A small fern breaks the record for the largest genome on Earth

May 31. () –

A species of New Caledonian fork fern (Tmesipteris oblancolata) contains more than 50 times more DNA than humans, up to a record 100 meters from being untangled.

This is the largest amount of DNA stored in the nucleus of any living organism on the planet, and has dethroned the Japanese flowering plant species Paris japonica, which held this record since 2010.

Additionally, the plant has achieved three Guinness World Record titles for the largest amount of DNA in the nucleus: largest plant genome, largest genome, and largest fern genome.

T. oblancolata is a rare species of fern found in the island nation of New Caledonia, a French overseas territory located in the southwest Pacific, about 1,200 kilometers east of Australia. The genus Tmesipteris is a poorly studied group of plants consisting of about 15 species, most of which are located on a series of islands in the Pacific and Oceania.

So far, scientists have only estimated the size of the genomes of two species of Tmesipteris, T. tannensis and T. obliqua, which were found to contain gigantic genomes, measuring 73.19 and 147.29 gigabase pairs (Gbp) respectively. . This is the unit of measurement used to help designate the length of DNA.

In 2023, lead authors Dr Jaume Pellicer and Dr Oriane Hidalgo, from IBB (Institut Botànic de Barcelona-CSIC) and previously from RBG (Royal Botanic Graden) Kew, traveled to New Caledonia to collect samples of Tmesipteris, which were then analyzed to estimate the size of their genomes. To do this, the nuclei of thousands of cells were isolated, stained with a dye, and then the amount of dye that had bound to the DNA within each nucleus was measured: the more dye, the larger the genome.

The analysis revealed that the T. oblancolata species has a record genome size of 160.45 Gbp, which is approximately 7% larger than that of P. japonica (148.89 Gbp). For comparison, the human genome contains about 3.1 Gbp spread over 23 chromosomes and, when stretched like a ball of wool, the length of DNA in each cell measures only about 2 m, reports the IBB in a statement.

In animals, some of the largest genomes include the marbled lungfish (Protopterus aethiopicus) at 129.90 Gbp and the Neuse River water dog (Necturus lewisi) at 117.47 Gbp. In stark contrast, six of the largest known eukaryotic genomes are held by plants, including European mistletoe (Viscum album) at 100.84 Gbp.

Surprisingly, having a larger genome is usually not an advantage. In the case of plants, species that have large amounts of DNA are limited to being slow-growing perennials, are less efficient at photosynthesis (the process by which plants convert the sun’s energy into sugars) and require more nutrients. (especially nitrogen and phosphates) to grow and compete successfully with their smaller genome neighbors. In turn, these effects can influence a plant’s ability to adapt to climate change and its risk of extinction.