Moving genes into plants

Researchers have developed several different methods for transforming (moving new genes into) plants. They sometimes use biological, sometimes physical methods to cause the transformation. Two methods are described below.

Agrobacterium tumefaciens

The first reliable way researchers found to transform plants was to use a bacterium, Agrobacterium tumefaciens, which naturally attacks plants at the junction between the root and shoot at the soil surface and causes the plant to form galls (tumors) on the crown. Agrobacterium causes these tumors by transferring a piece of DNA from the bacterium to the plant. This DNA is called the T-DNA, which stands for "transferred DNA." The T-DNA is part of a plasmid, or ring of DNA, in the bacterium. Researchers have manipulated the T-DNA to include pieces of DNA that they want to transfer into plants.

Steps for transforming plants with Agrobacterium

• Remove the T-DNA genes that normally cause tumor production.
• Add a marker gene for kanamycin resistance to the T-DNA.
• Include any other gene or genes that you want to transfer.
• Remove tissue explants from the plant.
• Incubate the wounded plant tissue with Agrobacterium carrying the modified plasmid.
• Put infected tissue on agar growth medium that contains kanamycin.
• Transformed cells grow; transfer these to medium that allows shoots to develop.
• Put shoots on a medium that promotes root growth, so plants grow.
• Transfer plants from agar medium to soil.

The Gene Gun

More recently, researchers developed a method for transferring genes by using a gene gun.

The following steps move DNA into plants via a gene gun, or, in other words, by particle bombardment.

• Mix DNA with microscopic particles of tungsten or gold. The DNA is precipitated onto the particles.
• Put the DNA-coated particles on the end of a large, plastic bullet.
• Load the bullet into a gun barrel and position the target &endash; plant tissue &endash; at the end of the barrel.
• Fire the gun, accelerating the bullet to the end of the barrel where it is stopped by a plate with a small hole in it. The small, DNA-coated particles fly through the hole and hit the target tissue.
• Some particles pass through cell walls into cells. Some DNA comes off the particles and some ends up in plant cell nuclei, where it joins the chromosome and transforms the plant cell.