Talking Biotech 059 Increasing Photosynthesis Efficiency

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Now here's your host, Hi everybody, and welcome to the Talking Biotech Podcast. It's the weekly podcast where we discuss contemporary issues in science and technology, with a focus on biotechnology— new innovations that can help people and the planet. I'm Kevin Folta, and today it's really a pleasure to be able to speak with a scientist who's made some pretty big waves in his career, but most recently in the last, last week. We've understood that photosynthesis has long been the holy grail of plant biology in terms of can we manipulate it, can we make plants more efficient. And this last week in the, in the journal Science, Dr. Stephen Long from the University of Illinois and University of Lancaster in the UK published work that shows that there is more latitude And how we may be able to get more from this system. And Dr. Long is a renowned scientist, a fellow of the Royal Society, but in 2016 was designated as one of the 250 most influential scientific minds. And it's an objective measure of their impact based upon publication. And that's a, that's a real honor and something that I know I check it every year and never even come close. But thank you very much for being with us, Dr. Long.

Thank you.

Thank you.

And so just to start off, could you please talk about what your laboratory does, the many areas of research that you conduct?

Yeah, the primary work of our laboratory is really looking at the process of photosynthesis, both from a theoretical viewpoint and a practical viewpoint. So in the theoretical work, we're modeling the process and looking at where we might be able to gain efficiency in the conversion of sunlight right the way through to carbohydrates. Where we see the most promising opportunities, then we're manipulating those genetically to really see, does this result in an increase in photosynthesis and productivity?

And when we talk about photosynthesis, and this is something that I know that many people have a pretty good idea, at least as to what it is in theory, and, and that it's the way in which plants are harnessing light to do some work and build structures and have metabolism. But with as much as we know about this process, how much more latitude is there? I mean, where are the inefficiencies?

Well, if we look at crop photosynthesis overall, really our best crops, you know, most elite cultivars Are converting the solar energy they receive into plant biomass at an efficiency of around about 1 to 2%. But if we look at the theoretical conversion efficiency, that should be much closer to 10%. That's conversion of visible solar radiation into biomass. So there should be a lot of latitude there to improve productivity through photosynthesis.

And so where are we losing it if there's a big difference between what we're seeing and what's theoretically possible?

We lose it at many points. The process of photorespiration, which burns off a significant amount of the carbon that's assimilated in C3 crops. C3 crops include soybean, wheat, rice, cassava, most of our legumes. So that is a major inefficiency. The enzyme which catalyzes the conversion of carbon dioxide or fixation of carbon dioxide, we know to be quite inefficient as well. And in relation to the Science article, we also lose efficiency when We have fluctuations in the environment, particularly light. So if light levels drop or rise, it takes some time for photosynthesis to actually adapt to that change. And so we're losing productivity at all of those points.

And really, it's that last step that your paper deals with. But where does— how exactly does a plant lose that efficiency? And, you know, what's a good analogy maybe between that, how that inefficiency manifests in the plant?

Yes, it's rather like, you know, say we, we go out into the sun and we— it's too bright, we put on our sunglasses, and then we go into the shade and it takes us a while to take our sunglasses off. This is rather what— like what a leaf is doing. Crop leaves in full sunlight are receiving far more light energy than they can actually use. If they don't dissipate that excess energy, it actually becomes damaging. So it will cause oxidation, almost bleaching, you know, rather like if we leave our clothes in the sun for a long time. So the leaf protects itself by developing a change which dissipates that excess energy as heat. Now a cloud comes along and the leaf is now limited by light. However, even though it's limited by light, it carries on losing a large piece of that absorbed light heat, even though it could now use it all in photosynthesis. And it takes minutes, can take over half an hour, for the leaf to adjust back so that it's using that light at maximum efficiency. And so we'd identified that as a major problem in theory. And then working with Chris Niogi at the University of California, Berkeley, We worked out 3 proteins that we thought from theory would accelerate this recovery, and so we increased the amounts of those proteins in tobacco, grew those eventually after many tests in the laboratory, grew those in field trials, and we saw the predicted increase in productivity.

And was it an increase of all 3 genes in the plant that were overexpressed, or was it just maybe one or another that seemed to have a positive effect?

No, it required all 3 genes.

