May 10, 2006

Basic info

Send

Biological safety system

Viruses as Trojan horses

Viruses are feared because they trigger plant diseases. They have a crafty strategy – using other cells for their own multiplication and causing plants to produce viral proteins. Attempts are being made to exploit this ability for scientific purposes. But first there are safety problems to be overcome.

Unlike micro-organisms or cells of higher living organisms, viruses do not have their own metabolism. They consist – basically – of DNA (or RNA) and a protein coat. In order to multiply, they have to invade other cells. The genetic system of the host cell then begins to create successive copies of the virus.

Potato virus X: The ideal vessel for producing proteins of commercial interest in plants?

Within the affected organism viruses multiply rapidly. If the viral infection of a plant lasts for some time, more and more of its cells will produce virus proteins. They can make up several per cent of the plant’s total protein. Geneticists are attempting to exploit this ability to produce new recombinant proteins in comparatively high concentrations in plants. This is of interest for e.g. producing active pharmaceutical substances in plants.

Viral full-length clones are variants of a naturally occurring plant virus produced with the help of molecular biological methods. They comprise the complete genome of a virus, which means that they contain all the information necessary for the multiplication and spread of the virus in a host plant. Foreign genes, e.g. genes that code for a protein of commercial interest, can now be inserted into these full-length clones. If the modified full-length clone is inserted into plants, their cells will produce not only the virus protein, but also the desired new protein (see diagram).

The main advantage of this method is the high yield of foreign protein. Only two or three weeks after infection with the full-length clone, the plants with the desired protein can be harvested. The plant itself is not genetically modified.

A serious disadvantage , however, is that new (chimeric) viruses capable of multiplying are produced in the infected plants. This means that a practical application of full-length clones is only justifiable if there are suitable safety systems in place that prevent the spread of the modified viruses.

Results: A suitable safety system has been developed in a completed SiFo research project. A transport-defective virus was used that can only systemically infect transgenic plants that express the transport protein. This prevents the undesirable spread of the virus and enables the safe synthesis of foreign proteins via viral full-length clones.