Abstract
Chloroplast NAD(P)H dehydrogenase complex (NDH) reduces the plastoquinone pool nonphotochemically, which functions in cyclic electron flow around photosystem I. In order to clarify the physiological role of NDH, we isolated nuclear mutants, crr2 (chlororespiratory reduction 2-1, 2-2) affected in the chloroplastic NDH activity in Arabidopsis by using chlorophyll fluorescence imaging system. Accumulation of NDH complex is specifically impaired in crr2 alleles. Consequently, crr2 lacks the NDH activity drastically, although the photosynthetic electron transport is unaffected. CRR2 encodes a member of AtPCMP family which is related with the PPR proteins predicted to function in the post-transcriptional regulation of organellar gene expression. Northern analysis revealed that crr2 has a defect in the intergenic processing of chloroplast RNA between rps7 and ndhB. We conclude that CRR2-dependent intergenic processing is essential for the ndhB translation and the formation of NDH complex.
