They discovered the largest genome on the planet

Scientists have discovered an organism whose cell nucleus contains more DNA than the cell nucleus of any other organism on Earth.

The organism in question is a plant native to New Caledonia.

Tmesipteris oblancolata is a rare species of fern found in the New Caledonia Archipelago, a region located in the southwestern Pacific Ocean, and on some neighboring islands such as Vanuatu. The genus Tmesipteris, in itself, is a poorly studied group of plants consisting of about 15 species, most of which are distributed on various islands in the Pacific Ocean and Oceania. This is a unique and fascinating genus of ferns, whose ancestors appeared in evolutionary history about 350 million years ago, long before dinosaurs appeared on Earth.

In 2023, researchers from the Barcelona Botanical Institute (IBB), a joint center of the Barcelona Museum of Natural Sciences Consortium (CMCNB) and the Superior Council for Scientific Research (CSIC), in Spain, traveled to New Caledonia to collect specimens. of Tmesipteris, which were subsequently analyzed to estimate the size of their genomes using flow cytometry technology. Analyzes revealed that Tmesipteris oblancolata has the genome size record, at 160.45 Gb, which is approximately 7% larger than the genome size of Paris japonica (148.89 Gb), a plant endemic to Japan that has held this record since 2010.

Given that a base pair (the basic unit of DNA consisting of two nucleotides) is about 0.34 nanometers long, if we could detect all the DNA from a single cell of this fern, it would be about 100 meters long. In comparison, in the human genome, which contains approximately 3.1 gigabytes distributed over 23 chromosomes, the DNA in each cell is only about 2 meters long.

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Details of the reproductive structures of Tmesipteris oblancolata. (Photo: Orian Hidalgo/Paul Fernandez)

Over a decade of research on genome sizes

This study, conducted by researchers from the Barcelona Botanical Institute, with the participation of CSIC's Royal Botanic Garden (RJB), Kew Gardens in the UK, Queen Mary University of London in the UK, and the New Caledonian Herbarium, is not the result of chance. As Jaume Pellicer, a researcher at the Botanical Institute of Barcelona, ​​put it: “Based on previous studies, we already expected the presence of giant genomes in Tmesipteris, so this discovery, far from being an accidental breakthrough, is the result of more than just a decade of research exploring the diversity of genome sizes among the plants.

To date, specialists around the world have studied the genome size of nearly 20,000 eukaryotic organisms, “revealing an extraordinary diversity of genome sizes throughout the tree of life,” Pellicer adds. Moreover, this character has been observed to have a profound impact not only on their anatomy, because “larger genomes need larger cells to house them, but also on how they function, develop, and where and how they live,” says Urian Hidalgo. , researcher at the Botanical Institute in Barcelona.

“Surprisingly, larger genome size is not necessarily reflected in a greater number of genes. Organisms with giant genomes often contain an excess of so-called transposable elements.” These repetitive elements were first described by Dr. Barbara McClintock when analyzing maize chromosomes. It is the discovery for which I received the Nobel Prize in Medicine,” notes researcher Ramon y Cajal from CSIC at the Royal Botanical Garden in Madrid, Lisa Pokorny.

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With these observations in mind, the question researchers now ask is why some species have such giant genomes and whether there is a limit to the amount of DNA an organism can harbor in each cell.

“So far, only a few animal and plant groups have been shown to have genomes exceeding the 100 Gb range. Among animals, some of the largest genomes include those of the lungfish (Protopterus aethiopicus), with 129.90 Gb. And the genome of the river newt (Necturus lewisi), with 117.47 Gb. However, it is striking that six of the largest eukaryotic genomes known to date are found among plants, including, for example, European mistletoe (Viscum album), with 100.84 Gb,” concludes Paul Fernandez. Researcher at IBB.

The study is titled “160 Gb Prickly Fern Genome Breaks Eukaryote Size Record.” It has been published in the academic journal iScience. (Source: RJB/CSIC)

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