Engineering of Crassulacean Acid Metabolism (CAM) Modules into C3 Species Via Synthetic Biology Approach

Crassulacean acid metabolism (CAM) is a specialized photosynthetic pathway that enhances water use efficiency (WUE) in CAM plants in comparison with C₃ and C₄ plants. The CAM biochemistry features two temporally-separated modules: 1) a carboxylation module for nocturnal CO₂ fixation and accumulation of malic acid in the vacuole; and 2) a decarboxylation module for release of CO₂ from malate during the daytime. From the genomics resources available for two obligate CAM species Agave americana (monocot) and Kalanchoë laxiflora (eudicot), we identified the key genes involved in the CAM carboxylation and decarboxylation processes. Multiple genetic circuits were created for the CAM carboxylation and decarboxylation modules using synthetic biology approach. These genetic circuits were introduced into two model plants species (i.e., Arabidopsis and tobacco) for testing and optimization of the circuit design. Furthermore, the CAM genetic circuits are being transformed into poplar, an important C₃ bioenergy crop. This research has a great potential for accelerating the genetic improvement of WUE and drought tolerance in bioenergy and food crops.