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Tiny fern contains 50 times more DNA than humans

A seemingly unassuming fern from the remote island of New Caledonia has made a big splash in the world of science.

Researchers have discovered that ferns of the species Tmesipteris oblanceolata possess a genome that dwarfs all others known to date.

Genome and its measurement

A genome is the entire collection of an organism’s genetic material, its DNA. This DNA houses all the necessary instructions for the organism’s growth, development, functioning, and reproduction. 

DNA itself is a long, complex molecule composed of four chemical building blocks called bases: adenine (A), cytosine (C), guanine (G), and thymine (T).

Specific sequences of these bases form genes, which act as blueprints for creating proteins. Proteins are essential molecules that carry out a vast array of tasks within cells, from providing structural support to catalyzing chemical reactions.

Beyond genes, the genome also contains stretches of DNA that do not code for proteins. These non-coding regions play crucial roles in regulating gene activity, determining when and where genes are turned on or off. They also contribute to maintaining the structural integrity of chromosomes, the thread-like structures that package and organize DNA within cells.

The size of a genome, measured in base pairs (bp), varies greatly across different species. For instance, the human genome comprises roughly 3.1 billion base pairs, whereas some plants and animals have significantly larger genomes.

Tiny fern with a huge amount of DNA

The genome of the Tmesipteris oblanceolata fern contains a massive 160.45 gigabase pairs (Gbp) of DNA. This quantity is over 50 times larger than the human genome, which is approximately 3.2 Gbp. 

To visualize the immense size of this fern’s DNA, consider that if the DNA from a single Tmesipteris cell were stretched out end-to-end, it would exceed 100 meters in length. This surpasses the height of London’s Elizabeth Tower, famously home to Big Ben.

The extraordinary size of the Tmesipteris oblanceolata genome has garnered it recognition from the Guinness World Records. It currently holds the following titles:

  • Largest plant genome: This signifies that Tmesipteris oblanceolata has the most extensive amount of DNA compared to any other known plant species.
  • Largest genome: This title confirms that Tmesipteris oblanceolata possesses the largest genome of any organism on Earth, encompassing all life forms.
  • Largest fern genome: This indicates that within the fern family, Tmesipteris oblanceolata boasts the most extensive amount of DNA compared to any other fern species.

Importance of genome size

The size of an organism’s genome, or the total amount of DNA it possesses, is a significant factor influencing various aspects of its biology and survival.

Larger genomes often correlate with slower growth rates due to the increased time and resources required for DNA replication and cell division. 

Additionally, organisms with larger genomes may exhibit reduced efficiency in photosynthesis, the process by which they convert light energy into chemical energy. This is because the maintenance and functioning of a larger genome demand more energy, potentially diverting resources away from photosynthetic processes.

Furthermore, organisms with larger genomes typically have higher nutrient requirements, particularly for nitrogen and phosphorus, which are essential for DNA synthesis and other cellular functions. 

These increased demands can pose challenges in nutrient-limited environments, making it more difficult for these organisms to compete with those possessing smaller genomes.

The cumulative effects of slower growth, reduced photosynthetic efficiency, and increased nutrient requirements can significantly impact an organism’s ability to adapt to changing environmental conditions

In the face of environmental fluctuations, organisms with larger genomes may be less able to adjust their physiological processes or compete for resources, potentially increasing their vulnerability to extinction.

Fern surpasses predictions

“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,” said lead researcher Dr. Jaume Pellicer.

“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,” added Dr. Ilia Leitch, a senior research leader at the Royal Botanic Gardens, Kew.

The discovery of this DNA giant serves as a powerful reminder of the vast diversity that exists within the plant kingdom.

“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,” said Dr. Leitch.

The exploration of the Tmesipteris genome is far from over. Scientists are eager to delve deeper into the secrets this remarkable fern holds, unlocking further insights into the boundaries of biological possibility. 

As we continue to explore the world of plant genetics, we are reminded that even the most unassuming organisms can harbor extraordinary surprises.

The study is published in the journal iScience.


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