Researchers at Washington State University have discovered an unexpected adaptation in a plant virus that appears to have been borrowed from their photosynthesizing hosts — a sensitivity to light.

In a recent article published in the journal Frontiers in Plant Science, professor of plant pathology Hanu Pappu and colleague Michael Neff, director of WSU’s molecular plant sciences graduate program, said they have found that tomato spotted wilt virus may respond to light and plant growth hormone.

Tomato spotted wilt belongs to a group known as tospoviruses, which are responsible for an estimated $1 billion in crop losses annually, Pappu said. Tospoviruses afflict a wide array of food crops including peanut, pepper, potato, onion and soybean, among many others.

Tospoviruses only have five genes but they carry other genetic material with no known function and have a reputation for borrowing chunks of genetic code from their hosts. In their research, Hanu and his team found genetic signatures within this morass that are also present in many plants and bacteria. Neff and Pappu’s post-doctoral researchers, Ying Zhai and Hao Peng, conducted a series of experiments that confirmed these stolen genetic sequences could be switched on or off with light or hormones.

Viruses are not-quite-alive infectious agents that are metabolically inert outside of a host cell. They are generally frugal in the amount of genetic material they carry — most viruses have just enough to ensure survival and reproduction. Pappu said tomato spotted wilt would not have stitched these photosensitive qualities into its own genome or evolved to keep them if it weren’t to the virus’ benefit.

Pappu, who has been studying plant viruses for more than 30 years, said while it’s long been accepted that these viruses have co-evolved with the plants they inhabit, it was nonetheless a surprise to see a virus that had apparently appropriated photosensitive qualities from their plant hosts.

Next, Pappu and his team will work to identify the part these genetics play in the life cycle of the plant and possibly use light or hormonal stimuli to manage the disease. If light can be used to disrupt the viral lifecycle or suppress the disease, it could have a potentially huge impact on crop loss, he said.

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