The Posttranslational Modifications Of Maize PPDK And The Analysis Of Evolutionary Significance On Phosphorylation At PPDK-Ser528

photosynthesis is a process that coverts solar insolation into chemical energy in plants, and it’s one of the most important factors of crop yield. In crops, approximately ninety percent dry weight come from photosynthesis. As we all know that the photosynthetic efficiency of C4plants is prominently higher than C3plants. Genetically modifying C3plants with the key enzymes of photosynthesis in C4plants has broad application prospects. So, it is very important to research the expression pattern and the activity regulative of the key enzymes of photosynthesis in C4plants, which may provide us some theoretical basis and directions about how to genetically modifying C3plants.Maize is a typical C4plants, which own high photosynthetic efficiency. Pyruvate orthophosphate dikinase (PPDK) is one of the most important key enzymes in C4plants, which catalyzes the generation of phosphoenolpyruvate from pyruvate during C4photosynthesis, phosphoenolpyruvate is the initial receptor of carbon dioxide (CO2). There are two copies of PPDK gene, which generate three transcripts and the expression of them are tissue specific in maize. In the leaf of maize, the dominated expression gene is C4PPDK, which own a chloroplast signal peptide. It was reported previously that phosphorylation and dephosphorylation at Thr527of PPDK lead to inactivation and activation respectively. Here we found that not all of the PPDK, but only a few amounts took part in C4photosynthesis and the reversible phosphorylation at Thr527of these PPDK were strictly regulated by light intensity. We pinpointed the PPDK signal peptide cleavage site, uncovered partial N-terminal acetylation, and revealed phosphorylation at four Ser/Thr residues, three of which were previously unknown in maize. phosphorylation at three of the sites, but not at Thr527is regulated by light-dark treatment. In vitro experiments indicated that Thr527and Ser528, are targets of the PPDK regulatory protein (PDRP); and two hydrogen bonds between Ser528and Gly525is evolutionarily conserved for PPDK-RP to phosphorylate Thr527, and the phosphorylated Thr527is also a prerequisite for phosphorylation of Ser528. This data suggested that the regulation of maize C4PPDK activity is more complicated than what reported previously,and it indicated that the mechnisim of the regulation of PPDK phosphorylation may play a significant role in C4plants evolution.