Methods for Genetically Engineering a Plant

By Robert Hager
FDA Consumer
January-February 2000

Two very different techniques exist for giving a plant new genetic characteristics. But both share several steps.

Step 1: The DNA that encodes the genetic information for the desirable trait must be isolated.

At Step 2, the different techniques diverge into an "a" path and a "b" path:

In Step 2a, the new DNA is linked to a circular ring of genetic material called a transfer plasmid. Plasmids act like molecular taxicabs that carry genes from one place to another. The plasmid can be absorbed by a bacterium that transfers it to plant cells.

At Step 3a, the bacterium attaches to the plant cells, liberating the plasmid inside. The new DNA migrates to the plant's chromosome where the gene for the new trait is permanently integrated (Step 4).

At Step 5, the modified plant cells are identified and placed into a cell culture to multiply. As the cells reproduce, the new gene is reproduced along with them.

The bioengineered plant cells are then grown in a special culture (Step 6) that causes the cells to differentiate into the unique types of cells that make up the plant.

Finally, Step 7, the plantlets are transferred from the laboratory culture to soil where they grow like normal plants, except now they carry a gene that can give them a new, beneficial trait.

The alternative pathway uses a completely different gene-delivery technique. In Step 2b, naked DNA encoding the desired trait is painted on microscopic metal particles.

In Step 3b, the miscroscopic particles are then loaded into a so-called "gene gun" and fired as projectiles at plant cells growing in the laboratory. The miniature, gene-carrying bullets penetrate the plant cells where the fluids inside wash the DNA off the metal particles.

As before, in Step 4, the DNA migrates into the cell's nucleus, where the genetic material is permanently integrated into the chromosomes. The rest of the sequence is the same.