Flower has longest genome

2010-10-08 08:27

London - Researchers at London's Kew Gardens say they've discovered the longest genome in the world - and that it belongs to a rather ordinary-looking white flower.

The scientists said the Paris japonica has a genetic code 50 times longer than that of a human being and edges out its nearest competitor, the marbled lungfish.

A genome is the full complement of an organism's DNA, complex molecules that direct the formation and function of all living organisms. Scientist Ilia Leitch said on Thursday that the code for Paris japonica is so long that if it were stretched out it would be taller than Big Ben (about 90m).

Leitch and her colleagues suspected the plant might have a larger-than-usual genetic code as its relatives have rather large ones too. But the sheer size of this flower's genome caught them by surprise.

"We certainly didn't expect to find it," she said.

Impressed

A genome is the full complement of an organism's DNA, complex molecules that direct the formation and function of all living organisms. The size of an organism's genome is typically measured by the number of bases it contains - base pairs being the building blocks of DNA.

The human genome, for example, has about three million bases and measures about 2m in length.

The marbled lungfish has a whopping 130 million bases. And the 30cm flower studied by Leitch turns out to have 150 million.

Outside experts were impressed.

"This is certainly an enormously large genome," said Nick Lane, a fellow at the Department of Genetics, Evolution and Environment at University College London. "I don't know of any larger genomes among plants or animals."

Still, he cautioned that micro-organisms known as amoebas might have even longer codes, saying that the record "might not last long".

Both Leitch and Lane said the find illustrates the staggering diversity of genome sizes. While Paris japonica and the marbled lungfish have huge ones, other genetic codes are minuscule - the parasite known as Encephalitozoon intestinalis, for example, carries approximately 2 300 bases.

Intrigued

It's not always clear why the range varies so wildly. Bigger genomes don't necessarily mean a more complex organism.

Whereas genes are generally supposed to correspond to some traits - blonde hair, for example, is genetically determined - in organisms with huge genomes, many genes don't appear to correspond to anything.

"Effectively, some cells carry massive amounts of 'junk', or at least non-coding DNA, whereas others have very little," Lane said.

Leitch said that geneticists are still discussing the question of why some organisms carry masses of non-coding DNA, and that the study of organisms such as the Paris japonica can help add to the debate.

"It's a question that's long intrigued scientists," she said.

The results of her team's research are being published in the Botanical Journal of the Linnean Society.

- SAPA