Background information: The EU sponsored “Transcontainer” project

Biological Contaiment

The Transcontainer project is aimed at developing GM plants in which artificially added genes (“transgenes”) are locked up and unable to spread to other plants, thereby facilitating co-existence and enhancing biosafety of GM plants.

All crops in the Transcontainer project have been chosen based on their relevance for European agriculture. As an important representative for the cultivation of plants for their seeds, the oilseed rape is being used in the research project. Tomato and eggplant represent plants grown for their fruits. The third group of agricultural plants are sugar beet, rye grass, red fescue and birch, which are grown for vegetative parts such as wood, beet and grass.

The researchers develop several types of biologically contained genetically modified plants and investigate three main strategies:

  • Plastid transformation
  • Controllable flowering
  • Controllable fertility

Plastid transformation – keeping things to oneself

Plastids are small organelles within a plant cell and have their own genetic information; an example of plastids is chloroplasts, in which photosynthesis takes place. It is known that, in some plants, these plastids are not carried by the pollen. Scientists then try to incorporate the foreign gene into the plastids instead of the plant genome and, as a consequence, the introduced gene is not spread by the pollen and is “biologically contained”.

Controllable flowering – turning down the flowers

Some crops are not grown for their seeds or fruits but for their vegetative parts. Inhibiting flowering may prevent the spread of pollen and seeds of GM plants. Current flowering control strategies are built on two groups of genes, which have been used in the lab to obtain floral repression: the CETS gene family and the MADS-box genes.

The CETS genes include the Terminal Flower1 genes, which repress flowering. Transcontainer is aimed at using this gene family to advance flowering control technologies and to demonstrate their potential to create non-flowering sugar beet, red fescue, perennial rye grass, poplar and birch. Since such GM plants do not flower, the potential of spreading the foreign genes through pollen would be reduced significantly.

The same strategy will be employed with the MADS-box genes. These include flower inducers and floral repressors, which already have been tested extensively for their effects on flowering. Transcontainer is aimed at developing flowering control strategies in sugar beet, red fescue, perennial rye grass, poplar and birch.

Controllable fertility – interfering with hormones

The idea behind this approach is to contain the transgene by developing plants that are unable to produce fertile pollen. The research project addresses several strategies. One includes transgenic parthenocarpy, an artificially induced production of fruits without pollination or fertilisation. This results in seedless fruits. Recently, several methods of transgenic parthenocarpy, based on the use of the DefH9-iaaM gene, have been developed for tobacco tomato, eggplant, strawberry, raspberry, melon and chicory. The DefH9-iaaM gene is a chimeric construct consisting of the iaaM gene from the bacterium Pseudomonas syringae pv. savastanoi under the control of the promoter from the DefH9 gene from the snapdragon plant. The iaaM gene codes for an enzyme that interferes with the plant’s biosynthesis of the plant hormone auxin. Transcontainer will use transgenic parthenocarpy as biological containment for tomato and eggplant.

Another strategy for controllable fertility is based on reversible transgenic sterility. In this case, a range of transgenic methods is available to develop plants which abort young flower buds and thus become sterile, whereby dispersal of transgenes by pollen or seeds is blocked. However, a shortcoming of these non-reversible transgenic sterility methods is that they preclude options for further breeding and seed production. Therefore, various transgenic methods have been developed in which sterility can be gained or lost by design. One approach is the Recoverable Block of Function (RBF). This uses a blocker gene that interrupts a specific molecular function in the plant, leading to death of the plant or its seeds, and a second recovery gene that restores the blocked function in the plant. The blocker and recovery genes are physically linked to a transgene with a desirable trait in one construct, so that they integrate into the plant genome together and remain united during sexual reproduction. The recovery gene is designed to be activated by a physical treatment, for instance by a heat shock, or by being sprayed with a chemical, such as alcohol. The dispersal of pollen or seed with the recoverable block of function construct therefore results in progeny that will die or be unable to reproduce because the recovery gene will be inactive. Transcontainer aims at investigating and developing the RBF technology with alcohol induction for oilseed rape.

Biological containment – benefits for the society?

The Transcontainer project also covers the assessment of the socio-economic impacts of biologically contained GM crops. The scientists are using the so-called Real Option Model, which has been developed in the EU research project ECOGEN and which estimates the ‘maximum incremental social tolerable irreversible costs’ of the use of GM crops. It takes into account reversible and irreversible costs and benefits for the private sector, such as technology providers, farmers and agro-food chain operators, as well as for the public sector, as reflected by issues of regulations, environment, biodiversity and more. With a view to biologically contained GM crops, the Real Option Model will be expanded to the reversible and irreversible private and public costs and benefits related to compliance with co-existence requirements through biological containment.