Environmental Safety Strategies for Stopping the Spread of Foreign Genes

For many genetically modified plants, it would be desirable to make sure foreign genes do not spread to conventional crops or propagate in the environment. A new generation of transgenic plants engineered to produce pharmaceuticals (molecular pharming) or specialty chemicals may soon be grown commercially. Methods are needed to keep such genes and genes products out of the food supply chain. The same methods could also be used to keep transgenic traits like pest or disease resistance out of natural ecosystems.

Foreign genes under house arrest: Biological methods for preventing the spread of foreign genes in the environment

Genes, including transgenes, can be passed along and spread when crops pollinate and fertilise other crops or closely related plants in the wild. Wind pollinated plants release large quantities of pollen into the air, which can be blown considerable distances. Insect pollinated plants attract bees or butterflies to distribute their pollen to distant breeding partners. This is why most strategies for stopping the spread of foreign genes work either by stopping the spread of pollen or by disrupting its function.

Biological contaiment: Plants without pollen?

Strategy A: Male sterility - Stopping pollen production Pollen is produced by the male parts of a plant’s flowers. If a plant is male sterile, it is unable to produce pollen. Male sterile plants are already available for maize, sunflower, and rapeseed, some of which were made male sterile by genetic engineering. Male sterile plants have been used to facilitate controlled cross-pollination, but they could also be used to prevent a plant from passing along its genetic material. Unfortunately, this approach is impractical for crops whose value depends on successful pollination for forming fruit and seeds. This is the case for cereal crops, rapeseed, and maize.

Chloroplasts in plant cells

Strategy B: Chloroplast transformation - Keeping pollen transgene-free To keep foreign genes "locked in", they can be kept out of a transgenic plant's pollen. Normally, transgenes are added to the genetic information found in the nucleus. Chloroplasts, however, are another type of organelle found in plant cells that contain genetic information. In most flowering plants, pollen contains no chloroplasts at all, only carrying the genetic material found in the nucleus. Upon pollination, the new plant embryo only contains chloroplasts from the egg cell, which comes from the mother plant. Therefore, pollen spread has nothing to do with the spread of the genetic information contained in chloroplasts. If chloroplasts are genetically modified, the pollen from such "transplastomic" plants does not contain foreign genes. There are, however, several plants that are exceptions to the rule, having some chloroplasts in their pollen. The reliability of this approach to “biocontainment” is currently under research.

Stopping transgenic plants from sprouting: A safe way to stop the spread of foreign genes?

Strategy C: Keeping transgenic seeds from sprouting Another way to prevent the spread of transgenic plants is using systems that restrict seed germination. Although farmers would still be able to grow transgenic seeds they buy from seed companies, any seeds formed by unintended cross-pollination would be unable to grow. Several such systems have been patented and many more are under development.

One of these systems was originally developed to prevent farmers from using a portion of their harvest as seed for the following growing season. For seed companies, this means producers are forced to re-buy transgenic seed each year and abide by patent laws. Although the system offers the advantage of stopping the spread of transgenes in the environment, threats to the sovereignty of farmers have aroused considerable criticism. Links to documents addressing this debate are provided on this page.

One hurdle for seed sterility systems has to do with seed propagation. To enable seed production, sterility must be reservible. The interplay of elements used for blocking and restoring viability is very complex. Considering the complexity of induced sterility systems, it is difficult to insure that successful out-crossing will never happen.

Another type of seed sterility system only prevents the germination of seeds that form when pollen from the trangsgenic plant fertilises different crops or wild plants. This strategy offers protection against out-crossing, but still enables farmers to retain and replant seed.

Various names for seed sterility systems have been used in recent years: “Terminator Technology”, “Technology Protection System (TPS)”, “GeneGuard” and others – but the most favoured term used today is “gurt” (genetic use restriction technology).

All these systems for stopping the spread of transgenes were developed in recent years and are still undergoing evaluation regarding their function and reliability. With all of these approaches, isolated cases of out-crossing are still considered possible. Nonetheless, they could still be a very helpful tool for restricting the spread of transgenes in agricultural landscapes and in natural habitats.