A genome blooms

Leah Eisenstadt, October 22nd, 2010 | Filed under
  • Paris japonica has the largest genome of any organism studied.
    Image courtesy of Ray Drew

The Royal Botanic Gardens, Kew is a lovely place to explore, where visitors can stroll among the treetops nearly 60 feet above the ground, tunnel through an interactive play area shaped like a plant, or get a close-up view of piranha, poison-dart tree frogs, and baby water dragons.

But behind the scenes, hundreds of scientists at Kew work to protect plant diversity worldwise by preserving more than 37,000 DNA samples from diverse plants, building the largest wild plant seed bank, and conducting research on plants with economic or biological importance. Kew can also make some extraordinary claims, due to its impressive collections of botanical specimens.

Tallest: The Temperate House at Kew houses the world’s tallest indoor plant, the Chilean Wine Palm, Jubaea chilensis. When last measured in 1985, the tree stretched 58 feet high, and is still slowly growing today.

Smelliest, biggest: Kew also house several specimens of Titan Arum (Amorphophallus titanum), a giant bloom that reaches eight feet in height and emits a foul stench reminescent of rotting meat, inspiring its nickname, the “corpse flower.” (One will be blooming soon…if you’re in the neighborhood!)

Most comprehensive: Kew’s Herbarium is home to the largest and most comprehenive collection of fungi, with over 1.2 million specimens of mushrooms, molds, and other fungi.

Kew can now add another superlative to their impressive list: largest genome.

Their latest discovery comes from Kew’s Jodrell Laboratory, where they found that Paris japonica, a small, white flower from Japan, has the largest genome of any organism studied! The previous record holder, the marbled lungfish, has 132.83 picograms of DNA (a picogram is one-trillionth of a gram), while the flower’s genome is 15% bigger at 152.23 picograms. If stretched out, the scientists say, the genome would be taller than Big Ben in London.

The smallest genome yet reported (at least among eukaryotes, or organisms with nuclei enclosed in membranes) is found in an intestinal parasite (0.0023 picograms of DNA), and the human genome falls in between, at 3.0 picograms and 3 billion “letters” of DNA. The flower’s genome is a whopping 150 billion letters long, making it 50 times the size of the human genome.

The diversity of genome sizes among organisms is an interesting scientific phenomenon with implications for biodiversity and conservation. In this case, size does matter. Plants with large genomes are at greater risk of extinction, are less adapted to pollution, and less able to tolerate environmental extremes. A larger genome also requires more time to copy, meaning cells divide more slowly, preventing plants with large genomes from growing in habitats that require them to grow rapidly.

Be warned: the size of a genome may be misleading. A huge genome doesn’t necessarily mean an organism has an exceptional number of genes. The size of Paris japonica’s genome includes both its protein-coding genes and non-coding DNA. And the number of genes doesn’t fully correlate with complexity: the mustard plant Arabidopsis thaliana has more genes (about 25,000) than are in the human genome, which contains roughly 21,000 genes.

Scientists at the Broad and elsewhere conduct research to identify all the parts of genomes — both working and not — to better understand how the diversity and variation among genomes yields the stunning array of organisms seen in nature. Researchers may someday learn why this tiny flower packs such a heavy genetic punch.

Paper cited: Pellicer J, Fay MF, Leitch IJ. 2010. The largest eukaryote genome of them all? Botanical Journal of the Linnean Society

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