Researchers have identified Tmesipteris oblanceolataa New Caledonian fern as having the largest genome on record, surpassing the previous record holder Parisian Japonica. This discovery, detailed in iScience magazine, reveals that this fern contains over 50 times more DNA than humans and highlights the significant implications that larger genomes have on plant biology and adaptation. Credit: SciTechDaily.com
The Tmesipteris oblanceolata fern sets new record for largest genome, impacting plant growth and adaptation insights.
- New Caledonian Fern kinds awarded 3 Guinness World Records titles; The largest plant genome, the largest genome, and the largest fern genome for quant DNA in the nucleus
- Stretched, on Tmesipteris oblanceolata genome is taller than the Big Ben tower in London
- The discovery raises new questions about how precisely DNA can be stored in cells
- The study will help scientists understand how genome size affects species in the face of biodiversity loss and climate change
A record breaking genome
A new record has been found for the largest amount of DNA stored in the nucleus of any living organism on the planet. The details are presented in a new study published in the journal iScience on 31 May by researchers from the Royal Botanic Gardens, Kew and the Botanical Institute of Barcelona (IBB-CSIC) in Spain.
Reaching more than 100 meters of tangled DNA, the New Caledonian branched fern species Tmesipteris oblanceolata was found to contain over 50 times more human DNA, dethroning the Japanese flowering plant species Paris japonica, which had held this record since 2010. Additionally, the plant has achieved three Guinness World Records titles for largest plant genome, largest genome and largest fern genome for the amount of DNA in the nucleus.
Study reveals Tmesipteris oblanceolata has the largest genome, offering new perspectives on plant evolution and challenges. Credit: Q
Fern’s natural habitat and research methodology
T. oblanceolata is a rare species of fern found in the island nation of New Caledonia, a French overseas territory located in the southwest Pacific Ocean, about 750 miles east of Australia, and some of the neighboring islands such as Vanuatu. The genus Tmesipteris is a poorly studied group of plants consisting of about 15 species, most of which occur in a number of Pacific islands and Oceania.
So far, scientists have only estimated the size of the genomes of two species of Tmesipteris— T. tannensis and T. obliqua – both were found to contain giant genomes, 73.19 and 147.29 gigabase pairs (Gbp), respectively.
In 2023, lead authors Dr Jaume Pellicer and Dr Oriane Hidalgo of IBB and previously of RBG Kew traveled to New Caledonia to collect samples of Tmesipteris, which were then analyzed to estimate the size of their genomes. This involved isolating the nuclei of thousands of cells, staining them with dye, and then measuring how much dye had bound to the DNA in each nucleus – the more dye, the larger the genome.
Breakthrough findings and comparisons
The analysis revealed the species T. oblanceolata to have a record genome size of 160.45 Gbp, which is about seven percent larger than that of P. japonica (148.89 Gbps).
When revealed, the DNA from each cell of this fern will be taller than the Elizabeth Tower in Westminster, London, which is 96m tall and home to the world-famous Big Ben. In comparison, the human genome contains about 3.1 Gbp spread over 23 chromosomes, and when stretched out like a ball of yarn, the length of DNA in each cell is only about 2 meters.
Implications of genome size for plant biology
Dr Pellicer, a researcher in evolutionary biology, said: “Tmesipteris is a unique and fascinating small genus of ferns whose ancestors evolved around 350 million years ago – long before dinosaurs walked the Earth – and is notable for its predominantly epiphytic habit [it grows mainly on the trunks and branches of trees] and limited distribution in Oceania and a few Pacific islands. For a long time we thought that breaking the previous Paris japonica size record would be an impossible mission, but once again the limits of biology have surpassed our most optimistic predictions.
“Based on our previous research, we expected the existence of giant genomes in Tmesipteris. However, the discovery of the largest genome of them all is not just an achievement of scientific research, but the result of a nearly fourteen-year journey into the boundless complexity and diversity of plant genomes.
To date, scientists worldwide have estimated the genome sizes of over 20,000 eukaryotic organisms, revealing in the process a wide range of genome sizes across the tree of life. In turn, these have been found to have profound effects not only on their anatomy, as larger genomes require larger cells to house them and take longer to replicate, but also on how they function , evolve and where and how they live.
Among 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 possessing large amounts of DNA are limited to being slow-growing perennials, they are less efficient at photosynthesis (the process by which plants convert solar energy into sugars) and need more nutrients (especially nitrogen and phosphates) to grow and compete successfully with their neighbors with smaller genomes. In turn, such effects can affect a plant’s ability to adapt to climate change and its risk of extinction.
Reflections on genomic diversity and future research
Dr Elijah Leitch, Senior Research Lead – Character Evolution, at RBG Kew, said: “Who would have thought that this small, nondescript plant, which most people would probably pass by without warning, could hold a world record for the size of genome. 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. 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.
Adam Millward, Managing Editor of Guinness World Records, said: “To think that this innocuous-looking fern boasts 50 times more human DNA is a humbling reminder that there is still so much to the kingdom of the plants we don’t know, and that the record holders aren’t always the showiest on the outside.”
Reference: “160 Gbp fork fern genome betters size record for eukaryotes” by Pol Fernández, Rémy Amice, David Bruy, Maarten JM Christenhusz, Ilia J. Leitch, Andrew L. Leitch, Lisa Pokorny, Oriane Hidalgo, and Jaume Pellicer, 31 May 2024 Mr. iScience.
DOI: 10.1016/j.isci.2024.109889
The study identifying the genome size of Tmesipteris oblanceolata was carried out by an international team of researchers from the Royal Botanic Gardens Kew, Queen Mary University of London, the Herbarium of New Caledonia and the Spanish Research Council (CSIC).
