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Rice production needs to see a 50% increase by 2030 to keep up with population growth, but as the climate warms, rice plants will likely become less efficient. Fortunately, scientists are working on a pretty clever potential solution.

Hosted by: Olivia Gordon

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Sources:

http://www.fao.org/newsroom/en/focus/2004/36887/
http://www.thenewhumanitarian.org/report/91012/asia-key-facts-about-rice
https://c4rice.com/
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https://academic.oup.com/jxb/article/52/suppl_1/381/2897250
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3244903/
http://symposia.biochemistry.org/content/61/1
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https://c4rice.com/the-science/photosynthetic-pathways/
https://academic.oup.com/pcp/article/53/12/2030/1869922
https://www.cell.com/molecular-plant/pdf/S1674-2052(14)60940-0.pdf
https://c4rice.com/the-science/engineering-photosynthesis-what-we-are-doing/
https://c4rice.com/the-project-2/project-goals/
https://thericejournal.springeropen.com/articles/10.1186/s12284-014-0029-y

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https://commons.wikimedia.org/wiki/File:Cross_section_of_Arabidopsis_thaliana,_a_C3_plant..jpg
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(Intro)

More than half of the world's population depends on rice to survive, but as the population grows, that demand is becoming harder to meet.  Right now, rice yield just isn't growing as fast as the global headcount, and there's only so much room for more farms, so unless we figure out an alternative, we might run into a serious problem.  Thankfully, this is something researchers are already working on and some of them have come up with a pretty clever potential solution.

To grow more rice, they're trying to entirely change the way the plant photosynthesizes.  Normally, rice uses what's called C3 photosynthesis.  This method is used by the overwhelming majority of photosynthetic life on Earth and it first evolved at least 2.7 billion years ago.  There's a lot to say about how this method works, but there are only a few things you need to know to understand rice.  

The first is that all the steps in C3 photosynthesis take place in the same area.  It all goes down in spongy tissues between the leaves' veins.  The second thing is that this process is kicked off by an enzyme called RuBisCo.  RuBisCo uses water, carbon dioxide, and energy to create an acid with three carbon molecules, hence, C3.  Then, that acid undergoes a bunch of other reactions and ultimately becomes a sugar that feeds the plant.  C3 photosynthesis is hugely important.  It's responsible for the millions of tons of rice we eat every year, along with most of our other food energy, and generally, it works pretty well, but it's not perfect, especially when it gets hot.  Honestly, it's mostly RuBisCo's fault.

As the temperature increases, RuBisCo doesn't always process carbon dioxide when it's trying to make that three carbon acid.  Instead, it can sometimes process oxygen.  That wastes energy and water but doesn't actually create anything helpful for the plant and it's a problem especially relevant to rice.  As the climate warms, rice plants will likely become less efficient, wasting all kinds of energy that could otherwise be turned into food.  It doesn't have to be this way, though, because C3 isn't the only kind of photosynthesis.

About 3% of terrestrial plant species, including some crops like corn, use a method called C4.  Kind of like C3, it gets its name because it starts off by creating an acid with four carbons, but the way it makes and processes that acid is very different.  For one, RuBisCo isn't involved in creating that molecule.  A different enzyme is responsible for that, one that can only process CO2.  Secondly, once that acid is created, it doesn't stay in the leaves' spongy tissue.  Instead, it's moved to a group of cells called a bundle sheath.  There, it's broken back into CO2, RuBisCo takes over, and everything proceeds as normal.  

This process may sound like it would decrease efficiency, but it actually helps things flow more smoothly.  It sticks RuBisCo in its own little corner and only gives it carbon dioxide molecules.  That means there's no risk of the enzyme going rogue and processing a bunch of oxygen, so the plant as a whole is much more efficient.  

Now, C4 does have some downsides, like it's not as efficient in cooler temperatures, but in general, it seems like it would be great if we could engineer at least some rice plants to use this method.  That would just require, you know, dramatically changing the way they use photosynthesis.  Not a big deal or anything.  Maybe, though, it's not as impossible as you might think. 

See, scientists have noticed that evolutionary pressure was so strong that C4 and the structures that make it possible evolved multiple times, more than 60, in fact.  This suggests that going from C3 to C4 might not be that much of an ordeal.  Instead, researchers are hoping it may just require some relatively subtle changes to the plant's genetic code.  So maybe to convert a plant like rice to a drought-tolerant, ultra-efficient C4 machine, you might just have to tweak a few parts of its DNA.  That's what scientists are investigating right now.  

By studying plants like corn, they're trying to identify the exact mutations responsible for C4 and then engineer those changes into plants like rice, and they're making some good progress.  For example, some evidence has suggested that the anatomy needed for C4 might just be the result of genes for veins being expressed in the leaves as well as the roots.  So now it's just a matter of figuring out how to make that happen in actual rice plants.  

This might sound like a whole lot of trouble just to mess with how a crop works, but one team tackling this predicts that C4 rice would have 50% more efficient photosynthesis and would use half as much water as normal rice.  It should even require less nitrogen.  Some of the researchers involved in this work estimate that this could boost global rice yield by 30-50%, which would be amazing.  After all, rice production needs to see a 50% increase by 2030 to keep up with population growth, so C4 rice could be the answer we need.

Of course, even if C4 solves our rice problem, there will be plenty of other challenges to tackle in 2030 and many of them will likely be studied using artificial intelligence.  AI can seem daunting, but there are great ways to learn about it, like Brilliant's course on artificial neural networks.  The course starts with the basics and eventually gets you to more advanced techniques.  Along the way, there are all sorts of helpful diagrams and almost 30 quizzes where you can test your knowledge.  Brilliant also has a bunch of other courses about science, engineering, and math and they're working on new content all the time.  Much of it is also available offline through their app.  If you want to learn more, you can go to brilliant.org/scishow.  If you're one of the first 200 people to sign up at that URL, you'll get 20% off an annual premium subscription.

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