Shared expression of Crassulacean acid metabolism (CAM) genes predates the origin of CAM in the genusYucca

Highlight:Although large differences in metabolism exist between C3and CAM species, we find that many CAM genes have shared expression patterns regardless of photosynthetic pathway, suggesting ancestral propensity for CAM.Abstract:Crassulacean acid metabolism (CAM) is a carbon-concentrating mechanism that has evolved numerous times across flowering plants and is thought to be an adaptation to water limited environments. CAM has been investigated from physiological and biochemical perspectives, but little is known about how plants evolve from C3to CAM at the genetic or metabolic level. Here we take a comparative approach in analyzing time-course data of C3, CAM, and C3+CAM intermediateYucca(Asparagaceae) species. RNA samples were collected over a 24-hour period from both well-watered and drought-stressed plants and were clustered based on time-dependent expression patterns. Metabolomic data reveals differences in carbohydrate metabolism and antioxidant response between the CAM and C3species, suggesting changes to metabolic pathways are important for CAM evolution and function. However, all three species share expression profiles of canonical CAM pathway genes, regardless of photosynthetic pathway. Despite differences in transcript and metabolite profiles between the C3and CAM species, shared time-structured expression of CAM genes in both CAM and C3Yuccaspecies suggests ancestral expression patterns required for CAM may have predated its origin inYucca.