The genetic factors of the host determine the composition of the virus communities

Plants can be infected with multiple viruses at the same time. However, the composition of the pathogen community varies, even if the individuals belong to the same species and the same population. Ecologists from the University of Zurich have now shown that these differences are mainly due to genetic variation between hosts. Loss of genetic diversity could therefore make species more vulnerable to infection and extinction.

Viruses are omnipresent throughout the plant and animal kingdom, but most of them are still unknown to science. Researchers have only recently developed improved analytical techniques and statistical tools to address one of the key questions: Why are some individuals more susceptible to viruses, while others remain unharmed?

The combination of pathogens is important

It is already known that genetic differences can make animals or plants more resistant to a specific virus. However, it is becoming increasingly clear that most organisms harbor not just one type of pathogen, but complex communities made up of different microbes. “Taking into account this diversity of infections is necessary to understand and predict the dynamics of the disease and the cost of the infection to the host,” says Professor Anna-Liisa Laine of the Department of Evolutionary Biology and Environmental Studies at the University of Zurich. For example, the first incoming pathogen could confer resistance to a second pathogen. But so far, little is known about the factors that determine the composition of virus communities.

With his research group at the universities of Zurich and Helsinki, Laine has now shown that genetic differences have a major impact on the diversity of the virus community that each individual supports. “This suggests that depletion of genetic diversity within a species can have significant consequences for the risk of virus infection,” Laine says.

Identical plants in different environments

For their study, the team used the common herb Plantago lanceolata, also known as ribwort plantain. Individuals of this plant can be cloned by root propagation, resulting in genetically identical offspring. Using this method, the researchers generated 80 clones from each of four different genetic variants of ribwort plantain and placed them among the naturally occurring ribwort plantain populations in four locations in the Åland archipelago in the Baltic Sea. The cloned plants were thus exposed to virus attacks in natural conditions. “By placing identical plants in different environments and keeping everything else constant, we were able to rigorously test the role of genetics,” Laine explains.

After two and seven weeks respectively, the researchers collected the leaves and determined which of the five recurrent plant viruses had infected the clones. They found that about two-thirds of the plants were infected with at least one virus, while nearly a quarter of those carried more viruses. Overall, they found 17 different combinations, ranging from two to five viruses per plant.

Most significant hereditary factors

Sophisticated statistical models therefore allowed researchers to discern how various factors – genetics, location, plant size, herbivore damage and interaction between viruses – influenced the composition of viral communities. The results revealed that host genetic differences explained most of the observed variation. “Although we suspected that the genotype would play a role, we were very surprised that it turned out to be the most important determinant,” says Laine. Another important factor was the local environment, while others such as plant size and herbivores showed only minor effects.

“This shows for the first time that genetic differences, most likely in immunity genes, are critical to how these different communities of pathogens assemble within hosts,” says Laine. “One of the next steps will now be identifying the underlying genes.”

Genetic diversity makes species stronger

The results highlight the importance of genetic diversity within species. The loss of diversity makes species much more susceptible to viral infections, with far-reaching consequences for biodiversity. The genetic diversity of natural populations is already being depleted due to the human destruction of natural habitats.

According to Laine, these findings could also be applied in agriculture to improve resistance to pathogens in cultivated plants: “The incorporation of genetic diversity into crop systems should be adopted as a sustainable means of controlling disease in agriculture. Not just individual pests, but entire communities of pathogens. ”