Mar 22 2022

Transgenic Plants and Space Travel

Published by under Astronomy
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Spending extended time in space presents many challenges, on of which is prolonged microgravity. Artificial gravity through rotation is not yet practical. We may see rotating space stations this century, but not space ships, and there are no practical concepts for how to produce artificial gravity on the Moon or Mars. NASA’s approach to this and other similar problems is mitigation – they can’t prevent the problem, so learn to deal with its effects. On the ISS, for example, astronauts undergo a daily resistance training regimen to stave off bone and muscle loss.

Exercise alone, however, is not enough to prevent bone loss (osteopenia), which is about 1-2% per month on average. This may be acceptable for a several month stint on the ISS, but NASA is planning a 3 years mission to Mars in the 2030s. That would entail about 10 months travel time to and from Mars, and about a year on Mars itself. That’s 20 months in microgravity and one year in Mars gravity, which is 38% of Earth’s. This is why NASA is investing in advanced space ship concepts – “get there fast” is their primary strategy for mitigating the risks of deep space travel.

Another category of mitigation measures is medical. If we can understand the physiology of microgravity, then perhaps we can develop medical interventions to compensate. For example, they are developing a negative pressure body suit to essentially suck fluids into the lower extremities, to simulate the effects of gravity and prevent some of the negative effects of fluid redistribution in long term microgravity, such as negative effects on the eyes.

One way to mitigate bone loss is through the daily injection of parathyroid hormone (PTH), which stimulates bone growth. While this works, transporting all the medicine and syringes necessary for three years of such injections on the entire Mars crew is not practical. Researchers are therefore working on other methods. One idea was recently presented at the American Chemical Society (ACS) Spring 2022 meeting – using genetically engineered lettuce which contains a transgene that makes a modified PTH. This is potentially a great idea for several reasons.

First – growing hydroponic vegetables is extremely useful for long duration space missions. Most of the food consumed by astronauts is freeze-dried or canned. If they are going to have access to fresh vegetables, they are going to have to grow them locally. Fresh vegetables, such as lettuce, would be a highly useful addition to their diet, but also would be helpful for their psychological health. Long missions on Mars would also benefit from maximally utilizing local resources. Carrying three years of food for all the crew is difficult (but obviously possible) but imagine if a self-sustaining farm could be created on Mars. This could be hydroponic, or even use modified Martian soil. Such a farm would also produce oxygen for breathing and for fuel. It would require water, which could be theoretically locally sources, and make food from CO2 in the Martian atmosphere and processed astronaut waste. Another advantage is that seeds are very small, and transporting them to Mars would not use up significant space or weight.

In order to have plants that grow optimally in these conditions genetic engineering would be useful. We could use other cultivation techniques as well, but there is no reason not to use the full range of technologies for developing cultivars with desired properties. Using transgenic methods (meaning inserting genes from a distant species) also creates the possibility of using plants to produce pharmaceuticals or other desired chemicals. The more astronauts can locally produce on Mars the better. Plants, therefore, would not only be a critical source of food and oxygen, they could also be portable pharmaceutical factories.

The current study involves a transgenic lettuce that produces a modified PTH. They combined the PTH protein with the fragment crystallizable (Fc) domain of a human antibody. The PTH-Fc protein is more stable, has higher bioavailability, and will remain in the blood for longer than pure PTH. The plant produces 10-12 milligrams of PTH-Fc per kilogram of fresh lettuce, which means astronauts would have to eat about 8 cups a day to meet their needs of preventing bone loss. While this is feasible, the authors admit that this is a “big salad”. However this is just round one. They still have a lot of transgenic plants to investigate and some may have significantly higher expression. They have time to tweak the GMO lettuce to get the PTH-Fc concentration even higher. Hopefully they can get it to the “side salad” per day level.

This approach opens up a lot of possibilities, beyond just mitigating osteopenia (or the more severe osteoporosis) from long space travel. Astronauts could potentially have a veritable pharmacy that they can grow locally as needed. Also, even just for food and nutrition having a variety of plants (not just lettuce) will be highly useful. That salad could eventually contain tomatoes, cucumbers, peppers, and beans.

This technology can also have applications on Earth. Hydroponic gardening, as I discussed previously, is very land and water use efficient, and will likely be a critical farming method going forward. Developing cultivars optimized for hydroponics would be useful in space an on Earth. But also, developing plants with enhanced nutrients and even pharmaceuticals, like PTH-Fc, can have applications on Earth. In poor countries without access to adequate medical care (which obviously is a problem that should be addressed directly), the negative effects can at least be mitigated for now by making available transgenic plants to provide needed drugs.  And since this method also produces food, it isn’t displacing food production.

Regardless of which applications prove feasible, growing transgenic pharmaceutical plants is a good technology to develop.

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