Scientists have succeeded for the first time in sequencing the genes in 6,000-year-old barley seeds, making these the oldest plant genome to be reconstructed to date.
The 6,000-year-old Chalcolithic barley grains were retrieved from Yoram Cave in Israel, close to the Dead Sea.
Genetically, the prehistoric barley is very similar to present-day barley grown in the Southern Levant, supporting the existing hypothesis of barley domestication having occurred in the Upper Jordan Valley.
The analysed grains, together with tens of thousands of other plant remains, were retrieved during a systematic archaeological excavation headed by Uri Davidovich, from The Hebrew University of Jerusalem, and Nimrod Marom, from University of Haifa in Israel.
The cave is very difficult to access and was used only for a short time by humans, some 6,000 years ago, probably as ephemeral refuge, researchers said.
Most examination of archaeobotanical findings has been limited to the comparison of ancient and present-day specimens based on their morphology. Up to now, only prehistoric corn has been genetically reconstructed.
In this research, the team succeeded in sequencing the complete genome of the 6,000-year-old barley grains.
"These archaeological remains provided a unique opportunity for us to finally sequence a Chalcolithic plant genome. The genetic material has been well-preserved for several millennia due to the extreme dryness of the region," said Ehud Weiss, of Bar-Ilan University.
In order to determine the age of the ancient seeds, the researchers split the grains and subjected half of them to radiocarbon dating while the other half was used to extract the ancient DNA.
"For us, ancient DNA works like a time capsule that allows us to travel back in history and look into the domestication of crop plants at distinct time points in the past," said Johannes Krause, from the Max Planck Institute for the Science of Human History in Jena.
The genome of Chalcolithic barley grains is the oldest plant genome to be reconstructed to date.
Wheat and barley were already grown 10,000 years ago in the Fertile Crescent, a sickle-shaped region stretching from present-day Iraq and Iran through Turkey and Syria into Lebanon, Jordan and Israel.
Up to this day, the wild forms of these two crops persist in the region and are among the major model species studied at the Institute of Evolution in the University of Haifa.
"It was from there that grain farming originated and later spread to Europe, Asia and North Africa," said Tzion Fahima, of the University of Haifa.
The findings were published in the journal Nature Genetics.
