Adapting to a new climate
18 December 2008 by Terry Brown
How did barley learn to thrive in a damp, chilly north European climate? Terry Brown and team think they've found the answer in an unexpected place - Iran.
Wild barley grows naturally in warm, dry areas of Turkey and south-west Asia, but cultivated barley grows successfully in the much cooler and wetter climate of northern Europe. You might imagine that changes needed to adapt to these new conditions occurred in the crop as agriculture spread across Europe, but we have found that the situation is more complicated.
One of the important genetic mutations was already present in wild barley when the species was domesticated some 10,000 years ago, but in plants growing in Iran, over 1,000 kilometres east of the area where farming began. So, how did this mutation find its way to northern Europe?
We complain about wet British summers, but secretly many of us are pleased to live in a green landscape.
The mutation affects the time of year when the plants flower. We complain about the wet British summers but secretly many of us are pleased to live in a green landscape. In warm, arid areas most plants, including barley, flower early in the year, so that seeds are produced before the conditions get too hot and dry.
In northern Europe, the landscape remains green because the growing season is longer. Wild barley will grow in northern Europe, but it still flowers early in the season and so is less productive than it might be. Many types of cultivated barley have become better adapted to the northern European climate by flowering later in the year, enabling a longer period of growth before setting seed.
One of the genes in barley that controls flowering time is called Photoperiod-H1. A single mutation in this gene is associated with the change from early to late flowering. When we initially searched for this mutation in wild barley we were unable to find it, and we began to think that the mutation must have occurred in the crop as agriculture spread northwards through central Europe around 6000-5000 BC.
Hold the press conference
Huw Jones from the National Institute for Agricultural Botany, searching for variation in flowering time among barley landraces
We became quite excited when our archaeological colleagues told us that there might have been a pause in the spread of agriculture somewhere around Hungary, lasting a few centuries. Perhaps during this pause the critical mutation occurred, allowing agriculture to continue its advance northwards?
A neat story, definitely one for Nature, but before writing the paper and arranging the news conferences we decided to test a few more samples of wild barley, just to be sure. These new samples were from Iran and not obviously relevant to European agriculture, but in some of them we found the flowering time mutation.
We now think that the mutation originated in wild barley growing in the foothills of the Zagros mountains, where the growing conditions might be similar to those of northern Europe. But how did the mutation get into cultivated plants in northern Europe? The main centre for barley domestication was the Israel-Jordan region, but early farmers in Iran also domesticated barley from their local wild populations.
Cultivated barley has adapted to northern Europe by flowering later in the year, enabling a longer period of growth before setting seed.
Possibly these included some plants with the flowering time mutation, which then found its way via movement of grain or cross-breeding between plants into the crop that the first farmers took with them into Europe. Probably the mutation was quite rare in this crop, but was selected for when agriculture reached northern Europe.
That would be the easy explanation, but we are also exploring alternatives. Some crops were introduced into Europe after the original spread of agriculture. Could late-flowering barley be an example of one of these more recent additions? And did it enter Europe through Turkey and Greece, the route taken by the initial spread of agriculture? A more direct route from Iran to northern Europe would be through Transcaucasia and north of the Black Sea. We are now searching for the flowering time mutation in cultivated barley from Russia and other parts of northeast Europe to test this possibility.
Terry Brown is professor of biomolecular archaeology in the Faculty of Life Sciences at the University of Manchester. Huw Jones, Lydia Smith, Wayne Powell are researchers based at the National Institute for Agricultural Botany (NIAB), Huntingdon Road, Cambridge, CB3 0LE