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Virus helps plant attract pollinators: pathogen's effects ensure stable supply of hosts, study suggests.

Instead of destroying its leafy hosts, one common plant virus takes a more backhanded approach to domination. It makes infected plants more attractive to pollinators, ensuring a supply of virus-susceptible hosts for generations to come.

The strategy might discourage resistance from building up in the plant population, University of Cambridge biologist John Carr and colleagues report August 11 in PLOS Pathogens.

"It looks like the pathogen is cheating a little bit--but in a way that helps its host," Carr says.

Plants give off cocktails of volatile chemicals that send signals to pollinators, predators and other plants. Carr's team found that tomato plants infected with cucumber mosaic virus gave off a different chemical cocktail than noninfected plants--and that bumblebees preferred the infected plants' brew.

When infected tomato plants didn't get pollination assistance, they produced fewer seeds on their own than their healthy counterparts. But when bumblebees helped out, infected plants' seed production was similar to that of healthy ones.

The virus benefits, too. By ensuring that sick plants can still reproduce, "those genes enabling susceptibility to the virus will stay in the population," Carr says.

The team found that cucumber mosaic virus changes plants' chemicals by disrupting the plants' natural defenses against disease.

Plants can identify when bits of foreign genetic material (like those from a virus) have worked their way inside. Specialized silencing enzymes snap into action and chop up the invaders. But a cucumber mosaic virus protein called 2b disrupts this process by binding to the silencing molecules so that they can't do their job.

That lets the virus infect the plant more easily--and it changes the way the plant turns its genes on and off. When the researchers tested a virus that didn't have the gene for the 2b protein, infected plants didn't shift their chemical cocktails the way the plants infected with the fully functioning virus did.

The link between the 2b protein and volatile production is a major finding that could help scientists better understand how viruses manipulate their hosts, says Penn State biologist Andrew Stephenson.

But further work is needed to convincingly show that the increased pollination is really a benefit for the plant, he says. Although infected plants produced more seeds, those seeds could be less likely to germinate, he says. And the shift in chemicals could lure aphids (which transmit the virus from plant to plant) just as much as bumblebees.

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Title Annotation:LIFE & EVOLUTION; cucumber mosaic virus
Author:Hamers, Laurel
Publication:Science News
Geographic Code:1USA
Date:Sep 17, 2016
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