And so when we talk about how these 3 genes help with that process, is there a way to explain how they do it? Like, what is the mechanism, maybe without getting into the real deep minutiae of non-photochemical quenching. But how, how do they— how does it work? How does it allow the plant to recover faster?

Sure. This— during the development of this protection, which tends to occur quite quickly, the xanthophyll violaxanthin is converted to zeaxanthin. And we know that that zeaxanthin is is a very important element in inducing this non-photochemical quenching, i.e., the conversion of absorbed light into heat. And so once the leaf goes into shade, that zeaxanthin is converted back to violaxanthin, and they interact with a third protein that we call PSBS. So we've basically upregulated the enzyme that converts violaxanthin to zeaxanthin, i.e., zeaxanthin being the protective compound. And we also upregulated the enzyme which converts zeaxanthin back to violaxanthin. So basically we've accelerated that cycle of conversion between violaxanthin to zeaxanthin and back to violaxanthin. We could, of course, have accelerated it by just upregulating the enzyme which converts zeaxanthin to violaxanthin. But then what that would mean is the leaf couldn't protect itself. So by upregulating both, the leaf can protect itself quickly, but it can also remove that protection, if you like, the sunscreen, very rapidly as well.

I see. So that was, that was the one part that even, even in thinking about this wasn't 100% clear for me, but now it makes really good sense. We'll take a short break here. This is a conversation with Dr. Stephen Long, who's a professor of crop sciences at the University of Illinois and University of Lancaster in the UK. We're talking about how do you make photosynthesis more efficient and Keying off of points made in this week's Science magazine. We'll be right back in just a moment.

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Thank you.

Bye.

So we're back on the Talking Biotech podcast today, speaking with Dr. Stephen Long, who's a professor of crop sciences at the University of Illinois and University of Lancaster in the UK. And today we're talking about how do you make the process of photosynthesis more efficient. And in the second part of the podcast, we'll talk a lot about why that matters and what are some of the long-term possibilities if we can develop crops that have a better capacity of fixing carbon by using light. So maybe the next experiment that people— next question people would like to know is, why were the experiments done in tobacco?

Yes, yes, I realize that sounds odd. Tobacco is very easy to genetically change. And so that was one of the reasons why we use tobacco. The other is, of course, it is It is a crop. It produces a lot of leaves, which is very important for the traits we're looking at because this trait is engineering the ability of the plant to adapt to shade. And of course, leaves shade each other, and that's dynamically changing as leaves move in the wind, as the sun crosses the sky, and so on. And so unlike our other model, plant Arabidopsis, tobacco is a real crop and a good proxy for other crops.

And maybe another interesting question along that line is, think, what about plants that, say, live in a canopy, like, and have to deal with things like sunflex, like Oxalis, where here's a plant that is— has to be able to protect itself by having physical movement of the leaves, and then gradually reset. Have these kinds of processes been explored in those kinds of organisms where maybe they have novel ways of solving the problem?

Well, we, we do know that all flowering plants use this same mechanism of protecting themselves against excess sunlight. Certainly, it'd be an interesting question as to whether plants such as Oxalis have maybe already achieved this upregulation that we've conducted. But as far as I'm aware, that's not been investigated.

Oh, cool. Well, next idea, right?

Yes.

Well, one of the really nice things about your work is that, you know, many of us, we do these experiments and we publish our first trials from, say, chambers or from work in the laboratory. But your work was actually done in the field. And what did you actually find when you translated these results to an actual field situation?

Well, we've— as probably anyone who's conducted a field experiment knows, they don't always go easily. And in fact, we, after seeing promising signs in controlled environments, we moved to the field. We actually did our first field trials in 2014. And these are replicated field trials. So basically you've got several plots of each of your genotypes and of course the untransformed material as well. And we got our first transformants, first genetically changed plants. We tested in 2014 and we did see a stimulation of yield then. Then we wanted to repeat that in 2015. with a more elaborate experiment. Unfortunately, Illinois received its highest rainfall on record in the beginning of June, and that completely washed away our plots. So we then had to repeat that this year. And this year we saw very clearly— we got 3 sets of plants that have been genetically modified, each upregulating these 3 proteins and the original unmodified plants. And the modified one showed between a 14 to 20% increase in productivity. And that, of course, was statistically very significant.

