February 7, 2014
RNA Study On Barley Virus Reveals Key Link To The Crusades
redOrbit Staff & Wire Reports - Your Universe Online
Researchers at the University of Warwick have sequenced an ancient RNA genome for the first time ever. The RNA belonged to a barley virus once thought to be just 150 years old, but has now been determined to date back at least 2,000 years, revealing how extreme farming during the time of the Crusades contributed to its spread.
Although ancient DNA genomes have been sequenced before, ancient RNA genomes have not, since RNA breaks down around 50 times faster than DNA.
But in extremely dry conditions, such as those at the site in Qasr Ibrim in Lower Nubia where the barley was found, RNA can be better preserved, allowing the researchers to successfully sequence its genome.
Using the ancient RNA to calibrate estimates of the rate of mutations, the researchers were able to trace the evolution of the Barley Stripe Mosaic Virus to a probable origin of around 2,000 years ago, but potentially much farther back to the domestication of barley in the Near East around 11,000 years ago.
BSMV is transmitted through seed-to-seed contact, so it is likely to originally have been transferred from the wild grass population to an early-cultivated form of barley while the seeds were stored.
“It is important to know as much as we can about virus evolution as emerging infectious plant diseases are a growing threat to global food security, and of those viruses account for almost half,” said study leader Dr. Robin Allaby, of the School of Life Sciences at the University of Warwick in the UK.
“History tells us about the devastation caused by the emergence of disease from wild hosts in disparate countries, such as the Central American origin of the oomycete that led to the Irish potato famine," said Allaby.
“We need to build up an accurate picture of the evolution of different types of virus so we can make better decisions about policies on plant movement," he continued.
“The medieval RNA from Qasr Ibrim gives us a vital clue to unlock the real age of the Barley Stripe Mosaic Virus," he added. “It is very difficult to understand how a plant disease evolved by solely relying on recent samples, however this 750-year-old example of the virus allows us to more accurately estimate its evolution rates and date of origin."
“Without the Medieval RNA evidence, the virus appears to be much younger than it actually is, when in fact its origins go back thousands of years," said Allaby. “It’s possible that other viruses that similarly appear to be very recent may in fact have a more ancient origin.”
The researchers believe that the ancient BSMV genome came from a time of rapid expansion of the plant disease in the Near East and Europe that coincided with the Crusades, in which the Christian lands of Europe fought the Muslim territories of the Near East. The seventh Crusade of Louis IX in 1234 is the most closely aligned date to the origin of the virus expansion.
The researchers believe the massive war effort could have caused the virus to spread, fueled by an intensification of farming in order to feed the armies engaged in the campaign.
This made contact with cultivated barley and wild grass more likely, providing opportunities for the virus to ‘jump’ into the crop, the researchers said.
Genetic evidence also suggests a split into an east and west BSMV lineage around the end of the 15th century, around 100 years after the Mongol Empire stabilized the Silk Road. It is likely that BSMV was transported to the east via trade routes such as the Silk Road in the late Medieval period. More recently, the virus appears to have spread to the US from Europe around 120-150 years ago.
The study was published February 6 in the journal Scientific Reports.