Study shows surprising scale of plant virus

We rely on pollinators like bees for all kinds of different crops. But that same flexibility could put plants at risk for disease, according to new research from Pitt.

In the first study of virus hitchhikers on pollen grains, Pitt biologists show that a variety of viruses travel on pollen, especially in areas close to agriculture and human development where bees dominate.

“Our understanding of viruses on pollen in general was non-existent prior to this study,” said Professor Emeritus Tia-Lynn Ashman of the Department of Biological Sciences at the Kenneth P. Dietrich School of Arts & Sciences. “Most of what we know about plant viruses comes from agricultural species that are obviously diseased. We just had no idea what was going on there.”

Since most previous research has focused on a small handful of viruses, the team didn’t know what to expect in their search, or even if they should expect much.

“That was one of our questions,” Ashman said. “Do we not know much about these viruses because there aren’t many of them, or we just don’t know how to look at them?”

By sequencing the genetic material found on the pollen grains of 24 plant species across the United States, the group found signs of numerous plant viruses already shown to travel on pollen – as well as six new species, three new variants of ‘known species and incomplete virus traces of more than 200 others that have never been identified before.

The team, including Pitt biologist James Pipas, former Ph.D. student Andrea Fetters (A&S’21G) and Ph.D. student Amber Stanley, published their research in the journal Nature Communication January 26. For viruses, the tiny spiny carriers of plant genetic material we know as pollen provide a convenient way to move from host to host. It is also a direct path to a plant’s reproductive organs, the part of a plant where the cells are not covered with a hard outer surface. In this way, it’s similar to how viruses invade our own bodies through our less protected noses and mouths.

Ashman offered another analogy: “Pollinators are essentially the intermediaries for the sex of plants – since plants cannot get up and move to another plant, they depend on an intermediary,” she said. . “So you can link this to a sexually transmitted disease.”

Pushing this point home, the researchers found that the pollen produced by plants with more flowers that help them attract pollinators also harbored more types of viruses. The team also observed a greater variety of pollen-borne viruses in areas close to human habitation and agriculture. Ashman suspects that one reason for this pattern could be honey bees: since they visit a wide variety of flowers over a large area, they meet all the criteria for spreading viruses. Native pollinators are much more specialized.

This is a lesson not only for the way we farm, but also for backyard beekeepers.

“Bees have the potential for super-spreading,” Ashman said. “People think beekeeping at home helps pollinators. But when we do an activity like bringing bees into town, we bring whatever comes with them. »

Including, perhaps, any viruses they catch on their travels. As for what these viruses do — whether they harm pollinators and plants or paradoxically help them — that will be for future studies to determine. Either way, the work shows yet another way humans can put the brakes on when we design ecosystems for our own benefit.

“It’s a caveat to how when we change our environment, we potentially change these virus-host interactions,” Ashman said. “All of these things are interconnected.”

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