Bladderwort Genome: Tiny but Terrific
A detailed study of the carnivorous Bladderwort plant has revealed a most curious genetic history in which genes are added and deleted over and over again. This has left it with a small yet densely packed genome with more genes than plants with six times the amount of DNA.
Despite how they sound, these bladderworts are not found in an ingredients list for Harry Potteresque potions. These carnivorous aquatic plants (Utricularia gibba) are found on most continents in bogs and the edges of ponds. They consist of one or multiple flowers that poke out of the water while the majority of their mass lies below resembling intertwined matts of mostly leafless twigs.
They appear interesting enough I suppose but their real beauty is revealed when you peer at their genetic code as researchers have done the past few years.
Most recently, a new study in the journal “Molecular Biology and Evolution” describes a genome with quite a history to it. It appears that throughout much of their tenure on earth, bladderworts have repeatedly expanded and reduced their genomes. In fact, they identified at least three separate events in which bladdwords duplicated the entirety of the genes encoded in their DNA. The fact that their genome is small however means that they are equally adept at discarding genes as well.
The result of the bladderwort’s apparent love/hate relationship with its genes is a genome that is quite extraordinary on multiple levels.
1) Its genome is exceedingly small for multicellular plant life, even compared to closely related aquatic carnivorous plants.
2) Despite this small size, the number of genes it contains is greater than other plants with genomes as much as 6 times larger. For example, bladderworts have 28,500 genes while grapes have 26,300 despite having a genome 600% larger.
3) Perhaps most extraordinary of all, bladderwort’s genome’s consist almost entirely of functional genes with almost no non-coding dna (so-called junk dna). Humans, for example, are at the other end of this spectrum. 98.5% percent of our genes are non-coding meaning they don’t obviously function to create proteins or to control other genes. Bladderwort’s genome, on the other hand, is only 3% non-coding. It essentially consists of genes from top to bottom. The implication of this could be far-reaching since there’s been an ongoing debate as to how essential non-coding genes are to life. As molecular biologist and study co-author Victor Albert said:
“At least for a plant, junk DNA really is just junk – it’s not required,”
Does this mean that all the junk in our trunk is superfluous as well? It may. It certainly seems like it is for plants. We have in the past found some function for some of our erstwhile junk DNA. I’m sure that in the future we could find some more but it seems fairly certain, after decades of searching, that the vast majority of what we call junk dna is truly junk in the trunk. It also just makes sense, in light of evolution and genetics, that bits of old obsolete (human and viral) genes would accumulate and hang around as long as they weren’t hurting anybody.
Ok, back to bladderworts. This creature’s bizarre genetic history has created some interesting adaptations. For example, genes optimized for carnivory (love that word) are well represented in its genome which makes sense since there’s great selective pressure to retain and improve those genes. These genes code for a special enzyme that breaks down meat so it’s easy to digest. No similar species has developed an enzyme quite like this.
Even more interesting though is the evolution of an underwater trap the bladderwort uses that is so successful that the plant doesn’t necessarily even need to root in soil to get its nutrients. The trap appears as bulbous outgrowths on its twig-like underwater branches that can create a negative pressure on the inside. When a creature disrupts one of the trigger hairs near the trapdoor, it opens up and sucks the creature and surrounding water inside where the digestive juices make short work of it. This process is blindingly fast taking 10 to 15 thousandths of second. This is so fast, in fact, that only relatively recently have cameras been fast enough to see what the hell was going on. So ingenious is this trap that it is also believed to be the most sophisticated structure in the entire plant kingdom.
Image Credit: Enrique Ibarra-Laclette and Claudia Anahí Pérez-Torres