Going viral is a good thing. Viral infections can help some plants attract more pollinators and produce more seeds, essentially boosting – rather than hurting – their evolutionary fitness, a new study has found.
Plants are known to emit volatile chemicals that deter herbivores or attract pollinators or seed dispersers. Some viruses can change those volatiles to attract insects, such as aphids, that damage plants but help transmit the virus between them.
Now, a team of researchers lead by John Carr from the University of Cambridge has shown in greenhouse experiments that a cucumber mosaic virus can change the types and amounts of chemicals emitted by an infected tomato plant, so that it attracts more bumblebees to pollinate it. As a result, the plants in their experiments produced more seeds.
Without pollination, the virus affected the plants negatively, decreasing their seed production, compared with non-infected plants. But when bumblebees were present, it had the opposite effect.
When the researchers then modelled what would happen under natural conditions, they found that such viruses could indeed enhance plant attractiveness to pollinators enough to make up for loss of fitness due to infection.
This means that the benefits of the virus could outweigh the drawbacks, allowing genes for susceptibility to persist in plant populations.
“To my knowledge, this is the first evidence that virus infection can make plants more attractive to pollinators,” says Carr.
The team can’t yet say how or why this process initially evolved. But they think that this is a case of mutualism, useful for all involved, including the bumblebees.
“Viruses reprogram plant metabolism and we can speculate that by chance this resulted in some beneficial changes for bees,” says Carr.
Infection protection
Although viruses can cause disease and crop losses in cultivated plants, “there is a growing realisation among plant virologists that in the wild, virus infection may be beneficial,” says Carr.
For example, his team has previously found that a protein made by the cucumber mosaic virus made infected Arabidopsis plants resistant to drought.
“The ability of cucumber mosaic virus to induce drought tolerance enhances the survival of its host and therefore of the virus itself during periods of environmental stress,” says Carr. “Indeed, under drought conditions, resistant plants may be at a disadvantage compared with infected ones.”
Carr thinks that this phenomenon could now be exploited to boost pollination of crops. “We can learn from the effects of the virus on pollinators,” he says. “Understanding how these volatile chemicals attract bees could be used to increase crop yields.”
John Walsh from the University of Warwick, UK, is intrigued by the findings. “This is the first evidence of this phenomenon. Such interactions, brought about by co-evolution between the three species – plant, insect and virus – are likely to be very important and need further research.”
