On the island of New Caledonia, a simple, nondescript species of fern has been identified as having the longest genome of any known living organism.
It is 50 times longer than a human, 7% longer than the previous species world record holder for the longest genome and 20% longer than the animal record holder.
It contains 416 chromosomes in each cell, compared to a human’s 23, and if revealed would climb higher than Big Ben in London’s Westminster.
Questions abound, as does admiration for the grandeur and mysteries of biological life.
“Compared to other organisms, plants are incredibly diverse when viewed at the DNA level, and this should give us pause to consider their intrinsic value in the larger picture of global biodiversity,” said Dr Ilia Leitch, senior research officer at the Royal Botanic Gardens, Kew.
“This discovery also raises many new and exciting questions about the upper limits of what is biologically possible, and we hope to solve these mysteries one day.”
Tmesipteris oblanceolata is a type of branching fern from New Caledonia that grows on the ground or from rotting tree trunks. A team from Kew and the Institut Botànic de Barcelona traveled to New Caledonia’s largest island, Grand Terre, to collect this species for research.
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The genomes of 20,000 species on the Tree of Life have been fully sequenced, and this literature shows that having a complex genetic code is not always an advantage.
Larger genomes require more resources for DNA replication, repair, and transcription, while a larger DNA sequence needs a larger nucleus and therefore a larger cell to accommodate it.
Dr Leitch told Reuters that “perhaps not surprisingly, species with larger genomes are at greater risk of extinction”, for a similar reason, one might assume that simpler machines with more few moving parts tend to last longer than complex and sophisticated machines with many; Honda Civic will run longer than Lamborghini Aventador.
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The previous record holder for the longest genome was the Japanese flowering plant species Parisian Japonica while the longest genome known from the animal kingdom is the African marble lungfish, (Protopterus aethiopicus).
The smallest genome is the fungus species Encephalitozoon intestinalis, with 2.6 megabase pairs. For context, the New Caledonian branched fern contains 168 gigabase pairs. An apt comparison would be to compare the file size of the original Tetris game to that of a modern open-world RPG like The Witcher or World of Warcraft.
For those more interested in DNA, Dr. Leitch and her colleagues at Q and IBB published a paper on the fern fork in which they wrote that variation in genome size and its relationship to species complexity “is known as “C-value paradox” or “C-value enigma” and has intrigued biologists for more than half a century.
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“Rapid advances in DNA sequencing now provide compelling evidence showing that variation in DNA quantity arises primarily from differences in the frequency of polyploidy, the abundance of noncoding repetitive DNA, and the dynamics of processes that amplify, erode, and delete DNA,” they write in their introduction.
However, with only 20,000 species whose genomes have been sequenced, the authors doubt that science has revealed the full extent of genome size diversity.
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