Tiny Fern contains the largest genome of any organism on Earth

the Tmesipteris oblanceolata Fern sets new record for largest genome, affecting plant growth and adaptation insights.

• New Caledonian fern Classify He won 3 Guinness World Records titles; The largest plant genome, the largest fern genome, and the largest quantitative fern genome DNA In the nucleus
• stretched, Tmesipteris oblanceolata The genome is taller than Big Ben in London
• The discovery raises new questions about how much 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

Genome breaks records

A new record has been discovered for the largest amount of DNA stored in the nucleus of any living organism on the planet. Details were presented in a new study published in the journal iScience on May 31 by researchers from the Royal Botanic Gardens, Kew, and the Botanical Institute of Barcelona (IBB-CSIC) in Spain.

The New Caledonian spiny fern species Tmesipteris oblanceolata, which contains more than 100 meters of unassembled DNA, has been found to contain 50 times more DNA than humans, and has dethroned the Japanese flowering plant species Paris japonica, which retained This record has been held since 2010. In addition, the plant has achieved three Guinness World Records titles for the largest plant genome, the largest genome, and the largest fern genome for the amount of DNA in the nucleus.

Tmesipteris oblanceolata has the largest genome, offering new perspectives on plant evolution and the challenges it faces, a study has revealed. Credit: Q

Natural habitats of ferns and study methodology

T. oblanceolata It is a rare type of fern found on the island of New Caledonia, a French overseas territory located in the southwestern Pacific Ocean, about 750 miles east of Australia, and some neighboring islands such as Vanuatu. The genus Tmesipteris is a poorly studied group of plants consisting of about 15 species, most of which are found across a range of Pacific islands and Oceania.

Until now, scientists have estimated the genome size of only two species of Tmesipteris – T. tanensis And T. oblique – Both were found to have gigantic genomes, at 73.19 and 147.29 gigabase pairs, respectively.

In 2023, lead authors, Dr Jaume Pellicer and Dr Orianne Hidalgo, from IBB and formerly at 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 a dye, and then measuring the amount of dye that bound to the DNA within each nucleus. The higher the number of dye, the larger the genome.

Leading results and comparisons

The analysis revealed the type T. oblanceolata For a standard genome size of 160.45 Gb, which is about seven percent larger than the genome size P. japonica (148.89 GB).

When uncovered, the DNA from every cell of this fern will be taller than the Elizabeth Tower in Westminster, London, which is 96 meters high and home to the world-famous Big Ben bell. For comparison, the human genome contains about 3.1 gigabytes spread over 23 chromosomes, and when stretched out like a ball of string, the DNA in each cell is only about 2 meters long.

Effects of genome size on plant biology

“Tmesipteris is a unique and fascinating small genus of fern, whose ancestors evolved about 350 million years ago – long before dinosaurs set foot on Earth – and are essentially epiphytic in nature,” says Dr Pellicer, an evolutionary biologist. [it grows mainly on the trunks and branches of trees] Limited distribution in Oceania and several Pacific islands. For a long time, we thought that breaking the previous Paris japonica size record would be an impossible task, but once again, the limits of biology have exceeded our most optimistic expectations.

“Based on our previous research, we expected giant genomes to exist in Tmesipteris. However, the discovery of the largest genome ever is not just an achievement of scientific exploration, but the result of an almost fourteen-year journey into the infinite complexity and diversity of plant genomes.”

To date, scientists around the world have estimated the genome sizes of more than 20,000 eukaryotic organisms, revealing in the process a wide range of genome sizes across the tree of life. These in turn have been found to have a profound impact not only on their anatomy, as larger genomes need larger cells to house them and take longer to reproduce, but also on how they function and develop and where and how they live.

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

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

Reflections on genome diversity and future research

“Who would have thought that this unassuming little plant, which most people would likely pass by without warning, could hold a world record for genome size,” says Dr Elijah Leach, lead researcher in the Department of Personality Evolution at RBG Kew. Otherwise, plants are incredibly diverse when viewed at the DNA level, and this should give us pause to think about their intrinsic value in the broader picture of global biodiversity. This discovery also raises many new and exciting questions about the upper limits of what is, we hope, biologically possible To solve these mysteries one day.

“The belief that this benign-looking fern contains 50 times more DNA than humans is a humbling reminder that there is still much we don’t know about the plant kingdom, and that record holders are not always “Most flashy on the outside.”

Reference: “160 Gb prickly fern genome breaks eukaryote size record” by Paul Fernandez, Remy Ames, David Broy, Martin J. M. Christenhuis, and Elijah J. Leach, and Andrew L. Leach, Lisa Pokorny, Oriani Hidalgo, and Jaume Pellicer, May 31, 2024, iScience.
doi: 10.1016/j.isci.2024.109889

The study, which determined the size of the Tmesipteris oblanceolata genome, was carried out by an international team of researchers from the Royal Botanic Gardens at Kew, Queen Mary University of London, the New Caledonian Herbarium and the Spanish Research Council (CSIC).