And how does that translate when we look at it in the context of food security and long-term sustainability? I mean, we know there's projections in food demand that are coming. How can this really help?

Well, as I mentioned before, this process is common to all flowering plants, and other crops use exactly the same mechanism. So we're confident that this is going to give a boost in yield to food crops as well. If we project forward, the United Nations Food and Agricultural Organization have suggested that by the year 2050, we're going to need to be producing 70% more food than we are today. And in fact, David Tillman's group at the University of Minnesota have suggested that number is closer to 100%. These numbers come from the fact that population is rising, but also the global population is becoming more urban. Urban diets require more food because there's transport and storage involved. They also tend to require more dairy products and more meat.

Yeah, and all of those have significant impacts because you're trying— you now have to feed animals that, you know, the conversion of those calories in corn or soy or whatever they're feeding the animals to meat mass is pretty low. And so in some ways, many might argue that just by increasing photosynthesis and coming up with another solution like this, it really is delaying the issue of how do we deal with an unsustainable human population and demands from a growing middle class throughout the developing world? And how might you answer the critics on that?

Yes, I mean, that, that is certainly a point that is raised. But Of course, increasing productivity on the land that we're already using is not the only way we can obtain more food. If we don't increase productivity on the land we're already using, then what inevitably will happen is that agriculture will move onto yet more land, probably land which we really shouldn't be using for agriculture because it's more degradable, So that is going to do things like accelerate climate change, accelerate land degradation. So I think, you know, we can obtain more food in different ways. And I feel that boosting the productivity on the land we're already using is, is the best way forward.

Well, let's just say that those UN FAO projections aren't quite correct. And let's say that there really isn't a big increase in population and that that doesn't occur, then how is this technology still relevant?

Well, again, I think if we can produce more food on the land we're using now, that will give us a chance if, if actually we don't require the 70% increase. But we can still boost productivity on the land we're using today, then that will allow us to retire some of the land that we've already degraded in agriculture from agricultural use. It will release more land for other uses other than agriculture.

Yeah, I think those— that's been very well documented by agriculture economics folks who've Looked at that. If we look at your visions as to where this could integrate first in the issue of world food security, is there any place that you see as really the first target you would go after? Like, this is the problem I think would solve first if we could make this apply to a major food staple or maybe a biofuel crop. Where do you see that having the biggest impact right away?

Yes, I think the most important areas of the world to address are really sub-Saharan Africa and parts of South Asia as well, where we're seeing large growth in population, already quite high poverty levels. So I think the crops for those areas are cassava. You know, we've recently sort of pointed out that cassava, which is a major staple for much of sub-Saharan Africa, has hardly been improved as a crop. Rice, certainly, and probably cowpea, which is a major vegetable protein source again in sub-Saharan Africa.

So I think that these would be particularly important crops to target for And so that's the, the really the important part is in terms of feeding more people. What about the issue of climate change? Is it realistic that maybe these technologies could be brought into other non-food crops to help mitigate the effects of a warming planet?

Well, I've, I've also been a proponent, particularly in the United States, of Bioenergy. I mean, as as you know, in Florida there are large tracts of land in the Southeast United States which have adequate rainfall to support the growth of crops. Yet probably the soils are not really good enough to be competitive against the better soils of, for example, the Midwest. But these could support very important bioenergy crops such as sorghum, energy canes. And again, I think these technologies could be applied to those crops so that you could really get a very profitable bioenergy yield from, from that land. And we've, we've conducted calculations together with actually colleagues of yours at the University of Florida showing that you could provide a quite substantial amount of the US's energy use, particularly liquid fuels, from land in the southeast of the United States which has been abandoned from agriculture in the last 20 to 30 years.

That's really exciting because I'm always— I always think of You know, how do we create a carbon catcher forest? You know, how could we optimize natural spaces to maybe have slightly improved plants that still provide a way to sequester carbon, but maybe expanding ecosystems for wildlife and other applications? And it seems like a really interesting marriage between nature and technology, you know, and then of course the bioenergy side. Anything we can do to stop pulling carbon out of the planet. I know you've been working with Dr. Freddie Alpieter down here at the University of Florida. How are you using these processes to, say, boost the energy possibilities or the energy potential in a crop like sugarcane?

