A small, seemingly inconspicuous fern that grows alone on a remote island in the Pacific Ocean was crowned the Guinness World Record holder on Friday for having the largest genome of any organism on Earth.
The New Caledonian fern, Tmesipteris oblanceolatahas more than 50 times more DNA in the cell nucleus than humans.
If the DNA of one of the fern’s cells – which is just a fraction of a millimeter wide – were unraveled, it would stretch as far as 106 meters (350 feet), scientists said in a new study.
If the DNA were upright, it would be taller than the tower housing London’s famous Big Ben clock.
The fern’s genome weighed no less than 160 gigabase pairs (Gbp), the measure of DNA length.
That is seven percent larger than the previous record holder, the Japanese flowering plant Paris japonica.
The human genome is a relatively puny 3.1 Gbp.
If our DNA were unraveled, it would be about two meters long.
Study co-author Ilia Leitch, a researcher at Britain’s Royal Botanic Gardens Kew, told AFP that the team was “really surprised to find something even bigger than Paris japonica“.
“We thought we had already reached the biological limit. We are really pushing biology to the limit,” she said.
The fern, which grows five to ten centimeters high, is only found in New Caledonia, an area in the French Pacific that has recently experienced unrest.
Two members of the research team traveled to the main island, Grand Terre, in 2023 and collaborated with local scientists on the study, which was published in the journal iScience.
Guinness World Records awarded the fern the coveted “largest genome title.”
The victory of “this innocuous-looking” fern shows that “record holders are not always the flashiest on the outside,” said Adam Millward, editor-in-chief of Guinness World Records.
What is a genome again?
It is estimated that humans have more than 30 trillion cells in our bodies.
Inside each of those cells is a nucleus that contains DNA, which is like a “book of instructions that tells an organism like us how to live and survive,” Leitch explained.
All of an organism’s DNA is called its genome.
So far, scientists have estimated the genome size of about 20,000 organisms, just a fraction of life on Earth.
Among the animals, the marbled lungfish has the largest, at 130 Gbp.
Although plants have the largest genomes, they can also have incredibly small ones. The genome of the carnivorous Genlisea aurea is only 0.06 Gbp.
But we humans do not have to feel inadequate when we compare ourselves to the powerful T. oblanceolata.
All the evidence suggests that having a huge genome is a disadvantage, Leitch said.
The more DNA you have, the bigger your cells have to be to squeeze it all in.
For example, for plants, larger cells mean that the pores of the leaves must be larger, allowing them to grow more slowly.
It is also more difficult to make new copies of all that DNA, which limits their ability to reproduce.
This means that the most massive genomes are found in slow-growing, perennial plants that cannot easily adapt to adversity or face competition.
Genome size may therefore influence how plants respond to climate change, changing land use and other human-induced environmental challenges, Leitch said.
What’s all that DNA for?
There could be even larger genomes out there somewhere, but Leitch thinks this fern has almost reached its limit.
“I can’t understand how an organism with all this DNA actually functions,” she said.
Scientists don’t know what most of the DNA does in such huge genomes, she admitted.
Some say most of it is “junk DNA.”
“But that’s probably our own ignorance. Maybe it has a function, and we still have to find it,” Leitch said.
Jonathan Wendel, a botanist at Iowa State University who was not involved in the study, agreed that it was “amazing” how much DNA the fern contains.
But this represents only “the first step”, he told AFP.
“A great mystery is the meaning of all this variation: how do genomes grow and shrink, and what are the evolutionary causes and consequences of these phenomena?”
© Agence France-Presse