Temperature responses of Rubisco from Paniceae grasses provide opportunities for improving C 3 photosynthesis

Enhancing the catalytic properties of the CO 2 -fixing enzyme Rubisco is a target for improving agricultural crop productivity. Here, we reveal extensive diversity in the kinetic response between 10 and 37 °C by Rubisco from C 3 and C 4 species within the grass tribe Paniceae. The CO 2 fixation rate (kcatc) for Rubisco from the C 4 grasses with nicotinamide adenine dinucleotide (NAD) phosphate malic enzyme (NADP-ME) and phosphoenolpyruvate carboxykinase (PCK) photosynthetic pathways was twofold greater than the kcatc of Rubisco from NAD-ME species across all temperatures. The declining response of CO 2 /O 2 specificity with increasing temperature was less pronounced for PCK and NADP-ME Rubisco, which would be advantageous in warmer climates relative to the NAD-ME grasses. Modelled variation in the temperature kinetics of Paniceae C 3 Rubisco and PCK Rubisco differentially stimulated C 3 photosynthesis relative to tobacco above and below 25 °C under current and elevated CO 2. Amino acid substitutions in the large subunit that could account for the catalytic variation among Paniceae Rubisco are identified; however, incompatibilities with Paniceae Rubisco biogenesis in tobacco hindered their mutagenic testing by chloroplast transformation. Circumventing these bioengineering limitations is critical to tailoring the properties of crop Rubisco to suit future climates.