Adapting C4 photosynthesis to atmospheric change and increasing productivity by elevating Rubisco content in Sorghum and Sugarcane

Meta-analyses and theory show that with rising atmospheric [CO2], Rubisco has become the greatest limitation to light-saturated leaf CO2-uptake (Asat) in C4 crops. So would transgenically increasing Rubisco increase Asat 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 13-25% and up to 90% respectively. Asat increased 12-15% 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 37-81% increase in greenhouse-grown sugarcane. This suggests a potential opportunity to achieve substantial increases in productivity of this key economically important clade of C4 crops, future proofing their value under global atmospheric change.