Article

Chloroplast unusual positioning1 is essential for proper chloroplast positioning.

Department of Biology, Faculty of Science, Graduate School of Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
The Plant Cell (impact factor: 8.99). 01/2004; 15(12):2805-15. DOI:10.1105/tpc.016428 pp.2805-15
Source: PubMed

ABSTRACT The intracellular distribution of organelles is a crucial aspect of effective cell function. Chloroplasts change their intracellular positions to optimize photosynthetic activity in response to ambient light conditions. Through screening of mutants of Arabidopsis defective in chloroplast photorelocation movement, we isolated six mutant clones in which chloroplasts gathered at the bottom of the cells and did not distribute throughout cells. These mutants, termed chloroplast unusual positioning (chup), were shown to belong to a single genetic locus by complementation tests. Observation of the positioning of other organelles, such as mitochondria, peroxisomes, and nuclei, revealed that chloroplast positioning and movement are impaired specifically in this mutant, although peroxisomes are distributed along with chloroplasts. The CHUP1 gene encodes a novel protein containing multiple domains, including a coiled-coil domain, an actin binding domain, a Pro-rich region, and two Leu zipper domains. The N-terminal hydrophobic segment of CHUP1 was expressed transiently in leaf cells of Arabidopsis as a fusion protein with the green fluorescent protein. The fusion protein was targeted to envelope membranes of chloroplasts in mesophyll cells, suggesting that CHUP1 may localize in chloroplasts. A glutathione S-transferase fusion protein containing the actin binding domain of CHUP1 was found to bind F-actin in vitro. CHUP1 is a unique gene identified that encodes a protein required for organellar positioning and movement in plant cells.

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Keywords

actin binding domain
 
Arabidopsis defective
 
chloroplast photorelocation movement
 
CHUP1 gene encodes
 
coiled-coil domain
 
complementation tests
 
effective cell function
 
fusion protein
 
glutathione S-transferase fusion protein
 
green fluorescent protein
 
leaf cells
 
Leu zipper domains
 
mesophyll cells
 
multiple domains
 
N-terminal hydrophobic segment
 
novel protein
 
plant cells
 
Pro-rich region
 
single genetic locus
 
unique gene