How is it that the carnivorous bladderwort's genome is bigger on the inside?
The study builds on previous work by its main author, Victor Albert of the University at Buffalo. In 2013, Albert found that Utricularia gibba, commonly known as carnivorous bladderwort, lacked the "junk" DNA (regions of DNA that don't directly code for proteins) that most organisms have in abundance. For humans, some estimate that over 90 percent of DNA is so-called junk -- but now we know that much of this genetic info has other roles, some of which we might just not understand yet.
In the case of the bladderwort, however, it seems that coding DNA is all the plant has time to keep. Only around 3 percent of the plant's DNA is so-called junk. It's genes all the way down.
The new study suggests that the plant may owe its super-compact genome to a long history of rampant DNA editing. Basically, the aquatic, carnivorous little plant is gaining and throwing away DNA at an unusually rapid pace. In fact, Albert and his colleagues believe that the plant's genome has duplicated entirely at least three times. But instead of just adding all of those redundant genes to its DNA (the way crops like wheat have), it has kept cutting out the chaff.
"It turned out that those rates of evolutionary turnover -- especially the rate of loss -- was incredibly high compared to other plants," Albert said. "The genome was subjected to some heavy duty deletion mechanisms."
When genes turnover all the time, only the really important ones -- in this case, ones that allow the plant to break down meat fibers and ones that help it keep its cell walls water-tight -- survive from generation to generation.
"It's the kind of thing we were really hoping to see," Albert said. The fact that genes really useful to aquatic (and carnivorous) life prevailed indicates that natural selection drove this creature's nifty DNA pruning.
But Albert and his colleagues still don't know why this particular bladderwort is a serial repeater and deleter. It has hundreds of close relatives -- also aquatic and carnivorous -- that have much larger genomes with much more junk DNA, even though they live in the same habitat and vie for the same resources.
"It might just not be as good at repairing its DNA as its close friends are," Albert suggested. In future studies, he and his colleagues hope to pinpoint the drive behind this fascinating mechanism.