Functional characterization of AtCPSFL1-dependent thylakoid biogenesis

• Applicant: Alexander Paul Hertle, Ph.D.
• Subject Area: Plant Physiology ; Plant Biochemistry and Biophysics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452589609

Photosynthesis describes the essential biological process that leads to the conversion of light, water and CO2 into high-energy organic compounds and oxygen. In plants, the light reactions of photosynthesis occur in thylakoids, an extensive membrane system within the chloroplast. While the molecular composition of thylakoid membranes has largely been deciphered, the mechanisms underlying membrane biogenesis remain elusive and many factors involved are unknown. Recently, I could show that a plastid localized Sec14-like protein is essential for chloroplast and thylakoid biogenesis. Representatives of the Sec14 superfamily regulate membrane transport events between multiple membrane systems and have been named after the initially described founder of this protein family, which has a function in the secretory pathway. SEC14-dependent redistribution and concentration of signaling lipids in specific membrane domains triggers vesicle formation in two ways: it changes the biochemical properties of the membrane and leads to the recruitment of effector proteins involved in vesicle formation. The role of the CHLOROPLAST LOCALIZED SEC FOURTEEN LIKE protein (CPSFL1) in chloroplast development strongly suggested a function of this protein in plastid vesicle transport. This assumption was further supported by biochemical and genetic analyses. However, the exact molecular function of CPSFL1 in chloroplast and thylakoid biogenesis remained to be elucidated. As a DFG fellow, I propose an interdisciplinary and complementary work program to characterize the functional role of CPSFL1 in chloroplast biogenesis. This program seeks to determine the molecular composition of chloroplast vesicles. Furthermore, the aim of this program is to characterize the in vivo lipid ligand(s) of CPSFL1 and analyze the effect that CPSFL1 levels have on the lipid composition of chloroplast membranes and plant lipid homeostasis. In addition, protein-protein interactions of CPSFL1 will be analyzed with the aim to further elucidate the concerted mechanistic and regulatory roles that CPSFL1 and its protein interactors play in chloroplast and thylakoid biogenesis. In preliminary work, I could show that heterologous CPSFL1 expression in E. coli causes alterations in the membrane transport processes of this host. Thus, I propose to additionally characterize the molecular function of CPSFL1 in E.coli. In summary, by characterizing CPSFL1 protein and lipid interactions in plants and in E.coli and elucidating their molecular roles, the work proposed here will generate new fundamental insights into the functional mode of Sec14-like proteins that underlies cellular membrane traffic events in general and the role of CPSFL1 in chloroplast biogenesis specifically.

• DFG Programme: Research Grants