Poster: Photosynthesis

Abs # 317: Characterization of an Arabidopsis thaliana mutant with impaired psbO, one of genes encoding an extrinsic 33-kDa protein of oxygen-evolving complex

Presenter:	Murakami, Reiko , murakami@kais.kyoto-u.ac.jp
Authors	Murakami, Reiko  (A)   Ifuku, Kentaro  (A)   Takabayashi, Atsushi  (A)   Shikanai, Toshiharu  (B)   Endo, Tsuyoshi  (A)   Sato, Fumihiko  (A)
Affiliations:	(A): Graduate school of biostudies, Kyoto University (B): Graduate School of Biological Sciences, Nara Institute of Science and Technology

An extrinsic 33-kDa component protein of the oxygen-evolving complex in photosystem II (PSII) is essential for photosynthetic oxygen evolution, and appears to play a central role in the stabilization of the manganese cluster. In Arabidopsis thaliana, the extrinsic 33-kDa proteins are encoded by two genes, psbO and psbO2. To isolate the Arabidopsis mutants that have defects in either of the 33-kDa proteins, we used chlorophyll fluorescence analysis as first screening. We, then, identified a mutant, LE18-30 (psbo1), with low accumulation of the 33-kDa protein, by the second screening with SDS-PAGE. Further DNA sequence analysis of the mutant revealed that Gln159 of psbO was replaced with stop codon by a single point mutation. The mutant showed low quantum yield of photosystem II and the poor activity of oxygen evolution, resulting in much slower growth than the wild-type. Although the mature products of two genes, psbO and psbO2, have quite similar primary structures, PsbO2 could be resolved from PsbO as a faster moving protein on SDS-PAGE. Two polypeptides also could be separated by an anion exchange chromatography. These findings indicate the difference between two 33-kDa proteins in terms of surface charges and binding affinity. The clear phenotype of psbo1 and the difference in the chemical properties between two isoproteins suggest their functional difference. Expression of recombinant Arabidopsis 33-kDa proteins in Escherichia coli is on-going for the functional characterization of PsbO and PsbO2.