Identification of a novel protein, CRR7, required for the stabilization of the chloroplast NAD(P)H dehydrogenase complex in Arabidopsis.
An Arabidopsis thaliana mutant, crr7 (chlororespiratory reduction), was isolated using chlorophyll fluorescence imaging to detect reduced activity in NAD(P)H dehydrogenase (NDH). The chloroplast NDH complex is considered to have originated from cyanobacteria in which the NDH complex is involved in respiration, photosystem I (PSI) cyclic electron transport and CO2 uptake. In higher plants the NDH complex functions in PSI cyclic electron transport within the chloroplast. Despite exhaustive biochemical approaches, the entire subunit composition of the NDH complex is unclear in both cyanobacteria and chloroplasts. In crr7 accumulation of the NDH complex was specifically impaired. In vivo analysis of electron transport supported the specific loss of the NDH complex in crr7. CRR7 (At5g39210) encodes a protein of 156 amino acids, including a putative plastid target signal, and does not contain any known motifs. In contrast to CRR2 and CRR4, involved in the expression of chloroplast ndh genes, CRR7 is conserved in cyanobacterial genomes. Although CRR7 did not contain any transmembrane domains, it localized to the membrane fraction of the chloroplast. CRR7 was unstable in the crr2-2 mutant background, in which the expression of ndhB was impaired. These results strongly suggest that CRR7 is a novel subunit of the chloroplast NDH complex.
Kamruzzaman Munshi
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M
Graduate School of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashiku, Fukuoka, Japan 812-8581.
Kobayashi
Yoshichika
Y
Shikanai
Toshiharu
T
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D002736:Chloroplasts / Q000201:enzymology*; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004579:Electron Transport / Q000502:physiology; D004795:Enzyme Stability; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D008969:Molecular Sequence Data; D009252:NADPH Dehydrogenase / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; C508069:CRR7 protein, Arabidopsis; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D009252:NADPH Dehydrogenase