title: C4 Photosynthesis evolved in grasses via parallel adaptive genetic changes.
abstract: Phenotypic convergence is a widespread and well-recognized evolutionary phenomenon. However, the responsible molecular mechanisms remain often unknown mainly because the genes involved are not identified. A well-known example of physiological convergence is the C4 photosynthetic pathway, which evolved independently more than 45 times [1]. Here, we address the question of the molecular bases of the C4 convergent phenotypes in grasses (Poaceae) by reconstructing the evolutionary history of genes encoding a C4 key enzyme, the phosphoenolpyruvate carboxylase (PEPC). PEPC genes belong to a multigene family encoding distinct isoforms of which only one is involved in C4 photosynthesis [2]. By using phylogenetic analyses, we showed that grass C4 PEPCs appeared at least eight times independently from the same non-C4 PEPC. Twenty-one amino acids evolved under positive selection and converged to similar or identical amino acids in most of the grass C4 PEPC lineages. This is the first record of such a high level of molecular convergent evolution, illustrating the repeatability of evolution. These amino acids were responsible for a strong phylogenetic bias grouping all C4 PEPCs together. The C4-specific amino acids detected must be essential for C4 PEPC enzymatic characteristics, and their identification opens new avenues for the engineering of the C4 pathway in crops.
authors.affiliation: Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland. pascal-antoine.christin@unil.ch
authors.forename: Pascal-Antoine
authors.initials: PA
authors.lastname: Christin
authors.forename: Nicolas
authors.initials: N
authors.lastname: Salamin
authors.forename: Vincent
authors.initials: V
authors.lastname: Savolainen
authors.forename: Melvin R
authors.initials: MR
authors.lastname: Duvall
authors.forename: Guillaume
authors.initials: G
authors.lastname: Besnard
mesh_terms: D019943:Amino Acid Substitution; D019143:Evolution, Molecular; D005818:Genetic Engineering; D008969:Molecular Sequence Data; D010730:Phosphoenolpyruvate Carboxylase / Q000235:genetics*; D010788:Photosynthesis / Q000235:genetics*; D010802:Phylogeny; D006109:Poaceae / Q000235:genetics*; D012641:Selection, Genetic
chemical_list: D010730:Phosphoenolpyruvate Carboxylase