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Evolution News and Views

A New Darwinian Hero: The Bladderwort

A diminutive carnivorous plant that lives on the surface of water and consumes microorganisms by ingesting them by means of its tiny bladders, the bladderwort species Utricularia gibba has emerged as an unlikely hero of Darwinian apologetics. The myth of "junk DNA" had taken serious damage from the release of the ENCODE papers, which suggested widespread functionality across the human genome, including in those vast non-protein-coding territories that were once dismissed as mere accumulated genetic flotsam.

The newsworthy novelty of U. gibba, the humped bladderwort, is that it gets by on a much more concise genome than other plants: just 3 percent of its genome does not code for proteins. That suggests to some wishful thinkers that perhaps here is the proof that "junk DNA" is junk after all. If the bladderwort can get by without it, so could we.

The occasion for the collective cry of "See, we told you so!" is a paper in Nature, "Architecture and evolution of a minute plant genome." From the abstract:

Despite its tiny size, the U. gibba genome accommodates a typical number of genes for a plant, with the main difference from other plant genomes arising from a drastic reduction in non-genic DNA. Unexpectedly, we identified at least three rounds of WGD in U. gibba since common ancestry with tomato (Solanum) and grape (Vitis). The compressed architecture of the U. gibba genome indicates that a small fraction of intergenic DNA, with few or no active retrotransposons, is sufficient to regulate and integrate all the processes required for the development and reproduction of a complex organism.

The L.A. Times is relieved:

How’s this for spring cleaning? Scientists have discovered that a carnivorous plant deletes so much of its own junk DNA that it has hardly any left. The finding, published online in Nature, hints that such noncoding DNA may not be as important as some scientists believe.

"Junk DNA is probably well named as junk. There doesn’t seem to be any glorious reason or function behind it," said Victor Albert, a University at Buffalo molecular evolutionary biologist and one of the lead authors on the study.

Live Science exults: "'Junk' DNA Mystery Solved: It's Not Needed"!

But this is just silly. There are many examples in plants of non-protein-coding
DNA that plays essential roles in metabolism and development. Generalizing the results from one plant (and an atypical one, at that) to all plants and animals is about as illogical as you can get.

See Chapters 4-7 of Jonathan Wells's The Myth of Junk DNA. Or go to PubMed and do a search on "microRNAs in plants." Here, we've done it for you. For more on the general subject, look at the dozens of papers that were published last September by researchers with the ENCODE project, though those focused mainly on animals. And don't forget to make use of our archives at ENV: search for "junk DNA." You're welcome, we've done that for you too.