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 fertilize 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 formation Pollen is produced by the male parts of a plant’s flowers. By means of gene technology, male sterile cultivars have been made and are already available for maize, sunflower, and rapeseed. The system of male-sterile plants has been used to enable controlled cross-pollination and is also capable to prevent a plant from passing along its genetic material. Unfortunately, this approach does not work for plants that need successful pollination leading to the formation of 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 the transgenic cultivar, they can be prevented from making it into a plant’s pollen. Normally transgenes are added to the nucleus. But also chloroplasts contain genetic information that can also be a target for genetic engineering. In most flowering plants, pollen contains no chloroplasts at all. Pollen only carries the genetic material found in the nucleus. Upon pollination, the new plant embryo contains only chloroplasts of maternal origin from the egg cell. Therefore, pollen spread has nothing to do with the spread of the genetic information contained in chloroplasts. There are, however, several plants that are exceptions to the rule, having some chloroplasts in their pollen. How reliable this type of “biocontainment” works is currently being under research in several research projects.

Preventing seed germination of transgene plants. A safe way to stopp the spread of foreign genes?

Strategie C: Transgenic Plants with sterile seeds A different approach for preventing the spread of transgenic plants is the construction of systems for the restriction of seed germinating. These systems either block the production of viable seeds in the transgenic plant or confer seed sterility also to its offspring when pollen escapes. In the second case, also an out-crossing of the transgenic traits to wild relatives can be undermined. Meanwhile, several systems are patented and lots of new are under development.

A problem of seed sterility systems is seed propagation for maintenance of the breeding line. To ensure this, sterility must be recoverable achieved by additional introduced genetic elements like nucleases or inducible cell toxins. The interplay of these elements for blocking and restoring of viability is very complex. So predictions how reliable these seed sterility systems will work to stop transgen spread are hard to make.

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

All the systems for stop spreading transgenes described here are developed in recent years and are still under evaluation regarding their functionality and reliability. It seems to be a fact for all different approaches that in isolated case the out-crossing protection can be undermined. But in general they will offer a very helpful tool to restrict transgene spread in agricultural landscapes and in natural habitats.