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
Aim of this project is
1. to identify the myosin isoforms, belonging to different
2. to characterize their specific function and to study their
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).