Scientists are resurrecting ancient enzymes to improve photosynthesis

A Cornell University study describes a breakthrough in the quest to improve photosynthesis in certain crops, a step towards adapting plants to rapid climate change and increasing yields to feed 9 billion people by 2050.

The study, “Improving the efficacy of Rubisco by resurrecting its ancestors in the nightshade family,” published April 15 in Scientists progress. The lead author is Maureen Hanson, Liberty Hyde Bailey Professor of Plant Molecular Biology at the College of Agriculture and Life Sciences. First author Myat Lin is a postdoctoral research associate in Hanson’s lab.

The authors developed a computational technique to predict favorable gene sequences that make Rubisco a key plant enzyme for photosynthesis. The technique allowed scientists to identify promising candidate enzymes that could be incorporated into modern crops and ultimately make photosynthesis more efficient and increase crop yields.

Their method relied on evolutionary history, where researchers predicted Rubisco genes 20 to 30 million years ago, when Earth’s carbon dioxide (CO2) were higher than they are today and the plants’ Rubisco enzymes were adapted to these levels.

By resurrecting the ancient Rubisco, early results show promise for developing faster and more efficient Rubisco enzymes to incorporate into crops and help them adapt to future hot and dry conditions as human activities increase CO scavenging the heat.2 gas concentrations in the Earth’s atmosphere.

The study describes the predictions of 98 Rubisco enzymes at key points in the evolutionary history of plants in the nightshade family, which include tomato, pepper, potato, eggplant and tobacco. Researchers are using tobacco as an experimental model for their studies of Rubisco.

“We were able to identify predicted ancestral enzymes that have superior qualities compared to current enzymes,” Hanson said. Lin developed the new technique to identify predicted ancient Rubisco enzymes.

Scientists know they can increase crop yields by speeding up photosynthesis, where plants convert CO2water and light into oxygen and sugars that plants use to produce energy and to build new tissues.

For many years, researchers have focused on Rubisco, a slow enzyme that extracts (or fixes) carbon from CO2 to create sugars. Besides being slow, Rubisco also sometimes catalyzes a reaction with oxygen in the air; in doing so, it creates a toxic byproduct, wastes energy, and renders photosynthesis inefficient.

Hanson’s lab had previously tried using Rubisco from cyanobacteria (blue-green algae), which is faster but also reacts easily with oxygen, forcing researchers to try to create micro-compartments to protect the oxygen enzyme, with mixed results. Other researchers have tried to design a more optimal Rubisco by making changes to the amino acids of the enzyme, although little is known about the changes that would lead to the desired results.

In this study, Lin reconstructed a phylogeny – a tree-like diagram showing the evolutionary relationship between groups of organisms – of Rubisco, using Solanaceae plants.

“Getting a lot of [genetic] Rubisco sequences in extant plants, a phylogenetic tree could be constructed to determine which Rubisco probably existed 20 to 30 million years ago,” Hanson said.

The benefit of identifying potential ancient Rubisco sequences is that carbon dioxide levels may have reached 500 to 800 parts per million (ppm) in the atmosphere 25 to 50 million years ago. Today, CO trapping heat2 levels are rising sharply due to many human activities, with current measurements around 420 ppm, having remained relatively constant below 300 ppm for hundreds of millennia until the 1950s.

Lin, Hanson and colleagues then used an experimental system developed for tobacco in Hanson’s lab and described in a 2020 Nature Plants paper, which uses E. coli bacteria to test the effectiveness of different versions in a single day. by Rubisco. Similar tests carried out in factories take months to verify.

The team found that the ancient Rubisco enzymes predicted from modern Solanaceae plants showed real promise of being more effective.

“For the next step, we want to replace the existing Rubisco enzyme genes in tobacco with these ancestral sequences using CRISPR [gene-editing] technology and then measure how it affects biomass production,” Hanson said. “We certainly hope that our experiments will show that by adapting Rubisco to current conditions, we will have plants that will give better yields.

If their method proves successful, these effective Rubisco sequences could be transferred to crops such as tomatoes, as well as those of other plant families, such as soybeans and rice.

The study was funded by the US Department of Energy.

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