In genetics, sizes often come with surprises. One tiny fern, Tmesipteris oblanceolata, also known as the Fork Fern, proved this phrase true, taking the scientific community by storm when it broke the record for the largest known genome. Researchers reported this discovery on May 31, 2024, stating that the plant, which is small enough to fit in the palm of your hand, harbors a full set of genetic instructions over 50 times the size of the human genome.
Where Did This Plant Come From?
Compromised of approximately 15 species, the genus Tmesipteris is an understudied group of plants primarily found across various Pacific Islands and Oceania. Previously, scientists had only estimated the genome sizes for two species of Tmesipteris—T. tannensis and T. obliqua—revealing their gigantic genomes at 73.19 and 147.29 gigabase pairs (Gbp), respectively.
The unassuming Tmesipteris oblanceolate is a rare species that mainly grows on larger forest plants rooted on the island nation of New Caledonia, about 750 miles east of Australia. It’s a fascinating fern whose ancestors evolved around 350 million years ago, well before dinosaurs stomped on Earth. In 2023, researchers Dr. Jaume Pellicer and Dr. Oriane Hidalgo traveled to New Caledonia to collect samples of Tmesipteris. They embarked on this journey to study six fork fern species in hopes of better understanding their evolution and functionality in the organisms that wield them.
The researchers extracted cells from the ferns’ leaves and isolated their nuclei, which house the genome. They calculated the size of each genome by staining the nuclei’s DNA with a fluorescent dye and comparing how much these nuclei fluoresced relative to those from plants with smaller genomes. This analysis revealed genetic champion, Tmesipteris oblanceolata, with a whopping 160 billion base pairs in its DNA. The fern may only grow up to 15 centimeters long, but the DNA from a single cell of this plant would stretch longer than a football field, while human DNA would only cover about six feet.
The Significance of Giant Genomes
Dr. Pellicer and his colleagues also claim the discovery of the previous record holder for the largest known genome. Paris japonica, a flowering plant that grows in Japan, took the throne in 2010 at about 150 billion nucleobases. Dr. Pellicer says, “For a long time, we thought that breaking the previous size record of Paris japonica was going to be an impossible mission, but once again, the limits of biology have surpassed our most optimistic predictions.”
To date, scientists have estimated the genome sizes of over 20,000 eukaryotic organisms around the world, uncovering a vast diversity of genome sizes across the tree of life. This variation affects not only their anatomy—since larger genomes require larger cells to house them and more time to replicate—but also their functionality, evolution, and ecological niches.
Plants exhibit remarkable DNA diversity compared to other organisms, underscoring their intrinsic value in the grand scheme of global biodiversity. This inspires us to consider the biological upper limits and find new answers to questions about what is possible in nature. The fact that a tiny fern—so small you might not even notice stepping on it—holds the new Guinness World Record for the largest known genome serves as a reminder that we still have much to learn about the plant kingdom. Record holders often go unnoticed, but the beauty of this plant lies on the inside.
So, who will be the next record holder for the largest known genome? And will it be another case of size that comes with a surprise? We’ll patiently wait for Earth’s next genetic giant.
Riley Bell
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