title: Rubisco evolution in C₄ eudicots: an analysis of Amaranthaceae sensu lato.
abstract: BACKGROUND
  Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyses the key reaction in the photosynthetic assimilation of CO₂. In C₄ plants CO₂ is supplied to Rubisco by an auxiliary CO₂-concentrating pathway that helps to maximize the carboxylase activity of the enzyme while suppressing its oxygenase activity. As a consequence, C₄ Rubisco exhibits a higher maximum velocity but lower substrate specificity compared with the C₃ enzyme. Specific amino-acids in Rubisco are associated with C₄ photosynthesis in monocots, but it is not known whether selection has acted on Rubisco in a similar way in eudicots.
  
  
  RESULTS
  We investigated Rubisco evolution in Amaranthaceae sensu lato (including Chenopodiaceae), the third-largest family of C₄ plants, using phylogeny-based maximum likelihood and Bayesian methods to detect Darwinian selection on the chloroplast rbcL gene in a sample of 179 species. Two Rubisco residues, 281 and 309, were found to be under positive selection in C₄ Amaranthaceae with multiple parallel replacements of alanine by serine at position 281 and methionine by isoleucine at position 309. Remarkably, both amino-acids have been detected in other C₄ plant groups, such as C₄ monocots, illustrating a striking parallelism in molecular evolution.
  
  
  CONCLUSIONS
  Our findings illustrate how simple genetic changes can contribute to the evolution of photosynthesis and strengthen the hypothesis that parallel amino-acid replacements are associated with adaptive changes in Rubisco.
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, United Kingdom. maxim.kapralov@plants.ox.ac.uk
authors.forename: Maxim V
authors.initials: MV
authors.lastname: Kapralov
authors.forename: J Andrew C
authors.initials: JA
authors.lastname: Smith
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Filatov
mesh_terms: D027703:Amaranthaceae / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D019143:Evolution, Molecular; D017343:Genes, Plant / Q000502:physiology; D008969:Molecular Sequence Data; D010788:Photosynthesis / Q000235:genetics; D010802:Phylogeny; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics*; D012274:Ribulosephosphates / Q000378:metabolism; D012641:Selection, Genetic
chemical_list: D012274:Ribulosephosphates; C001933:ribulose-1,5 diphosphate; D012273:Ribulose-Bisphosphate Carboxylase