How’s this for spring cleaning? Scientists have discovered that a carnivorous plant deletes so much of its own junk DNA that it has hardly any left. The finding, published online in Nature, hints that such noncoding DNA may not be as important as some scientists believe.
"Junk DNA is probably well named as junk. There doesn’t seem to be any glorious reason or function behind it," said Victor Albert, a University at Buffalo molecular evolutionary biologist and one of the lead authors on the study.
Only 2% of the human genome is actually made up of functional elements such as genes, according to Albert. The rest of it is non-coding DNA that doesn’t appear to carry active, relevant information for that living creature’s proper functioning (i.e. for building proteins).
But the carnivorous bladderwort plant, Utricularia gibba, has only about 3% junk, according to an international team of researchers -- which is unusual even by plant standards. About 97% of its code actually consists of genes -- making it a lean, mean genetic machine.
U. gibba is a feathery carnivorous plant that forms mats over water and traps single-celled organisms and tiny crustaceans in submerged, millimeter-wide bladders. It draws nutrients from those tiny carcasses in environments where the soil is often very nutrient-poor.
U. gibba's genome is already short -- it’s made of 82 million base pairs, while humans have over 3 billion base pairs, Albert said. Even the basic "lab rat" of plant science, Arabidopsis, has a genetic code that’s about 1.5 times as long as U. gibba's.
And yet the plant packs efficiently, stuffing all its useful genetic code into a fraction of the sprawling DNA real estate afforded other plants and animals.
Repeated segments buried in the plant's DNA show them that the entire genome has been duplicated three times since its lineage split off from its common ancestor with the tomato and the grape -- and yet this regular doubling of the code hasn’t increased its length. Clearly the plant must be cutting unnecessary DNA faster than it’s adding it, the researchers concluded.
The scientists aren’t sure why this particular bladderwort has such a tiny, efficient genetic code. It may be pure chance, Albert said, particularly since other carnivorous plants' codes can stretch much longer.
But it does show that perhaps all that junk DNA — which some scientists have argued serves some undiscovered purpose — may be getting more credit than is due, in humans as well as plants.
"The bladderwort certainly shows that at least one plant makes a perfectly good plant without it," Albert said. "By extension, I would say it's suggestive that maybe junk DNA in general isn't of much importance."
For more on carnivorous plants in the U.S., check out this Column One on carnivorous plant poaching.
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