To assess the promise of using transplastomic plants for containing foreign genes, researchers intend to produce a document compiling all of the information that is currently available on the topic. In addition to the review, this project also has an experimental component to measure how often genetically modified chloroplasts “leak” into pollen.
To get an idea of how much "paternal leakage" occurs - that is, when some plastids end up in pollen - researchers use transplastomic plants as pollen donors to see if the resulting seeds turn out to be GMOs. To accomplish this, researchers start by generating transplastomic tobacco lines with an antibiotic resistance marker gene. Because the plants will be transplastomic, the pollen should be free of the antibiotic resistance gene.
To find out if this is really the case, male sterile tobacco plants are pollinated using pollen from the transplastomic tobacco. Because male sterile tobacco does not produce pollen, the resulting seed set will have been entirely fathered by the transplastomic tobacco. To find out of the resulting seed set is truly free of transformed plastids, the seeds are grown on antibiotics, which would normally kill the plant. If some of the seedlings survive, it would suggest that some transformed plastids were indeed transferred via pollen.
The review found that for the large part, data on the frequency of transgene transmission via plastids by pollination is scarce. Therefore, it is particularly important to conduct the research involved with this project to obtain data on this important biocontainment issue.
The review will be published in the scientific journal Topics in Current Genetics in 2007.
The researchers have developed an experimental system that facilitates selection for occasional paternal plastid transmission. In a large screen, the team detected low-level paternal inheritance of transgenic plastids in tobacco.
The research led to the conclusion that plastid transformation provides an effective tool to increase the biosafety of transgenic plants. However, the method does not completely prevent transgenes in pollen and therefore must be combined with additional containment methods to eliminate the residual outcrossing risk in cases where pollen transmission must be prevented altogether.
The research has been published in the scientific journal Proceedings of the National Academy of Sciences.
Chloroplast transformation and transgene containment
Public Deliverables of the Co-Extra project
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Max Planck Institute for Molecular Plant Physiology, Germany