Transgenic plants contain genetic material (foreign or artificial) stably integrated into their genome that has been introduced by methods other than classical breeding & thus is passed on the successive generations.
27.1.    Methods of gene transfer in plants 
There are two types of effective gene transfer to plants, the first is based on the use of Agrobacterium as a biological vector and the second is the direct gene transfer method.
27.1.1.    Indirect gene transfer using Agrobacterium as the vector 
The Ti plasmid is present in Agrobacterium tumefaciens.
Agrobacterium is a naturally occurring, gram-negative bacteria. The A. tumefaciens and A. rhizogenes are being considered as natural genetic engineers.
A. tumefaciens cause crown gall disease via inserting T-DNA into the host.
T-DNA own size is 15-30kb; consists of 25 bp imperfect direct repeats necessary for trimmer and integration into a plant genome called Border sequences.
T-DNA codes for phytohormones and opines.
Opines used as carbon & nitrogen source and are catabolized by Agrobacterium.

Genes required for transfer of T-DNA:-
T-DNA transfer (polar process) initiates at right border and terminates at left border.

Monocot plants as wheat, barley, rice, maize are generally resistant to Agrobacterium infection. Hence, for them, the direct method of gene transfer is used.
27.1.2.    Methods of direct gene transfer:-

27.2.    Advantages of transgenic plants:-
(1)    Development of insect, virus and herbicide-resistant plants.
Insecticidal resistance \rightarrow gene of bacterium Bacillus thuringiensis inserted in crop plants to that insect attempting to eat these plants are killed.

2.    Development of stress tolerant plant like oxidative stress and salt stress.
3.    Modification of plant nutritional content like amino acids, lipid, vitamin, iron.
Ex. Golden rice enriched in provitamin A developed by introducing 3 genes involved in the biosynthetic pathway of carotenoid, the precursor of vit A.
4.    Plants as a bioreactor for the production of antibodies, polymers etc.
(a)    Plant bodies \rightarrow Monoclonal antibodies synthesized in transgenic plants.
(b)    Edible Vaccines \rightarrow Promote the production of specific antibodies by human immune system once the vaccine is administered
to the patient.
(c)    Polymer Polyhydroxybutyrate \rightarrow used to make biodegradable plastic-like material.
5.    Delayed ripening \rightarrow Tomatoes have been engineered so that express less polygalacturonase enzyme i.e. involved in fruit ripening. 
Flavr – savr is the trademark for these tomatoes.
27.3.    Molecular Farming \rightarrow Application of genetic engineering in which genes of animal or human origin are introduced into plants or farm animals for cost-effective production of therapeutic products such as antibodies, blood products, hormones etc.

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