Poster: Cytoskeleton: Structure & Function

Abs # 1112: CHUP1 is essential for proper chloroplast positioning

Presenter:	Wada, Masamitsu , wada-masamitsu@c.metro-u.ac.jp
Authors	Wada, Masamitsu  (A) (B)  Oikwa, Kazusato  (A) (B)  Kasahara, Masahiro  (B)   Kiyosue, Tomohiro  (B)   Kagawa, Takatoshi  (B) (C)  Suetsugu, Noriaki  (A) (B)  Kanegae, Takeshi  (A)   Takahashi, Fumio  (A) (B)  Niwa, Yasuo  (D)
Affiliations:	(A): Tokyo Metropolitan University, Graduate School of Science (B): National Institute for Basic Biology (C): Japan Science and Technology Corporation, PRESTO (D): University of Shizuoka, Graduate School of Nutritional and Environmental Sciences

Intracellular distribution of organelles should be crucial to perform appropriate cell functions. Chloroplasts change their intracellular position to optimize photosynthetic activities in response to light conditions. Through screening of mutants defective in the chloroplast photorelocation movement, we isolated six mutant clones in which chloroplasts do not spread in cells but accumulate to the bottom of the cells. These chup (chloroplast unusual positioning) mutants were shown to comprise one genetical locus by complementation tests. Observation of the positioning of other organelles, such as mitochondria, peroxisomes and nuclei revealed that chloroplast positioning and movement is specifically impaired in this mutant. The CHUP1 gene encodes a novel protein containing putative multifunctional domains such as a coiled-coil domain, an actin-binding domain, a proline-rich region and two leucine-zipper domains. A GST-fusion protein containing the actin-binding domain of CHUP1 actually bound to F-actin in vitro. To our knowledge, CHUP1 is the first component identified which is required for organelle positioning and movement in plant cells.