title: Three PsbQ-like proteins are required for the function of the chloroplast NAD(P)H dehydrogenase complex in Arabidopsis.
abstract: Arabidopsis has three PsbQ-like (PQL) proteins in addition to the PsbQ subunit of the oxygen-evolving complex of PSII. Recent bioinformatic and proteomic studies suggested that the two PQL proteins, PQL1 (At1g14150) and PQL2 (At3g01440), might function in the chloroplast NAD(P)H dehydrogenase (NDH) complex; however, their molecular function has not been characterized. In this study, we examined the function of the chloroplast NDH in the Arabidopsis pql1 and pql2 mutants. Post-illumination increases in Chl fluorescence, which are caused by an NDH-dependent cyclic electron flow, were absent in both mutants, indicating that PQL1 and PQL2 are required for NDH activity. In the thylakoid membranes of wild-type plants, PQL1 and PQL2 were tightly associated with the NDH-PSI supercomplex and protected from protease treatments, while unassembled PQLs were not stably accumulated in mutants lacking known NDH subunits. Subunit stability of the NDH complex was affected differently in the thylakoid membranes of the pql1 and pql2 mutants. These data indicate that PQL1 and PQL2 are novel NDH subunits and differ in their functional roles and in their binding sites in the NDH complex. Furthermore, functional analysis on PQL3 (At2g01918) using the pql3 mutant suggests that PQL3 is also required for NDH activity. Proteins homologous to each PQL protein are found in various plant species, but not in cyanobacteria, algae, mosses or ferns. These results suggest that seed plants that have NDH activity in chloroplasts specifically developed three PQL proteins for the function of the chloroplast NDH complex.
authors.affiliation: Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Yabuta
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ifuku
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takabayashi
authors.forename: Seiko
authors.initials: S
authors.lastname: Ishihara
authors.forename: Kunio
authors.initials: K
authors.lastname: Ido
authors.forename: Noriko
authors.initials: N
authors.lastname: Ishikawa
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Endo
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Sato
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology*; D004269:DNA, Bacterial / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D009252:NADPH Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D045331:Photosystem I Protein Complex; C036483:T-DNA; D009252:NADPH Dehydrogenase