The largest genome on the planet is present in a small fern | Science | EUROtoday

The tree of life has this stuff. A fern, which can seem to be a not too complicated organism, seems to be the dwelling being with the biggest genome. It grows in New Caledonia (an island in Oceania below French sovereignty) and if the 160,750,000,000 base pairs of its DNA could possibly be positioned on high of one another, it might rise to 100 meters, 50 occasions greater than human DNA. The discovery raises new questions on how a lot genetic materials could be saved in cells and in regards to the lack of correlation between complexity and genetics.

On the fallen trunks of the forests of New Caledonia grows the Tmesipteris oblanceolata, a fern that belongs to a genus of vascular crops of which there are solely fifteen species. At least two of her first cousins ​​had been recognized to have big genomes. But till now, the organism that contained DNA with the best variety of base pairs was one other plant, the Paris Japonica. Now a number of researchers who characterised the genetic size of the P. japonicahave found that the genome of the T. oblanceolata It is 7% greater.

In a brand new research printed within the scientific journal iScience, researchers from the Royal Botanic Garden of Kew (United Kingdom) and the Institut Botànic de Barcelona (IBB-CSIC) current the outcomes of their work with this fern, demonstrating that it has the biggest quantity of DNA saved within the nucleus of its cells. any dwelling eukaryotic organism on the planet. If it had been a ball to unravel, the T. oblanceolata would lengthen between 105 and 106 meters. “It is not an iconic plant, it does not have flowers, nor is it striking. In fact, it is a weed that, if you are not looking for it, you would trample it without realizing it,” says Jaume Pellicer, researcher on the Institut Botànic. ”It doesn't even seem like a fern, it doesn't seem like the standard picture we now have of them. But it has one thing that makes it particular, it has an enormous genome,” he recollects.

“It is not an iconic plant, it does not have flowers, nor is it striking. In fact, it is a weed that, if you are not looking for it, you would trample it without realizing it”

Jaume Pellicer, researcher on the Botanical Institute of Barcelona (IBB-CSIC)

In 2023, Pellicer and his IBB colleague Oriane Hidalgo traveled to New Caledonia to gather samples of Tmesipter, which they then analyzed to estimate the scale of their genomes. In its quick model, the method requires isolating the nuclei of 1000’s of cells, staining them with a fluorescent dye, after which measuring how a lot dye had sure to the DNA inside every nucleus: the extra dye, the bigger the genome. “To calculate the size, we use internal standards, cultivated plants such as pea, rice or tomato, which are very well known,” says Pellicer. In this case, the usual they used was garlic, which is the cultivated plant with the best variety of base pairs, of their case, 34 gigabases (Gbp; every one is 1,000 million base pairs). bases). By comparability, the human genome incorporates about 3.2 Gbp unfold over 23 chromosomes, and when stretched, the size of DNA in every cell barely exceeds two meters.

“Tmesipter is a unique and fascinating small genus of ferns, whose ancestors evolved about 350 million years ago, long before dinosaurs walked the Earth, and is distinguished by its primarily epiphytic habit [que crece principalmente en troncos y ramas de árboles]”says Pellicer. In an interview by video name, he acknowledges that after they encrypted the genome of the P. japonica Years in the past, they believed they’d reached the restrict, that there could possibly be no different organism bigger in genetic phrases. “The hypothesis that perhaps there was no greater diversity was based on the fact that there would be no possibility of biologically maintaining a genome beyond 150 gigabases. We were wrong,” he provides.

Such a big genome has its prices. It requires extra vitality assets when replicating DNA, dividing cells. In bigger cells, the integrity of the bodily construction requires a better vitality enter. It is extra expensive at a metabolic stage. “That's why we think it makes them less advantageous when it comes to adapting to constant changes, both climate and pollution,” explains Pellicer. They have reproductive cycles which might be a lot slower as a result of the cell cycle is for much longer than in a plant with a small genome. And the demand for vitamins required to construct nucleic acids is way better. “So we believe that, throughout evolution, they have been eliminated,” provides Pellicer. In reality, he concludes, “giant genomes are the exception; despite the extraordinary diversity of genomic sizes that exist, the vast majority of plants have small or very small genomes, which is why we are so interested in them.”

Biologists understand it because the C-value paradox: the scale of the genome doesn’t correlate with the complexity of the organism, and this has puzzled them for many years. “It was thought that the more complex an organism was, the larger the size of its genome must be. Now we know that this is not the case,” feedback the IBB researcher. “And it is mainly due to the fact that most of the genome is made up of repetitive DNA sequences, which has been called junk DNA because it was believed that it had no function,” he provides.

None of the ten organisms with the biggest genome could possibly be, seen with human eyes, a really complicated dwelling being. Besides the T. oblanceolata and the P. japonica, one other fern of the genus of the primary seems on the record and the European mistletoe, which closes the record, with 100.84 Gbp. In this high ten there are solely 4 animals, such because the marbled lungfish (129.90 Gbp) or the Neuse River water canine (117.47 Gbp), associated to salamanders.

Pol Fernández, co-author of the research and in addition from the IBB, offers some causes for the order of the record of the biggest genomes: “The majority are plants and at the genomic level they are capable of being viable by doing many hybridization processes. When there are such gigantic genomes it is because there have been many duplications of genomes, amplifications of repeated elements and this in plants we know is much more frequent and gives viable species more frequently than in animals.”

To date, scientists around the world have estimated the genome sizes of more than 20,000 eukaryotic organisms, in the process revealing 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 replicate – but also on how they function, evolve and where and how they live. .

“Who would have thought that this small, unassuming plant, which most people would probably walk past without noticing, could hold a world record for genome size?” concludes Ilia Leitch, of Royal Botanic Gardens, Kew, in a be aware. She provides: “Compared to other organisms, plants are incredibly DNA diverse, and that should lead us 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 biologically possible, and we hope to solve these mysteries one day.”

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