This is the oldest known plant virus ever recovered from an archaeological sample.
Researchers studying the ruins of Canyon de Chelly National Monument, a famous Native American archaeological site in Arizona, have managed to uncover a previously known plant virus, which incidentally is the oldest one ever found.
The credit goes to a team of scientists led by Marilyn Roossinck, a professor of plant pathology and environmental microbiology at Pennsylvania State University. Roossinck and her colleagues stumbled upon the virus while examining ancient plant material discovered at an Ancestral Puebloan ruin known as Antelope House.
According to Science Daily, more than two tons of plant refuse were recovered from the canyon’s ancient dwelling in the 1970s, when the National Park Service first excavated Antelope House. The Native American tribes that inhabited the area planted a variety of crops, including maize, beans, and squash.
The newly discovered virus was retrieved from ancient maize cobs dating back 1,000 years and is an RNA virus belonging to the family Chrysoviridae. These viruses are known to infect both plants and fungi and are extremely persistent, plaguing “their hosts from generation to generation by transmission through seeds and can remain in their hosts for very long time periods,” Roossinck’s team explains in a paper published in the Journal of Virology.
The newfound chrysovirus, dubbed Zea mays chrysovirus 1, was extracted from 312 maize cobs. While this is not the first time that scientists have retrieved an RNA virus from ancient samples — a handful of these viruses were found during archaeological digs over the years — the Zea mays chrysovirus precedes the others by a few hundred years.
“The previous record holder for oldest plant virus, a barley stripe mosaic virus found in North African barley, was about 750-years-old,” shows an article from the journal Nature.
Roossinck’s team determined the age of the virus via carbon dating and managed to extract three nearly complete genomes of the new chrysovirus. As she pointed out, the most striking thing about the find was that the virus had been preserved within the maize samples for a millennium.
“That implies that the virus might confer some potential benefit to the plant, but we haven’t shown that yet,” explained Roossinck.
Upon comparing the maize found at Antelope House with modern corn samples, the team made another interesting discovery.
“When we analyzed modern corn samples, we found the same chrysovirus with only about 3 percent divergence from the ancient samples,” said Roossinck. “Most RNA viruses, with short generation times and error-prone replication, evolve rapidly. However, persistent viruses have very stable genomes.”
The ruin of Antelope House, the settlement that yielded the discovery, is located on the floor of Canyon de Chelly — a national monument spanning 131 square miles. Found in northeastern Arizona, the area preserves ancient dwellings of indigenous tribes from the Ancestral Puebloans to the Navajo and is renowned as North America’s longest continuously inhabited region.
“People have lived in these canyons for nearly 5,000 years — longer than anyone has lived uninterrupted anywhere on the Colorado Plateau,” notes the National Park Service.
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