The Calvin-Benson-Bassham cycle in C4 and Crassulacean acid metabolism species

Abstract

The Calvin-Benson-Bassham (CBB) cycle is the ancestral CO₂ assimilation pathway and is found in all photosynthetic organisms. Biochemical extensions to the CBB cycle have evolved that allow the resulting pathways to act as CO₂ concentrating mechanisms, either spatially in the case of C₄ photosynthesis or temporally in the case of Crassulacean acid metabolism (CAM). While the biochemical steps in the C₄ and CAM pathways are known, questions remain on their integration and regulation with CBB cycle activity. The application of omic and transgenic technologies is providing a more complete understanding of the biochemistry of C₄ and CAM species and will also provide insight into the CBB cycle in these plants. As the global population increases, new solutions are required to increase crop yields and meet demands for food and other bioproducts. Previous work in C₃ species has shown that increasing carbon assimilation through genetic manipulation of the CBB cycle can increase biomass and yield. There may also be options to improve photosynthesis in species using C₄ photosynthesis and CAM through manipulation of the CBB cycle in these plants. This is an underexplored strategy and requires more basic knowledge of CBB cycle operation in these species to enable approaches for increased productivity.

Keywords: C(4); CAM; CO(2) assimilation; Calvin-Benson-Bassham cycle; Crop improvement; Photosynthesis.