Engineering of photorespiration-dependent glycine betaine biosynthesis improves photosynthetic carbon fixation and panicle architecture in rice

Abstract

In C3 plants, photorespiration is an energy expensive pathway that competes with photosynthetic CO2 assimilation and releases CO2 into the atmosphere, potentially reducing C3 plant productivity by 20%–50%. Consequently, reducing the flux through photorespiration has been recognized as a major way to improve C3 crop photosynthetic carbon fixation and productivity. While current research efforts in engineering photorespiration are mainly based on the modification of chloroplast glycolate metabolic steps, only limited studies have explored optimizations in other photorespiratory metabolic steps. Here, we engineered an imGS bypass within the rice mitochondria to bypass the photorespiratory glycine toward glycine betaine, thereby, improving the photosynthetic carbon fixation in rice. The imGS transgenic rice plants exhibited significant accumulation of glycine betaine, reduced photorespiration, and elevated photosynthesis and photosynthate levels. Additionally, the introduction of imGS bypass into rice leads to an increase in the number of branches and grains per panicle which may be related to cytokinin and gibberellin signaling pathways. Taken together, these results suggest diverting mitochondrial glycine from photorespiration toward glycine betaine synthesis can effectively enhance carbon fixation and panicle architecture in rice, offering a promising strategy for developing functional mitochondrial photorespiratory bypasses with the potential to enhance plant productivity.