May 13, 2013
Carnivorous Plant Ditches Its ‘Junk’ DNA
Brett Smith for redOrbit.com — Your Universe Online
There are approximately 3 billion base pairs in the human genome, however, only about 2 percent of those are actual genes. The rest is considered ℠junk´ DNA. For years, scientists have puzzled over the question of why so much of the human genome appears to be useless, and a new study on a bizarre wetland plant could be the key to solving the genetic mystery.
Utricularia gibba is a carnivorous plant that uses a specialized bladder to suck in bugs like a vacuum cleaner. What makes the plant particularly noteworthy for geneticists, however, is the fact that 97 percent its genome is comprised of actual genes.
"The big story is that only 3 percent of the bladderwort's genetic material is so-called 'junk' DNA," said“¯study researcher Victor Albert, a biology professor from the SUNY University at Buffalo.
"Somehow, this plant has purged most of what makes up plant genomes.”
According to a report of their study published in the journal Nature, the plant has spent many generations deleting the junk from its DNA.
“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,” Albert said.
Junk DNA, or non-coding DNA, is genetic material that does not translate into proteins, which are the building blocks of life. Some theories have posited that non-coding DNA can play a role in converting DNA into RNA, feeding into the cell´s machinery.
However, the new Nature study asserts that some organisms´ build up of genetic junk may not provide any direct benefit.
Co-author Luis Herrera-Estrella from the Laboratorio Nacional de GenÃ³mica para la Biodiversidad (LANGEBIO) in Mexico told National Geographic when he first sequenced the plant´s genome that he expected to find a pared back genome containing only the most essential genes and without any spare genetic parts.
However, U. gibba actually has more functional genes than similar plants with bigger genomes. The carnivorous plant has about 80 million DNA base pairs — translating into about 28,500 genes. Its comparable relatives, grapes and tomatoes, have much larger genomes — about 490 and 780 million base pairs, respectively.
The researchers also found many copies of some genes U. gibba shares with its relatives — the tomato and the grape. This led them to believe U. gibba duplicated its entire genome at least three times during its history before beginning the process of deleting its genetic junk.
The team asserts that some organisms are biased toward deleting non-coding DNA while others are biased toward insertion and replication.
“There are these natural currents that underlie genome dynamics,” Albert told National Geographic. “The key to the evolution of genome size may be the extent to which these opposing forces can be tolerated by natural selection.”
Despite its smallish genome, U. gibba is a unique and complicated plant. It lives in freshwater wetlands and captures prey using tiny bladders. By pumping water from these tiny chambers, the plant turns each one into a vacuum that can vacuum up and trap unsuspecting insects.