METACAM · Metabolic flexibility in drought: Leveraging Portulaca for defining design principles for a combined C4-CAM pathway

Rising heatwaves and drought are severely affecting the capacity of crops to retain water and capture CO2 during photosynthesis, resulting in global yield reductions. One of the most promising approaches to enhance crop production in stressful conditions is to synthetically modify the photosynthetic capacity of plants. In nature, some lineages have evolved mechanisms like C4 photosynthesis and the Crassulacean acid metabolism (CAM) to cope with some of these aspects; While C4 species are extremely efficient at CO2 fixation but vulnerable to severe drought, CAM plants are less productive but very capable of coping with significant drought periods. Engineering a joint C4-CAM system that uses CAM features to fight drought, while still relying on the power of C4 can be a game-changer to increase crop resilience. For decades, the coexistence of C4 and CAM was considered incompatible in nature. An exception to the rule is found in the genus Portulaca where C4 species can trigger CAM when droughted. Despite the huge bioengineering potential of Portulaca, the molecular enablers that allow for C4-CAM to exist in this clade remain elusive. Previous phylogenetic and morphological studies across Portulaca indicate the combined C4 (Kranz anatomy) and CAM (succulence) leaf anatomy might be the main facilitator of C4-CAM. By combining anatomical studies, cell specific metabolomics and genomics with synthetic biology, I aim to identify the basic molecular determinants of the C4-CAM switch in Portulaca, and to leverage this knowledge to transfer CAM anatomical features to C4 species outside Portulaca as a proof of principle. This will set the basis for new rounds of engineering to achieve a fully functional C4-CAM switch. METACAM will provide a quantum leap to our understanding on how incompatible metabolic pathways can be designed, built and integrated in multicellular organisms which is broadly applicable to crop engineering.