Humped bladderwort

The humped bladderwort is a fine example of the mantra “It’s not the size that counts, it’s how you use it.” Alongside being quite the little aquatic predator, adorned with a series of miniature traps which use vacuum pressure to ensnare prey, this humble-looking plant has a genome that is proving to be an evolutionary marvel. The carnivorous species may have the same number of genes as the gargantuan Norway spruce, but in terms of overall size, it is 250 times smaller.

While that fact alone is enough to know that this plant’s genome is pretty remarkable, new research has delved even deeper into its genetic makeup, revealing more fascinating features. According to the study, this species of bladderwort (Utricularia gibba) actually has a significantly smaller genome than many other well-known plant species, such as grape, yet boasts thousands more genes.

This new work actually builds on previous research conducted by members of the same team and led by University at Buffalo’s Victor Albert. Back in 2013, they published an intriguing study in Nature which found that an astonishing amount of U. gibba’s DNA was protein-coding material. In fact, only 3% of it was non-coding, i.e. not responsible for the production of a protein. That’s a considerably small amount when we compare this figure to that of our own genome, which is estimated to be well over 90% non-coding, and highly unusual for flowering plants.

So to what does this species owe its super-compact genomic features? According to the researchers, U. gibba’s case is one of rapid and “rampant” DNA editing; not only was its entire genome duplicated several times, but it was then remodeled by vast deletion events.

“The story is that we can see that throughout its history, the bladderwort has habitually gained and shed oodles of DNA,” Albert said in a news release. “With a shrunken genome, we might expect to see what I would call a minimal DNA complement: a plant that has relatively few genes—only the ones needed to make a simple plant. But that’s not what we see.”

Take grapes, for example—they stuff around 26,300 genes into their genome, which is 2,200 less than U. gibba. Yet the latter manages to cram all of these 28,500 genes into just 80 million base pairs (building blocks) of DNA, which is six times fewer than the number of base pairs found in grapes.

What appears to have happened is that throughout its history, U. gibba experienced three whole genome duplication events, and possibly also some smaller duplications. This meant that the plant had redundant copies of each gene, which were swiftly removed by deletion events. But during these mass deletions, less important and non-coding stretches were also removed, leaving only those essential genes that are capable of withstanding this deletion pressure. What was left was a highly compact genome crammed with various enhancements, such as numerous genes that facilitate its carnivorous lifestyle. For example, they found an abundance of genes for enzymes that help the plant dissolve meat.

Although we know how this fascinating plant seems to have carved such a gene-rich genome, it’s unclear at this stage why it has done this. Hopefully, future studies will help identify any of the driving forces that may be at play.