Tmesipteris oblanceolata , a type of fork fern native to New Caledonia in the southwest Pacific has been found to have the genome size of 160.45 Gigabase pairs (Gbp)/IC (1C = nuclear DNA content in a gametic nucleus). This is about 7% larger than that of Paris japonica (148.89 Gbp/1C), a Japanese plant that had held this record since 2010. For comparison, human genome size is 3.1 Gbp/1C (i.e., 3.1 billion base pairs per gametic nucleus). Thus, the genome of T. oblanceolata is about 50 times bigger than human genome.
The ferns belonging to Tmesipteris were thought to have giant genomes based on indications from previous studies. However, it took researchers about a decade of exploration of diversity of genome sizes among plants to arrive at the current finding about the actual genome size of T. oblanceolata
There is extraordinary variation in genome sizes of about 20,000 eukaryotic organisms studied so far. Of these, only few plants and animal groups have genomes bigger than 100 Gbp. Lungfish (Protopterus aethiopicus) at 129.90 Gbp, and the river newt (Necturus lewisi) at 117.47 Gbp are examples from animal groups. The European mistletoe (Viscum album) with 100.84 Gbp is an example from plant kingdom. Interestingly, Six of the largest eukaryotic genomes are found among the plants.
Larger genome size does not necessarily mean larger number of genes. Repeated transposable elements may account for large genome sizes.
***
References:
- Fernández, P. et al. A 160 Gbp fork fern genome shatters size record for eukaryotes. iScience. Published 31 May 2024. DOI: https://doi.org/10.1016/j.isci.2024.109889
- Institut Botànic de Barcelona 2024. Research news – The largest genome on the planet has been discovered in a fern. Posted 31 May 2024. Available at https://www.ibb.csic.es/en/2024/05/the-largest-genome-on-the-planet-has-been-discovered-in-a-fern/
***
