Abstract
NAD(P)H dehydrogenase (NDH) of chloroplasts is involved in PSI cyclic electron transport. Eleven and three subunits are encoded by the chloroplast genome and nuclear genome, respectively. Comparison with the bacterial NDH complex indicates the existence of some unidentified subunits functioning in electron donor binding in plants. An Arabidopsis gene, CRR7 was identified in the mutant which specially lacks NDH activity. In crr7, the level of the NDH complex was reduced. CRR7 (At5g39210) encodes a protein containing 156 amino acids with a plastid targeting signal and localized to the thylakoid membranes. CRR7 is hydrophilic protein without any transmembrane domain and does not contain any known motifs. CRR7 is conserved in cyanobacterial genomes. CRR7 was unstable within the crr2-2 , in which the expression of ndhB was impaired. These results strongly suggest that CRR7 is a novel subunit of the chloroplast NDH complex.
