By Will Dunham
(Reuters) – Did you think the living organism with the largest genome could be the blue whale, an African elephant or perhaps a giant sequoia tree? fern that grows in the French overseas territory of New Caledonia, in the southwest Pacific Ocean.
New research shows that this fern species, called Tmesipteris oblanceolata, has a genome – all of an organism’s genetic information – that is 7% larger than that of the previous record holder, the Japanese plant Paris japonica, and more than 50 times the size of the human genome.
The metric for genome size was the number of base pairs, the fundamental units of DNA, in an organism’s cell nuclei. If stretched out like a ball of yarn, the length of the DNA in each cell of this fern would stretch nearly 106 meters, taller than New York’s Statue of Liberty, London’s Big Ben clock tower or India’s Taj Mahal. . . The human genome would extend just 2 meters.
The fern grows mainly on the ground or on fallen tree trunks in New Caledonia, about 1,200 km east of Australia, and on neighboring islands such as Vanuatu.
“We can say that this species is not very showy. It is a small plant, normally 10 to 15 centimeters (4 to 6 inches) tall, which can easily go unnoticed by those who are not specifically looking for it,” said the evolutionist. biologist Jaume Pellicer, from the Barcelona Botanical Institute (IBB), co-main author of the study published Friday in the magazine iScience.
The specimens used in the study were collected last year on Grande Terre Island, New Caledonia. Their leaf-like structures are not true leaves, but rather flattened stems. It belongs to a family of ferns whose evolutionary lineage separated from other ferns about 350 million years ago, approximately 120 million years before the appearance of dinosaurs.
A large genome is not considered beneficial.
“We think that Tmesipteris oblanceolata has such a large genome, not because of any evolutionary advantage, but simply because, for a reason we don’t yet know, it has failed over time to efficiently remove non-functional or redundant DNA sequences,” Pellicer said.
DNA, which carries an organism’s genetic information, is made up of two linked strands that coil into a shape called a double helix, which looks like a twisted ladder. The base pairs make up the rungs of the ladder.
MULTIPLE CONSEQUENCES
Genome size has multiple consequences. For example, larger genomes require more resources for DNA replication, repair and transcription – a process a cell uses to produce the proteins an organism needs to function.
“This increased demand may overwhelm the plant’s energetic and nutritional resources, which could otherwise be used for growth, reproduction and stress responses,” said IBB evolutionary biologist and study co-lead author Oriane Hidalgo.
Larger genomes require larger cells to house them and take longer to replicate DNA, slowing the cell division that supports growth. This could reduce a plant species’ ability to compete for light, water and nutrients, making it more ecologically constrained, Hidalgo said.
Scientists wonder why some organisms have large genomes and others do not.
“This is a really intriguing question. But what is clear is that there is no relationship between genome size and organism complexity,” said plant geneticist and study co-author Ilia Leitch of the Royal Botanic Gardens Kew in London.
There is also no relationship between the physical size of an organism and the size of its genome. The tiny fern’s genome is about 6,000% larger than that of a blue whale, the largest animal on Earth, and about 4,650% larger than that of an African elephant, the largest land animal. It is also about 1,500% larger than the giant sequoia, the tallest plant.
The marbled lungfish of Africa has the largest known animal genome. The fern is almost 25% larger.
Scientists have assessed the genome size of about 20,000 organisms that have clearly defined nuclei, with large genomes being the exception rather than the rule.
“Genome size is an important character of biodiversity, as it has been shown to play a role in influencing how, where and when a plant is able to grow and compete, and respond to environmental challenges such as climate change and pollution,” he said. Leitch.
(Reporting by Will Dunham in Washington; Editing by Daniel Wallis)
