One, big part of the DNA, the noncoding DNA, informally termed as “junk DNA,” is not needed by complex organisms, says new research by an international research team led by the Laboratorio Nacional de Genómica para la Biodiversidad (LANGEBIO) in Mexico and the University of Buffalo. This study was directed by LANGEBIO Director and Professor Luis Herrera-Estrella and UB Professor of Biological Sciences Victor Albert.
The study involved a carnivorous plant and is going to be published in the journal Nature. It might also have implications for the human genome, of which 98 percent is junk-DNA. This amount varies from species to species, with the human genome consisting 98 percent of this junk-DNA and about 2% of a typical bacterial genome being the noncoding DNA.
It was believed that this part of DNA might be playing some hidden, useful role. At one time it was thought that this dark and hidden part of DNA contained genetic parasites that copy segments of DNA and paste themselves repeatedly in the genome.
Albert told LiveScience, "Nobody's really known what junk DNA does or doesn't do." For many years, it was argued whether this noncoding DNA had some mysterious function. A project called Encyclopedia of DNA Elements (ENCODE) aimed at finding out the part played by 3.3 billion base pairs that do not code for proteins. The discovery was that around 80 percent of the genome had some role such as whether genes turn on. Other scientists strongly criticized this.
Scientists Albert and his colleagues sequenced the genome of the carnivorous bladderwort plant, Utricularia gibba. This plant is a wet soil or fresh water plant that sucks in microorganisms swimming nearby into its 1-milimeter-long bladders.
The base pairs of this plant’s genome are much less when compared with other plants.
It seemed that bladderwort plant removed a lot of the noncoding DNA from itself and still was able to functions alright without it.
"Somehow, this plant has purged most of what makes up plant genomes. What that 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," says Albert.
The plant, by the help of some genetic oddity, had its whole genome duplicated. It had two full copies of the genome three separate times. Although it diverges from breed tomato, it still somehow kept its tiny genome.
Herrera-Estrella says, "This surprisingly rich history of duplication, paired with the current small size of the bladderwort genome, is further evidence that the plant has been prolific at deleting nonessential DNA, but at the same time maintaining a functional set of genes similar to those of other plant species.”
“Why then the extra baggage? No one knows for sure. Plants with large genomes don't seem to do badly,” says Albert.
Albert believes that this stripping off of junk-DNA may simply be inherent and some plants may just have a bias towards deleting a great deal of noncoding DNA, while others have a built-in bias in the opposite direction that is toward DNA insertion.