Identification and characterization of a stable intermediate in photosystem I assembly in tobacco

• Published in: The Plant journal : for cell and molecular biology Vol. 90; no. 3; pp. 478 - 490
• Main Authors: Wittenberg, Gal, Järvi, Sari, Hojka, Marta, Tóth, Szilvia Z., Meyer, Etienne H., Aro, Eva‐Mari, Schöttler, Mark A., Bock, Ralph
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.05.2017
• Subjects: Assembly; Biosynthesis; Deficient mutant; Flowers & plants; Leaves; Maturation; Membrane proteins; Membranes; Nicotiana - genetics; Nicotiana - metabolism; photosynthesis; Photosynthesis - genetics; Photosynthesis - physiology; photosystem assembly; photosystem biogenesis; Photosystem I; Photosystem I Protein Complex - genetics; Photosystem I Protein Complex - metabolism; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Plants (botany); Prostheses; Prosthetic groups; Proteins; Structure-function relationships; thylakoid membrane; Thylakoid membranes; Thylakoids; Thylakoids - metabolism; Tobacco; photosystem biogenesis; thylakoid membrane; photosynthesis; photosystem assembly
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.13505

Summary Photosystem I (PSI) is the most efficient bioenergetic nanomachine in nature and one of the largest membrane protein complexes known. It is composed of 18 protein subunits that bind more than 200 co‐factors and prosthetic groups. While the structure and function of PSI have been studied in great detail, very little is known about the PSI assembly process. In this work, we have characterized a PSI assembly intermediate in tobacco plants, which we named PSI*. We found PSI* to contain only a specific subset of the core subunits of PSI. PSI* is particularly abundant in young leaves where active thylakoid biogenesis takes place. Moreover, PSI* was found to overaccumulate in PsaF‐deficient mutant plants, and we show that re‐initiation of PsaF synthesis promotes the maturation of PSI* into PSI. The attachment of antenna proteins to PSI also requires the transition from PSI* to mature PSI. Our data could provide a biochemical entry point into the challenging investigation of PSI biogenesis and allow us to improve the model for the assembly pathway of PSI in thylakoid membranes of vascular plants. Significance Statement Photosystem I (PSI) is one of the most intricate protein complexes in nature. However, our understanding of the assembly pathway of PSI in seed plants remains rather limited. Here, we report the characterizaiton of PSI*, a stable assembly intermediate in the biogenesis pathway of plant PSI, which contains only a defined subset of PSI subunits and also lacks the LHCI antenna. Furthermore, we identify the PSI low molecular mass subunit PsaF as a potential rate‐limiting factor in PSI biogenesis. These findings could provide a biochemical entry point into furthre investigation of PSI assembly and allow us to propose a revised model for the assembly pathway of PSI in thylakoids.