The biggest genome in organism

1. The biggest genome in organism

2. Paris japonica (Japanese canopy plant)The genome of the Japanese canopy plant contains 50 times more DNA than the human genome and is 15% larger than the previous record holders (the marbled lungfish and a trillium).

3. Species information • Scientific name:Paris japonica (Franch. & Sav.) Franch. • Common name(s): Japanese canopy plant (English); kinugasa-sou (Japanese) • Synonym(s):Trillidiumjaponicum, Trillium japonicum, Kinugasa japonica • Conservation status: Not yet evaluated according to IUCN Red List criteria. • Habitat: Humus-rich soils of the subalpine woodland regions of the mountains of northern and central Honshu, Japan. • Key uses: Ornamental, edible (fruits). • Known hazards: None known.

4. Taxonomy • Class:Equisetopsida • Subclass:Magnoliidae • Superorder:Lilianae • Order:Liliales • Family:Melanthiaceae • Genus:Paris

5. Geography & Distribution • The canopy plant is restricted to Japan, where it grows in the central and northern mountains of Honshu Island.

6. Description • Paris japonica is a perennial plant with a bud-bearing rhizome (underground stem). Adult plants can reach a height of 35-75 cm and have a solitary stem with about 7-10 obovate leaves (12-25 cm wide) in a pseudo-whorl. In Japan P. japonica blooms between May and August, producing a single, stalked, star-like flower composed of up to 10 whitish tepals (2.5-3.5 cm). The fruit, which is a berry or fleshy capsule, becomes dark purple when mature and contains scarlet seeds.

7. Uses • The canopy plant is planted as an ornamental in gardens. Mature fruits are reported to be edible.

8. This species at Kew • Two specimens of Paris japonica grow at Kew, and are exhibited in the Davies Alpine House during their flowering period. One of the specimens was collected from the foothills of Shirouma-dake Nagano-ken, Honshu, and donated to the Royal Botanic Gardens, Kew, by the Japanese Alpine Rock Garden Society

9. Plant DNA C-values database part of the ongoing research into genome diversity in angiosperms (flowering plants) in general, and monocots in particular, genome sizes have been measured in a wide range of plants and incorporated into the Plant DNA C-values database. Recent work has particularly focused on monocot families in the Liliales which includes the family Melanthiaceae. The discovery of the enormous genome in Paris japonica was certainly a surprise, especially as it now holds the record for being not only the largest plant genome but also the largest for any eukaryote. This makes P. japonica an interesting source of information which may help us to understand why some plant genomes get so big and how the enormous amounts of DNA are organized and function.

10. Discovering the largest genome known to science • Genome size is the total amount of DNA in the nucleus of an organism, and includes both the genes and the non-coding sequences of DNA. There is a staggering diversity of genome sizes. The smallest genome so far reported (0.0023 picogram (pg) of DNA) is found in a parasite (Encephalitozoonintestinalis) of humans and other mammals. The human genome, at 3.0 pg, is 1,300 times larger than this, but this pales into insignificance when compared to the size of the genome in some other animals and plants

11. Among animals, some amphibians have enormous genomes, but the largest recorded so far is that of the marbled lungfish (Protopterusaethiopicus) with 132.83 pg. Among plants, the record holder for 34 years was a species of fritillary (Fritillariaassyriaca, Liliaceae). However earlier this year a Dutch group knocked the fritillary off the top spot when they found that a natural hybrid of trillium (Trillium × hagae), related to herb Paris quadrifolia, had a genome just 4% larger than the fritillary (132.50 pg).

12. This was widely thought to be approaching the maximum size that a genome could reach, until this summer when a team of Kew scientists discovered that the genome of another close relative of herb paris, Paris japonica from Japan, is a staggering 15% bigger than the genome of either the trillium or the lungfish at a whopping 152.23 pg. • IliaLeitch, Research Scientist at the Jodrell Laboratory at Kew says “We were astounded when we discovered that this small stunning plant had such a large genome - it’s so large that when stretched out it would be taller than the tower of Big Ben.”

13. “Some people may wonder what the consequences are of such a large genome and whether it really matters if one organism has more DNA than another. The answer to this is a resounding “yes, it does”, and the consequences operate at all levels from the cell up to the whole organism and beyond. In plants, research has demonstrated that those with large genomes are at greater risk of extinction, are less adapted to living in polluted soils and are less able to tolerate extreme environmental conditions – all highly relevant in today’s changing world.”