2,000-year-old Egyptian object unravels genetic mystery of 'plant love life' – 08/10/2021 – Science
"It's like a fascinating detective story," Colombian researcher Óscar A. Pérez Escobar describes to BBC News Mundo, the BBC's Spanish-language news service.
The scientist, from the Royal Botanic Gardens of Kew, in London, UK, and his colleagues revealed the complex "love life" of a plant centuries ago.
And they did it thanks to an object that someone buried, more than 2,000 years ago, in an Egyptian mummified animal cemetery.
Deciphering the genetic secrets of this artifact allowed unraveling the domestication of a plant whose fruit is consumed by millions of people around the world: the date palm.
And this information is fundamental for the future, says Pérez Escobar.
He is one of the lead authors of the new study on this discovery, published in the scientific journal Molecular Biology and Evolution and the result of an international effort. Kew researchers worked in cooperation with 15 institutions on four continents.
The study was based on the so-called "archegenomics", a science that the scientist compares to a "time machine".
Pérez Escobar spoke with BBC News Mundo, the BBC's Spanish news service, about the discovery, its importance in the face of climate change and the vocation it discovered among orchids in Colombia's cloud forests.
BBC News Mundo: Where was found the Egyptian artifact that revealed, as you say, "the love life" of this plant thousands of years ago?
Pérez Escobar: The object we studied was found in the animal necropolis of Saqqara, Egypt. The site is of great archaeological interest because millions of mummified animals were found there, among other artifacts, which allowed understanding the ways of life and the evolution of Egyptian societies in different periods of time.
The artifact is 2,100 years old according to carbon-14 isotope dating analysis.
It was found during an expedition led in 1971 by the Egyptian Exploration Society (now Ministry of Egyptian Antiquities) and first studied by English botanist Frank Nigel Hepper (1929-2013), who was associated with the Royal Botanic Gardens of Kew at the time. . The object was donated by the Egyptian Society of Exploration to the British institution for scientific research.
BBC News Mundo: In the study, you and your colleagues describe the artifact as mysterious. Do we know what it was used for?
Pérez Escobar: When the artifact was found, it was thought to be a kind of support to support the head, but there were no similar records of objects with that function.
However, a similar object found in the same location, but better documented, indicates that its true use was for sealing liquid storage vessels.
BBC News Mundo: Could you explain to us how difficult it was to extract the genetic material, as well as the effort required to do it?
Pérez Escobar: It was a real challenge to access the genetic code of our archaeological sample, which in the study we called the "Saqqara date tree". Compared to archaeological remains of animals, plant tissues are generally not so well preserved, especially over time scales of thousands of years.
This is mainly because bones tend to preserve DNA better and don't compare to plant cuticle or lignin, which are weaker protective barriers.
BBC News Mundo: How did you and your team manage to sequence this genetic material?
Pérez Escobar: It took one year's worth of experiments (conducted at the University of Potsdam, Germany) to get a useful representation of the genetic code of this object.
We had to repeatedly sequence millions of DNA fragments from the Saqqara date palm because, due to its age, the DNA was at a very advanced degree of deterioration.
That's because, once the date palm leaf used to make the vase prints at that time separates, its genetic code or DNA is no longer repaired and begins to break down into billions of fragments, or to put together artificial mutations in those fragments.
The effects of these two processes accumulate exponentially over time. In addition, date palm leaves are very rich in fiber, which does not store as much DNA as the juiciest tissues, such as seeds or leaves from other crops, such as olive or corn.
No one had ever extracted DNA from ancient date palm tissues until then.
BBC News Mundo: What did you find out about the history of this date palm?
Pérez Escobar: Our study revealed for the first time that the date palm we consume today had a love affair with two other closely related date trees known as the Phoenix sylvestris (or wild date palm, also called the sugar date palm) and the Phoenix theophrasti ( or Cretan date palm), which are currently found in places where the date palm we know is not.
(The Cretan date palm is found in coastal areas of Crete and Turkey, and the sugar date palm is a typical Asian species from Bangladesh and southeast India to Nepal, Pakistan and the Western Himalayas.)
BBC News World: How did these species cross?
Pérez Escobar: One hypothesis is that they intersected through human-to-human commerce. Another hypothesis is that the other date palms shared the same areas, but later, with climate change, they ended up being isolated from each other.
Thanks to the DNA extracted from the vase print, we can be sure that these romantic relationships would have taken place 2,100 years ago.
BBC News World: Why is it so important to find out which species the Saqqara date palm has crossed in the past?
Pérez Escobar: That's super interesting because our study shows us that plant life is much more complicated than it looks, and sometimes it involves other species that have no apparent usefulness to humans.
But these species can keep in their genetic codes the secret to resisting adverse weather conditions or diseases, thanks to genes that can often be lost in the process of domestication of a culture.
