Genetically modified plants must be safe for the environment and suitable for co-existence with conventional and organic crops. Towards such safety, a major hurdle is posed by the potential out-crossing of the transgene via pollen movement. Several Co-Extra research projects address this question by investigating biological containment strategies for transgenes. One group studied chloroplast transformation in tobacco and now has published promising results.
Led by Ralph Bock from the Max Planck Institute of Molecular Plant Physiology in Germany, the group studied genetically modified tobacco in which the transgene was integrated in chloroplasts. In certain plant species, such as tobacco, chloroplasts are not inherited from the male, and therefore, transgenes in these plastids cannot be disseminated by pollen. Since past literature reported contradicting figures on the reliability of this process, the Co-Extra researchers analysed more than two million seedlings and found that less than 20 in 1,000,000 inherited the transgene. In the pollen of adult plants, the rate was even lower, remaining below 3 in 1,000,000. This reduction is due to the fact that some parts of the seedlings are lost during their development into mature plants.
Because tobacco has a strong tendency towards self-fertilisation, the reliability of transplastomic plants is assumed to be even higher under field conditions. Therefore, the researchers believe that only one in 100,000,000 GM tobacco plants actually would transmit the transgene via pollen. Such values are more than satisfactory to ensure co-existence. However, for GM crops used in the production of pharmaceuticals, or in other cases in which absolutely no out-crossing is permitted, the researchers recommend the combination of chloroplast transformation with other containment methods, such as cytoplasmic male sterility or transgene mitigation strategies.