FOR 2092: Biogenesis of Thylakoid Membranes: Spatiotemporal Organisation of Photosynthetic Protein Complex Assembly

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Photosynthetic electron transport is mediated by multi-subunit pigment-protein complexes which are situated in a specialized membrane system, named thylakoids. Despite a detailed knowledge on the structure and function of these complexes, little is known on their assembly during thylakoid membrane biogenesis. The emerging picture of this process depicts a highly-ordered scaffold of assembly factors that integrates the incorporation of proteins and organic as well as inorganic co-factors in a step-wise manner. Recent work has also indicated that the production line for photosynthetic complexes is initiated at biogenic membrane sub-compartments from where it proceeds via discrete and conserved assembly intermediates to generate a functional energy converting apparatus. The FOR2092 Research Unit has set out to disentangle the molecular principles of the spatiotemporal organization of thylakoid membrane biogenesis by applying a multidisciplinary, systematic approach combining unique expertise in molecular genetics, biochemistry, biophysics and ultrastructural analyses. The concept includes the comparative investigation of a set of suitable model organisms that enables one to follow the complete evolutionary path for the development of thylakoid complexity from primordial cyanobacteria to chloroplasts of vascular plants. By focusing on distinct assembly factors and the spatiotemporal organization of their working mode, the joined forces of FOR2092 members have recently discovered a variety of new molecular aspects of thylakoid biogenesis. The findings include details of photosystem II and photosystem I assembly, membrane insertion of thylakoid proteins, organic and inorganic co-factor incorporation and formation of biogenic membrane structures. In addition, both genetic and biochemical approaches have identified several new components of the intricate assembly factor network for thylakoid biogenesis. In sum, this obtained body of evidence now forms the solid basis for a proceeding comprehensive study of the biogenesis process which will be complemented by comparative analysis of the pigment-free ATPase complex as well as state-of-the-art studies on thylakoid ultrastructure in situ. The consortium envisions that by answering the questions how, where and when the different assembly processes take place and are integrated during thylakoid maturation, the development of knowledge-based strategies for the targeted modification of the biogenesis process in a broad set of photosynthetic model organisms will become feasible in the future.