Chup1 - a chloroplast movement protein and its interactions

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.