by Tmesipteris free, an obscure species of fork fern found in New Caledonia, a French territory in the South Pacific. Just 4 to 6 inches tall, the humble plant is, in one particular way, the most remarkable living thing on earth.
“You would walk over it. You could even walk on it without knowing it,” said Ilia Leitch, plant evolutionary biologist and senior research leader at the UK’s Royal Botanic Gardens, Kew. “But there’s this great secret in it.”
Recently, T. oblanceolata into the Guinness book of world records after a team of scientists determined that the fern has the largest known genome of any living organism. Encased in the nucleus of each of its cells are 160.45 billion base pairs – 160.45 billion rungs of the twisted double helix ladder that is the plant’s DNA.
T. oblanceolata has more genes than the big California redwood (Sequoia sempervirens) or the blue whale (Musculus Balaenoptera). It is 50 times more DNA than Homo sapiens, the species that discovered DNA in the first place. The results were published in iScience magazine.
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“We were really surprised when we found out how big this genome was,” said botanist Jaume Pellicer of the Institut Botànic de Barcelona in Spain, who co-authored the study with Leitch. “We already knew there were huge genomes in the genus but we didn’t expect the one inside Tmesipteris free, it was going to break any previous record.”
A genome contains all the information cells need to direct the growth and development of the organism. But life doesn’t offer instructions in the neater, neater, more complex way of Ikea or Lego assembly manuals – so ferns with jumbo genetic codes.
Measuring genome size is “not a way to measure genome complexity or coding capacity,” said Elliot Meyerowitz, a Caltech biologist who was not involved in the research.
It’s just a minuscule slice of the genetic material around which most plant and animal cells lie with direct instructions on how to make the building blocks that make up living things. Less than 2% of the human genome actually codes for proteins. For the fork fern, the research team estimates that less than 1% of its genome does.
The rest is called non-coding DNA. Among the biggest questions in evolutionary biology is understanding what that non-coding genetic material does and why cells move around it.
half a century ago, scientists out of their jobs this noncoding stuff as “junk DNA,” a term now considered “a reflection of our own ignorance,” Leitch said.
It’s not that he doesn’t do anything, she said. We still don’t understand all that he does.
In recent years, researchers have discovered that manipulating or deleting some of these non-coding sequences affects gene expression. This suggests that at least some of this material plays a role in the processes that “switch” genes on and off, “like an orchestra conductor, saying who comes in here and who should be quiet here, ” said Leitch.
This complex choreography of gene expression is how we find the incredible diversity within our own species and across the kingdoms of living things.
“The final milestone in this area of research is to understand how these genomes function and are structured,” Pellicer wrote in an email. “But right now, it’s like trying to read an instruction book without even knowing where page one is!”
T. oblanceolata displaces the previous genome record holderA fairly medium-sized flowering plant called Paris Japan that there are 149 billion base pairs. While there may be something else out there packing a bigger genetic punch, botanists believe these plants are at the pinnacle of the amount of DNA a living thing can have.
“If it’s not the biggest, it’s very close,” Leitch said of the fork fern genome. “Having so much DNA has so many ramifications that I think we’re at the limit of what biology can deal with.”
An organism must divide its cells to grow, and before it can do that it must copy all the DNA in its cells. Copying a massive genome is a huge investment of time, energy and nutrients, Leitch said. For plants, larger genomes are associated with slower growth and less efficient photosynthesis.
As a result, organisms with huge genomes tend to be found in stable environments with little competition, Leitch said. That is true T. oblanceolatagrowing slowly Paris Japan and the marble lung fishholder of the largest genome in the animal kingdom (almost 130 billion base pairs).
Unfortunately for T. oblanceolatastable conditions are increasingly difficult to come by in a rapidly changing climate.
“As long as they’re stable, as long as things don’t change, selection won’t drive them out, so to speak,” Leitch said. “I would predict that if the environment changed, they would not be in a good position.”
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This story originally appeared in the Los Angeles Times.
