From Grist, March 13:
Scientists studying the plant have discovered a new way to boost the efficiency of rubisco — the enzyme that powers life on Earth — and hope to transfer the trick to crops.
You are here because of a single, all-important enzyme. But don’t look inward to find ribulose-1,5-bisphosphate carboxylase/oxygenase, known more mercifully among scientists as rubisco. Instead, look to the food you eat and the trees that manufacture oxygen, as this is the protein that makes photosynthesis possible. Without it, life on Earth as we know it would not exist.
For all that heavy lifting, rubisco is remarkably inefficient. The enzyme converts carbon dioxide into sugars that sustain plants. But it is easily confused, and will react with oxygen in a process that creates a toxic byproduct, wastes energy, and limits how quickly plants can grow. (Which is not to fault rubisco: This is a very difficult reaction to pull off, and just look at how many plants have been getting it right for hundreds of millions of years.) That includes the essential crops that feed humanity — grains, vegetables, fruits — that could theoretically grow better if their rubisco worked more efficiently. This problem becomes more urgent as global temperatures rise, because this essential protein gets even less efficient in the heat.
Enter the hornwort. This tiny plant, which is related to mosses, grows as a green sheet on the ground. It’s the only known land plant that’s found a way (evolutionarily speaking) to supercharge rubisco by concentrating CO2 around the enzyme.
Now, an international team of scientists says it has figured out how hornwort does this, and how it may be able to apply that superpower to crops. That could mean massively improved yields, so farmers wouldn’t need to cultivate as much land to grow the same amount of food. “It’s very impressive,” said Robert Wilson, a biochemist who studies rubisco at the Massachusetts Institute of Technology. (Wilson wasn’t involved in the research but does collaborate with one of the scientists.) “It’s interesting, because it’s a completely new and novel mechanism through which an important aspect of rubisco biochemistry occurs.”
Scientists have long known that some species of algae also improve the efficiency of rubisco. Inside their chloroplasts — the structures within cells where photosynthesis hums along — they’ve developed specialized compartments known as pyrenoids. These concentrate CO2 around the enzyme, minimizing its reaction with oxygen. “It prevents rubisco from touching oxygen, because it puts it into a house and then pumps a bunch of CO2 into the house,” said Laura Gunn, a synthetic plant biologist at Cornell University and coauthor of a new paper describing the work. “So the rubisco is completely, completely saturated with CO2, and all the oxygen is outside the house.”
But because algae are so distantly related to the foods we eat, it would be challenging to genetically modify crops to mimic those pyrenoids. On the other hand, the hornwort is more closely related. These researchers discovered that it has a unique way of making these pyrenoid structures, due to a protein they’re calling RbcS-STAR. Rubisco in all plants is made of proteins, but the hornwort’s version has an extra “tail,” which helps tether the enzymes together to create compartments into which CO2 pumps, increasing the efficiency of the process....
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