Humans adjust to changes in temperature by putting on a sweater or taking off layers. Plants adjust to temperature changes, in part, by switching the way they express the protein that performs the critical first step of photosynthesis, according to new research from Cornell, Texas A&M and Stockholm University. 

Rubisco is the most abundant protein on Earth, and it is responsible for fixing carbon so that plants can convert it into photosynthetic energy. Better understanding of the basic science underpinning rubisco’s function, therefore, has implications for increasing agricultural yields, improving carbon sequestration technology and understanding how plants may adapt to a warming climate. 

In the paper “Rubisco Kinetic Acclimation at the Holoenzyme Level,” published April 15 in Proceedings of the National Academy of Sciences, the researchers demonstrate that while rubisco’s protein core remains consistent, parts of its exterior can be swapped out, akin to an outfit. A stiffer exterior is preferred in the heat, for protection, and a looser one in the cold, to increase efficiency. This study, using the mustard-family plant Arabidopsis, is the first to show how rubisco acclimates to temperature changes in any plant species. 

“We know that some plants are better adapted for hot or cold based on millennia of evolution – tulips do well in cold and hibiscus prefers hot, for example. We wanted to know, can rubisco change its activity on the fly to perform better when temperatures change day to day? And it does,” said Laura Gunn, assistant professor of plant biology in the School of Integrative Plant Science in the College of Agriculture and Life Sciences (CALS) and corresponding author of the paper. “This is really important because there’s a lot of crop loss from unpredictable weather, like heat waves or cold snaps. If we know this exists, could we exaggerate it? Could we engineer plants that can adapt even more quickly and be better suited to a wider range of weather extremes?”

Rubisco is made up of eight large and eight small subunits – the large subunits form the protein core while the small subunits bind to its exterior. Together, they form an enzymatic machine that can take in carbon dioxide and pump out sugar that powers plant growth. To understand how these machines react to temperature, Gunn and her colleagues used cryogenic electron microscopy to document the structure of two rubiscos from Arabidopsis. 

At a brisk 10 degrees Celsius (50 degrees Fahrenheit), rubisco was assembled with a small subunit that enables it to move faster and perform more reactions per second. But when the temperature was raised to 30 degrees Celsius (86 degrees Fahrenheit), this small subunit was swapped with one that makes rubisco slower and more rigid – a self-protective mechanism that prevents the protein from making mistakes or even falling apart, said Bryce Askey, a doctoral student in Gunn’s lab and first author of the paper. 

“The really fascinating thing is that the differences between these ‘cool’ and ‘hot’ small subunits are really minor – it’s only eight amino acid differences,” Gunn said. “But they are able to change the function of the enzyme quite dramatically. The next step is to figure out exactly how those protein ‘sweaters’ change rubisco’s fit and function, so we can start designing custom versions tuned for different conditions.” 

This study is the first to document how rubisco acclimates to temperature changes in any plant species. Gunn wants to determine how widespread this phenomenon is across the plant kingdom, and future research will explore temperature acclimation in  six other agriculturally relevant plant species: rice, potato, soybean, cotton, barley and maize.

Contributors included Bryce Askey, doctoral student in plant biology; Maddie Ceminsky and Yongsheng Wang, doctoral students in biochemistry, and molecular and cell biology; and Zhen Guo Oh, visiting scholar in the School of Integrative Plant Science (CALS).

The research was supported by the U.S. Department of Energy, National Science Foundation, National Institutes of Health and the Welch Foundation. 

Krisy Gashler is a writer for the College of Agriculture and Life Sciences.