Evolutionary implications of C sub(3)-C sub(4) intermediates in the grass Alloteropsis semialata

• Published in: Plant, cell and environment Vol. 39; no. 9; pp. 1874 - 1885
• Main Authors: Lundgren, Marjorie R, Christin, Pascal-Antoine, Escobar, Emmanuel Gonzalez, Ripley, Brad S, Besnard, Guillaume, Long, Christine M, Hattersley, Paul W, Ellis, Roger P, Leegood, Richard C, Osborne, Colin P
• Format: Journal Article
• Language: English
• Published: 01.09.2016
• Subjects: Alloteropsis
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.12665

C sub(4) photosynthesis is a complex trait resulting from a series of anatomical and biochemical modifications to the ancestral C sub(3) pathway. It is thought to evolve in a stepwise manner, creating intermediates with different combinations of C sub(4)-like components. Determining the adaptive value of these components is key to understanding how C sub(4) 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 C sub(3) and C sub(4) genotypes. Analyses of delta super(13)C, physiology and leaf anatomy demonstrate for the first time the existence of physiological C sub(3)-C sub(4) intermediate individuals in the species. Based on previous phylogenetic analyses, the C sub(3)-C sub(4) individuals are not hybrids between the C sub(3) and C sub(4) genotypes analysed, but instead belong to a distinct genetic lineage, and might have given rise to C sub(4) descendants. C sub(3) A. semialata, present in colder climates, likely represents a reversal from a C sub(3)-C sub(4) intermediate state, indicating that, unlike C sub(4) photosynthesis, evolution of the C sub(3)-C sub(4) phenotype is not irreversible.