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A Naturally Occurring Transgenic Organism - The Crawling Leaf!

By LariAnn Garner (LariAnnNovember 21, 2008

The headline is more than just an attention-grabber, as you can see from the thumbnail picture. As incredible as it appears to be, this organism was not cooked up in a top-secret transgenic lab somewhere. The Crawling Leaf (Elysia chlorotica) is a naturally living and breeding life form that has been on this planet since well before humans started tinkering with recombinant DNA. Read on for the startling story . . .

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Turning Over a New Leaf!

I've seen and studied strange plants and strange animals, but it has been a while since I was stunned by something in the natural world. When I found out about what I'm going to share with you today, I was stunned! For me, learning of the existence of the Emerald Sea Slug (Elysia chlorotica) is one of the most exciting experiences to come my way in some time, not just because of the sheer strangeness of the organism, but because it is a mind-blowing example of a natural transgenic process in the so-called higher life forms.

Before this organism came to my attention, I had trepidations about the progress of genetic engineering. My thought was that combining genes from two completely different life forms was akin to spinning a roulette wheel whose outcome was going to change the natural world drastically, perhaps disastrously. This unassuming Sea Slug has quieted those trepidations for me, at least a little, because if such dissimilar gene transfer can occur naturally, then for humans to do it artificially is not as far distant from natural processes as I thought.

Real Energy Independence

You see, the green color of the Emerald Sea Slug is not just the result of a simple pigmentation, but is due to active, operational chloroplasts derived from its algal food source (Vaucheria litorea)! Once the Sea Slug has incorporated these into its body structure, they provide food energy for the animal just as they do for the free-living algae. But just having the chloroplasts in body is not enough for this to work; otherwise, all of us who have eaten green vegetables could forego eating just as the Sea Slug does!

In reality, the organism also needs the associated DNA from the algal genome. This is to enable the manufacture of needed proteins for the chloroplasts in the same manner as they are provided to plastids within the algal cells. So the real surprise here is that the Sea Slug has incorporated the required algal DNA into its own DNA so the algal plastids (now Sea Slug plastids) can receive the proteins they need to function according to specification. You read right - the relevant DNA from the algae is incorporated into the DNA of the Sea Slug and continues performing the function it performed for the algae, but now instead of helping the algae proliferate, it is helping the Sea Slug live a life without having to eat. A note of scientific humor here is that these plastids are known as kleptoplasts, or stolen plastids!

Once the enormity of this is grasped, amazing possibilities come to mind. Imagine a novel approach to eliminating hunger by eliminating the need to eat. Or, with more genetic sophistication, engineering a gene/plastid set that enables a person or animal who is going to be unable to find food (as in a long space voyage) to make their own food for a specific period of time. Once the time has elapsed, the gene shuts off and the plastids are absorbed, leaving the person none the worse for wear. I have no doubts about the fascinating possibilities here. Even as you read this, the genome of both the Emerald Sea Slug and the alga are being mapped. That's how scientists discovered that this mollusc had actual algal DNA included as an integral part of the Sea Slug genome.

Some excellent sources for more extensive information about this organism and the phenomenon of horizontal gene transfer can be found at SymBio - A Look into the Life of a Solar Powered Sea Slug, Going Green and The Further Adventures of the Emerald Green Sea Slug.

Image Credit: University of Maine

  About LariAnn Garner  
LariAnn GarnerLariAnn has been gardening and working with plants since her teenage years growing up in Maryland. Her intense interest in plants led her to college at the University of Florida, where she obtained her Bachelor's degree in Botany and Master of Agriculture in Plant Physiology. In the late 1970s she began hybridizing Alocasias, and that work has expanded to Philodendrons, Anthuriums, and Caladiums as well. She lives in south Florida with her partner and son and is research director at Aroidia Research, her privately funded organization devoted to the study and breeding of new, hardier, and more interesting aroid plants.

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