RUBISCO, which helps make photosynthesis happen, is the most plentiful enzyme on the planet. But it's not the most efficient. Can a team of researchers give it a boost?
Meet the Enzyme Driving Photosynthesis
Published: February 22, 2021
David Pogue: Usually you hear about efficiency, like of a gas engine, measured in terms of percentage, how much fuel is ultimately converted to energy. What’s the percentage efficiency for a plant?
Lisa Ainsworth: Well, in terms of how much of the light energy it turns into sugar, it’s pretty low maybe around three percent%.
David Pogue: Three percent? That’s terrible. .
Lisa Ainsworth: That’s the plan.
David Pogue: To improve photosynthesis, two researchers, Amanda Cavanagh and Paul South, have focused on one of its key molecules. It has a very catchy name.
Amanda Cavanagh: So the molecule is what we biologists call an enzyme. And so it does the work. Enzymes are like biological workers. And the enzyme’s called RUBISCO.
Paul South: It’s RUBP, or ribulose bisphosphate carboxylase oxygenase.
Amanda Cavanagh: And it’s, for most plant biologists, one of our favorite enzymes on the planet.
Paul South: Yeah RUBISCO is our shortened term for it.
David Pogue: Mainly because it’s fun to say.
Amanda Cavanagh: Well it’s super fun to say.
David Pogue: RUBISCO.
Amanda Cavanagh: Of course. RUBISCO. But, it is also a really cool enzyme because it makes life on Earth possible.
David Pogue: RUBISCO may not look so special but it is arguably the most important enzyme on the planet because of its critical role in photosynthesis. RUBISCO’s job is to grab a molecule of carbon dioxide and feed it into a molecular machine that’s building carbon chains. That means, any carbon atom, that’s part of any plant anywhere got there thanks to RUBISCO, or one of its close variants. And because we eat plants or animals that ate plants that also includes just about every carbon atom in your body—all approximately eight hundred, million, billion, billion of them. That’s 26 zeroes. Not bad RUBISCO, not bad.
Paul South: Yeah so if it’s ever come from a plant, it had to have gone through that enzyme of RUBISCO.
David Pogue: That’s wild. How come there’s not a memorial to RUBISCO in Washington? It seems like, sort of important.
RUBISCO is important and that’s why it’s the most plentiful protein on Earth. But just because you’re important, doesn’t mean you’re entirely competent.
Paul South: It’s, in this case, not the best enzyme in the world.
Amanda Cavanagh: It’s got a hard job, so it’s doing its best, but at the same time it exists in an atmosphere that’s not predominantly carbon dioxide, it’s mostly oxygen.
Paul South: And about one in every four or five reactions it grabs oxygen instead of carbon dioxide.
David Pogue: That’s right. RUBISCO screws up about a fifth of the time. Instead of attaching a carbon dioxide, it attaches an oxygen molecule. And that’s trouble.
You’re saying nature has created a screwed-up little worker enzyme?
Paul South: Yeah so 400 million years ago, when this enzyme evolved, there wasn’t very much oxygen in the air.
David Pogue: All right. So I’m the little RUBISCO enzyme and like on the conveyor belt here. And like carbon dioxide, carbon dioxide, carbon dioxide, carbon dioxide, oxygen and I- I don’t notice I accidentally grabbed oxygen out of the box.
Paul South: And it produces compounds that are inhibitory to photosynthesis, so it kind of starts to shut things down.
David Pogue: I mean it’s been going on for billions of years and nobody has cared.
Amanda Cavanagh: Yeah, well..
David Pogue: I mean, it all basically works.
Amanda Cavanagh: Photosynthesis right now is sort of a victim of its own success, RUBISCO certainly is. So by oxygenating the atmosphere via photosynthesis, you now have a huge amount of oxygen in the atmosphere but you need a carbon dioxide to make the reaction work.
David Pogue: So what happens when RUBISCO screws up? The result gets shipped out through a couple other parts of the cell to where the mess is taken apart and recycled, all of which consumes a lot of energy.
So, if you could fix this inefficiency problem, the plant might make more soybeans, corn, whatever it is?
Amanda Cavanagh: That’s exactly it. Then they will have that energy to put towards something that we will consider useful like making more food for us to eat.
David Pogue: Is this just a crazy theory or is this some indication that this could actually work.
Amanda Cavanagh: There is quite a bit of evidence that this is working. So right now, we have this tested in a couple of model species.
David Pogue: It is tropical in here.
Amanda and Paul take me to the greenhouse to see one example. Using two genes one from algae and the other from a pumpkin, they’ve modified tobacco plants to address RUBISCO’s “sloppy work.”
And why are we using tobacco plants?
Amanda Cavanagh: Yeah tobacco’s a really useful model crop for us.
David Pogue: Why tobacco? Turns out it’s one of the easiest plants to genetically manipulate which makes it a common test subject.
Paul South: They have definitely shown improvements in plant growth and total biomass, and we’ve been studying the rates of photosynthesis, and we are pretty confident now that our model crop is successful in this pathway, and now we’re really interested in moving these into something we like to eat.
David Pogue: Reducing the energy penalty crops pay for RUBISCO’s mistakes could be huge. In soybeans, a 25% reduction could result in plants that produce more than 60 million more bushels a year.
Amanda Cavanagh: This to a lot of people is an idea that might be out there, but if we can get it, if we can get this moonshot approach to work, then we’re going to have more food. And so that’s really what drives what I do.
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