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+++ MITARBEITER - Projektbeschreibung (Katharina Klug) +++

„Molecular Biology (Characterization of characean myosins)“

Katharina Wiemann
Post Doc

In plant cells, myosin is the molecular motor responsible for actin-based motility processes such as cytoplasmic streaming and directed vesicle transport. In Arabidopsis at least 8 myosin-like genes have been identified representing two distinct classes.

Some of the Arabidopsis myosin genes are preferentially expressed in different plant organs, indicating different functions of the isoforms. A nucleotide sequence of a characean myosin was identified from thallus extracts of Chara corallina and, recently, our group has identified a partial sequence of a class XI myosin from C. globularis rhizoids.

In this cell type, the interaction of different myosins with the actin cytoskeleton is very obvious and plays a crucial role for the various processes involved in gravity-oriented tip growth. In the small apical part of the cell, myosins fulfill a number of different functions; they manage to coordinate the precise positioning and the gravity-affected transport of statoliths; they deliver secretory vesicles to the tip and they control the structural integrity and anchorage of the growth-organizing Spitzenkörper. This suggests that the distinct classes of myosins differ considerably in terms of binding domains and in how their activity is regulated. Only one up to a few classes are supposed to be intimately involved in the gravitropic signaling pathway and thus be regulated in their activity. It seems likely that the myosins are also regulated at the transcriptional level throughout gravity sensing and the gravitropic response.

Aim of this project is

1. to identify the myosin isoforms, belonging to different classes
2. to characterize their specific function and to study their localization
3. to analyze myosin isoforms with respect to their (transcriptional) regulation during the response to a gravitropic stimulus. Temporal and spatial resolution and gene silencing experiments as well as overexpression studies shall elucidate the specific function and regulation of the different isoforms.


Fig 1. A class XI myosin isolated from a Chara species comprises different structural and functional domains. The N-terminal head includes the highly conserved ATP-binding site. The neck domain is composed of six IQ motifs. The coiled-coil structure is characterized by conserved tandem-repeats and interrupted by coiled-coil breaking motifs (figure from Christoph Limbach, PhD thesis, Bonn 2006).

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