Insights into CPSFL1 Induced Membrane Dynamics: A Multifaceted Regulator Linking Vesicle Formation to Thylakoid Biogenesis

Light drives plant life through photosynthesis, a process that takes place in the thylakoid membrane of the chloroplast, an organelle of cyanobacterial origin. The formation of thylakoid membranes within the chloroplast involves the eukaryote-specific factor CHLOROPLAST SEC14 LIKE PROTEIN 1 (CPSFL1), which shares strong sequence homology with the vesicle trafficking regulator SEC14. CSPFL1 is essential for vesicle formation, yet its specific molecular function in this process has remained unclear. In this study, we characterized CSPFL1 functions both in vitro and in vivo. Using a minimal membrane system of giant unilamellar vesicles (GUVs), we show that CPSFL1 alone can induce vesiculation. This process is mediated by lipid binding and membrane deformation, driven by curvature sensing and lipid-protein electrostatics. When expressed in the prokaryote E. coli , the eukaryote-specific CSPFL1 induces membrane curvature and vesicle formation. Plastid CPSFL1 co-purifies with vesicular structures. Lipid compositional analysis of CPSFL1-induced vesicles from bacteria reveals the presence of quinone precursors as cargo, linking CSPFL-mediated vesicle formation to prenylquinone transport. Together, our data suggest that during plant evolution, the eukaryotic vesicle formation system was co-opted for the transport of membrane integral metabolites from the inner envelope to the thylakoid membrane.