Overexpression of both Rubisco and Rubisco activase rescues rice photosynthesis and biomass under heat stress

Global warming threatens food security by decreasing crop yields through damage to photosynthetic systems, especially Rubisco activation. We examined whether co-overexpression of Rubisco and Rubisco activase improves the photosynthetic and growth performance of rice under high temperatures. We grew three rice lines-the wild-type (WT), a Rubisco activase-overexpressing line (oxRCA) and a Rubisco- and Rubisco activase-co-overexpressing line (oxRCA-RBCS)-and analysed photosynthesis and biomass at 25 and 40 degrees C. Compared with the WT, the Rubisco activase content was 153% higher in oxRCA and 138% higher in oxRCA-RBCS, and the Rubisco content was 27% lower in oxRCA and similar in oxRCA-RBCS. The CO2 assimilation rate (A) of WT was lower at 40 degrees C than at 25 degrees C, attributable to Rubisco deactivation by heat. On the other hand, that of oxRCA and oxRCA-RBCS was maintained at 40 degrees C, resulting in higher A than WT. Notably, the dry weight of oxRCA-RBCS was 26% higher than that of WT at 40 degrees C. These results show that increasing the Rubisco activase content without the reduction of Rubisco content could improve yield and sustainability in rice at high temperature.