A small fern from New Caledonia holds the record for the largest genome

She is one of the giants. Not by its size – it measures on average 15 centimeters – but by that of its genome, “the largest ever discovered, surpassing the human genome by more than 50 times”, announces the magazine Nature in a general public article.

This plant is the fern Tmesipteris oblanceolata. Originally from New Caledonia, it also grows in different archipelagos of the South Pacific. It won this title thanks to its 160 billion base pairs (the “letters” of DNA), or 11 billion more than the previous record holder, the flowering plant. Paris japonica.

The animal with the largest genome, a freshwater bony fish from Africa (Protopterus aethiopicus) has 130 billion base pairs, compared to 3.2 billion base pairs in humans.

These are the results of a study recently published in iScience, for which the authors of this work compared more than 20,000 organisms. One of them, Jaume Pellicer, from the Botanical Institute of Barcelona, ​​co-discoverer of the “gargantuan genomee de Paris japonica” in 2010, recalls Nature, thought it would be impossible to surpass this record. What he imagined to be a biological limit was therefore exceeded by 7%.

A needle in a haystack

Ilia Leitch, an evolutionary biologist at the Royal Botanic Gardens in Kew, United Kingdom, who participated in this new work, does not hide her astonishment at Nature. Since only a small part of the genome of Tmesipteris oblanceolata corresponds to genes that code for proteins, he wonders how the cellular machinery manages to access genetic information. “It’s like trying to find a few books with instructions on survival in a library of millions of books – it’s just ridiculous,” he summarizes.

As for why and how the fern evolved to have so many base pairs, it remains a puzzle to scientists. Julie Blommaert, a genomics specialist at the New Zealand Plant and Food Research Institute, offers one explanation, “although not very exciting”.

“This enormous genome could simply be neither detrimental nor particularly helpful to the plant’s ability to survive and reproduce,” she considers. Also Tmesipteris oblanceolata would she just have “continued to accumulate base pairs over time.”

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