Gene flow of transgenic seed-expressed traits: Biosafety considerations

There are a few instances where seed-expressed traits may pose a biosafety risk, depending on the species, the trait, and where it is cultivated. The fewest ecological risks of pollen flow are posed to the natural environment, as there are few crops growing in or near pristine environments that have interbreeding relatives, or bear traits that could disrupt ecological balances. Some seed-expressed traits might pose an agro-ecological risk if introgressed into related weeds. Only pharmaceutical or industrial seed-expressed traits are likely to introgress into other varieties of a crop at regulatory red flag levels due to zero tolerance at the most sensitive levels of detection when grown at normal separation distances. Other traits would be below regulatory thresholds if required separations distances are met. Two of the three transgenic containment methods described (plastome transformation, attenuated viruses) are unlikely to work with seed-expressed traits. Transgenic mitigation could be used where the seed-expressed trait is linked with a trait that is positive or neutral to a crop but deleterious to its wild or weedy relative. Typical mitigation traits are dwarfing, no seed shattering, and lack of secondary dormancy. There are special mitigator genes, such as transgenically dominant sugary endosperm that might be appropriate for pharmaceutical traits. Biosafety gene flow protection mechanisms are also needed to prevent wild type poisonous seed crops (e.g. castor and Jatropha) from introgressing toxin genes into seeds of varieties where these toxins have been transgenically eliminated.