GMO gene flow and biological containment: locking up the transgene

Piet Schenkelaars is a molecular biologist and founder of the Dutch company Schenkelaars Biotechnology Consultancy. He is also one of the work package leaders of the EU research programme “Transcontainer”. In this interview, he describes its research goals and explains how biologically contained GM plants may facilitate co-existence in the future.

Piet Schenkelaars investigates biological methods for transgene containment.
Piet Schenkelaars investigates biological methods for transgene containment.
What is the origin of the name for the “Transcontainer” research programme and what is its overall goal?

The name of the European research programme Transcontainer  describes its overall goal in a nutshell, that is, the “containment” (or confinement) of “transgenes”. We aim to develop GM plants containing a foreign gene that is safely locked up. In other words: we are working on solutions to prevent the possible spread of a transgene from a GM plant to other plants. These technologies have several potential advantages, such as that the implementation would facilitate the co-existence of GM crops and conventional crops, while at the same time reducing the potential flow of transgenes to wild relatives and weeds. Likewise, we are investigating ways to prevent the dispersal of seeds from GM plants by mammals, birds or during the harvest, inhibiting the flow of the transgene to sexually compatible conventional plants. All those technologies consequently enhance the ecological safety of GM.

Which strategy will you pursue to reach this goal?

In fact, we will investigate and develop several strategies for the biological containment. One of these is “plastid transformation”. Plants have organelles named plastids, such as the chloroplasts in which photosynthesis takes place. In our approach we will use the fact that those plastids contain their own gene set, which has been found to be not carried by pollen and which, in some plants, is inherited only from the mother. If we are able to incorporate the transgene of interest in the chloroplast instead of the plant genome, this means that the transgene cannot be transferred to other, conventional plants by the pollen – then the transgene has been “biologically contained” and cannot spread to other neighbouring fields. We plan to develop sugar beet and oilseed rape with those transgenic chloroplasts.

In another approach, you prevent plants from flowering. How is that possible?

This is a strategy that we will develop for plants in which the vegetative parts, instead of the flowers, are of interest to farmers. One example of such a plant is the sugar beet, from which we use the beet and not the flowers themselves. What we wish is to repress flowering and thus to prevent dispersal of pollen and seeds. We plan to use several genes to develop such flowering control strategies [see background information].

This sounds promising.

Yes. However, pollination and seed-set are required for seed production. So, in order to enable further breeding, we complement these flowering control technologies with fertility restorer functions. Additionally, other crops are grown for their seeds and fruits, such as rape seed and tomatoes - flowering is then required to obtain a harvest.

How do you want to solve this problem?

For those cases, we need to find other ways of biological containment. Within the scope of Transcontainer, we are working on controllable fertility technologies. We are using several ideas to obtain male-sterility – that is, making plants unable to produce fertile pollen. The strength of this research is the fact that male sterility occurs naturally and has been investigated intensively. We think, though, that transgenic generated sterility may well be more reliable for a number of crops.

The Transcontainer project will induce parthenocarpy in eggplant.
The Transcontainer project will induce parthenocarpy in eggplant.
Are there other ways to “provoke” sterility?

Indeed, and we are investigating those as well. One strategy is based on parthenocarpy – this is the natural or artificially induced production of fruits without pollination and fertilisation, and results in seedless fruits. It has been observed occasionally in nature and the reason has been found in specific mutations. It can also be stimulated by spraying plant hormones, which the organism usually produces after pollination. Those hormones indicate to the plant that it has been pollinated, even though this actually has not taken place. In the Transcontainer project, we will induce parthenocarpy by introducing a specific gene into tomato and eggplant.

What are farmers’ benefits from biological containment strategies?

These technologies will facilitate co-existence by containing GM plants next to conventional plants in neighbouring fields. This has the potential to allow the application of shorter isolation distances between GM plants and fields with conventional or organic crops. The use of flowering control technologies, let’s say, in sugar beet, might also increase yields, because undesirable early flowering and bolting is prevented and the energy of the plant is utilised completely for the beet instead of for the flowers. Parthenocarpy might also have some positive “side effects”. The absence of seeds in grapes or oranges might represent “added value” for the consumer, as seeds with their bitter taste often are not desired.

Does all this research have anything to do with the controversially discussed terminator technologies?

Transcontainer’s research is aimed at developing biological containment strategies. We do not have the goal of restricting the use or propagation of crops, which is the main purpose of terminator technologies. Several of the containment technologies we are developing, such as male sterility and parthenocarpy, are already generally accepted and in use, and also will be complemented with fertility restoring functions. One of the seven containment technologies we’re investigating has some similarity to terminator technologies, but in this case we also will add a fertility restorer function.

For the biological containment of transgenes in tomato, parthenocarpy is only suitable, if no seeds are wanted.
For the biological containment of transgenes in tomato, parthenocarpy is only suitable, if no seeds are wanted.
Does this mean that farmers will be able to use seeds from their harvest for the next season?

Transcontainer is specifically designed for the European agriculture, but European farmers generally do not save seeds from the crops they grow. This is mostly due to the better seed quality and the uniformity of commercial seeds. Obviously, with parthenocarpic seedless tomato and eggplant, no seeds can be saved. In cases in which seeds are wanted, we employ other features, such as male-sterility or controllable fertility. We plan to develop controllable fertility with oilseed rape by introducing fertility restorer functions.

Will you assess the safety of the transgenic plants?

Indeed. We will assess the biosafety of the biological contained GM plants, and this will also include an assessment of the food and feed safety.

Which environmental effects will you investigate?

Our research will include analyses of the impact of the biological containment gene constructs on wild relatives, on animals and on human health. Obviously, the potential environmental effect in the case of failure of the containment technologies will be assessed as well. For each biological containment method, there are specific risks to be considered.

Can you give an example for those specific risks?

In the case of plastid transformation, we have the transgene in the chloroplasts instead of in the complete genome. What we will do is to assess whether the transgene might jump from the chloroplast genome to the nuclear genome, as well as whether the genetically modified chloroplasts are strictly not inherited by the pollen even under conditions of stress.

Do you already have first results?

It’s still too soon. In the first two years of the project, the research partners are developing the genetic constructs for the biological containment and incorporating them into the plants. Functional GM plants therefore are expected in the third year only.

Thank you for the interview.