Is old-fashioned photosynthesis up to the task of managing the enormous amount of carbon (roughly 36 billion tons per year) that we're pumping into the atmosphere?
A biotechnology startup in California doesn't think so.
That's why researchers at Living Carbon have been hard at work manipulating arboreal DNA to make a new type of tree that more effectively captures atmospheric carbon and holds onto it for a very, very long time. And they've made a lot of progress.
Yumin Tao, the company's VP of biotechnology, leads the team that figured out how adding a few genes from pumpkins and green algae could supercharge photosynthesis, significantly increasing the amount of carbon an engineered tree can store in its tissues. IE sat down with Tao to discuss what his team has accomplished and how it might — might — help solve one of our planet's biggest challenges.
This interview has been edited for length and clarity.
IE: What is the science team at Living Carbon trying to do?
Yumin Tao: Our mission is really to use cutting-edge plant biotechnology to find a solution to climate change based on a form of nature.
We use all kinds of tools to improve carbon drawdown from the atmosphere and to sequester, or fix, the carbon in the form of plants. We also expand the life of the fixed carbon so that it doesn't get back to the atmosphere as early or as often as it normally does.
How are you engineering trees to suck up more carbon?
On a global scale, trees have already been doing a fantastic job of helping humanity to reduce carbon. In photosynthesis, carbon gets converted into sugars and nutrients for downstream usage by essentially all living organisms.
The biochemical basis of photosynthesis depends on a central enzyme called RuBisCo. RuBisCo essentially takes carbon dioxide from the air, fixes it, and converts it into all the biomolecules. However, RuBisCo also takes oxygen in place of CO2 in a reaction called oxygenation that produces a toxic byproduct called glycolate.
How does that influence a tree’s ability to pull carbon dioxide from the atmosphere and store it in its tissues?
Plant cells must undergo an energy-intensive and complicated process called photorespiration to break those compounds down. This not only wastes energy but also loses a lot of fixed carbon in the form of CO2, which gets released into the air again. It's a wasteful process that a lot of plants do.
The primary focus for carbon drawdown is really trying to tackle this problem, trying to reduce or inhibit or prevent photorespiration from happening in plants. Therefore, we channel this energy into plant growth.
How do you do that?
We engineered a bipartite type of technology. The first part uses a technology we call RNAi [RNA interference]. It can inhibit the expression of a glycolic transporter, which is what ordinarily sends glycolate out of the chloroplast for photorespiration.
The second part is TK. We want to engineer a TK for enzymes in the chloroplast that can then consume or convert glycolate back into CO2 within the chloroplast. By using a combination of both these approaches, we are able to reduce photorespiration.
How does reducing photorespiration affect the tree? Does it affect long-term carbon storage?
This strategy produces more biomass in the trees. It gives you more timber wood, but it doesn't increase the durability or increase the life of the carbon in its fixed form. We are heavily engaged in a number of research projects to find a solution to keep this fixed carbon in plants for longer. I can't talk too much about those projects yet.
Why are you using genetic engineering rather than traditional breeding methods to create these trees?
Traditional breeding methods have been a huge challenge in the forest industry because of a number of factors. Number one is that the life cycle of trees is very long compared to agricultural crops. It will usually take more than 10 years for a tree to flower and be ready for breeding. The next cycle takes another 10 years or more.
Number two, even if you can do breeding, the amount of improvement is very limited. Getting a one percent enhancement in productivity is huge.
In the experiments that we did — of course, they were greenhouse experiments — we showed more than a 50 percent biomass enhancement, which is probably unthinkable using traditional breeding.
Let's talk about that experiment. You and several colleagues shared the paper, which hasn’t yet been peer-reviewed, with the scientific community in February. What species of trees were you working on and why?
Poplar trees. The experiment reported in that paper serves as a proof of concept for the bipartite technology. We wanted to use a tree species that’s easy to handle with existing technology and that's already well understood by the scientific community.
The poplar is a model species for trees, and that's why we choose to work with it first.
What's different between your trees and regular poplar trees?
The tree that we created has an RNAi designed to target the glycolate transporters and reverse engineer TK, a two-enzyme shunt pathway. So that's the only difference between that one and the unengineered poplar tree.
