An international team of scientists has uncovered a surprising molecular strategy used by a rare group of land plants. The finding could one day help researchers redesign important crops such as wheat and rice so they convert sunlight into food far more efficiently.
The research was led by scientists at the Boyce Thompson Institute (BTI), Cornell University, and the University of Edinburgh. It addresses a major limitation in agriculture involving Rubisco, the enzyme that captures carbon dioxide from the air during photosynthesis.
Rubisco and the Limits of Photosynthesis
Rubisco plays a central role in life on Earth, but it has a major flaw. The enzyme works slowly and can easily interact with oxygen instead of carbon dioxide, which wastes energy and reduces how effectively plants grow.
“Rubisco is arguably the most important enzyme on the planet because it’s the entry point for nearly all carbon in the food we eat,” said BTI Associate Professor Fay-Wei Li, who co-led the research. “But it’s slow and easily distracted by oxygen, which wastes energy and limits how efficiently plants can grow.”
Over time, some organisms have evolved ways to overcome this inefficiency. Many types of algae, for example, place Rubisco inside small structures in their cells called pyrenoids. These microscopic compartments concentrate carbon dioxide around the enzyme, allowing it to operate more efficiently.
Researchers have long hoped to introduce this type of carbon concentrating system into food crops, which do not naturally have pyrenoids. However, transferring the complex machinery from algae into land plants has proven extremely difficult.
Hornwort Plants Reveal an Unexpected Strategy
A breakthrough came when scientists examined hornworts, the only land plants known to contain carbon concentrating compartments similar to those found in algae. Because hornworts share a closer evolutionary relationship with crop plants than algae do, researchers suspected their molecular tools might be easier to transfer.
What they discovered turned out to be very different from what they expected.
“We assumed hornworts would use something similar to what algae use — a separate protein that gathers Rubisco together,” said Tanner Robison, a graduate student working with Li and a co-first author of the paper. “Instead, we discovered they’ve modified Rubisco itself to do the job.”
The RbcS-STAR Protein and Rubisco Clustering
The key element is an unusual protein component the researchers named RbcS-STAR. Rubisco itself is built from both large and small protein pieces. In hornworts, one version of the small component includes an extra segment called the STAR region.
This additional tail behaves like molecular velcro. It causes Rubisco proteins to stick together and form clustered structures inside the cell.
To determine whether STAR could function in other plants, the researchers ran several experiments. They first introduced the RbcS-STAR component into a closely related hornwort species that does not naturally form pyrenoids. After the change, Rubisco shifted from being spread throughout the cell to forming concentrated structures resembling pyrenoids.
The scientists then tested the same idea in Arabidopsis, a plant widely used in laboratory research. Once again, Rubisco gathered into dense compartments inside the chloroplasts.
“We even tried attaching just the STAR tail to Arabidopsis’s native Rubisco, and it triggered the same clustering effect,” said Alistair McCormick, professor at the University of Edinburgh, who co-led the research. “That tells us STAR is truly the driving force. It’s a modular tool that can work across different plant systems.”
Potential Path Toward More Efficient Crops
The fact that this mechanism works across different plant species makes the discovery especially important for agriculture. It suggests that scientists may be able to trigger Rubisco clustering in crop plants simply by adding this universal velcro component.
However, researchers emphasize that more work is still needed. In addition to clustering Rubisco, plants must also efficiently deliver carbon dioxide to the enzyme.
“We have built a Rubisco house, but it won’t be an efficient house unless we update the HVAC,” said Laura Gunn, assistant professor at Cornell University, who co-led the research. The team is now working to address this challenge.
A Step Toward More Sustainable Food Production
Even so, the discovery represents an important advance in the effort to improve photosynthesis. Increasing photosynthetic efficiency even slightly could raise crop yields while reducing the environmental impact of farming. This goal is increasingly important as scientists seek ways to produce more food sustainably for a growing global population.
“This research shows that nature has already tested solutions we can learn from,” said Li. “Our job is to understand those solutions well enough to apply them where they’re needed most — in the crops that feed the world.”
The study was published in Science, with equal contributions from four early-career scientists: Tanner A. Robison, Yuwei Mao, Zhen Guo Oh, and Warren S.L. Ang. The corresponding authors were Laura H. Gunn, Alistair J. McCormick, and Fay-Wei Li.
