(CN) --- A team of researchers in Abu Dhabi successfully germinated 2,000-year-old date palm seeds, yielding viable plants whose DNA they were able to sequence in a major feat of modern genomics.
Judean date palms, Phoenix dactylifera L. to be precise, are a previously extinct variety and the oldest plants germinated from seeds ever to undergo full genomic sequencing. By comparing its genome with those of modern varieties, the researchers were able to better understand how this species evolved over time. Despite the seeds’ advanced age, the authors didn’t find any significant mutations present in their DNA.
The international team comprised of researchers from the United States, Abu Dhabi, Israel and France wanted to find out exactly how these date palms adapted over the past 2,000 years. They planted 35 seeds that were excavated from archaeological sites in the southern Levant, of which seven successfully germinated --- the oldest of which they named Methuselah. The team released their findings Monday in a new study published in the journal PNAS.
“Resurrection genomics is an alternative to ancient DNA approaches in studying the genetics and evolution of past and possibly extinct populations,” said the authors in their study. “By reviving biological material such as germinating ancient seeds from archaeological and paleontological sites, or historical collections, one can study genomes of lost populations.”
As their name would imply, Judean date palms originated around the eastern Mediterranean, and were a popular cultivated variety. Roman author Pliny the Elder described them glowingly in his natural history treatise as having an “extremely sweet sort of wine-flavour like that of honey.”
According to the authors, sometime between the 4th century B.C. and the 2nd century A.D., these date palms increasingly incorporated DNA from a wild type, Phoenix theophrasti, which can be found growing freely today on the Greek isles surrounding Crete. They believe the gene transfer that occurred 2,200 years ago points to the growing influence of the Roman Empire in the region during that period.
“We were able to study the genomes of the plants that came out of these 2,000-year-old seeds and showed that by that time period there was already evidence that date palms had acquired genes from the related Cretan palm,” explained Michael Purugganan, professor of biology at New York University Abu Dhabi, in an email. “We believe the hybridization of the date palm from the Middle East with the wild Cretan palm gave rise to the date palms now found in North Africa, like the Medjool variety we get at our grocery stores. So the analysis allows us to see that by 2,000 years ago this process of hybridization had already occurred.”
As a result of all this hybridization, certain genes which may have ceased to be advantageous in the past, but which may again be helpful today, could be rediscovered and possibly even reintroduced in the future through genetic modification.
“Yes, absolutely, and that is something we all hope for --- that a specific gene variation that is now lost in modern varieties can now be re-introduced from these now revived plants,” Purugganan said when asked by email about the possibility of using CRISPR technology to reintroduce desirable traits that have long since gone extinct.
As fossilized DNA degrades, its molecules are shortened and chemically modified, reducing the amount of viable genetic material that scientists can recover. And because plants lack the protective bone tissue found in vertebrate fossils, they’re even more prone to degradation over time. Thankfully, because viable seeds from the species were recovered from archeological sites, researchers didn’t have to rely on fossilized plant material --- they just grew their own.
“I think the date palms seeds are special both because of the dry and arid environments these plants grow which can help preserve the seeds, and also maybe there is something special about dates that they can remain alive as seed for so long,” Purugganan said in the email. “But this may not be limited to date palms - other old seeds have been recovered, and in one case --- using tissue culture --- seed from a plant species was regenerated after being buried in Siberian permafrost for 30,000 years. So there may be other opportunities out there. Right now we hope our study will inspire other scientists to do the same sort of study we did in other ancient material.”
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