After the initial reports in 1983 of successful genetic transformation of tobacco, petunia and sunflower plants using Agrobacterium to mediate gene transfer, this technique was tried on many other crop plants.
It was almost easier to name the crop plants NOT reported as being genetically modified using Agrobacterium.
There were, however, a very important group of crop plants not amenable to this transformation technique. The cereals.
In the early years of plant genetic engineering, corn (maize), wheat, barley, oats, etc., all resisted efforts at genetic transformation using the Agrobacterium-based technology. The reasons are complex, but suffice it to say here that it was mainly due to the fact that they are all monocots. The cereals not only don’t serve as good hosts for Agrobacterium, but also can’t be regenerated very easily via tissue culture, which is a critical step in Agrobacterium-mediated genetic transformation.
So, what were the poor cereal breeders to do?
In 1988, it was reported (see ref. 1 below) that maize could be genetically transformed by bombarding maize embryos (isolated from seeds) with extremely small tungsten micro-projectiles (0.6 or 2.4 microns in diameter) coated with DNA. Thus, these researchers avoided having to use Agrobacterium to deliver the foreign DNA into plant cells and, by using maize embryos, the necessity of generating plants from somatic cells.
And so the gene gun was born.
So, by 1990, there were multiple ways to genetically transform plants. And the race was on to develop commercially available (and profitable) GMOs.
The first GMO approved by the USDA for human consumption was the “Flavr Savr” tomato in 1992. And by 1996, Roundup Ready® soybeans were sold by Monsanto. As indicated in the graph above, both herbicide-tolerant (HT) and insect-resistant (Bt) genetically engineered (GE) crops have been widely adopted by U.S. farmers. (For more info click on figure.)
Though their GE crops have sold well, biotech companies want to protect their investments by limiting or preventing the ability of growers to save seeds from GE crops. One way is through litigation. Another way is through technology.
Officially called the Technology Protection System (TPS), a way was found to block the germination of seed produced by GE plants.
Briefly, this so-called “terminator” technology incorporates genes into GE plants that, when expressed, are lethal to seed embryos. (see ref. 2 below for more information)
T-GURTs Are “Traitors”
Another technological way to prevent farmers from saving and replanting seeds from GE crop plants would be to incorporate traits into the GE plants that would require a special chemical for second-generation seeds to germinate. Sort of like a special key for the lock.
Officially known as Trait-specific Genetic Use Restriction Technology or T-Gurt (a.k.a., “Traitor” technology), this method incorporates a genetic control mechanism that requires yearly applications of a proprietary chemical to activate desirable traits. (see ref. 2 below for more information)
Bottom Line: These days, the genetic transformation of plants, even cereals, has become routine. And there are even ways to insert “locks and keys” into your GE plants.
1. Klein, T.M., Fromm, M.E., Weissinger, A., Tomes, D., Schaaf, S., Sleeten, M. & Sanford, J.C. (1988) “Transfer of foreign genes into intact maize cells with high-velocity microprojectiles.” Proceedings of the National Academy of Sciences (USA) Vol. 85, pp. 4305-4309. (PDF)
2. “Terminator” Technology, Department of Soil and Crop Sciences, Colorado State University.
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