For as long as I have been a biologist, I have believed wholeheartedly in the promise of genetic engineering. In my lab alone, we have put the gene that makes fireflies glow into mouse cells. Therefore if we transfer these cells into a recipient mouse, we can follow the cells within the body by using highly sensitive cameras. This has had major implications on our research because now we are able to track the cells within the mouse overtime without having to kill the recipient mouse.
I have already written about the impressive science of gene therapy and recombinant DNA in my post about synthetic life. However there was one thing that I didn’t address that truly conveys the power of genetic manipulation. That is the ability to transfer genetic material across species barriers. In the past, you could only pass favorable traits was through selective breeding, which in itself is inherently slow and inefficient. Now almost every aspect of biology is transferable between species, and can be done with much more efficiency.
Photosynthesis in Animals?
So it got me to thinking? Is it possible to genetically alter animals so that they too could undergo Photosynthesis? Photosynthesis, the process of using the energy from sunlight to create sugars from carbon dioxide and water, is currently limited to plants, algae and some bacteria. It has already been proven that photosynthesis occurs within the organelle Cholorplasts. Since this organelle is essentially made from proteins, then theoretically if we isolate the necessary proteins, and their respective DNA template, to make Cholorplast, we can transfer that material to a new host species.
There is indeed one multicellular animal that has been shown to perform photosynthesis. There is a Green Sea Slug that eats algae, incorporates the chlorophyll, and is able to utilize the organelles for the rest of it’s life. It shows that multicellular animals have the potential for photosynthesis, but is still one step short of the ultimate holy grail.
Hurdles to Overcome
Obviously there is a major hiccup with this theoretical concept. When I mentioned gene transfer before, usually it was with one protein. An organelle such as Chloroplast will have hundreds of proteins. In an article I just read recently, which I can’t seem to find right now, it mentioned there are upwards of 500 genes are uniquely found in plants. Even more daunting is that close to half of the genes are uncharacterized.
But not only is it a challenge to know which of the genes are absolutely necessary for photosynthesis, we also have the complication of expression. If all the proteins are overexpressed, the cell would become overcrowded and in turn die. How do we regulate it’s expression, in an animal model, so that the optimal level of protein expression is achieved.
We COULD have some level of expression control. Every gene requires a specific promoter that must be activated in order for the protein to be transcribed. So we could easily at a “skin cell” promoter to out plant genes so that, in the very least, are only expressed on skin cells. This would be an obvious choice, given skin cells will be most likely to collect sunlight for photosynthesis. Still, going back to the previous point, how do we control the expression?
Lastly, would photosynthetic animals created enough sugar to make the arduous task worth it? Before I address this question, the reason sugar is important is because during metabolism, it’s stored energy is transferred to a molecule called ATP. ATP is a common currency of energy in all biological creatures. ATP is used in EVERY chemical reaction that requires energy; it is used in muscle contraction, neural stimulation, metabolism….literally EVERYTHING. Sure plants make lots of sugars, and in turn, lots of ATP. However, plants are inherently immobile. Movement requires TONS of ATP. Simply bending your finger uses billions of ATP molecules. So back to the original question, could animal photosynthesis make enough sugar/ATP to sustain itself? (Honestly, I doubt it, but I’ll address this more in the implications section below.)
Even though there are more problems to figure out than there are solutions, the implications of creating photosynthetic animals is HUGE. Imagine we genetic modified a cow so that it’s skin cells underwent photosynthesis, constantly creating sugar while grazing in the field. Given a sizeable chunk of it’s sugar is now coming directly from sunlight, theoretically the cow wouldn’t eat as much. That means the farmer can keep more food for his family. That cut costs for individual users and on a global scale, we would have more food to distribute to starving countries.
Also, given carbon dioxide is used up to create sugar, theoretically the cow would sequester CO2 from the atmosphere. Given our current problem with overproduction of CO2, this is another benefit. Obviously, the a single cow won’t have a significant influence on global CO2 levels, but if millions of “green cows” were present, they would make some contribution to curbing our current problem.
I realize i’m viewing this whole scenario through rosy colored glasses, and that this concept is about as difficult as curing AIDS. But that should only motivate scientists to accept the challenge. Effectively they could solve many of our worlds current problems with one elegant solution. So this is my official call to arms….calling all botonists, biologists, and chemists, I urge you to combine your genius to achieve this goal. I mean, who doesn’t want to see a “green cow?”