The gene-deletor technology can provide an effective tool to remove all functional transgenes from pollen and seeds of sexually propagated plants A modified version of the current ‘gene-deletor’ technology can used in sexually propagated crops, such as corn, rice, soybean, sunflower, canola and sorghum, etc. One possible strategy is to include a chemically inducible RNAi-FLP recombinase gene in the gene-deletor system, called a repression system. This RNAi recombinase gene can be activated by application of a specific chemical inducer and subsequently represses the FLP recombinase expression. As a result, all transgenes will not be excised from pollen or seed at that generation. In the subsequent generation when the plants are grown on farmers’ land, however, the highly efficient gene-deletor system will lead to excision of all functional transgenes from pollen and seeds because the inducing agent is not applied.
One important feature of the repression system used in the 'gene-deletor' system is that the repression system does not need to be 100% efficient. Seed companies can easily remove or kill undesirable "non-transgenic" (seeds in which the functional transgenes have been excised) resulting from the inefficient expression of the recombinase RNAi gene. Seed companies can, for instance, use an appropriate herbicide or antibiotics to kill non-transgenic seeds at early stages of seed development. The herbicide or antibiotics applied at early stages of seed formation should eliminate more than 98% of "non-transgenic" seeds. If there are some (small %) certified seeds are non-transgenic, it should not cause a meaningful yield loss to farmers. Some people believe that having 1- 3 % of non-transgenic plants in a Bt transgenic plant field may be beneficial to reduce the potential risks for development of Bt resistant insects. Finally, repressing the recombinase expression is a task of seed companies, not farmers, during production of certified seeds. Because acreages for certified seed production are relatively small, it is easier to achieve a relatively uniform application of a chemical inducer and therefore to have a high efficiency to repress the recombinase expression.
For addtional information, please read the article by Li, Duan and Smith.