Poster: Organelle Biogenesis

Abs # 1127: ARC3, a regulation factor of chloroplast division, is a junction point of prokaryotic and eukaryotic regulatory system

Presenter:	Shimada, Hiroshi , hshimada@bio.titech.ac.jp
Authors	Shimada, Hiroshi  (A)   Koizumi, Masato  (A)   Kuroki, Kouta  (A)   Mariko, Mochizuki  (A)   Fujimoto, Hitoshi  (A)   Masuda, Tatsuru  (A)   Ohta, Hiroyuki  (A)   Takamiya, Ken-ichiro  (A)
Affiliations:	(A): Tokyo Institute of Technology

arc3 (Accumulation and Replication of Chloroplast) mutant of Arabidopsis thaliana has a few abnormally large chloroplasts in the cell. Fine mapping analysis showed that ARC3 gene is a fusion gene of prokaryotic, FtsZ, and eukaryotic, phosphatidylinositol-4-phosphate 5-kinase (PIP5K), genes. The fusion protein of the full-length ARC3 and GFP (green fluorescent protein) is exclusively located in chloroplast as well as A. thaliana FtsZ. The eukaryotic homologous region of ARC3 was part of PIP5K. ARC3 protein showed no PIP5K activity, but it was phosphorylated, similar to A. thaliana PIP5K, by A. thaliana protein in vitro, and the phosphorylation rate using endogenous protein fraction from dark grown plant was higher than that from light grown plant, suggesting that light-dependent regulation of ARC3 via phosphorylation of PIP5K domain occurs in chloroplast division. Our results indicate that ARC3 is a functional prokaryotic and eukaryotic fusion protein, and suggest that ARC3 is a junction point in signal transduction through which the eukaryotic nucleus regulates prokaryotic chloroplast division.