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GENETIC ENGINEERING. GENETIC ENGINEERING…. Is a technique to alter the chemistry of genetic material (DNA & RNA). Altered genetic material is introduced into a host organism. This changes the Phenotype of the host organism. STEPS IN PLANT GENETIC ENGG.
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GENETIC ENGINEERING… • Is a technique to alter the chemistry of genetic material (DNA & RNA). • Altered genetic material is introduced into a host organism. • This changes the Phenotype of the host organism.
STEPS IN PLANT GENETIC ENGG. • Identification & isolation of the agronomically important gene. • Isolation of a Plasmid from the bacterium Agrobacterium tumefaciens. • The plant gene of interest is integrated into the DNA of the Plasmid using restriction endonuclease & ligase enzymes. • The recombinant plasmid is introduced into the cultured plant cells. • The plasmid DNA integrates into the plant cell’s chromosomal DNA.
As the plant cells divide, each daughter cell receives a copy of the plasmid DNA and the gene of interest it carries. • These cells give rise to a plantlet. • On transfer into the soil, it grows into a new plant. • This plant expresses the new gene.
GENETICALLY MODIFIED ORGANISMS (GMOs) • Plants, bacteria, fungi and animals, whose genes are altered by manipulation are called Genetically Modified Organisms (GMOs) • GM Plants have been useful in : • Making crops more tolerant to abiotic stresses (Cold, drought, salt, heat) • Reducing reliance on chemical pesticides. (GM plants are pest resistant) • Increased efficiency of mineral usage. • Enhancing nutritional value of food. Eg Vit A enriched rice.
Bt COTTON • The bacterium Bacillus turingenesis is a common soil bacterium. • It produces a toxic insecticidal protein. • This toxin is a crystal protein( Cry) • There are several kinds of Cry proteins, toxic to different groups of insects.
The gene coding for these Cry proteins is called cry gene. • There are a number of cry genes: • cryIAc • cryIIAb • These two produce toxins against cotton boll worms. • cryIAb controls corn borer.
Biotechnologists have been able to isolate the gene responsible for the production of toxin. • Incorporate it into the Agrobacterium Ti plasmid. • This in turn can be introduced into many crop plants. • The new GM Bt cotton is resistant to some caterpillar pests.
PEST RESISTANT PLANTS • Several Nematodes parasitize a wide variety of plants. • A nematode Meloidegyne incognitia infects the roots of tobacco plants and reduces their yield. • RNA interference (RNAi) was used to prevent this infestation. • RNAi is a method of cellular defence in eukaryotes.
RNA Interference • RNAi is a mechanism that inhibits gene expression at the stage of translation or by hindering the transcription of specific genes. • Specific messenger RNA is silenced due to the complementary ds RNA molecule. • The ds RNA binds to the mRNA and prevents its translation.
ds RNA could be from an infection by viruses having RNA genomes or mobile genetic elements called transposons. • Through Agrobacterium vectors, normal copy of genes specific to the nematodes are introduced into the host plant.
The genes of Nematodes are introduced into the host plant. • It produces both sense and antisense RNA in the host cells. • These two RNAs being complementary to each other, formed a double stranded (ds) RNA. • This ds RNA initiated RNA interference and silenced the specific messenger RNA of the nematode.
Thus in the transgenic host, the parasite could not survive expressing the specific interfering RNA. • Thus the tobacco transgenic plant could be saved from the attack of the nematode.
Genetically Engineered Insulin • Insulin is an important life saving drug for diabetic patients. • It is a proteinaceous hormone secreted by the Beta cells of islets of Langerhans. • Each Insulin molecule has 51 amino acids arranged in two chains – A and B chains, bearing 21 and 30 amino acids respectively. • These chains are connected by S-S disulphide bridges
The insulin obtained from pigs has a different amino acid at one point. • The cattle Insulin differs at three points. • Insulin from pig and cattle, sometimes produces allergic reactions. • By using recombinant DNA technology, it is possible to produce human insulin.
In humans Insulin is synthesized as a prohormone which needs o be processed before it becomes functional. • The prohormone contains an extra stretch called C peptide. • This C peptide is removed to form mature Insulin. • On 5th July 1983, an American firm Eli lilly produced the first genetically engineered human insulin by the name Humulin.
Two DNA sequences corresponding to A and B chains were produced. • They were introduced into plasmids of E.coli to produced Insulin chains • A and B chains were produced separately, extracted and combined by creating disulphide bonds. • This formed human Insulin.
