Adapting C₄ photosynthesis to atmospheric change and increasing productivity by elevating Rubisco content in sorghum...

Meta-analyses and theory show that with rising atmospheric [CO₂], Rubisco has become the greatest limitation to light-saturated leaf CO₂ assimilation rates (A_sat) in C₄ 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 C₄ crops, future proofing their value under global atmospheric change.