Holger Jeske: Working with the dangerous twins

<ic:message key='Bild vergrößern' />

Before unique double-stranded structure of the Gemini virus was finally confirmed to be true, Holger Jeske’s model of two joined icosahedra met with much scepticism. Quelle: Holger Jeske

23.10.2008  - 

Tomatoes shrivel, cassavas grow string-like thin, and cotton plants only manage to produce marble-sized buds: When the Gemini virus, also known as the twin virus, strikes, it can pose serious risk to entire harvests. Almost all of the major field crops are susceptible to the disease. A Gemini virus was described for the first time by molecular biologist Holger Jeske. 30 years ago, the researcher from the University of Stuttgart chose the peculiarly shaped Abutilon mosaic virus for the subject of his thesis.

In Eastern and Central Africa, cassavas are an extremely important plant: They are economically versatile, as food, as cattle feed, and as a source of starch for industry. Moreover, they can tolerate nutrient-poor soils, as well as drought, and can be grown with comparatively little effort, as well as harvested at any time.

In the 1970s, a viral disease broke out in the cassava fields of Uganda that even to this day leaves farmers powerless. So-called Gemini viruses cause the plants to wither away before destroying them altogether. In the meantime, the pathogen has made its way across the trade routes, spreading out from the African continent to become pervasive around the globe. In West Africa alone, Gemini viruses are held responsible for crop losses estimated at two billion US dollars.

Gemini viruses also infect cereals

An international network, which includes the Stuttgart-based Molecular Biology and Virology Professor Holger Jeske among its members, is working on reigning in the spread of the virus. This is because Gemini viruses infect more than just cassava plants: Some of the most versatile viruses are oriented in particular towards corn, beans or cotton. These have begun to pose a global risk.In Brazil, it is mostly soy that is threatened; in the United States it is tomatoes and sugar beet. The virus has even been known to appear in Germany: The Bavarian State Institute for Agriculture, for example, has warned against Gemini viruses that cause stunted growth in winter barley, winter wheat, oats and rye.

Stuttgart University, Department of Molecular Biology and Plant Virology. The wind howls outside Holger Jeske’s office on the 9^th floor.  Hanging on the wall hang are two green balls, nestling together like baubles on a Christmas tree. "Imperfect icosahedra," clarifies Jeske, describing the form of the balls, which are made up of twenty identical triangles. Indeed, this is how the Gemini virus, which Jeske discovered 30 years ago using an electron microscope at around the same time as the first fields in Africa were being ravaged, appears when you take a closer look.

During his thesis, he examined the Flowering Maple (Abutilon), an ornamental plant that has been actively bred since the 19th Century, largely because of its mosaic-like yellow-green leaves. The plant is not a willing ornament. The distinct pattern on the leaves can be traced back to Gemini viruses, which damage the plants’ cells. "If the virus didn’t have such a conspicuous form under the electron microscope, I would probably have confused it with the ribosomes in the cell," says the scientist today. Did the breeding of Abutilon provide an outlet for the epidemics? Jeske does not think so: "Based on our current genetic characterisation of the viruses, we can rule that out. There are different types of virus at work here.”

Virus able to overcome classically bred resistance

The genetic studies are one of the ways with which Jeske and his colleagues are hoping to contain the spread of the virus. The studies enable the scientists to pursue new pathways, but above all to better understand how the virus overcomes classically bred resistance in crops, which has been known to occur time and time again.

The Gemini viruses leave a pretty pattern on the leaves of the ornamental plant Abutilon.Quelle: Holger Jeske

Jeske and his colleagues are now using genetic engineering to breed resistant plants. They identified two transport proteins of plant origin that the virus exploits in order to spread. These could provide a starting point for a resistance. Alternatively, small, modified pieces of viral DNA in the plants could ensure that only defective viruses are manufactured when an infection does occur.

Recognising sick plants as early as possible

Jeske laid down the groundwork for resistance research during his time in the 80s as a junior research group leader at the Center for Applied Molecular Biology of Plants in Hamburg (ZAMP).

 Shortly after the field of genetic engineering in Germany was given some decisive momentum by the first gene centre, ZAMP, founded in 1987, gave a helpful push of their own. On the initiative of the Free and Hanseatic City of Hamburg, a major research cluster for the genetically supported research of plants was established at the Institute for General Botany at the University of Hamburg.Jeske says that he is still benefiting from the experiences gained at the time: "I had few teaching responsibilities and could fully concentrate on the research. I still draw on the lessons of the past, and sometimes even get out my samples from the refrigerator from my time in Hamburg."

Until resistant plants are a reality, the diagnosis of the disease and the destruction of infected plants is the only way to prevent the spreading of the disease, as they cannot be treated. In order to identify diseased plants, Jeske wants to exploit the viruses’ own method of DNA amplification. Once the virus DNA appears in sufficient quantities, it can be detected with a kind of genetic fingerprint.

"This simple procedure works without expensive laboratory equipment, meaning that it’s suitable for those countries where the funds for equipment are lacking," says Jeske. This means that seedlings - where you can’t yet see the onset of the disease - can be identified as sick and burnt before they reach the fields.

To further improve diagnostic capabilities, Jeske, together with scientists from Spain and France, founded an international reference centre in Stuttgart in 2007, which gathers DNA samples of viruses from all over the world in a single database. On top of this, in Stuttgart, scientists from developing countries receive the opportunity to learn the methods of working with DNA. "We also benefit from this close cooperation with the involved countries," says Jeske. "We gain a better understanding of the agricultural reality on the ground, and can orient our research accordingly.”