An international team including researchers from Cornell University, the Boyce Thompson Institute, the University of Edinburgh, and others has uncovered how hornwort plants use a modified protein, RbcS-STAR, to cluster the key photosynthetic enzyme Rubisco into pyrenoid-like compartments. This mechanism boosts carbon capture and could enhance crop yields by up to 60 percent while reducing needs for water and fertilizers.
Rubisco, or ribulose-1,5-bisphosphate carboxylase/oxygenase, is the planet's most important enzyme for photosynthesis, fixing carbon dioxide into sugars that fuel plant growth and form the basis of the food chain. However, it is slow and prone to binding oxygen instead, especially in warming climates, leading to energy waste, toxic byproducts, and stunted growth.
Hornworts, small land plants related to mosses, overcome this using RbcS-STAR, a version of Rubisco's small subunit with an extra 'tail' or segment that acts like velcro or a tether. This modification clusters Rubisco enzymes into dense compartments akin to algal pyrenoids, concentrating CO2 and minimizing oxygen interference.
"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 Fay-Wei Li, associate professor at the Boyce Thompson Institute and Cornell University, co-leader of the study. "But it's slow and easily distracted by oxygen, which wastes energy and limits how efficiently plants can grow."
Unlike algae, which use separate proteins for clustering, hornworts modify Rubisco itself. "We assumed hornworts would use something similar to what algae use—a separate protein that gathers Rubisco together," said Tanner Robison, graduate student and co-first author. "Instead, we discovered they've modified Rubisco itself to do the job."
The team demonstrated RbcS-STAR's modularity by introducing it into a hornwort species lacking natural pyrenoids and into Arabidopsis, a model flowering plant. In both, pyrenoid-like structures formed—even when just the STAR tail was attached to native Rubisco. "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 and co-leader. "That tells us STAR is truly the driving force. It's a modular tool that can work across different plant systems."
"It prevents rubisco from touching oxygen, because it puts it into a house and then pumps a bunch of CO2 into the house," explained Laura Gunn, synthetic plant biologist at Cornell and coauthor. The researchers estimate this could boost crop growth and yields by up to 60 percent, allowing plants to close stomata more often to conserve water. It may also reduce reliance on energy-intensive synthetic fertilizers.
Challenges remain, including engineering efficient CO2 delivery to the clusters. "We have built a Rubisco house, but it won't be an efficient house unless we update the HVAC," Gunn noted. Robert Wilson, a biochemist at MIT, praised the findings: "It’s very impressive... it’s a completely new and novel mechanism through which an important aspect of rubisco biochemistry occurs."
The study, published in Science in 2026, offers a path to engineering better photosynthesis in crops like wheat and rice for sustainable agriculture amid rising global food demands.