Smallest plant genome

Currently the smallest known genome (i.e., total amount of DNA in the nucleus of a cell) for any plant using best-practice methods is just 12.56 million base pairs (megabase pairs, or Mbp), identified in the unicellular marine alga Ostreococcus tauri. The research was published in the journal Proceedings of the National Academy of Sciences on 1 August 2006. The human genome, by contrast, is comprised of c. 3.2 billion base pairs.

At roughly 0.8 micrometres in diameter, these tiny green algae are among the smallest free-living eukaryotes on Earth. As well as the number of base pairs, genome size can also be expressed as a weight: the total DNA of O. tauri weighs in at a mere 33 femtograms (1 femtogram = 0.000000000000001 g).

The research was conducted by the Centre National de la Recherche Scientifique, Université Pierre et Marie Curie-Paris (both France), Ghent University (Belgium) and the University of Miami (USA), led by Evelyne Derelle.

Among terrestrial plants, the smallest genome record goes to the carnivorous Genlisea tuberosa, a corkscrew plant endemic to Brazil, with a genetic makeup of 61 Mbp, according to a study in Annals of Botany in December 2014.

At the other end of the scale, the largest plant genome – as well as for any organism assessed to date using best-practice methods – is 160.45 billion base pairs for the Tmesipteris oblanceolata fork fern, native to tropical forests in New Caledonia and other nearby Pacific islands, as reported in iScience on 31 May 2024.