Biology

In recent years the use of novel methods for transfer of genes over a wide range of organisms, leading to the production of transgenic plants, has been recognized as one of the thrust areas of biotechnology. Gene transfer methods in plants make use of a variety of target cell types, which include cultured cells, meristem cells (it is a type tissue) from immature embryos, shoots or flowers and pollen or zygotes through chloroplast or nuclear transformation (P K Gupta). The uptake of foreign DNA or transgenes by plant cells is called transformation. A variety of techniques have been used to introduce transgenes into plant cells. Stable transformations may be either non-integrative, or integrative. In non integrative stable transformations, the transgene is maintained (chloroplast transformation). But such transformations are not passed to the next generation. On the other hand integrative stable transformations results when the transgene becomes integrated into the plant genome (nuclear transformation), these integrations are heritable (B D Singh).
Chloroplast transformations Transformation of chloroplast genome was successfully achieved in Nicotiana tabacum.  The plants carrying transgenic chloroplast are often described as transplastomic plants. Plastids transformation was first reported in chlamydomonas and then tobacco. These plants are preferred over transgenic plants (integrative stable transformations) for the following reasons
 (i) Several preferred genes reside in chloroplast genome, and are therefore suited to express efficiently in the chloroplast only.
 (ii) Protein synthesis machinery in the nucleus and the cytoplasm is not suited to the transcription and translation of desirable microbial genes that are often intended to be transferred in the transgenic crops. In contrast, the protein synthesis machinery of chloroplast resembles that of prokaryotes, so that the genes of prokaryotic origin are appropriately expressed, when transferred to a chloroplast.
(iii) The transgenes transferred to the chloroplast show more expression which leads to the accumulation of foreign proteins in the chloroplast.
(iv) Multiple genes, which associated with complete biosynthetic pathway, transferred to the chloroplast genome in a single phase event, otherwise called as transgene stacking which is not possible in nuclear transformation. This gives a greater opportunity to express entire pathway in a single event.
(v) Due to shift of loci from one position to another or due to shift of another segment in vicinity of locus expression will change. This is called as position effect, which is absent in plastids.
 (vi) Transplastomic plants are eco friendly when compared to transgenic plants. They also eliminate the toxic effect of transgene on useful insect fauna like butterflies etc., which may ingest the transgenic pollen.
(vii) Gene silencing will be absent.
(vii) Since transgenic products are localized with in the chloroplast pleiotropic effect will be absent.
Due to the above benefits chloroplast transformation exploited in so many crops like Chinese cabbage, rice, potato, tomato, rapeseed, carrot, cotton, soybean, lettuce etc.,
Production of recombinant protein this involves the following steps
Identification of the desired gene of a particular protein
Isolation of the desired gene or DNA fragment.
Insertion of the geneDNA segment in a Suitable vector. A vector is a DNA molecule capable of autonomous replication that is used as a carrier of the DNA segment to be cloned.
Introduction of the recombinant DNA into a suitable host (The introduction of recombinant DNA into a host is called transformation).
Selection of the transformed host cells.