CAM Biodesign: Engineering Crassulacean Acid Metabolism into C3 Plant to Improve Water-Use Efficiency

Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that exploits a temporal CO₂ pump with nocturnal CO₂ uptake to improve the water-use efficiency (WUE) and the adaptability of plants to hotter and drier climates. Introducing the CAM photosynthetic machinery into C₃ photosynthesis plants (CAM Biodesign), such as Arabidopsis and Populus, is expected to confer enhanced WUE in order to allow plants to withstand long episodes of drought or perhaps even expand C₃ crop production into semi-arid regions. Tissue succulence engineering in C₃ plants may be a key anatomical attribute for enhancing the efficient operation of engineered CAM in C₃ photosynthesis species. Specifically, increased tissue succulence is expected to afford increased mesophyll cell and vacuole size in order to increase malate storage capacity and to reduce intercellular air space to limit the diffusion of CO₂ from the leaf. Furthermore, the proper circadian clock-controlled and mesophyll-specific promoters are required to reconstitute CAM (or C₄) enzymes in target C₃ plants. Lastly, developing an effective multi-gene assembly strategy for large number of the CAM gene cassettes is necessary to ensure stable expression of each CAM gene cassette within complex gene circuits. This study summarizes current step achieved to date for CAM Biodesign including tissue succulence engineering, CAM gene and promoter mining, and vector set construction for multi-gene assembly of gene circuits in C₃ photosynthesis plants.