Published online 13 September 2010 | Nature | doi:10.1038/news.2010.464
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Taking molecular snaps of ancient crops
RNA molecules could help to reveal plant breeding in action hundreds of years ago.
Ewen Callaway
Archaeologists interested in the genetics of ancient organisms have a new molecular tool at hand — RNA. Two teams of scientists have decoded RNA from ancient crops in the hope of understanding the subtle evolutionary changes that accompanied the process of plant domestication.
Unlike DNA, which remains largely unchanged throughout the life of an organism, RNA molecules offer a snapshot of the activity of a cell, indicating which genes are turned on and off, and to what extent.
As a crop raised for 6,000 years across the Americas, maize is ripe for studies of ancient plant breeding.PIXFOLIO / Alamy
"With ancient DNA you can see what an ancient organism might have looked like. With ancient RNA we can see what it actually looked like," says Sarah Fordyce, a molecular biologist at the University of Copenhagen, who presented the RNA transcriptomes (the whole set of RNA molecules present) of 700–850-year-old maize (corn) seeds at a conference there last week.
Ancient RNA is also a lot more likely to catch evolution in action than DNA, says Robin Allaby, an evolutionary geneticist at the University of Warwick, UK, whose team has sequenced small regulatory RNAs from ancient Egyptian barley seeds. Increasingly, biologists are discovering that the differences between organisms are due not to mutations that change the sequence of protein-coding genes, but to the genes' activity.
Important as RNA is to evolution, it isn't an obvious molecule to study in ancient specimens. RNA is notoriously difficult to work with because it is much less stable than DNA. Biologists working with fresh RNA struggle to prevent it breaking down, and extracting it from samples that are hundreds or even thousands of years old seemed pointless, Allaby says. "There was a strong ethos that even if there was any RNA around, it would be too degraded to do anything with."
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