Evolutionary changes of phosphoenolpyruvate transporter (PPT) during the emergence of C4 photosynthesis

C4 photosynthesis is a complex trait, which evolved from its ancestral C3 photosynthesis by recruiting pre-existing genes. The evolutionary history of enzymes involved in the C4 shuttle has been extensively studied. Here we analyze the evolutionary changes of phosphoenolpyruvate (PEP) transporter (PPT) during its recruitment from C3 to C4 photosynthesis. Our analysis shows that 1) among the two PPT paralogs, i.e. PPT1 and PPT2, PPT1 is an ancestral copy while PPT2 is a derived copy; 2) during C4 evolution, PPT1 shifted its expression from predominantly in root to in leaf, and from bundle sheath cell to mesophyll cell, supporting that PPT1 was recruited into C4 photosynthesis; 3) PPT1 gained increased transcript abundance, gained more rapid and long-lasting responses to light during C3 to C4 evolution, while PPT2 lost its responsiveness to light; 4) PPT1 gained a number of new cis-elements during C4 evolution; 5) C4 PPT1 can complement the phenotype of Arabidopsis PPT1 loss-of-function mutant, suggesting that it is a bidirectional transporter and its transport direction did not alter during C4 evolution. We finally discuss mechanistic linkages between these observed changes in PPT1 and C4 photosynthesis evolution.\n\nHigh lightDuring the process of C4 photosynthesis evolution, PPT not only experienced changes in its expression location and transcript abundance, but also acquired new cis-elements in its promoter region and accumulated protein variations.