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3 Questions: Petal Pushers - Scientists Say Japanese Plant Has World's Longest Genome

The Paris Japonica, a Japanese flower.

The Paris Japonica, a Japanese flower.

Scientists at London's Kew Gardens say a simple yet striking flower from Japan is holding the longest genome ever discovered in its white petals. The Paris Japonica's genetic code is so long that researchers say it would be taller than the famed British clock tower, Big Ben, if stretched out. VOA talks to Ilia Leitch, a researcher with Kew's Jodrell Laboratory, about the discovery.

How does the Paris Japonica's genome compare to ours?

All organisms are made up with cells and so in our body, we've got billions of cells. And each of those cells has a nucleaus, and in that nucleaus is DNA. And as you know, we all have 46 chromosomes in our own cells. And if you took the DNA out from that and unraveled it, it would stretch about two meters. However, if you do the same for this plant, this Paris Japonica, if you unravelled all its DNA, it would stretch over a 100 meters. So you sort of visualize it in that respect. That's an awful lot of DNA packaged into its cells.

What does that mean in terms of the plant's traits? Is it more complex than us?

No, not really. Because actually, the number of genes that we have and the number of genes that Paris Japonica has is probably not hugely different. So what this difference in human genome size means is that huge amounts of the DNA are actually made of what we call non-coding DNA. So DNA that is not a gene, it's not coding for a particulr protein, like for making skin, or eyes and things like that. It's non-coding DNA and a lot of it is just highly repeated sequences, of DNA sequences, which is the same. You've got the same sequence repeated thousands and thousands of times.

And I guess what we're tying to understand is why does it have so much DNA? What is all this DNA doing? Because, well it depends on how you define perhaps intelligence, but it's not more intelligent or more complicated than we are, and yet it has all this extra DNA. So it's not related to the sort of structure of the organism, and we're trying to understand what all this extra DNA does and why does it matter.

What are the consequences of having an extraordinarily long genome?

If you go just the very basic level of every time a cell wants to divide, it's got to copy that DNA to make sure that the daughter cells have one copy of each. And the more DNA you have, the longer it takes for that DNA to be copied. And the result of this is it has sort of knock-on consequences at the whole plant level because if you take so long to divide your cells, you can't be an annual for example. You can't grow quick enough to complete all your cell divisions to produce a plant and to flower and produce seed in a single year, which is what an annual plant does.

It does affect their risk of extinction. There are studies which have been done which suggest that species with very big genomes are at greater risk of extinction than those with smaller genomes, so it has that impact on that organism. It certainly tells us because we know of the effects of all this DNA on the plant, becuase you know they're going to take a long time to grow, we just have to look after them very carefully. We can't speed up the rate at which they grow, but they're going to need more protection because they're more suceptible to becoming extinct because they can't cope with change so well.