Genetically modified organisms could potentially do a lot of good for the world, like ending the spread of diseases, or maybe one day helping us grow more food to feed the hungry.
There's a big problem, though. When you release altered species out into the wild, how can you prevent them from breeding with untweaked organisms living in their natural environment, and producing hybrid offspring that scientists can't control or regulate?
"This is a problem that has been recognised for a while," says synthetic biologist Maciej Maselko from the University of Minnesota.
Together with his team at the university's BioTechnology Institute, Maselko has come up with a radical solution to this scientific dilemma – but it's not one that any procreation-inclined GMOs will like too much.
"We want something that's going to be identical to the original in every way, except it's just genetically incompatible," Maselko explained to Nature.
To achieve such a thing, the researchers pioneered something they call 'synthetic incompatibility', or SI for short.
In a study released last October, the team described how synthetic incompatibility acts as a "genetic barrier to sexual reproduction between otherwise compatible populations [by activating] lethal gene expression in hybrid offspring following undesired mating events".
In other words, you might not be able to stop genetically modified plants, animals, and micro-organisms from mating with their organic counterparts out there in the world, but you can at least exercise some deadly control over what happens next.
To do so, the researchers rely on the ubiquitous genetic editing tool CRISPR-Cas9 – but instead of editing target genes and replacing them with alternative genetic code, synthetic incompatibility does something quite different.
Making use of a new class of molecular tools called 'programmable transcription factors', the researchers are able to alter gene expression in any offspring produced by interbreeding between a GMO and species in the wild.
"This approach is particularly valuable because we do not introduce any toxic genes," Maselko explains.
"The genetic incompatibility results from genes already in the organism being turned on at the wrong place or time."
And turning on the genes – or putting them into overdrive, as it were – can be used to devastating effect.
In their study last year, the team demonstrated synthetic incompatibility in brewer's yeast, where over-activated genes in the yeast offspring basically made them self-destruct – thanks to an unregulated protein called actin making the organisms inflate until they exploded.
But the team have their eyes set on more than mere yeast. Synthetic incompatibility – which they say could work in "virtually any sexually reproducing organism without changing how they are normally grown" – is already being trialled on other synthetic creatures.
In new research being presented this week, the team is discussing how experiments have also curtailed offspring from the common fruit fly, Drosophila melanogaster.
"Animal applications of SI include genetic biocontrol of pest species, replacing disease vector populations with engineered non-vector organisms, preventing gene flow between genetically engineered fish or livestock and their non modified counterparts as well as the genetic biocontainment of experimental systems such as gene-drives," the researchers explain in an abstract.
In other research co-funded by DARPA, the team is looking at how synthetic incompatibility could also be used to curb the encroachment of invasive fish species like carp, which threaten commercial fishing operations in the US worth billions of dollars.
Nematodes and plants are also on the horizon for synthetic incompatibility, and while it's too early to say whether the approach will be adopted by other scientists working in the field of genetic population control, it looks like the researchers' tool could help enable all kinds of new GMO applications.
Some researchers in the team have discussed include engineering fish that can break down contaminants in polluted water, or helping to regulate specialised plants in agriculture.
"We get a lot of medications from plants, but the plants that naturally make those medications only do so in really tiny quantities," says Maselko.
"One of my goals is to see if we can get the genes responsible for making those drugs into plants that we can grow on massive scales, such as corn, rice, or wheat."
The initial findings are reported in Nature Communications, and the newer research is being presented at the Plant and Animal Genome Conference in San Diego this week.