Yeah, so together with Professor Alpieter, we've been looking at the issue of could we make sugarcane into an oil accumulating plant. You probably know that most of the biodiesel in the United States is made from soybean oil. The problem with that is that soybean will give you about a barrel of oil per acre, so you're going to need many, many acres for biodiesel to ever really have an impact. However, if we could convert the sugar which sugarcane produces into biodiesel, i.e., engineer the plant so that it metabolizes that sugar into the oil that we can then convert to biodiesel, we would produce about 17 barrels per acre. And so that's what we've set about doing with Professor Altpeter, and we've had quite a bit of success. We've got quite a long way to doing that, and at the same time, we've also used the photosynthetic traits we've been talking about to boost the photosynthesis and productivity of sugarcane. And we calculated that on the land in the Southeast where you could plant sugarcane, and that extends quite a bit north of where we're growing sugarcane today in Florida and Louisiana, we could produce enough oil to cover about 2/3 of the country's use of diesel. So that would be a very substantial reduction in our greenhouse gas emissions. And of course, it will give us a source of oil, which is essentially inexhaustible.

You've got some really good leads on new technology that can help improve the process of of carbon fixation. But what is really— is your lab working on the next steps of translating this to crop plants now? Or, or, you know, what are the next real good steps?

Well, certainly with the work that was published in Science, we're now testing that in rice, cassava, and cowpea, these crops I mentioned, We should shortly be testing it also in corn and in soybean and probably in wheat as well. So that, that will be an important next step. But we are working on several other aspects of the photosynthetic process because we don't think this is the only one. I mentioned at the beginning photorespiration, and a colleague of mine at Illinois is working very closely on that. We're also looking at carbon metabolism, regenerating the acceptor for carbon dioxide, and we've got some quite promising leads on that as well.

Oh, very good. It's exciting to see the translation in the solving actual problems, and that, that's always exciting for me, and I know resonates with listeners. Really, kind of the, the last thing I'd like to touch on here today is I know you know the situation with Dr. Sharon Gray, and I was curious, would you mind maybe touching on the story a touch and giving us a little bit of background? It's something that I've blogged about and something I'd like our listeners to at least think about.

Sure, yes. I taught Sharon and her husband, Cody Markelz, as undergraduates, and then I served on both of their graduate committees. In fact, Sharon's major advisor was actually my former postdoc Andrew Leakey, so I often thought of Sharon as my academic granddaughter. Sharon was really one of the most exceptional students I ever taught. She was very passionate about her work, but such a nice person as well. She always had a smile, she always had a good thing to say about everyone, but she was as sharp as nails academically. And I think all of us who came in contact with her felt, you know, she is going to be a real star of the future. And she was a very successful postdoc in Siobhan Brady's laboratory in Davis, and both of them were actually in Ethiopia as part of a Gates Foundation-funded project when this freak accident happened that took her life away. But we Nevertheless, we feel that really the memorial to Sharon, I think, will be a great opportunity to follow some of the things that Sharon represented, in particular successful women scientists in plant biology.

And Sharon has a page that's been established to Help fund a Sharon Gray Memorial Scholarship, which will go towards educating women in science or for more training for women in science. And it's located at www.gofundme.com and then forward slash Sharon Beth Gray, G-R-A-Y. And I really do urge everybody to go there and make a donation in her name. It's one of these situations that I never met Sharon. But when you understand the impacts that our students and postdocs can make to our lives and to our programs, to our universities, how they enrich us, it sends shockwaves across the community to read that somebody who is engaged in simply advancing her career and advancing science and broadening opportunities for others in other nations would have such a tragic situation. I do urge others to, to please go there and, and make a donation. And, uh, let's make sure that her memory, uh, continues, um, uh, in a very positive way for women in science. So, um, so thank you for sharing that. I, I really do appreciate it. Uh, if people want to learn more about your program, Dr. Long, is, is there a, um, a website that you could refer them to, or are you visible on social media?

Sure. There's a website for our Gates Foundation project, so if you Google RIPE, that's R-I-P-E, at Illinois, you'll find that. The website is just ripe.illinois.edu. And also, if you want to look more broadly at what my lab does, you can Google Long Lab, L-O-N-G Excellent.

Now I'll make sure that all the links are available on this week's podcast-associated website. So thank you very much, Dr. Stephen Long. We really appreciate you joining us today on the Talking Biotech Podcast.

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