Nocturnal expression of Crassulacean acid metabolism (CAM) genes predates the origin of CAM in the genus Yucca.

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 C 3 to CAM at the genetic or metabolic level. Here we take a comparative approach in analyzing time-course data of C 3 , CAM, and C 3 -CAM intermediate Yucca (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 comparisons of the C 3 and CAM species link gene expression to carbohydrate metabolism and gene network co-expression analyses revealed compositional and functional changes to networks containing canonical CAM genes. Observed differences in carbohydrate metabolism and antioxidant response between the CAM and C 3 species reveal alternative sugar and starch degradation pathways, underscoring the need for more comparative metabolomic analyses to understand the evolution of CAM from C 3 . Despite many differences in transcript and metabolite profiles between the C3 and CAM species, shared time-structured expression of CAM genes in the C 3 species suggests ancestral expression patterns required for CAM may have predated its origin in Yucca .