micro ballistic method.
Main features of this method are presented below:
(i) It is used with meristems, immature embryos, embryo genic callus, suspension culture and hypocotyls.
(ii) This method is simple than plasmid method and does not have host specificity.
(iii) High cost of gene gun prohibits use of this method.
(iv) There is no control over the copy number and site of foreign gene integration.
3. Direct DNA Transfer Method:
This method involves electro proton and is used with protoplast. Hence regeneration from protoplast is basic requirement of this method. This method has limited applications.
Main features of this method are given below:
(i) It is used with protoplast culture.
(ii) It has host specificity.
(iii) The regeneration is slow.
(iv) It is cheaper method of foreign gene transfer.
4. Micro-Injection Method:
In this method, plasmid DNA is delivered into host cells by microscopic needles, known as micro-injection.
Main features of this method are presented below:
(i) It is used with protoplast culture.
(ii) This has no host specificity.
(iii) The regeneration is slow from protoplast.
(iv) It is inexpensive method of foreign gene transfer.
Out of these, first two methods, viz., plasmid method and gene gun method are widely used for development of transgenic crop plants. Other two methods are not in much use.