Molecular and expression analysis of pyruvate orthophosphate dikinase genes in Chlamydomonas reinhardtii reveals potential roles in carbon metabolism regulation

Chlamydomonas reinhardtii is a widely used model organism for studying photosynthesis and carbon metabolism in microalgae. However, the molecular basis of carbon flux regulation and its potential link to biomass and lipid accumulation remain insufficiently understood. Pyruvate orthophosphate dikinase (PPDK), a key enzyme in C4 photosynthesis, plays a central role in carbon fixation and metabolic regulation in higher plants, yet its presence and function in green algae remain largely unexplored. In this study, we report the isolation and molecular characterization of two PPDK genes from C. reinhardtii. Both genes were successfully cloned and shown to encode functional enzymes based on sequence conservation and structural features. Expression analysis revealed that ppdk transcripts are differentially regulated in response to changes in carbon dioxide and ammonium availability, suggesting a role in metabolic adaptation to environmental conditions. Phylogenetic analysis indicated that one isoform (PPDK2) is more closely related to plant PPDKs than to bacterial or protozoan counterparts, supporting an evolutionarily conserved function. Furthermore, sequence alignment demonstrated strong conservation of catalytic residues and substrate-binding domains across species. Collectively, these findings provide new insights into the presence and potential functional relevance of PPDK in green algae and suggest a possible role in the regulation of carbon metabolism, with implications for improving biomass production and metabolic engineering in microalgal systems.