Tmesipteris oblanceolata — a rare species of fork fern found on the island nation of New Caledonia, an overseas French territory situated in the Southwest Pacific — has become a world record holder. At 160.45 billion base pairs (Gbp), this record-breaking genome challenges current understanding and opens new avenues to explore the evolutionary dynamics of genomic gigantism.
Tmesipteris oblanceolata. Image credit: Pol Fernández.
Tmesipteris is a relatively understudied small genus made up of 15 species, most of which occur in Oceania and several Pacific Islands.
Until now, scientists have only estimated the size of the genomes for two Tmesipteris species — Tmesipteris tannensis and Tmesipteris obliqua — both of which were found to contain gigantic genomes, at 73.19 and 147.29 Gbp, respectively.
In 2023, Dr. Jaume Pellicer from Royal Botanic Gardens, Kew, and colleagues traveled to New Caledonia to collect samples of Tmesipteris, which were then analyzed to estimate the size of their genomes.
The analysis revealed Tmesipteris oblanceolata, also known as Tmesipteris truncata, to have a record-breaking genome size of 160.45 Gbp, which is about 7% larger than the genome of the Japanese flowering plant species Paris japonica (148.89 Gbp). For comparison, the human genome contains about 3.1 Gbp distributed across 23 chromosomes.
“Tmesipteris is a unique and fascinating small genus of ferns, whose ancestors evolved about 350 million years ago — well before dinosaurs set foot on Earth — and it is distinguished by its mainly epiphytic habit (it grows mainly on the trunks and branches of trees) and restricted distribution in Oceania and several Pacific Islands,” Dr. Pellicer said.
“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.”
“Based on our previous research we anticipated the existence of giant genomes in Tmesipteris.”
“That said, discovering the largest genome of them all is not just a feat of scientific exploration, but the result of an almost fourteen-year journey into the boundless complexity and diversity of plant genomes.”
Genome size diversity across eukaryotes: (A) current distribution of genome sizes across major lineages of plants, animals, and fungi; (B) top 10 of the largest genome size records available in eukaryotes. Image credit: Pol Fernández et al., doi: 10.1016/j.isci.2024.109889.
“Who would have thought this tiny, unassuming plant that most people would likely walk past without notice, could bear a world-beating record in genome size,” said Dr. Ilia Leitch, also from Royal Botanic Gardens, Kew.
“Compared to other organisms, plants are incredibly diverse when viewed at the DNA level, and that should make us pause to think about their intrinsic value in the wider 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.”
The team’s paper was published in the journal iScience.
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Pol Fernández et al. A 160 Gbp fork fern genome shatters size record for eukaryotes. iScience, published online May 31, 2024; doi: 10.1016/j.isci.2024.109889
Source : Breaking Science News