Spatial resolution of an integrated C 4 +CAM photosynthetic metabolism.

C 4 and CAM photosynthesis have repeatedly evolved in plants over the past 30 million years. Because both repurpose the same set of enzymes but differ in their spatial and temporal deployment, they have long been considered as distinct and incompatible adaptations. Portulaca contains multiple C 4 species that perform CAM when droughted. Spatially explicit analyses of gene expression reveal that C 4 and CAM systems are completely integrated in Portulaca oleracea , with CAM and C 4 carbon fixation occurring in the same cells and CAM-generated metabolites likely incorporated directly into the C 4 cycle. Flux balance analysis corroborates the gene expression findings and predicts an integrated C 4 +CAM system under drought. This first spatially explicit description of a C 4 +CAM photosynthetic metabolism presents a potential new blueprint for crop improvement.