Researchers from Associate Professor Yu Heng Lau's group at the University of Sydney and Professor Spencer Whitney's group at Australian National University have spent five years tackling a fundamental problem: how can we make plants fix carbon more efficiently?
The team engineered nanoscale "offices" that can house an enzyme called Rubisco in a confined space, enabling scientists to fine-tune compatibility for use in crops. This approach is expected to help crops produce food with fewer resources.
Rubisco is a common enzyme in plants, essential for fixing carbon dioxide during photosynthesis - the chemical process that uses sunlight to make food and energy for plants. Despite its importance, Rubisco is surprisingly inefficient. "Rubisco is very slow and can mistakenly react with oxygen instead of CO2, which triggers a whole other process that wastes energy and resources. This mistake is so common that food crops such as wheat, rice, canola, and potatoes have evolved a brute-force solution: mass-produce Rubisco," said lead researcher Dr Taylor Szyszka from the ARC Centre of Excellence in Synthetic Biology and School of Chemistry at the University of Sydney.
In some leaves, up to 50 percent of the soluble protein is just copies of this one enzyme, representing a huge energy and nitrogen expense for the plant. "It's a major bottleneck in how efficiently plants can grow," said Davin Wijaya, a PhD candidate at the Australian National University, who co-led the study.
Some organisms solved this problem millions of years ago. Algae and cyanobacteria house Rubisco in specialised compartments and supply them with concentrated CO2. These "home offices" help the enzyme work faster and more efficiently, with everything it needs close at hand.
Scientists have tried for years to install natural CO2-concentrating systems into crops. But the simplest Rubisco-containing compartments from cyanobacteria, called carboxysomes, are structurally complicated. They need multiple genes working in balance and can only house their native Rubisco.
The Lau and Whitney team used encapsulins - simple bacterial protein cages requiring just one gene to build. Think of it like Lego blocks snapping into place instead of assembling flat-pack furniture. The researchers added a 14-amino-acid "address tag" to direct Rubisco inside these compartments.
The team tested three Rubisco varieties: one from a plant and two from bacteria. They found that for more complex forms of the enzyme, Rubisco must be assembled first before the compartment forms. "Rubisco didn't assemble properly when trying to do both at once," Mr Wijaya said.
Dr Szyszka added: "Another advantage of our system is that it's modular. Carboxysomes can only package their own Rubisco, whereas our encapsulin system can package any type. Most excitingly we found the pores in the encapsulin shell allow for the entry and exit of Rubisco's substrate and products."
This research is just a proof of concept. Future work aims to add components that give Rubisco the high-performance environment it needs. Early-stage plant experiments are underway at ANU. "We know we can produce encapsulins in bacteria or yeast; making them in plants is the next step. Preliminary results look promising," Mr Wijaya said.
If successful, this technology could enable crops to fix CO2 more efficiently and produce higher yields while using less water and nitrogen fertiliser - important as climate change and population growth increase pressure on global food systems.
Research Report:Reprogramming encapsulins into modular carbon-fixing nanocompartments
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