According to a group of genetic scientists led by Prof Victor Albert of the University at Buffalo, the carnivorous plant Utricularia gibba, commonly known as the floating or humped bladderwort, houses more genes than several well-known plant species, such as grape, coffee or papaya – despite having a much smaller genome.
Scanning electron micrograph of the bladder of Utricularia gibba, color added; the plant is a voracious carnivore, with its tiny, 1-mm-long bladders leveraging vacuum pressure to suck in tiny prey at great speed. Image credit: Enrique Ibarra-Laclette / Claudia Anahi Perez-Torres / Paulina Lozano-Sotomayor.
Utricularia gibba is a flowering, free floating plant in the genus Utricularia (collectively called the bladderworts).
Bladderworts are found on every continent except for Antarctica. They are probably the most highly developed plants in the world and the most successful of the carnivorous plant genera.
There are at least 230 recognized distinct species that belong to the genus. Most of them grow in soil while others float in small ponds and ditches.
All species are carnivorous and capture small organisms by means of bladder-like traps.
To determine how bladderworts evolved their current genetic structure, Prof Albert and his colleagues compared Utricularia gibba to four related species. What they uncovered was a pattern of rapid DNA alteration.
“Its incredibly compact architecture results from a history of ‘rampant’ DNA deletion in which the plant added and then eliminated genetic material at a very fast pace,” said Prof Albert, who is the senior author of the paper published in the journal Molecular Biology and Evolution.
“The story is that we can see that throughout its history, Utricularia gibba has habitually gained and shed oodles of DNA.”
“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.”
In contrast to the minimalist plant theory, Prof Albert and his colleagues found that Utricularia gibba has more genes than some plants with larger genomes, including grape, as already noted, and Arabidopsis, a commonly studied flower.
A comparison with the grape genome shows Utricularia gibba’s genetic opulence clearly: its genome, holding roughly 80 million base pairs of DNA, is six times smaller than the grape’s.
And yet, the bladderwort is the species that has more genes: some 28,500 of them, compared to about 26,300 for the grape.
The plant is particularly rich in genes that may facilitate carnivory – specifically, those that enable the plant to create enzymes similar to papain, which helps break down meat fibers.
It is also rich in genes linked to the biosynthesis of cell walls, an important task for aquatic species that must keep water at bay.
“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,” Prof Albert said.
“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.
“Accordingly, we found a number of genetic enhancements, like the meat-dissolving enzymes, that make Utricularia gibba distinct from other species.”
“Much of the DNA it deleted over time was noncoding junk DNA that contains no genes,” Prof Albert concluded.
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Lorenzo Carretero-Paulet et al. High gene family turnover rates and gene space adaptation in the compact genome of the carnivorous plant Utricularia gibba. Mol Biol Evol., published online January 31, 2015; doi: 10.1093/molbev/msv020
