Red algae proteins are grafted onto the tobacco double growth plant

A Cornell researcher and his colleagues have solved an important piece of the molecular puzzle needed to improve plant productivity and increase carbon sequestration: They have successfully transferred key regions of a highly efficient red algae to a tobacco plant, using bacteria as an intermediary.

The study was co-authored by Laura Gunn, assistant professor in the School of Integrative Plant Science Plant Biology Section in the College of Agriculture and Life Sciences, and is featured on the cover of Plants in Nature.

The study centers on Rubisco, the most abundant protein in all ecosystems on Earth. Rubisco performs the first step in photosynthesis by fixing carbon, and it is found in various forms in a wide range of organisms, including plants, red and green algae and bacteria. Rubisco is slow and struggles to differentiate between oxygen and carbon dioxide, a problem that Gunn and many other Cornellians are working on. As a result, Rubisco often limits plant growth and crop yield.

One species of red algae, Griffithsia monilis (Gm), contains Rubisco that is 30% more efficient at fixing carbon than Rubisco in other organisms, including land plants. For at least 20 years, scientists have been interested in transplanting highly efficient GmRubisco into crops such as rice, wheat, soybeans and tobacco to increase their productivity; however, until now, no one has been able to successfully coax plants to express it.

This is because Rubisco requires several “chaperones” that are essential for the protein to fold, assemble and become active—there are seven such helpers in tobacco plants—and most of the chaperones in red algae are unknown, Gunn said.

In their study, Gunn and his co-authors were able to solve the 3D structure of GmRubisco and used this information to successfully graft a small number of regions from Rhodobacter sphaeroides (RsRubisco) into a bacterial Rubisco.

“RsRubisco is not very efficient, but it is very closely related to GmRubisco – they are like cousins ​​- which means that unlike land plant Rubisco, it accepts grafted sequences,” Gunn said. “RsRubisco also does not need any special chaperones for it to fold and accumulate in land plants.”

The change increased the carboxylation rate—the speed at which Rubisco begins the process of fixing carbon—by 60%, increased the efficiency of carboxylation by 22% and improved RsRubisco’s ability to distinguish between carbon dioxide and oxygen by 7%.

The authors then transferred their bacterial mutant to tobacco, where it doubled photosynthesis and plant growth, compared to tobacco grown with unmodified RsRubisco. Tobacco is the easiest plant on earth to manipulate Rubisco and therefore serves as a test case for developing a more efficient Rubisco that can be transferred to more agronomically relevant species, Gunn said.

“We’re not at the point where we’re outperforming wild-type tobacco, but we’re on the right track,” Gunn said. “We only need a relatively modest improvement in the performance of Rubisco, because even a very small increase throughout the growing season can lead to significant changes in plant growth and yield, and potential applications span many sectors: higher agricultural production;