Amino acid swap makes wheat more heat tolerant

Thermostats tell air conditioners to switch on when it’s hot and shut down when it’s cool.

Plants have Rubisco activase (Rca) that tells their energy-producing enzyme, Rubisco, to kick in when the sun is shining and stop when leaves are receiving less light.

To increase the efficiency of Rca and activate Rubisco faster, researchers at Lancaster University in Lancashire, United Kingdom, swapped out one amino acid. That enabled Rca in wheat to kickstart Rubisco quicker, suggesting that the modification could help protect crops in hotter temperatures in the future.

Researchers wrote in their report that the regulation of Rubisco, the gatekeeper of carbon fixation, by its molecular chaperone, Rca, is essential for photosynthesis and plant growth. Rca, though, is sensitive to moderate heat stress and becomes progressively less efficient as the temperature increases above the optimum level for photosynthesis. By identifying a single amino acid substitution, they were able to alter the properties of Rca in bread wheat, making it more heat tolerant.

“It has been known for a while that Rubisco activase is thermal sensitive; its ability to reconfigure and activate Rubisco decreases at temperatures that are just a few degrees above the temperature optimum of growth for each plant species,” Dr. Elizabete Carmo-Silva, senior lecturer at the university’s Lancaster Environment Centre, said in a news release. “We also know that the speed with which Rubisco activase turns on Rubisco when the sun shines could be improved to make the most of sunshine throughout the day and the cropping season, thereby making photosynthesis more efficient.”

She said that a big focus of their research was to identify the natural diversity in Rca by investigating its molecular properties, such as efficiency and temperature profiles for a number of Rubisco activase forms present in different plant species. They compared Rca forms in terms of their sequence of amino acids, the building blocks of proteins. Rubisco activase contains about 380 building blocks and there are 20 amino acid types that can be found in proteins. This means that in each of the 380 positions of the Rubisco activase sequence there could be one of 20 different amino acid types. By comparing the amino acid types present in each of the 380 positions, the object was to find differences in the amino acid type present at specific positions that may be associated with Rca efficiency and thermal tolerance.

“By comparing the two sequences of 380 amino acids we noticed that wheat Rubisco activase 2β has a type of amino acid called methionine at position number 159, while the wheat Rubisco activase form 1β has an isoleucine, which is a different type of amino acid,” Carmo-Silva stated in the release.

“To test the hypothesis that this amino acid difference could be associated with the observed differences in Rubisco activase efficiency and thermal tolerance, we swapped the methionine in the sequence of the Rubisco activase 2β by an isoleucine. Of the amino acid switches that we tested to date, this is the one that is showing more promise for improving the efficiency of carbon assimilation and resilience to global warming.”

The release states that naturally occurring wheat Rca 1β with an isoleucine amino acid works up to 39 C but is not good at activating Rubisco, whereas the naturally occurring 2β has a methionine amino acid, works up to about 30 C, and is good at activating Rubisco. The team has created a new version of 2β with an isoleucine amino acid that works up to 35 C and is good at activating Rubisco.

Carmo-Silva said that, while other factors may also improve Rubisco, the advantage of finding a single amino acid switch makes it easier to transfer this improvement to wheat plants.

Carmo-Silva said when researchers can demonstrate that these changes at the protein level make plants more efficient, they will then test them in the field. The end game of course is an improved wheat plant to be shared with farmers.

In addition, they are looking into other crops such as soybean and cowpea, each with different forms of Rca.

The research was published recently in The Plant Journal.

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