Male-sterile plants prevent the spread of transgenes

Topic

Most plants produce large quantities of pollen, which can be transported over long distances by the wind or by insects. If pollination occurs, traits can be transferred to related species. To prevent the newly introduced genes from spreading from genetically modified plants via pollen, the project aims to produce sterile plants with incompletely formed, infertile pollen by inhibiting pollen development.

A new approach being followed in this project is the inhibition of an enzyme called invertase, which is essential for pollen ripening. The invertase is expressed by the plant only locally during pollen formation and is in turn only inhibited at this time. The other parts of the plant are not affected.

Outside the cell, the invertase splits saccharose into the simple sugars fructose and glucose, which are then transported to the pollen cells via special cell wall proteins. If the invertase is inhibited during pollen development, the simple sugars needed by the developing pollen for its ‘nourishment’ are no longer available. As a result, no functioning pollen is produced and the plants are male-sterile.

In preliminary experiments it was shown on tobacco plants that pollen development is inhibited when the enzyme activity of the invertase is significantly reduced or disrupted. This project will use the same method to produce sterile maize and oilseed rape plants. In addition, the project is to establish a method that will make it possible to reverse temporarily the male sterility in the tobacco plants from the preliminary experiments so that they can be propagated. This approach is necessary to ensure that only male-sterile plants occur in the progeny and to avoid segregation.

The project will also investigate whether the findings from the preliminary experiments can be transferred to other transgenic tobacco strains.

Experiment description

Production of male-sterile plants: The aim of the experiment is to inhibit invertase activity in the anthers of maize and oilseed rape. Two methods are used to achieve this aim:

• The gene responsible for invertase is ‘switched off’ using the antisense technique .

• An invertase inhibitor which blocks the effect of the invertase is introduced into the plants.

With both approaches, genetically modified plants are produced and the male-sterile plants investigated further.

Further information on the procedure:

• Male sterility: plants without pollen

Sterility investigations: The pollen development of the plants with reduced invertase activity is investigated. If the expected sterility or reduced fertility is found, the pollen of these maize and oilseed rape plants will be characterised in greater detail with regard to their developmental disorders.

The investigations will focus on the carbohydrate metabolism. Since the anthers can take up no or only very small amounts of carbohydrates because of the disrupted invertase activity, this should have a significant effect on the carbohydrate metabolism of the anthers.

Restoring fertility in tobacco: To achieve this aim, a gene for a bacterial or yeast invertase, which is distantly related to the plant’s original invertase, is introduced into sterile tobacco plants. The introduced invertase gene is controlled by an inducible, anther-specific promoter . Unlike the plant’s own invertase, this invertase is not affected by the antisense repression or by the invertase inhibitor. Induction of this introduced invertase temporarily allows pollen development to take place, which will enable the reproduction of the transgenic plants under controlled conditions.

Inhibiting invertase activity in different tobacco strains: In preliminary experiments male-sterile plants were produced from the transgenic strain Nicotiana tabacum cv. Samsun SNN. This project will establish whether these findings can be transferred to other tobacco strains. The different tobacco strains will be transformed with the antisense construct from the previous experiments and then examined for invertase activity.

Results

Producing male-sterile plants: Four invertase variants were isolated from oil-seed rape, one of which is expressed only in the anthers. It has not yet been possible to isolate the promoter for this invertase.