title: Evolutionary implications of C3 -C4 intermediates in the grass Alloteropsis semialata.
abstract: C4 photosynthesis is a complex trait resulting from a series of anatomical and biochemical modifications to the ancestral C3 pathway. It is thought to evolve in a stepwise manner, creating intermediates with different combinations of C4 -like components. Determining the adaptive value of these components is key to understanding how C4 photosynthesis can gradually assemble through natural selection. Here, we decompose the photosynthetic phenotypes of numerous individuals of the grass Alloteropsis semialata, the only species known to include both C3 and C4 genotypes. Analyses of δ(13) C, physiology and leaf anatomy demonstrate for the first time the existence of physiological C3 -C4 intermediate individuals in the species. Based on previous phylogenetic analyses, the C3 -C4 individuals are not hybrids between the C3 and C4 genotypes analysed, but instead belong to a distinct genetic lineage, and might have given rise to C4 descendants. C3 A. semialata, present in colder climates, likely represents a reversal from a C3 -C4 intermediate state, indicating that, unlike C4 photosynthesis, evolution of the C3 -C4 phenotype is not irreversible.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Marjorie R
authors.initials: MR
authors.lastname: Lundgren
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Pascal-Antoine
authors.initials: PA
authors.lastname: Christin
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Emmanuel Gonzalez
authors.initials: EG
authors.lastname: Escobar
authors.affiliation: Botany Department, Rhodes University, Grahamstown, 6139, South Africa.
authors.forename: Brad S
authors.initials: BS
authors.lastname: Ripley
authors.affiliation: CNRS, Université de Toulouse, ENFA, UMR5174 EDB (Laboratoire Évolution and Diversité Biologique), 118 Route de Narbonne, Toulouse, 31062, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Besnard
authors.affiliation: Department of Primary Industry and Fisheries, Northern Territory Government, Darwin, NT, 0801, Australia.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Long
authors.affiliation: School of Chemistry and Biochemistry (honorary research fellow), University of Western Australia, Crawley, WA, 6009, Australia.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Hattersley
authors.affiliation: Beacon Bay, East London, 5205, South Africa.
authors.forename: Roger P
authors.initials: RP
authors.lastname: Ellis
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Leegood
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Colin P
authors.initials: CP
authors.lastname: Osborne
mesh_terms: D005075:Biological Evolution; D002247:Carbon Isotopes / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000033:anatomy & histology; D006109:Poaceae / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; C069767:phosphoenolpyruvate carboxylase kinase; D017346:Protein Serine-Threonine Kinases
keywords: C3-C4, C2 metabolism; CO2 compensation point; complex trait; grasses; oxygen inhibition; photorespiration; stable isotopes