Evolutionary implications of C3–C4 intermediates in the grass Alloteropsis semialata |
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| Authors: | Marjorie R. Lundgren Pascal‐Antoine Christin Emmanuel Gonzalez Escobar Brad S. Ripley Guillaume Besnard Christine M. Long Paul W. Hattersley Roger P. Ellis Richard C. Leegood Colin P. Osborne |
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| Affiliation: | 1. Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, UK;2. Botany Department, Rhodes University, Grahamstown, South Africa;3. CNRS, Université de Toulouse, ENFA, UMR5174 EDB (Laboratoire évolution and Diversité Biologique), Toulouse, France;4. Department of Primary Industry and Fisheries, Northern Territory Government, Darwin, NT, Australia;5. School of Chemistry and Biochemistry (honorary research fellow), University of Western Australia, Crawley, WA, Australia;6. Beacon Bay, East London, South Africa |
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| 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 δ13C, 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. |
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| Keywords: | C3– C4, C2 metabolism CO2 compensation point complex trait grasses oxygen inhibition photorespiration stable isotopes |
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