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Schmidt von Braun, Serena (2008): Chup1 - a chloroplast movement protein and its interactions. Dissertation, LMU München: Faculty of Biology
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Abstract

The molecular mechanisms of light dependent chloroplast movement could for a long time not be unravelled. But the recent discovery of a mutant deficient in chloroplast movement sparked new impulses in the field. This study investigates the molecular mechanisms of chloroplast movement based on the protein Chup1 and the interactions of Chup1 and cytoskeletal effectors. It is demonstrated that Chup1 is exclusively and directly targeted to the chloroplast surface in an N-terminus dependent manner. Analyzing a putative role of Chup1 as a linker between chloroplasts and the cytoskeleton, an interaction with actin is demonstrated which is independent on the filament status of actin. In accordance with this, binding of actin to the outer envelope of chloroplasts is demonstrated. Adding to the understanding of chloroplast movement, it is shown that Chup1 interacts with profilin. Furthermore, an enhancing effect of Chup1 on the interaction of profilin to actin could be demonstrated. As profilin is an actin binding protein and a potent modifier of the polymerisation status of actin filaments, a key role of profilin in chloroplast movement is suggested. For Chup1, an important role as a linker molecule in bridging chloroplasts to actin filaments and a regulatory function in actin polymerization is discussed. The investigation of the global expression profile revealed the effects of light treatment on chup1 mutant plants and the effects of blue light on wildtype plants. From cluster analysis, gene products participating in blue-light induced signalling are suggested. Furthermore, it is suggested, that gene expression is not involved in the regulation of chloroplast movement. A conclusive model of chloroplast movement can be presented.