BBC News Mundo: Revealing the domestication of crops from thousands of years ago could be the key to combating climate change…
Pérez Escobar: Knowing where the plants we currently consume come from and the form and timing of their domestication is vitally important for the improvement of these same cultures, especially in the conditions we live in today, with a climate that changes very quickly.
Knowing where these crops come from is essential to finding wild relatives with genes that can be useful for growing in adverse weather conditions or under the pressure of emerging diseases.
In the case of our study, knowing that the date palm shares genes with closely related species is very useful because it indicates that, when necessary, we could produce more robust dates in arid climates or with higher fruit production per plant, by crossing date palm crops and closely related species.
BBC News World: The study that you and your team conducted is an archaenomic application. What exactly is this science?
Pérez Escobar: Archaenomics has been extremely useful, for example, in understanding phenomena such as the relationship between humans and Neanderthals.
It basically consists of accessing fragments of the genetic code of plant or animal remains preserved under special conditions (facilitated by especially hot and dry climates, or preserved from sunlight).
The work of archaenomics on plants is a bit like the work a detective does in compiling evidence when an unusual event is suspected.
In the case of the date palm, previous studies already indicated that it had part of its DNA shared with the date palm tree, but it was not known when this love affair took place. Thanks to archaenomics, we were able to unravel these mysteries and provide a possible date when these exchanges had already taken place.
BBC News Mundo: How new is archegenomics and to what extent has it been made possible by the revolution in sequencing techniques?
Pérez Escobar: Access to the genetic code of fragments of plants or animals hundreds or thousands of years old has been developing for two or three decades. But at that time, due to technological limitations, it was possible to access a very limited number of DNA fragments and therefore we could learn very little about a particular object.
Now, thanks to the application of parallel sequencing of millions of DNA fragments (what we call new generation or genomic sequencing in some cases) extracted from fragments of ancient plants or animals, we can access entire representations of the genetic code of an individual that once existed hundreds or thousands of years ago.
Obviously, given the complexity of plant genetic codes and the degree of deterioration of plant or animal tissue thousands of years old, this is an ever-complicated task.
BBC News Mundo: Is archaenomics opening up a new world then?
Pérez Escobar: I would say yes! Archaenomics is like a time machine, in which we have an almost unique opportunity to go back to the past, in a certain period of time, and obtain secrets intimately linked to the existence of human beings, about the plants or animals on which we depend.
The development of new technologies in the not-too-distant future will allow us to easily go beyond the genetic code and even have a very detailed idea, for example, of the protein or nutritional content of plants that are thousands of years old, of the specific climatic conditions of the season in who lived or what their physical appearance was like in great detail.
BBC News Mundo: Could your work be applied to other cultures in the future?
Pérez Escobar: One of the cultures in which archegenomics can be applied is the olive tree (Olea europaeai). At Kew Gardens, there are precious collections of seeds that were found in Pharaoh Tutankhamun's sarcophagus! In addition, there is a large amount of material with its well-characterized genetic code that can be accessed for free.
Currently, the olive tree is a crop that is tremendously threatened by a bacterium that is causing the massive death of trees in Italy, Spain and Greece, and is estimated to cause enormous damage.
Archaeonomics can help us understand when this bacterium began to affect olive trees and whether some genotypes in the past were resistant to this disease.
BBC News Mundo: How did you come to work at Kew Gardens and how was your passion for plants born?
Pérez Escobar: I've been working at Kew for five years. I came as a postdoctoral researcher after finishing my doctorate in orchid evolution and systematics at the University of Munich, Germany.
But, since 2019, I have been lucky enough to work as a lead researcher.
My passion for plants started when I learned botany during my graduation at the National University of Colombia, when I was 17 years old. I took field trips to cloud forests in the Northern Andes mountain range, beautiful experiences.
I was fascinated at that time to know how it is possible that in such small spaces there was such a large density of plants, and to understand how they evolved over long (millions of years) and more recent (hundreds to thousands of years) time scales.
BBC News Mundo: What do you feel today when you hold in your hands the 2,000-year-old Egyptian artifact that is revealing these secrets?
Pérez Escobar: A great curiosity. For example, I can't help wondering how long it took to make it, how it was valued.
These are just some of the questions that cross my mind every time I visit our collection and see these objects that are thousands of years old.
BBC News Mundo: These objects must still contain many secrets…
Pérez Escobar: A very important message from our study is that there is still a lot to understand about the origin and evolution of the plants that humans depend on.
A lot of research funds have been invested over the last three decades in date palms, a crop that moves millions of dollars in different economies around the world, but the knowledge gaps that still exist are large.
For example, we do not understand with certainty all the kinship relationships of the 14 species of date palms that exist in the world.
So, no matter how much something looks like it's already been studied, there's always something new to discover!
-- Sent from my Linux system.
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