NDF6: a thylakoid protein specific to terrestrial plants is essential for activity of chloroplastic NAD(P)H dehydrogenase in Arabidopsis.
NAD(P)H dehydrogenase (NDH) is a homolog of respiratory complex I and mediates one of the two pathways of cyclic electron flow around PSI (CEF I). Although 15 ndh subunits have been identified in the chloroplastic and nuclear genomes of higher plants, no electron accepter subunits have been identified to date. To identify the missing chloroplastic NDH subunits, we undertook an in silico approach based on co-expression analysis. In this report, we characterized the novel gene NDF6 (NDH-dependent flow 6; At1g18730) which encodes a protein that is essential for NDH activity. NDF6 has one transmembrane domain and is localized in the thylakoid membrane fraction. Homologous proteins of NDF6 were identified in the genomes of terrestrial plants; however, no homologs have been found in cyanobacteria, which are thought to be the origin of chloroplasts and have a minimal NDH complex unit. NDF6 is unstable in ndhB-impaired or disrupted mutants of higher plants in which the chloroplastic NDH complex is thought to be degraded. These results suggest that NDF6 is a novel subunit of chloroplastic NDH that was added to terrestrial plants during evolution.
Graduate School of Biostudies, Kyoto University, Sakyoku, Kyoto, 606-8502 Japan.
Noriko
N
Ishikawa
Atsushi
A
Takabayashi
Satoshi
S
Ishida
Yasushi
Y
Hano
Tsuyoshi
T
Endo
Fumihiko
F
Sato
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D004269:DNA, Bacterial; D004795:Enzyme Stability; D017343:Genes, Plant; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D050505:Mutant Proteins / Q000302:isolation & purification / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009252:NADPH Dehydrogenase / Q000737:chemistry / Q000378:metabolism*; D010788:Photosynthesis; D021381:Protein Transport; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D020524:Thylakoids / Q000201:enzymology*
D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D008565:Membrane Proteins; D050505:Mutant Proteins; D009252:NADPH Dehydrogenase; C530972:PnsB4 protein, Arabidopsis; C036483:T-DNA