PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

Arabidopsis genes involved in chloroplast NDH activity. Toshiharu Shikanai^{*,1, 2}, Mihoko Hashimoto², Emi Kotera², Masao Tasaka², ¹ Kyushu University, Fukuoka, Fukuoka, Japan² Nara Institute of Science and Technology, Ikoma, Nara, Japan

ABSTRACT- Chloroplast NDH complex functions in PSI cyclic electron flow, as well as PGR5-dependent FQR pathway. NDH-dependent plastoquinone reduction can be monitored as a transient increase in chlorophyll fluorescence after turning off actinic light. We focused on this subtle change in fluorescence to screen Arabidopsis mutants (crr; chlororespiratory reduction) defective in NDH activity. For this purpose we modified the chlorophyll fluorescence imaging system which was originally developed to screen mutants with aberrant chlorophyll fluorescence levels in the light. So far we have identified 13 loci related to NDH activity. Two mutants, crr2 and crr4, are specifically defective in the accumulation of the NDH complex. Except for the defect in the NDH complex neither mutants display any phenotype, which is consistent with the results obtained by the knockout of chloroplast ndh genes. Both CRR2 and CRR4 genes encode members of PPR family. Some members of this family have shown to be involved in RNA maturation steps in chloroplasts or mitochondria. crr2 is defective in RNA processing between rps7 and ndhB, which is possibly essential for the ndhB translation. On the other hand, crr4 is defective in RNA editing creating an initiation codon of ndhD. In the genome this initiation codon is encoded by ACG, which is converted to AUG by CRR4-dependent RNA editing. Although CRR2 and CRR4 is structurally closely related each other, they are involved in different processes of RNA maturation. We consider that the members of PPR family function to recognize the target RNA and facilitate the access of the general factor involved in RNA maturation, including RNA processing and RNA editing.

KEY WORDS: NDH, PSI cyclic electron flow, Chloroplast, PPR