What did you learn from the experiment?
First we wanted to know if our design was successful. Does the technology reduce the expression of glycolate transporter inside the poplar tree? We found that it’s working like a charm. We saw the reduction of glycolate transporter in the engineered tree.
We also have data to show that the shunt pathway we engineered in the tree is also expressing at a level within the desired range.
Does that mean Living Carbon can reliably make trees that suck 50 percent more carbon out of the air?
No. For every kind of engineering technology, you have a lot of complexity. For instance, where those genes are inserted? Do they interfere with the native metabolic flow?
We took those through a series of experiments. We used photosynthesis measurement tools to gauge if the trees are performing photosynthesis at an enhanced rate. Some trees that contain essentially the same genetic elements have different photosynthesis rates just because of interactions between the genes that we put in and the genes that occur naturally within the plants. They give you a different readout.
We went through a selection process and eventually discovered a number of plants that are showing the desired change at the molecular level and also at the physiological level. They showed enhanced photosynthesis. Eventually, they’ll accumulate more biomass in their stems and leaves. Some actually showed enhancement in roots. We were more than happy to see all those results.
Are you conducting tests in the natural environment?
We would like to make sure the performance that we observe in the greenhouse environment holds in the field. In order to do that, we collaborated with Oregon State University to conduct a field test of our trees. Acting as an independent third party, the Oregon State researchers will conduct the tests. Whatever results they find will be really, really informative and useful.
What’s the timeline for that experiment?
Our trees were planted there last July, so they’ve been growing for less than a year. The trees are looking good now.
It seems challenging to study the long-term effect of your technology on trees given they live so long. Will these trees perform as expected 10, 50, and 100 years in the future?
Yes, we can't evaluate our trees 100 years from now. We’re working with timberland farmers to plant our trees on their land. Some of those deals are secured already.
The field trial with Oregon State University is relatively short. It's going to be a four-year trial. The field testing with the farmers will be much longer.
Are you concerned about the effect these trees might have on the forest ecosystem? Will they have a new effect on other plants, animals, or fungi?
Given the changes we made to the trees and previous knowledge accumulated by the greater scientific community about what engineered plants do to the whole ecological system, we really don't see any huge risk that we need to deal with right now.
Of course, our trees haven't been planted in the environment yet, so there may be some unknowns. But right now, we can’t think of any.
Susceptibility to fungal infection is something that we're actually trying to find a solution to improve. We're hopeful that we'll have that kind of data soon.
Many people have voiced concern about the releasing genetically modified trees into the wild. How can you be sure that Living Carbon trees won't lead to serious unintended consequences?
We don't want to create something that is counterproductive in terms of the whole ecosystem. We actually want to help preserve the current ecosystem.
We really want to provide a natural solution to climate change, not something artificial and standalone that is just for our own human benefit. The solution that we're providing is really for the benefit of the whole ecosystem.
We think the trees we've created will not have any downside impact on the ecosystem simply because the trait that we engineered is essentially just collecting energy from the sun. We're not competing with animals in the forest. If we succeed in creating this fungal-resistant trait, you may argue 'Hey, you prevented a food source for fungi.' But there are plenty of plants in the forest that can provide a food source for fungi, so we really don't see that as a problem. I can't imagine a world that is just planted with Living Carbon's photosynthesis-enhanced trees. That's not the end goal for us.
What's your most ambitious target in terms of maximizing the amount of carbon that can be stored in a tree? Is there a biological limit?
That’s the longer-term goal that we at Living Carbon are trying to achieve. We want to increase the carbon drawdown and keep the carbon fixed for longer, hopefully in a permanent form that doesn't go back to the environment at all. So we are actively testing ideas around that angle, to provide a solution to permanent carbon storage. We are actively exploring ideas and concepts, and that's a long-term goal for the company.
Editor’s Note: This is a part of our series PLANET SOLVERS, where IE explores climate challenges, solutions, and those who will lead the way.
Check out the other stories here: a timber cargo ship that sails without fossil fuels, a hydropanel that makes drinking water from air and sunlight, a high-flying kite that could power your home, and a tower that turns pollution into diamonds.