The C4 Rice Project

We find out how changing the way rice photosynthesises could lead to better crop yields...
07 March 2013

Interview with 

Helen Woodfield, University of Cambridge




An international team is currently working to secure the future of the staple food for 60% of the globe, rice. Naked Scientists Kate Lamble spoke to one of the members of the team, Helen Woodfield who's completing her PhD at the University of Cambridge.

Helen - So, I work on the C4 Rice project which is a large international corporation of people who are essentially working, trying to increase the yield of rice.  So, more rice grains power plant.

Kate - So, why is it so important for us to increase the yield of rice?

Helen - As I'm sure, most people know the population of the world is increasingC4 Rice Project at a much greater rate that we can keep up with in terms of food production. In 50 years' time, if population increases carry on in the projected way, then we're not going to cope. So, we need to be able to have more food.

Kate - So, how are you going about trying to increase the yield of rice?

Helen - There are different forms of photosynthesis. Most people have studied photosynthesis at school and it's a process where sunlight is converted from CO2 into sugars. Now, this process is inherently inefficient and there are various plants which have evolve mechanisms which will overcome this floor.  So yeah, the whole point of this project is try and put this specialised pathway called C4 into rice which is a C3 plant.

Kate - At school, I got told about photosynthesis, there weren't different types of photosynthesis. How does this C4 type of photosynthesis differ from the C3 photosynthesis?

Helen - So, in C3 photosynthesis, you have an enzyme called RuBisCO. That enzyme is a protein which catalyses the reaction. It turns one thing into something else. Now, the way that RuBisCO works is it takes CO2 and it turns it into something else, which will then go on and be processed into sugars. So, that's what happens in every plant that you look at. Now the problem is that the CO2 is a very similar structure to oxygen. If you look at the two molecules, they're very, very similar. So, RuBisCO sometimes can't tell the difference and it uses oxygen instead.

So, RuBisCO is like an old blind cook. It can't tell the difference between salt and sugar. Sometimes he uses salt, sometimes uses sugar, and obviously, the cake is going to be really different. The sugar ones are great, that's the CO2, the salt ones, really bad. So, what C4 does is it employs as a helper and this helper is a different enzyme. It lives in a different room and he can tell the difference. It only takes the sugar off the shelf. So, it only takes carbon dioxide, leaves the oxygen, and he passes the sugar to the cook in the other room where he's just happily away making cakes. And because he haven't got the option anymore, he only uses the sugar. So you only get good cakes and so, you only get the beneficial reaction.

Kate - What kind of plants have this more effective form?

Helen - Things like Maize, sugar cane, generally grasses. So, if you're watching a documentary which has a shot of Africa, all of the grasses that you see in that shot will be C4. But in terms of commercial applications, obviously, Maize is the highest one.

Kate - So, why don't we just get the world to eat more Maize?

Helen - So, I hadn't really appreciated how important rice is. I went to the Philippines as part of my project to work for a bit and everyone was very distressed I wasn't eating my 5 rice-a-day. I was like, "I can't deal with this, there's so much rice", but it is a massive cultural thing and although Maize is coming more and more into the food chain, bettering the crop that's already grown is much better option.

Kate - How can you make rice change the way it photosynthesises?

Helen - The approach that we're taking is we're actually copying the genes out of Maize. So, those genes, we're hoping that if we took the Maize versions the C4 ones, and we put them in rice, that they'll still act in a C4-like way.

Kate - And what results have you seen with that? Have they started to take on some effect of the C4?

Helen - The problem is, is that without the whole pathway, you're not going to ever achieve the end result. It's like putting in part of a painting and expecting someone to recognise it. We have to have the entire pathway and the anatomy altogether before I think we'll see any sort of improvements in photosynthesis. So, at this stage, we really are just playing around with trying to get the individual components in the right places at the right time, and then once we've got that sorted, we'll kind of build it all up, stack it altogether, and then make one plant that's got all of it.

Kate - It's quite a complicated process to essentially change the way that rice is set up. It must be quite an effective change for it to warrant this much effort.

Helen - Yeah, definitely.  We're predicting that if you put C4 into rice, then we'll have about a 50% increase in productivity. And the most compelling thing is that the C4 for photosynthesis has arisen at least 60 times across the evolution. The theory behind it is that if it's arisen so many times then trying to make rice to do it. Maybe it's not going to be as hard as we initially thought.

Kate - Why hasn't rice developed C4 photosynthesis itself?

Helen - The thing about the C4 pathway is that it does cost energy. So, you have to pay to pump the carbon around the plant in this specialised way. So, that's why you don't see C4 in this country for instance because you have this trade-off between the energy costs for running C4 and the energy cost for the photorespiration that you have if you don't have C4. And those costs change according to what the temperature is. So, in this country, there are 4, maybe 5 species which are C4, but all the rest are C3 plants, and that's because of the energy trade-offs. Why rice hasn't? I don't know because obviously, rice grows in the tropics which is quite hot.

Kate - If we're looking at this right and better in higher temperatures, does that mean that looking in the future with sort of climate change in the horizon that this might become applicable to more crops?

Helen - Definitely and the other great thing about C4 is because it's extracting CO2 from the atmosphere, it means that it can keep its stomata closed more. Stomata are basically little holes in the leaf through which gas can flow. But the other problem is that water loss happens through those holes. So, other than obviously reduces food quantities, we're really running out of water. and so, to make plants which are better at growing in low water conditions like C4 plants is also a huge benefit.

Kate - How far off are we from getting the C4 process into rice?

Helen - The overall outlook for the project is about 45, 50 years away, so it's definitely a long term project. A lot of people think, you're absolutely mad for trying this. It's so ambitious and we know so little about it really. When you think about the fundamentals of C4 and what controls it, we know so little still, but then if you didn't try, you'll never going to find out.


Add a comment