Poster: Photosynthesis

Abs # 360: Localization of Chlorophyllide a Oxygenase (CAO) in Chloroplasts

Presenter:	Yamasato, Akihiro , yamasato@snowbell.lowtem.hokudai.ac.jp
Authors	Yamasato, Akihiro  (A) (B)  Nagata, Nozomi  (A)   Ryouichi, Tanaka  (A)   Ayumi, Tanaka  (A)
Affiliations:	(A): Institute of Low Temperature Science, Hokkaido University (B): Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation

Higher plants maintain optimal photosynthetic efficiency under different light conditions by regulating the light-harvesting-antenna size. The antenna size of photosystem II is determined by the amount of light-harvesting complex II (LHCII) associated to the core complex. Formation and stabilization of LHCII require chlorophyll b in thylakoid membranes. Therefore, chlorophyll b synthesizing enzyme, chlorophyllide a oxygenase (CAO), is speculated to play a central role in the adaptation to light conditions. This idea was supported by the studies on the expression of cao gene under various light conditions. In addition to the gene expression, the localization of CAO is important to understand the regulation of LHCII formation. However, localization of CAO in chloroplast has not been elucidated. To determine the localization of CAO in chloroplasts, CAO from Arabidopsis thaliana was fused to synthetic green fluorescent protein (sGFP(S65T)), and over-expressed in wild-type and chlorophyll b-less (chlorina 1-1) strains under the control of CaMV35S promoter and TMV Omega sequence. The chimeric proteins were detected by immuno-blotting analysis using anti-GFP and anti-CAO antibodies and the phenotype of chlorina 1-1 was complemented. The GFP fluorescence was analyzed by confocal laser-scanning microscope and was found at the edge of chloroplasts. The fluorescence was also found at the inside of chloroplasts and this was confirmed by immuno-electronmicroscopy. These results suggested that CAO is localized at chloroplast envelope and thylakoid membranes.