Plant and Cell Physiology Advance Access originally published online on January 2, 2009
Plant and Cell Physiology 2009 50(2):383-393; doi:10.1093/pcp/pcn205
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A Novel Nuclear-Encoded Protein, NDH-Dependent Cyclic Electron Flow 5, is Essential for the Accumulation of Chloroplast NAD(P)H Dehydrogenase Complexes
1Graduate School of Biostudies, Kyoto University, Sakyo, Kyoto, 606-8502 Japan
2Center for Gene Research, Nagoya University, Chikusa, Nagoya, 464-8602 Japan
*Corresponding author: E-mail, tuendo{at}kais.kyoto-u.ac.jp; Fax, +81-75-753-6398.
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Abstract |
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The chloroplast NAD(P)H dehydrogenase (NDH) complex, which reduces plastoquinones in thylakoid membranes, is involved in PSI cyclic electron flow and chlororespiration. In addition to land plants, the NDH complex is conserved in cyanobacteria. In this study, we identified a novel NDH-related gene of Arabidopsis, NDH-dependent cyclic electron flow 5 (NDF5, At1g55370). Post-illumination increases in chlorophyll fluorescence were absent in ndf5 mutant plants, which indicated that NDF5 is essential for NDH activity. Sequence analysis did not reveal any known functional motifs in NDF5, but there was some homology in amino acid sequence between NDF5 and NDF2, a known NDH subunit. NDF5 and NDF2 homologs were present in higher plants, but not cyanobacteria. A single homolog, which had similarity to both NDF5 and NDF2, was identified in the moss Physcomitrella patens. Immunoblot analysis showed that NDF5 localizes to membrane fractions of chloroplasts. The stability of NdhH, a subunit of the NDH complex, as well as NDF5 and NDF2, was decreased in ndf5, ndf2 and double ndf2/ndf5 mutants, resulting in a loss of NDH activity in these mutants. These results indicated that both NDF5 and NDF2 have essential functions in the stabilization of the NDH complex. We propose that NDF5 and NDF2 were acquired by land plants during evolution, and that in higher plants both NDF5 and NDF2 are critical to regulate NDH activity and each other's protein stability, as well as the stability of additional NDH subunits.
Keywords: Arabidopsis - Cyclic electron flow - NAD(P)H dehydrogenase (NDH, EC 1.6.99.3)
Abbreviations:
AL, actinic light; BSA, bovine serum albumin; ETR, electron transport rate; 
PSII, quantum yield of PSII; Fm, maximal fluorescence with all PSII reaction centers closed in the dark-adapted state; Fm', maximal fluorescence of PSII in the light-adapted state; Fs, steady-state fluorescence in light; F0, minimum fluorescence at the open PSII reaction center; ML, measuring light; NDF, NDH-dependent cyclic electron flow; NDH, NAD(P)H dehydrogenase; NPQ, non-photochemical quenching; PQ, plastoquinone; RT–PCR, reverse transcription–PCR; SP, saturating pulse of white light.
(Received November 5, 2008; Accepted December 24, 2008)
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  M. Suorsa, S. Sirpio, and E.-M. Aro Towards Characterization of the Chloroplast NAD(P)H Dehydrogenase Complex Mol Plant, November 1, 2009; 2(6): 1127 - 1140. [Abstract] [Full Text] [PDF]
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