LAUSR

The chloroplast NADH dehydrogenase-like (NDH) complex is composed of at least 29 subunits and has an important role in mediating photosystem I (PSI) cyclic electron transport (CET) 1 – 3 . The NDH complex associates with PSI to form the PSI–NDH supercomplex and fulfil its function. Here, we report cryo-electron microscopy structures of a PSI–NDH supercomplex from barley ( Hordeum vulgare ). The structures reveal that PSI–NDH is composed of two copies of the PSI–light-harvesting complex I (LHCI) subcomplex and one NDH complex. Two monomeric LHCI proteins, Lhca5 and Lhca6, mediate the binding of two PSI complexes to NDH. Ten plant chloroplast-specific NDH subunits are presented and their exact positions as well as their interactions with other subunits in NDH are elucidated. In all, this study provides a structural basis for further investigations on the functions and regulation of PSI–NDH-dependent CET. Cryo-electron microscopy structures of the photosystem I–NADH dehydrogenase-like supercomplex in barley provide structural details to elucidate the functions and regulation of photosystem I-dependent cyclic electron transport in chloroplasts.