The role of cis-elements in the evolution of crassulacean acid metabolism photosynthesis

Crassulacean acid metabolism (CAM) photosynthesis is an innovation of carbon concentrating mechanism that is characterized by nocturnal CO(2) fixation. Recent progresses in genomics, transcriptomics, proteomics, and metabolomics of CAM species yielded new knowledge and abundant genomic resources. In this review, we will discuss the pattern of cis-elements in stomata movement-related genes and CAM CO(2) fixation genes, and analyze the expression dynamic of CAM related genes in green leaf tissues. We propose that CAM photosynthesis evolved through the re-organization of existing enzymes and associated membrane transporters in central metabolism and stomatal movement-related genes, at least in part by selection of existing circadian clock cis-regulatory elements in their promoter regions. Better understanding of CAM evolution will help us to design crops that can thrive in arid or semi-arid regions, which are likely to expand due to global climate change.