Species Having C₄ Single-Cell-Type Photosynthesis in the Chenopodiaceae Family Evolved a Photosynthetic Phosphoenolpyruvate Carboxylase Like That of Kranz-Type C₄ Species

Abstract

Spatial and temporal regulation of phosphoenolpyruvate carboxylase (PEPC) is critical to the function of C₄ photosynthesis. The photosynthetic isoform of PEPC in the cytosol of mesophyll cells in Kranz-type C₄ photosynthesis has distinctive kinetic and regulatory properties. Some species in the Chenopodiaceae family perform C₄ photosynthesis without Kranz anatomy by spatial separation of initial fixation of atmospheric CO₂ via PEPC from C₄ acid decarboxylation and CO₂ donation to Rubisco within individual chlorenchyma cells. We studied molecular and functional features of PEPC in two single-cell functioning C₄ species (Bienertia sinuspersici, Suaeda aralocaspica) as compared to Kranz type (Haloxylon persicum, Salsola richteri, Suaeda eltonica) and C₃ (Suaeda linifolia) chenopods. It was found that PEPC from both types of C₄ chenopods displays higher specific activity than that of the C₃ species and shows kinetic and regulatory characteristics similar to those of C₄ species in other families in that they are subject to light/dark regulation by phosphorylation and display differential malate sensitivity. Also, the deduced amino acid sequence from leaf cDNA indicates that the single-cell functioning C₄ species possesses a Kranz-type C₄ isoform with a Ser in the amino terminal. A phylogeny of PEPC shows that isoforms in the two single-cell functioning C₄ species are in a clade with the C₃ and Kranz C₄ Suaeda spp. with high sequence homology. Overall, this study indicates that B. sinuspersici and S. aralocaspica have a C₄-type PEPC similar to that in Kranz C₄ plants, which likely is required for effective function of C₄ photosynthesis.