Elucidating the role of Curvature Thylakoid (CURT)-like proteins in cyanobacterial cell division

• Applicant: Professor Dr. Marcel Dann
• Subject Area: Plant Physiology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 518024318

Cyanobacteria and chloroplasts are phylogenetic sister clades, both engage in oxygenic photosynthesis, and share most of the necessary molecular machinery and subcellular structures. One such structure are thylakoids - an intracellular membrane system that houses the pigment-binding and membrane-bound protein complexes of the photosynthetic electron transport chain. Thylakoids of higher plants form extremely complex 3D structures that serve to increase reactive surface area and to allow for functional subdivision of the system. In plants, CURT1 (Curvature Thylakoid 1)-like proteins are essential for the required restructuring of thylakoid membranes. Cyanobacteria possess closely related proteins – CurT-like proteins – that appear to have much less influence on their thylakoid architecture, though. However, recent observations from our group suggest that CurT has a significant and never before described influence on various cyanobacterial cell division processes, and physically interacts with key components of the cell division apparatus. We suggest that a previously observed but not further investigated population of CurT proteins in the plasma membrane fraction is actively involved in cell division. In addition, we hypothesise that CurT-induced openings in the thylakoid membrane layers are required for the precise determination of the cell division plane by the proteins MinC, MinD, and MinE which oscillate from cell pole to cell pole. CurT proteins thus seem to fulfil an important and hitherto unnoticed coordinative function that prevents cell division from being impaired by the intracellular thylakoid membrane system. The aims of this project are to elucidate (i) the functional role of CurT in cyanobacterial cell division in the model organisms Synechocystis sp. PCC6803 and Synechococcus sp. PCC7942, (ii) the functional differentiation between plasma membrane- and thylakoid-bound CurT populations, and (iii) the phylogenetic origin and functional radiation of CurT/CURT1 isoforms during the transition from free-living cyanobacteria to endosymbiotic chloroplasts. To this end, we will investigate the physical protein-protein interaction networks, as well as the functional relevance of previously observed post-translational modifications of cellular CurT proteins. In addition, we will functionally characterise a candidate gene we have identified, which presumably encodes one of the last surviving descendants of the evolutionary genetic precursor of modern CurT/CURT1 proteins. The combination of these findings will allow us to draw an unprecedented picture of the evolutionary genetic ancestry, continuous functional shift, and modern functional diversity of the fascinating determinant of thylakoid system architecture that is CurT/CURT1.

• DFG Programme: Research Grants