In a scientific first, Washington State University researchers have found a plant virus that could respond to a growth hormone and light.

“I was very surprised,” said Hanu Pappu, Samuel H. Smith Distinguished Professor and Chuey Endowed Chair in WSU’s Department of Plant Pathology. “We had no idea any plant virus had this adaptation, even though it’s been long accepted that viruses co-evolved with their hosts. And plants obviously respond to light, so this virus may have acquired the genetic sequences for light response from its hosts.”

In a recent article in the journal Frontiers in Plant Science, Pappu, his WSU colleague Michael Neff, and their respective post-doctoral researchers Ying Zhai and Hao Peng report that tomato spotted wilt virus, part of a group called tospoviruses, may be able to sense light and respond to plant growth hormones.

Pappu has worked for nearly two decades to understand and manage diseases caused by tospoviruses.

“Tospoviruses are estimated to cost over $1 billion annually in crop losses and the associated costs to control them,” Pappu said.

Closeup of the model plant Arabidopsis
Arabidopsis, a model plant, showing that a tospovirus sequence can respond to light and growth hormones.

They are efficient killers of many food crops including peanut, pepper, potato, onion, soybean and many more vegetable and legume crops.

These viruses contain only five genes, but they’re known for snatching bits of genetic code from their plant hosts.

In addition to the five genes, the virus contains other genetic material that doesn’t have a known function or use. After in-depth research, the team found the virus had some genetic signatures present in many plants and bacteria which were shown to respond to light and hormones. Zhai and Peng carried out a series of experiments to verify the activity of this viral sequence could be turned on or off by light or hormones.

Viruses are bare-bones infectious agents and carry the absolute minimum genetic information necessary for survival.

“There has to be some benefit to the virus, otherwise they wouldn’t have acquired and evolved to keep this genetic material,” Pappu said.

Now Pappu and his colleagues will look to find what role this genetic element plays in the virus’ life cycle. If they can find that, then it may be possible to disrupt that cycle and reduce the virus’ reproduction and spread using light or growth hormones, he said.

“It would be great if we could use these light and hormonal stimuli to suppress virus infections, leading to disease control,” Pappu said. “That could have a huge impact on reducing crop loss.”