There’s a new wave coming in agriculture.
It’s not about herbicides. It’s not about pesticides. It’s about using the tools that plants already have so we can achieve higher yields and feed people. You’ll be hearing more and more about this in the next few years, you can be sure, but a significant story just came out to illustrate where this is going.
Agriculture stories don’t usually generate much buzz, but this one sure did!
NPR: Scientists have 'hacked photosynthesis' in search of more productive crops
BBC: Genetically modified 'shortcut' boosts plant growth by 40%
Reuters: Breakthrough in plant engineering could boost productivity, feed millions more
Financial Times: New light on photosynthesis raises hopes of new green revolution
Los Angeles Times: Scientists improve on photosynthesis by genetically engineering plants
The Conversation: Reclaiming lost calories: Tweaking photosynthesis boosts crop yields
New Scientist: Fixing a flaw in photosynthesis could massively boost food production
Newsweek: Engineered plants without photorespiration ‘glitch’ could help feed millions in coming decades
Gizmodo: Genetic modification turbocharges photosynthesis and drastically improves crop growth
Agri-Pulse: Fixing photosynthetic glitch could boost crop yields by 40 percent
That’s because people have been talking about doing this sort of thing for a long time, but didn’t quite have the tools and the understanding. But we’re finally starting to see it poke through into reality:
A research group from the University of Illinois has announced in the journal Science that they’ve grown plants in the field up to 40% faster by addressing a longstanding quirk in the way plants build themselves out of carbon dioxide. “In the field” is a big deal, by the way, because a lot of greenhouse results that look promising don’t translate to the field. They used tobacco plants because they are easy to introduce DNA into, and they are large so that differences are easy to spot.
Here’s a picture from the greenhouse study (which makes for better comparative photos than the crowded field) — an average unmodified plant vs. an average modified plant:
In the decades ahead, there are going to be more and more mouths to feed. Crop yields are creeping upwards, but not nearly fast enough to keep up with population growth. There isn’t going to be any more arable land, and we’re already fertilizing and watering the heck out of our crops.
So haven’t we exhausted all we can do to grow plants efficiently, then? Aren’t we out of ideas?
No!
The one area we haven’t done very much about is photosynthetic efficiency, or the percentage of absorbed sunlight energy that actually winds up as plant material. That’s well short of where it could be in many plants.
First of all, we need to stop for a second and acknowledge one really important player. Without this, you and I wouldn’t be here, simple as that. It’s the most abundant protein on the planet. It’s called ribulose-1,5-bisphosphate carboxylase/oxygenase, or Rubisco for short.
Rubisco has one job. That’s to take a molecule with 5 carbons and attach carbon dioxide to it, making it a molecule with 6 carbons. You and I could not strut around with all of our big carbonaceous molecules if Rubisco didn’t do that. That 6-carbon molecule splits into two 3-carbon molecules, and those go on ultimately to make all sugars, proteins, fats, heme, hormones, steroids, you name it. No Rubisco, no people.
Like any friend, though, Rubisco isn’t perfect. It has one major flaw that holds it back from being as effective as it could. It’s promiscuous. In addition to reacting with carbon dioxide, it reacts with oxygen. Left unsupervised, it does that about ¼ of the time. And that’s a problem, because when Rubisco reacts with oxygen, it makes one 3-carbon molecule that is OK, but also a 2-carbon molecule that is essentially toxic waste.
For years, people tried to get Rubisco to stop doing that, but they couldn’t. If it were as simple as tweaking the protein sequence of Rubisco, nature would have figured that out a long time ago. But no known Rubisco from anywhere can avoid this problem. So we’re all stuck with this fact.
Nature has gone to great lengths to get around this problem. Photosynthetic plankton (who need to compete hard for carbon dioxide) have constructed little compartments to stash Rubisco in, so that oxygen can’t get to it. These are called carboxysomes:
This is one hell of a complicated solution, but it works. It’s convincing evidence (to me, at least) that Rubisco itself can’t be fixed. I mean, why would plankton go to THIS MUCH TROUBLE if they could have just tweaked Rubisco a little? Anyway, no oxygen can penetrate these little granules, but carbon dioxide (in the form of bicarbonate) can. That’s how these plankton avoid the toxic waste problem. They simply don’t let oxygen anywhere near Rubisco.
People are trying to reconstruct these carboxysomes in plants, and it’s really hard, but they’re making good progress on that. This is all part of that new wave I was talking about earlier. And it’s coming, too.
Some higher plants (called C4 plants) have gone so far as to keep Rubisco in separate types of cells altogether and protect those cells from oxygen. Other types of plants called CAM plants only let carbon dioxide in at night and stash it away as malic acid, then during the day they close their pores and release the carbon dioxide from malic acid so it’s concentrated around Rubisco. If this sounds like a lot of trouble to go through, it is. C4 and CAM plants are less efficient under most circumstances.
Most plants aren’t C4 or CAM plants, though. Most plants are C3 plants, and they don’t do anything to rein in Rubisco’s bad habits! They just let Rubisco run into oxygen all it wants! But then they have to clean up the mess. That is hard to do, and this diagram will prove that to you:
When Rubisco reacts with oxygen in C3 plants, our toxic waste molecule is glycolate, which you see circled in orange in the picture. If we leave the plant to its own devices, it’ll send glycolate out of the chloroplast (where Rubisco lives) and on to a complicated series of energy-sapping reactions just so it can be converted back into a plant-friendly molecule.
The +40% researchers’ breakthrough was eliminating all that by sweeping up glycolate right where it’s made. They tried three different approaches, labeled “1” to “3” in the picture. Each arrow is a protein that catalyzes the reaction that’s shown. Each of those proteins is encoded by a gene. Their best plants had pathway “3”, which takes the glycolate and just breaks it down to carbon dioxide, avoiding all the complication and, to boot, increasing the carbon dioxide concentration near Rubisco, so that Rubisco has less oxygen around to bother it. These researchers imported their genes from other organisms, so yes, we do have GMOs here.
But the REALLY good news is that all the genes in pathway 3 CAN BE FOUND IN PLANTS ALREADY. That means that in principle this can be done WITHOUT MAKING GMOs. The key plant proteins just don’t happen to live where Rubisco lives (in the chloroplast), but with a few tweaks they can be redirected there. We don’t have to import anything from any other organism. No Frankenstuff here.
But wait a minute, you’re saying. If this is so efficient, and plants have all the genes to do it, why didn’t they just do it themselves? Mostly it’s because plants don’t care what you want out of them. You want big juicy fruits and seeds, but they don’t care about you. They care about making fruits and seeds that have enough nutrients to get germination, and that’s it. They didn’t evolve to make you a sandwich. Their carefree C3 ways have been sufficient to meet their needs, even if you’re not on board.
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40% bigger tobacco plants! Does this solve all our problems? No, of course not. When this is tried in food crops, it’ll probably work in some but not others. Bigger leaves don’t always mean more grain.
But don’t worry. There are a whole lot of other things going on in this area, and you’ll hear about them before long. Trust me; the new wave is coming.