Structure and biogenesis of the chloroplast NAD(P)H dehydrogenase complex

Eleven genes (ndhA-ndhK) encoding proteins homologous to the subunits of bacterial and mitochondrial NADH dehydrogenase (complex I) were found in the plastid genome of most land plants. These genes encode subunits of the chloroplast NAD(P)H dehydrogenase (NDH) complex involved in photosystem I (PSI) cyclic electron transport and chlororespiration. Although the chloroplast NDH is believed to be closely and functionally related to the cyanobacterial NDH-1L complex, extensive proteomic, genetic and bioinformatic studies have discovered many novel subunits that are specific to higher plants. On the basis of extensive mutant characterization, the chloroplast NDH complex is divided into four parts, the A, B, membrane and lumen subcomplexes, of which subunits in the B and lumen subcomplexes are specific to higher plants. These results suggest that the structure of NDH has been drastically altered during the evolution of land plants. Furthermore, chloroplast NDH interacts with multiple copies of PSI to form the unique NDH–PSI supercomplex. Two minor light-harvesting-complex I (LHCI) proteins, Lhca5 and Lhca6, are required for the specific interaction between NDH and PSI. The evolution of chloroplast NDH in land plants may be required for development of the function of NDH to alleviate oxidative stress in chloroplasts. In this review, we summarize recent progress on the subunit composition and structure of the chloroplast NDH complex, as well as the information on some factors involved in its assembly. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts.

Research highlights
► Dozens of proteins have been shown to be subunits of the chloroplast NDH complex.
► Chloroplast NDH complex consists of A, B, membrane and lumen subcomplexes.
► Chloroplast NDH interacts with at least two copies of PSI to form the unique NDH–PSI supercomplex via Lhca5 and Lhca6.
► Several factors are required for assembly of the chloroplast NDH complex.
► Drastic alteration occurred not only in the structure but also in the biogenesis of NDH during the evolution from cyanobacteria to higher plants.