title: Evolution of a CAM anatomy predates the origins of Crassulacean acid metabolism in the Agavoideae (Asparagaceae).
abstract: Crassulacean acid metabolism (CAM) is a modified form of photosynthesis that has arisen independently at least 35 times in flowering plants. The occurrence of CAM is often correlated with shifts to arid, semiarid, or epiphytic habits, as well as transitions in leaf morphology (e.g. increased leaf thickness) and anatomy (e.g. increased cell size and packing). We assess shifts between C3 and CAM photosynthesis in the subfamily Agavoideae (Asparagaceae) through phylogenetic analysis of targeted loci captured from the nuclear and chloroplast genomes of over 60 species. Carbon isotope data was used as a proxy for mode of photosynthesis in extant species and ancestral states were estimated on the phylogeny. Ancestral character state mapping suggests three independent origins of CAM in the Agavoideae. CAM species differ from C3 species in climate space and are found to have thicker leaves with densely packed cells. C3 ancestors of CAM species show a predisposition toward CAM-like morphology. Leaf characteristics in the ancestral C3 species may have enabled the repeated evolution of CAM in the Agavoideae subfamily. Anatomical changes, including a tendency toward 3D venation, may have initially arisen in C3 ancestors in response to aridity as a way to increase leaf succulence for water storage.
authors: Department of Plant Biology, 2502 Miller Plant Sciences, University of Georgia, Athens, GA 30602, United States. Electronic address: heyduk@uga.edu.
authors: Karolina
authors: K
authors: Heyduk
authors: Donald Danforth Plant Science Center, 975 N. Warson Rd., St. Louis, MO 63132, United States.
authors: Michael R
authors: MR
authors: McKain
authors: Department of Plant Biology, 2502 Miller Plant Sciences, University of Georgia, Athens, GA 30602, United States.
authors: Falak
authors: F
authors: Lalani
authors: Department of Plant Biology, 2502 Miller Plant Sciences, University of Georgia, Athens, GA 30602, United States.
authors: James
authors: J
authors: Leebens-Mack
mesh_terms: D000070357:Asparagaceae / Q000033:anatomy & histology* / Q000378:metabolism*; D001483:Base Sequence; D005075:Biological Evolution; D002264:Carboxylic Acids / Q000378:metabolism*; D002980:Climate; D010788:Photosynthesis; D010802:Phylogeny; D025341:Principal Component Analysis; D013045:Species Specificity
chemical_list: D002264:Carboxylic Acids
keywords: CAM; Character evolution; Leaf anatomy; Photosynthesis; Phylogenomics; Sequence capture