Some DNA is Just Junk: Carnivorous Plant Reveals It's Unnecessary for Complex Life

Is some DNA just junk? It just might be, according to a new study. While genes make up about two percent of the human genome, the rest consists of a genetic material known as noncoding DNA. Now, researchers have shown that the large majority of this material may not actually be necessary for complex life.

Noncoding DNA is DNA that doesn't code for any proteins. This includes mobile elements called jumping genes that have the ability to copy (or cut) and past themselves into new locations of the genome. While scientists have spent countless hours puzzling over why noncoding DNA exists in such large amounts, they haven't nailed down a solid answer.

In previous studies, researchers have begun to offer an explanation for noncoding DNA. They hypothesized that about 80 percent appeared to play a role in biochemical functions, such as regulation and promotion of DNA conversion into its relative, RNA, which for genes, feeds into the machinery that makes proteins. Yet this theory fails to explain the existence of a certain bladderwort plant.

The genome of the carnivorous bladderwort plant, known as Utricularia gibba, possesses very little in terms of noncoding DNA. The smallest genome to ever be sequenced from a complex, multicellular plant, U. gibba is made mostly of genes and small pieces of DNA that control those genes. This is in stark contrast to other species that possess a large amount of noncoding DNA.

In fact, the researchers found that the plant has probably been deleting "junk" DNA from its genetic material over many generations. This could explain the difference between bladderworts and junk-heavy species such as corn, tobacco and humans.

"The big story is that only three percent of the bladderwort's genetic material is so-called 'junk' DNA," said Victor Albert, UB Professor of Biological Sciences, in a news release. "Somehow, this plant has purged most of what makes up plant genomes. What this says is that you can have a perfectly good multicellular plant with lots of different cells, organs, tissue types and flowers, and you can do it without the junk. Junk is not needed."

It's very possible that some species may simply have an inherent mechanistic bias toward deleting a great deal of noncoding DNA while others may have a built-in bias in the opposite direction. These biases are not due to the fact that one way of behaving is more helpful than the other, but because there are two innate ways to behave. Because U. gibba shows that having a bunch of noncoding DNA is not crucial for complex life, it means that junk DNA may be just that--junk.

The findings are published in the journal Nature.