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Genome of 6,000-year-old barley grains sequenced for first time

effectively a record of the past history of the individual grains
"By combining archaeobotany and crop-specific genetics, this study has produced novel insights into the origins of our one of our most important crop plants.

An international team of researchers from leading institutions in Scotland, Germany, Israel and the USA has succeeded for the first time in sequencing the genome of 6,000 year old barley grains from the Copper Age (the Chalcolithic). Their results, which report the oldest plant genome to be reconstructed to date, are published now in the online version of Nature Genetics.

The grains were retrieved from Yoram Cave in the cliffs of the Masada fortress in the Judean Desert in Israel, close to the Dead Sea. The team show that at the genetic level, the prehistoric barley is very similar to present-day cultivated barley grown in the surrounding regions and supports the existing hypothesis that an important site of barley domestication was in the Upper Jordan Valley.

Barley, and its close relative wheat, were already grown as long as 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.  To this day, the wild forms of these two crops persist in the region. It was from there agriculture initially spread to Europe, Asia and North Africa.

The ancient barley grains, along with other plant remains, were retrieved during a systematic archaeological excavation of Yoram Cave by a multidisciplinary team of Israeli scientists. The cave is very difficult to access and was likely used only for short periods of time by humans some 6,000 years ago, probably as a temporary refuge. 

Most examinations of archaeobotanical findings have to date been limited to morphological comparisons of ancient and present-day specimens. In this research, the team succeeded in sequencing the complete genome of the 6,000-year-old grains.

The grains had been well-preserved due to the extreme dryness of the region and, as a result, provided a unique opportunity for the researchers to characterize a Chalcolithic plant genome in considerable detail. They first split the grains and subjected one half to radiocarbon dating while the other half was used to extract the ancient DNA (aDNA).  They then sequenced the aDNA, which they explain “effectively contains a record of the past history of the individual grains”.  The aDNA provided a template that the researchers could then use to compare to resequenced wild lines, and to domesticated lines grown by farmers across the wider geographical range of the species.  

Their analyses showed that the grains cultivated 6,000 years ago were quite different at the genetic level from the wild forms that still exist in the surrounding region, but were closely related to present-day domesticated forms that are also grown close by. 

Their findings indicate that the domestication of barley was already well advanced 6000 years ago and that one origin of barley domestication was in the Upper Jordan Valley. They explain: “Our hypothesis is further supported by findings at two archaeological sites in the surrounding area where the earliest remains of barley cultivation have previously been found”.

Given the extent that the climate, the local flora and fauna, as well as the agricultural methods, have changed over this period of time led the group to conclude that conquerors and immigrants coming to the region did not bring their own grains with them from their former homelands, but rather cultivated locally adapted plants.

Professor Robbie Waugh, from the James Hutton Institute and the University of Dundee, explained: “This is a remarkable finding as it demonstrates that from the start of barley domestication some 10,000 years ago, after 4,000 years cultivated forms had already become quite different from their wild relatives, despite growing side by side in the same geographical region.”

By combining archaeobotany and crop-specific genetics, this study has produced novel insights into the origins of our one of our most important crop plants. DNA-analysis of archaeological remains of prehistoric plants provided the group with novel insights into the origin, domestication and spread of barley and may in future help identify beneficial genes that may be needed in the future but were lost during the domestication process.

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Printed from /news/genome-6000-year-old-barley-grains-sequenced-first-time on 12/11/19 05:45:57 AM

The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.