Dual-cycle CO₂ fixation enhances growth and lipid synthesis in Arabidopsis thaliana

Carbon fixation through the Calvin-Benson-Bassham (CBB) cycle accounts for the majority of carbon dioxide (CO₂) uptake from the atmosphere. The CBB cycle generates C3 carbohydrates but is inefficient at producing acetyl-coenzyme A (CoA) (C2), which is the universal precursor for synthesizing lipids. In this work, we introduced in Arabidopsis thaliana a new-to-nature CO₂ fixing cycle, malyl-CoA-glycerate (McG) cycle, which together with the CBB cycle forms a dual-cycle CO₂ fixation system. This cycle can fix one additional carbon by phosphoenolpyruvate carboxylase and convert the photorespiration product, glycolate, to acetyl-CoA. Plants with the McG cycle show enhanced protein abundance in their photosystems and enhanced photosystem II efficiency. McG plants had doubled CO₂ fixation rates under atmospheric CO₂, increased lipid production, pronounced growth enhancement, and tripled the seed yield.