title: C3-C4intermediates may be of hybrid origin - a reminder.
abstract: The currently favoured model of the evolution of C4photosynthesis relies heavily on the interpretation of the broad phenotypic range of naturally growing C3-C4intermediates as proxies for evolutionary intermediate steps. On the other hand, C3-C4intermediates had earlier been interpreted as hybrids or hybrid derivates. By first comparing experimentally generated with naturally growing C3-C4intermediates, and second summarising either direct or circumstantial evidence for hybridisation in lineages comprising C3, C4and C3-C4intermediates, we conclude that a possible hybrid origin of C3-C4intermediates deserves careful examination. While we acknowledge that the current model of C4photosynthesis evolution is clearly the best available, C3-C4intermediates of hybrid origin, if existing, should not be used for further analysis of this model. However, experimental C3× C4hybrids potentially are excellent systems to analyse the genetic differences between C3and C4species and, also using segregating progeny, to study the relationship between individual photosynthetic traits and environmental factors.
authors.affiliation: Institut für Molekulare Physiologie, Johannes Gutenberg-Universität Mainz, Mainz, Germany.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Kadereit
authors.affiliation: Institut für Molekulare Physiologie, Johannes Gutenberg-Universität Mainz, Mainz, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Bohley
authors.affiliation: Institut für Molekulare Physiologie, Johannes Gutenberg-Universität Mainz, Mainz, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Lauterbach
authors.affiliation: Institut für Molekulare Physiologie, Johannes Gutenberg-Universität Mainz, Mainz, Germany.
authors.forename: Delphine T
authors.initials: DT
authors.lastname: Tefarikis
authors.affiliation: Institut für Organismische und Molekulare Evolutionsbiologie, Johannes Gutenberg-Universität Mainz, Mainz, Germany.
authors.forename: Joachim W
authors.initials: JW
authors.lastname: Kadereit
mesh_terms: D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D006824:Hybridization, Genetic; D008958:Models, Molecular; D010788:Photosynthesis; D010944:Plants / Q000235:genetics* / Q000378:metabolism
chemical_list: D002244:Carbon
keywords: 
  Atriplex
  ; 
  Flaveria
  ; C2 photosynthesis; C4 photosynthesis; hybridisation experiments; intermediate phenotype; model of C4 evolution; photosynthetic traits