Hornworts carry a built-in molecular velcro that could supercharge photosynthesis in crops

Science, March 2026

Rubisco is the most abundant enzyme on Earth, and arguably the most important. It is the entry point for nearly all carbon in the food chain, capturing carbon dioxide from the air during photosynthesis. It is also painfully slow and easily distracted by oxygen, which wastes energy and limits how efficiently plants grow. If crop plants could concentrate CO2 around Rubisco the way algae do, yields could rise substantially.

Scientists have spent years trying to transplant the algae's trick, tiny compartments called pyrenoids that pack Rubisco together and flood it with carbon dioxide, into food crops. The effort has stalled because algal machinery does not transfer well to land plants. Now a team led by researchers at the Boyce Thompson Institute, Cornell University, and the University of Edinburgh has found a workaround in an unexpected place: hornworts.

The only land plants with a CO2-concentrating trick

Hornworts are small, flat plants that most people would walk past without noticing. But they hold a distinction in plant biology: they are the only land plants known to possess CO2-concentrating compartments similar to those in algae. Because hornworts share a more recent evolutionary history with crops than algae do, the research team hypothesized that their molecular machinery might transfer more readily.

What they found was unexpected. In algae, Rubisco clustering is driven by separate linker proteins that bind to the enzyme externally. The researchers assumed hornworts would use something similar. Instead, hornworts have modified Rubisco itself.

A protein tail that acts like molecular velcro

Rubisco is assembled from large and small protein subunits. In the hornwort Anthoceros agrestis, one version of the small subunit carries an extra tail of approximately 100 amino acids. The researchers named this extension RbcS-STAR (Sequestration Associated Region). The STAR tail causes Rubisco proteins to stick together and cluster into dense, pyrenoid-like structures.

The critical test was transferability. The team introduced RbcS-STAR into a closely related hornwort species that lacks pyrenoids. Rubisco reorganized from a scattered distribution into concentrated structures. They then tried the same experiment in Arabidopsis, a standard lab plant with no natural pyrenoids. Again, Rubisco formed dense compartments inside the chloroplasts.

In a final experiment, they attached just the STAR tail to Arabidopsis's native Rubisco. It triggered the same clustering effect. Alistair McCormick, professor at the University of Edinburgh and co-lead author, noted that this demonstrates STAR is a modular tool that works across different plant systems.

The house is built, but it needs HVAC

The clustering alone is not enough to boost photosynthesis. Concentrating Rubisco into a compartment only helps if carbon dioxide is actively delivered to that compartment. Laura Gunn, assistant professor at Cornell and co-lead author, used a construction analogy: the team has built a Rubisco house, but it will not be efficient without updated plumbing to deliver CO2.

The team is now working on engineering the delivery system. The advantage of using hornwort-derived components rather than algal ones is that hornwort and crop plant biology are more closely related, which improves the odds of compatibility.

What this could mean for agriculture

Improving photosynthetic efficiency even modestly could increase crop yields while reducing agriculture's environmental footprint. The current inefficiency of Rubisco is a fundamental bottleneck in food production. If the STAR approach can be combined with a CO2 delivery system and successfully engineered into wheat, rice, or other staple crops, the impact on food security could be substantial.

But that is a long path. Engineering a complete carbon-concentrating mechanism in crop plants involves multiple components working in concert, not just Rubisco clustering. The STAR discovery simplifies one part of the puzzle by providing a single, transferable module rather than requiring reconstruction of an entire algal pyrenoid system.

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.