The Bacterial Breakthrough- Using a "Natural Genetic Engineer" 

While genetic engineering has been around for thousands of years, modern GE technology is pretty new.  In 1977, Jeff Schell and Marc Van Montagu discovered the potential use of the soil bacterium Agrobacterium tumefaciens- which was realized to be a “natural genetic engineer.” The Agrobacterium is a naturally occurring pathogen in the soil that causes crown gall disease in plants by inserting its DNA into plant cells. The Agrobacteria have plasmid DNA along with their genomic DNA. The plasmid is what gets transferred into the plant cells. Scientists reasoned that if they could transform engineered plasmids with certain desired genes into the Agrobacterium, the bacteria would further inject this plasmid into a plant cell, creating a genetically modified plant.

First, scientists must determine the gene of interest that they wish to transfer to the target plant cells. For example, in Bt corn, scientists found the gene that produces a chemical toxic to the corn pest, bollworm and used it to genetically modify the corn. By using what are called restriction enzymes, or enzymes designed to cut at certain DNA sequences, scientists can “cut out” the gene of interest from the DNA of the original organism. This gene is then transformed into the plasmid DNA of the Agrobacterium, which has also had a piece of DNA cut out using restriction enzymes (the gene coding for crown gall disease).

A new, recombinant, plasmid has been made containing the desired gene(s). This plasmid can now be transformed (put back inside) into the Agrobacterium. 

Next, scientists take cells or tissue from the target plant and mix in the transformed Agrobacteria containing the new plasmid which has the desired DNA on it. A few of the plant cells may be injected with the new recombinant plasmid and start expressing the genes on the plasmid. The cells are grown and tested to determine which ones received the special plasmid. If the entire process was a success, you now have a genetically modified organism.

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