The Crop High-Efficiency Photosynthesis Functional Genomics Innovation Team at the Biotechnology Research Institute (BRI), Chinese Academy of Agricultural Sciences (CAAS), has successfully introduced a synthetic tartronyl-CoA (TaCo) metabolic pathway into the chloroplasts of rice plants. This breakthrough marks the first application of a “carbon-positive” photorespiratory bypass in plants — a pathway that not only minimizes carbon loss but also captures additional CO2 beyond the Calvin cycle. The findings were published in Plant Biotechnology Journal.
Photorespiration is a metabolic process in green plants that consumes oxygen and releases CO2 under light conditions. In C3 crops such as rice and wheat, photorespiration can result in the loss of 30–50% of photosynthetically fixed carbon, thereby limiting yield potential. Although several photorespiratory bypass strategies have been developed to reduce carbon loss, none had previously achieved a “carbon-positive” effect — one that enables net CO2 fixation beyond the Calvin cycle.
To construct this novel pathway, the research team combined three bacterial enzymes — glycolyl-CoA synthetase (GCS) from Erythrobacter sp. NAP1, glycolyl-CoA carboxylase (GCCM5) from Methylorubrum extorquens, and tartronyl-CoA reductase (TCR) from Chloroflexus aurantiacus. Through codon optimization, efficient chloroplast-targeting peptide fusion, and multigene module assembly, they created the TaCo photorespiratory bypass. When introduced into rice, this pathway was stably expressed in chloroplasts, converting glycolate into glycerate while fixing one additional molecule of CO2 — effectively transforming photorespiration from a carbon-consuming to a carbon-fixing process.
Field trials demonstrated that TaCo rice exhibited an 11.1%–17.2% increase in biomass and a 14.2%–20.2% increase in grain yield. Under high light and high CO₂ conditions, TaCo rice showed enhanced net photosynthetic rates, improved carboxylation efficiency, and significantly lower CO2 compensation points — clear evidence of its carbon-positive effect. Multi-omics analyses further revealed that the TaCo pathway promotes carbohydrate metabolism and cytokinin synthesis, facilitating grain development.
This pioneering work provides a new strategy for enhancing photosynthetic efficiency and yield potential in rice. Moving forward, the team plans to employ intelligent enzyme design to further optimize the conversion efficiency of glycolate to glycerate, thereby maximizing productivity gains.
This research was supported by the National Key Research and Development Program of China and the CAAS Innovation Project.
Original article: https://onlinelibrary.wiley.com/doi/10.1111/pbi.70258
Figure: Construction of a Carbon-Positive Photorespiration Bypass in Plant |