PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

CP29 is required for repair of Photosystem II in Chlamydomonas reinhardtii. Jun Minagawa^*,1, Ayumi Kanno¹, ¹ Inst. of Low Temp. Sci., Sapporo, Hokkaido, Japan

ABSTRACT- The light-harvesting complexes for PSII are generally divided into three categories; The core (CP47/CP43), minor (CP29/CP26/CP24), and major antenna (LHCII). While the minor antenna has been suggested to have some role on high energy quenching rather than harvesting light because of its localization and high content of xanthophyll cycle pigments, the Arabidopsis antisense plants of either CP26 or CP29 were reported to show no phenotype. In this study, we generated a knock-out mutant of one of the minor antenna proteins, CP29, in C. reinhardtii by RNAi technology. Transformants of the RNAi construct, b4i mutant, was initially confirmed to have less than 3% of Lhcb4 mRNA by RT-PCR and no CP29 protein by Westernblotting. The b4i mutant showed identical phenotype to the wild type when it was grown under low light conditions. But, the striking difference was that this mutant did not grow at all under high light conditions. To investigate the photoinhibitory events occurred in this mutant, the photosynthetic activity was examined during the course of high-light treatment in the presence or absence of chloramphenicol, an antibiotic inhibiting protein synthesis in chloroplast. The results indicates that the PSII is not particularly susceptible to photodamage, but the damaged center is not repaired in the b4i mutant. In the case of wild type cells, the damaged center is repaired within one hour after exposure to high-light. We thus concluded that CP29 is directly or indirectly involved in the repair process of damaged PSII centers.

KEY WORDS: photoinhibition, CP29, Chlamydomonas, RNAi