Horizon Europe Metacam Project: Metabolic flexibility in drought: Leveraging Portulaca to define design principles for a combined C4-CAM pathway

The increase in heat waves and drought is severely impacting crops' ability to retain water and capture CO2 during photosynthesis, resulting in global yield reductions. One of the most promising approaches to improving agricultural production under stressful conditions is to synthetically modify plants' photosynthetic capacity.

In nature, some lineages have evolved mechanisms such as C4 photosynthesis and crassulacean acid metabolism (CAM) to address some of these issues. While C4 species are extremely efficient at CO2 fixation but vulnerable to severe drought, CAM plants are less productive but highly capable of coping with significant drought periods. Designing a joint C4-CAM system that utilizes the characteristics of CAM to combat drought, while also drawing on the power of C4, may be a game changer for increasing 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 activate CAM during drought. Despite the enormous bioengineering potential of Portulaca, the molecular enablers that allow C4-CAM to exist in this clade remain elusive. Previous phylogenetic and morphological studies in Portulaca indicate that the combined leaf anatomy of C4 (Kranz anatomy) and CAM (succulence) could be the main facilitator of C4-CAM.

By combining anatomical studies, cell-specific metabolomics, and genomics with synthetic biology, my goal is to identify the basic molecular determinants of the C4-CAM switch in Portulaca and leverage this knowledge to transfer the anatomical features of CAM to C4 species outside of Portulaca as a proof-of-principle. This will lay the groundwork for further rounds of engineering to achieve a fully functional C4-CAM switch. METACAM will provide a quantum leap in our understanding of how incompatible metabolic pathways can be designed, engineered, and integrated in multicellular organisms, which is broadly applicable to crop engineering.