Plasmids are little packets of DNA found floating around inside bacteria. They're separate from and can replicate independent of the chromosomal DNA found in cells.
Montagu's lab showed that crown gall tumors were only caused by strains of Agrobacterium that carried a particular large plasmid; other strains that lacked the large plasmid were benign.
It was Nester and his co-workers, however, who in 1977 finally proved that a DNA transfer was actually taking place. They demonstrated that a specific segment of DNA from the large plasmid was transferred into the host plant's genetic structure.
"It was a major achievement," Nester said. "It's difficult to appreciate how far the field has advanced since then. The technology at the time was very crude. Just trying to identify the presence of foreign genes, of bacterial genes in a plant -- one gene out of several thousand -- required experiments that lasted several days. Now you can buy a kit and do it in hours."
The next major step toward genetic engineering of plants came when Chilton discovered that the T-DNA -- the segment of plasmid DNA that was transferred into the plant genome -- was bracketed by two specific base pair sequences. That suggested other genes could be transplanted into a plant if they were substituted for the T-DNA.
"Once it was proven that a DNA transfer was taking place, it wasn't difficult to conclude that this had significant commercial applications," Nester said. "My research didn't follow up on that," but Chilton's did. She went on to produce the first transgenic plant -- a herbicide-resistant tobacco plant -- and currently serves as distinguished science fellow for Sygenta Biotechnology.
Earlier this year she,
The award noted that Chilton's work "provided evidence that plant genomes could be manipulated in a much more precise fashion than was possible using traditional plant breeding."
Nester said the work on Agrobacterium serves as a case study for how basic research can lead to unforeseen consequences and commercial opportunities.
Although Initiative 522 to some extent seems to ask
He did note, however, that Agrobacterium "has been a terrific boon to plant molecular genetics. It's a mechanism that allows researchers to study many different systems, because of its ability to transfer genes from one organism to another."
"Agrobacterium is unique, as far as I know," Nester said. "Bacteria can transfer DNA to other bacteria, but Agrobacterium is the only organism I know of that can transfer to (plants or animals). It is a natural genetic engineer."
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