Adapting C 4 photosynthesis to atmospheric change and increasing productivity by elevating Rubisco content in sorghum and sugarcane

Meta-analyses and theory show that with rising atmospheric CO 2 , Rubisco has become the greatest limitation to light-saturated leaf CO 2 assimilation rates ( A sat ) in C 4 crops. So would transgenically increasing Rubisco increase A sat and result in increased productivity in the field? Here, we successfully overexpressed the Rubisco small subunit ( RbcS ) with Rubisco accumulation factor 1 ( Raf1 ) in both sorghum and sugarcane, resulting in significant increases in Rubisco content of 13 to 25% and up to 90% respectively. A sat increased 12 to 15% and Rubisco enzyme activity ~40% in three independent transgenic events of both species. Sorghum plants also showed increased speeds of photosynthetic induction and decreased bundle sheath leakiness. These improvements translated into average increases of 15.5% in biomass in field-grown sorghum and a 37 to 81% increase in greenhouse-grown sugarcane. This suggests a potential opportunity to achieve substantial increases in productivity of this key economically important clade of C 4 crops, future proofing their value under global atmospheric change.