3000-year-old wheat genetically sequenced
If you’ve ever left a box of cereal neglected in your cupboard for months, you’ll know that it takes a long time to go off. But will it last 3,000 years? It turns out the answer’s yes… or at least well enough to still read its genes, as scientists have just discovered, using grain harvested three more than 3 millennia ago. Phil Sansom…
Phil - This all started with an expedition to Egypt in the 1920s. There, English archaeologists uncovered some tiny grains of emmer wheat exquisitely preserved.
Laura - This was one of the first wheats that were domesticated in the Near East - around 10000 years ago.
Phil - The grains then moved to London to the Petrie museum of Egyptian archaeology. They sat there for 100 years until a scientists from UCL saw them featured on a BBC documentary. He and his colleagues got permission from the museum to try something new. Carbon date the wheat and then analyse its DNA.
Laura - We sequenced its genome of these like three thousand year old sample from Egypt. So it was very exciting to use a sample that had been in a museum and find nail results.
Phil - That is Laura Botigué, a geneticist who was part of a team sequencing the wheat samples.
Laura - What we sequenced were the husks, which are some sort of leaves that usually enclose the seed. So if you imagine a grain, a wheat grain that has this slightly around its shape which this beautiful golden colour.
Phil - Pairs of leaves each curled around the seed that had long since been eaten away by bugs.
Laura - The first step is to remove all the protein to free the DNA. You are in the blind when you do that because you follow the protocol pretty much like a recipe but you do not know the result until you sequence it. It's a bit challenging.
Phil - It works though and they produce the full genome of the ancient wheat. Every single one of its genes, they found that it had many of the helpful traits that crops have today, like big seeds that stayed on the plant when it's right. But the scientists main goal was to investigate how domesticated emmer wheat spread around the world. To do that they matched modern types of wheat, what are called 'land races' to the ancient genome to see which were most closely related.
Laura - At least the middle was surprising that we found that the closest relatives where land races that are or were cultivated in the Arabian Peninsula and in India and not the samples that used to be cultivated in the Mediterranean.
Phil - Why is that surprising. Well it's all about how early crop technology spread around the world.
Laura - This was a major transfusion in human history. It triggered a lot of changes in how populations lived and interactions between societies. This is sometimes called the Neolithic revolution and hunter gatherer populations were replaced by agricultural populations.
Phil - Scientists previously thought that when plants first got domesticated in places like the Middle East, the technology spread outwards in all directions at once to Europe, Africa and Asia. But this emmer wheat genome from Egypt was a way closer cousin to Asian land races than European ones. Maybe that means the technology came earlier to some areas than to others.
Laura - Probably there was a first wave of expansion towards the north and then Europe, and then there was a second wave of expansion towards the south of the Mediterranean and Asia.
Phil - The question is then why would technology have moved like that.There might be a European bias going on here but there might be something more.
Laura - One of the common problems is that usually Europe is better studied than other places. If you look at the archaeological sites I think that this theory of the later replacement matches the timing of the archaeological sites that you'll find. But because it's an understudied area (African nations) compared to Europe. I would say that at least it's intriguing to know why this happened at a later stage.
Phil - And the other big conclusion of the study is that lots of samples in museums might actually be treasure troves of DNA - even if they're not exactly going to make a healthy and nutritious breakfast.