Biologists Discovered Large Number of Plant Viruses Traveling with Pollen

Plants depend on pollen to reproduce effectively. New research shows that these same vehicles also serve a different purpose: they provide a free ride for plant viruses.



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Plants rely on other agents, most notably pollinators, to move pollen from the anther to the stigma. This is how fertilization and reproduction take place.

Findings by Pitt Biologists now show that pollinators, such as bees, can increase the risk of diseases in plants. For the first time, they found that hundreds of viruses travel on pollen grains from one point to another.

The reproductive organs of a plant do not have too much covering to enable fertilization to take place more easily. This leaves them a lot more vulnerable to penetration by invading viruses. As in humans, pathogens invade through parts of the body that are less protected.

Findings in this research, which appeared in Nature Communication, have implications for both agriculture and humans.

Pollen hitchhikers

Before now, researchers have explored only a small number of viruses in plants. Therefore, those behind the current study did not know whether to expect just a few viruses as well or more.

The University of Pittsburgh biologists wanted to have a deeper understanding of plant viruses on pollen, which was seemingly lacking.

“Most of what we know about plant viruses comes from agricultural species that are obviously sick,” said Tia-Lynn Ashman, a Distinguished Professor in the Department of Biological Sciences at the University of Pittsburgh. “We just didn’t really have an idea what was out there.”

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The researchers wondered whether little was known because the viruses are not many or have not been properly studied.

For this research, the team sequenced the genetic material found in the pollen grains of 24 species of plants in the United States. It observed not only the viruses that have been known to hitchhike on pollen but many more.

Ashman and her fellow researchers reported finding six new virus species as well as three new variants of species that were previously known. In addition, they found partial traces of over 200 that have never been identified.

Findings also showed that plants that have more flowers, and so more appealing to pollinators, are more likely to have a greater number of viruses on the pollen.

Link to humans

Furthermore, researchers noticed highly diverse plant viruses in locations that were close to agriculture and human habitation. They suspected honeybees as being responsible for spreading these infective agents in that they tend to cover a large area.

These findings matter not only for how regular agriculture is practiced. They are also a concern with backyard beekeeping due to honeybees’ “superspreader potential,” according to researchers.

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“People think that doing beekeeping at home is helping pollinators,” Ashman said. “But when we do an activity like bringing honeybees into the city, we’re bringing everything that comes with them.”

What effects plant viruses have are not clear. The Pitt biologists could not state precisely whether they harm both plants and pollinators or maybe even help them. There is a need for further research to ascertain that since it was not the focus of the current study.


The pollen virome of wild plants and its association with variation in floral traits and land use



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