Recently, the Crop High-Efficiency Photosynthesis Functional Genomics Innovation Team at the Biotechnology Research Institute of the Chinese Academy of Agricultural Sciences (CAAS) has, for the first time, created a new rice germplasm possessing both the C3 photosynthetic pathway and Crassulacean Acid Metabolism (CAM). This breakthrough opens a new pathway for cultivating high-photosynthetic-efficiency, high-yield rice. The related research findings have been published in the international journal ”Advanced Science”.
The plant features three major carbon fixation forms: C3, C4, and CAM. CAM plants temporally separate CO₂ capture and Rubisco carboxylation: they open their stomata at night, fix CO₂, and store it in the form of malic acid in vacuoles. During the day, they close their stomata, and the stored malic acid undergoes decarboxylation, creating a microenvironment with a high CO₂ concentration around Rubisco. This promotes the Rubisco-catalyzed carboxylation carbon fixation reaction. This carbon fixation mechanism endows CAM plants with greater tolerance to high temperatures and drought, as well as increased yield potential. However, how to engineer CAM into C3 plants has remained a significant challenge for the scientific community.
The research utilized synthetic biology techniques, including gene editing and multi-gene stacking, to design a facultative CAM metabolic pathway module. This module incorporates stomatal regulation, carboxylation, decarboxylation, and malate transport components. This engineered facultative CAM pathway was created in C3 rice, enabling the coexistence of both the C3 cycle and the CAM cycle within the same plant. The resulting CAM rice materials showed an approximately 21% increase in photosynthetic rate, and biomass and yield increases of about 20%. This demonstrates the carbon fixation and yield enhancement potential of implementing facultative CAM metabolism in rice.
However, using theslac1mutant (which has constitutively open stomata) as the chassis, while promoting CO₂ entry into mesophyll cells and enhancing carbon fixation, did not improve drought resistance. In the future, fine-tuning the stomatal regulation module could potentially reduce water evaporation, enabling the simultaneous improvement of photosynthetic efficiency, yield, and drought resistance.
This research was supported by the Major Project of Scientific and Technological Innovation 2030 (Grant No. 2024ZD04080) and the CAAS Innovation Project.
Original article:https://doi.org/10.1002/advs.202500418
Figure: Schematic Diagram of Facultative Crassulacean Acid Metabolism Pathway Engineering. |