Carnivorous plant with huge number of genes stumps scientists with tiny genome

(NaturalNews) Scientists have discovered that an already unusual plant known as the carnivorous bladderwort (Utricularia gibba) is even more mysterious than they had previously realized. According to a new study conducted by researchers from the University at Buffalo and published in the journal Molecular Biology and Evolution, the carnivorous bladderwort has a much smaller genome than other plants, containing much less DNA overall. Yet rather than having fewer genes, it actually has more of them.

For comparison, the grape has an average-sized plant genome of about 480 million DNA base pairs. The bladderwort's genome is six times smaller, with only 80 million base pairs. Yet the bladderwort has about 28,500 genes, more than the 26,300 in the grape's genome.

"The story is that we can see that throughout its history, the bladderwort has habitually gained and shed oodles of DNA," researcher Victor Albert said. "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."

Heavy duty genome deletion

The carnivorous bladderwort is a rootless plant that floats in the ocean, trapping prey with its tiny branches. This already made it unusual enough. Then in 2013, Albert and his fellow researchers discovered that the plant had a tiny genome due to a striking absence of what is typically called "junk" DNA: DNA that does not code for proteins. Increasingly, scientists are discovering that junk DNA actually serves an important role for most organisms, which could explain why it typically forms the bulk of the genome. The human genome, for example, is about 90 percent junk DNA.

The carnivorous bladderwort genome is only 3 percent junk DNA. That means the other 97 percent of it is genes.

Researchers are stumped by why the bladderwort would evolve such a super-efficient genome. In the new study, the University of Buffalo researchers sought to solve part of the puzzle by comparing the genomes of the bladderwort and several closely related plants. They discovered that in its evolutionary history, the bladderwort had gone through three separate episodes of duplicating its entire genome. Though gene duplication, as this is known, is a relatively common process in DNA, it does not typically occur with such frequency. Notably, the bladderwort also deleted much more of the redundant DNA following duplication than is usual.

"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."

Plant unique among close relatives

There is likely a strong evolutionary benefit to removing redundant DNA, the researchers speculated.

"When you have the kind of rampant DNA deletion that we see in the bladderwort, genes that are less important or redundant are easily lost," says Albert. "The genes that remain - and their functions - are the ones that were able to withstand this deletion pressure, so the selective advantage of having these genes must be pretty high."

Indeed, the researchers found that the bladderwort was particularly likely to delete genes that did not directly relate to survival, and to retain those related to traits such as breaking down food or maintaining strong cell walls.

"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 scientists still cannot explain why, if such heavy genome pruning is so beneficial, it is not found among closely related plants. Perhaps, Albert suggested, the bladderwort aggressively eliminates non-coding DNA to prevent dangerous mutations.

"It might just not be as good at repairing its DNA as its close friends are," he said.

(Natural News Science)

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