A Shot in the Dark

The early days of genetic engineering were pretty crude, especially for plant geneticists. But the technology to insert genes conferring traits like pest resistance into plants has revolutionized modern agriculture. Today a device with origins in a pest reduction battle of a different sort is responsible for virtually all the genetically modified soy and maize crops grown in the United States. It’s been dubbed the gene gun.

It all started in 1983, when Cornell University plant breeder John Sanford turned to biotechnology in his hunt for a shortcut past the lengthy and random cross-pollination process commonly used to create new plants. But penetrating a plant’s thick cell walls to deliver new genes for specific, desired traits was a challenge. While waging war against a backyard squirrel infestation with a BB gun, Sanford thought of using a similar gun to blast genes through the cell walls. He approached Edward Wolf and Nelson Allen, engineers at Cornell’s Nanofabrication Facility, for help designing projectiles to deliver the DNA. The duo decided that microscopic particles of tungsten could be coated with desired genes and shot directly into the cells using a gun. Preliminary tests involved an ordinary air pistol.

Theodore Klein, a postdoc in Sanford’s lab, tested the scheme on its first subject: an onion. But because the researchers couldn’t control the gun’s air bursts-the particles either didn’t penetrate the cells or destroyed them-early trials frequently left the lab walls splattered with onion bits. Sanford’s team then developed a device to use .22-caliber gunpowder charges that provided higher velocities and less shock. In this system, a specially designed plastic bullet charged down the gun barrel, coating itself with the pellets. At the barrel’s end, the bullet slammed up against a metal sheet, sending the particles flying at high speed through a small hole in the sheet and into the cells. Within several months, the onion experiments worked. By the mid-1980s, the team had also inserted foreign genes into tobacco, wheat and soybeans.

In 1990, Cornell sold the rights to the technology to DuPont. Since then, “gene guns” have gone through several refinements, making them much more precise. Meanwhile, researchers at Monsanto, Washington University in St. Louis and Ghent University in Belgium developed a competing method using a bacterium to inject DNA into plant cells. Plant geneticists now use both methods with about equal frequency to genetically modify crops.