Feb 19, 2007

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Biological containment

Seed sterility

One way of preventing transgenes from spreading, and thereby from outcrossing, is to engineer seed sterility. There are a number of different molecular biological concepts for producing plants with seeds that do not germinate, or that germinate only after treatment with chemicals. However, these "terminator" systems are controversial.

The “terminator” concept, which is one of the GURT technologies (Gene Usage Restriction Technologies) was actually developed to protect the intellectual property of plant breeders and seed growers and to prevent farmers from propagating the seed themselves.

It is not yet possible to predict whether the terminator concept will be used for this purpose in future. There is a fear that particularly in poor countries it will increase farmers’ dependence on the seed industry. Terminator technology is supposed to prevent farmers propagating the seed from plants themselves, forcing them to buy new seed every year. After heated discussions, at least a few agro-businesses have pledged not to use terminator technology. But since they suppress seed germination, GURT technologies like the terminator concept could in principle also be used to prevent the reproduction and spread of GM plants.

A number of different terminator systems have now been developed.

• A key element of all these systems is a lethal gene (called “terminator gene” in the illustration). Depending on the timing, expression of the lethal gene leads either to seeds that are incapable of germinating or to death of the seedling.
• This process is controlled by suitable promoters. During the final seed maturation stage lea promoters (lea stands for “late embryogenesis abundant”) activate the genes whose products control and accompany the drying process. Shortly after the seeds have swollen, germination-specific promoters activate the genes whose products break down substances from the storage tissue and transport them to the young seedling.

If the plants were to contain only lethal genes such as these, propagation would be impossible even for the plant breeders and seed producers. For this reason, the system requires other components that can be used to reverse the seed sterility. For this too there are a number of different systems. What they all have in common is that they involve inserting additional gene constructs into a plant alongside the lethal gene. These are usually linked to a promoter, which is activated by a chemical substance (inductor). When activated, the effect of this gene then neutralises the lethal gene.

• One system is based on GM plant seeds that are not capable of germinating. The farmer must purchase a suitable chemical along with the seed. The seed will germinate only when treated with this inductor chemical.
• In another system the GM plants form normal seeds, but before they are sold as seed they are treated with an inductor that activates the lethal gene. Farmers who sow this seed will get plants that produce seeds that mature but that are no longer able to germinate and cannot therefore be used for re-sowing.

To what extent these GURT technologies are in fact suitable for biological containment is not yet clear. There is not yet any scientifically based, reliable information or data on the practicability of these approaches or on the genetic stability of the individual components.