Genetic Engineering with Algae Boosts Crop Photosynthesis

Researchers with tobacco plants engineered to boost their photosynthesis (Australian National University)

4 September 2018. Researchers developed a genetic engineering technique adding algae genes to some staple crops for capturing more carbon dioxide during photosynthesis and improving their yields. A team from Australian National University in Canberra describes this process in yesterday’s issue of the journal Nature Communications.

A project in the lab of molecular biologist Dean Price and led by postdoctoral researcher Ben Long, is seeking to improve the way plant crops process carbon dioxide, to improve the efficiency of their photosynthesis in staple crops like wheat grown worldwide and cassava farmed in many developing regions. Improving the photosynthesis process — conversion of sunlight, water, and carbon dioxide to sugar — is a prime objective for boosting crop yields, and the focus of the Realizing Increased Photosynthetic Efficiency, or RIPE consortium, an international research group funding the study, and supported by the Bill and Melinda Gates Foundation, among other agencies and organizations.

An obstacle to increasing photosynthesis output in crops is a key catalytic enzyme known as ribulose-1,5-bisphosphate carboxylase/oxygenase or Rubisco that absorbs and converts carbon dioxide in the air to sugar. But that process is slow and prone to errors, since Rubisco cannot always discriminate between oxygen and carbon dioxide. The team’s solution is to genetically engineer plants with components of blue-green algae, also called cyanobacteria, that conduct photosynthesis much more efficiently.

Those key components of blue-green algae are carboxysomes that the researchers are adding to the photosynthesis engines of crop plants. “We are trying to insert a turbo-charged carbon-capturing engine into plants,” says Long in a university statement, “by mimicking a solution that cyanobacteria — the ancestors of modern plant chloroplasts, the green compartments where plants make their own food — found millions of years ago.” Long adds that, “inserting a carboxysome into a plant had been in the realm of science fiction and it has taken us more than five years to get to this point.”

Carboxysomes also use Rubisco, but in blue-green algae carboxysomes work much faster. “Unlike crop plants,” notes Long, “cyanobacteria use what’s called a ‘CO₂ concentrating mechanism’ to deliver large amounts of the gas into their carboxysomes, where their Rubisco is encapsulated.” As a result, say the researchers, these algae can capture carbon dioxide and produce sugar at 3 times the rate of normal crop plants.

The team tested their hypothesis with lab-grown tobacco plants, a well-researched species used as a model organism in many labs. The genetic engineering transferred a minimal gene set into the tobacco plant genomes that measurements show enable the plants to produce carboxysomes that conduct CO₂ processing and photosynthesis more efficiently, and increase plant yields up to 60 percent.

Their work with tobacco plants provides a proof-of-concept step, but the researchers say the findings indicate future commercialized engineering of more efficiently grown staple crops is feasible. Long and Price tell more about the project in the following video.

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