A virus can quickly and completely infect a plant by spreading through the plant's vascular system. This is analogous to human viruses spreading through the circulatory system in the human body. Santos Silva discovered that the cowpea mosaic virus could not penetrate the vascular system of some tobacco plants. In the future, researchers want to establish the reason for this.
Plants from the tobacco species Nicotiana benthamiana died when the researchers infected a leaf of the plant with cowpea mosaic virus. However, in a second tobacco species, Nicotiana tabacum, only the infected leaf turned yellow and the rest of the plant remained unharmed.
Viruses spread through a plant in two steps. The first step is from cell to cell within the inoculated leaf. However, as soon as the virus has reached a cell bordering the vascular system of the plant, it can also spread via the vascular system throughout the entire plant. To spread from cell to cell, the virus needs to enlarge existing channels connecting neighbouring cells by building up a tunnel to transport the virus from one cell into the other. This is because the natural channels connecting the cells are too narrow for the virus to pass through.
Viruses spread more quickly through the vascular system than from cell to cell. Santos Silva discovered that the cowpea mosaic virus could even penetrate the vascular system via the existing channel connections without enlarging them.
Up until now, a lack of appropriate technology made it difficult to study how viruses spread through the vascular system of plants. During her research, Santos Silva used a fluorescent protein from a jellyfish. By linking this protein to the virus, she could follow the virus infection through the plant.
In plants infected by the cowpea mosaic virus, the leaves become yellow and rot, and the plant gradually dies. It is estimated that on a worldwide scale, plant viruses cause more than fifty thousand million euros of damage per year. Knowledge about how viruses spread within plants could lead to strategies for obtaining virus-resistant plants.
The research was funded by the Netherlands Organisation for Scientific Research.