186 Y.-R.J.Lee·B.Liu
dependent on the presence of the PPB, the absence of KCA1 at the PPB site is
required for correct placement of the cell plate. Therefore, it would be of par-
ticular interest to identify the cargo molecule(s) of KCA1 in order to further
understand how KCA1 is linked to spatial regulation of cell division.
Another unresolved mystery is how microtubules and microfilaments cross
talk at the cell division site. It is known that microfilaments play a role in divi-
sion plane determination, but not cell plate formation per se (Palevitz 1980).
Our recent results indicate that plant kinesins containing the CH (calponin
homology) domain interact with microfilaments (Preuss et al. 2004). Certain
members of this plant specific kinesingroup may integrate microfilaments
with microtubules at the cell division site.
4
Myosins in Plant Cytokinesis: Vesicle Transport Continued
Most myosins, except for Myosin II, are implicated in vesicle transport in fun-
gal and animal cells (Berg et al. 2001). Among them, fungal Myosin V plays
a role in vesicle transport during cytokinesis/septation (Mulvihill et al. 2006).
Both plant Myosin VIII and XI are more closely related to animal and fungal
Myosin V than to other myosins (Lee and Liu 2004). Moreover, Myosin XI is
thoughttoshareacommonancestorwithMyosinVasbothcontainthe“di-
lute” domain towards their C-termini, which is considered to be involved in
vesicle trafficking (Berg et al. 2001; Foth et al. 2006). But how they might be
involved in cytokinesis remains to be determined. A pharmacological study
with drugs disturbing myosin activities shows that certain myosin(s) may
contribute to cell plate expansion and alignment in Tradescantia stamen hair
cells (Molchan et al. 2002). This finding has been echoed by a recent genetic
study showing that Myosin XI MYA2 plays a role in cell plate alignment in
Arabidopsis (Holweg and Nick 2004).
Functional analysis of plant Myosin XI is complicated by the fact that this
subfamily has many members. InA. thaliana, for example, 13 out of its 17
myosins are in this subfamily (Reddy and Day 2001a)! Potential functional re-
dundancy would make functional studies more tedious and time consuming.
Nevertheless, their potential role in cytokinesis will be revealed by careful ge-
netic and cell biological studies in the near future using existing or soon to be
available tools.
5
Concluding Remarks
The complexity and novelty of plant kinesin and myosin superfamilies im-
plies that fascinating intracellular motile activities powered by these cy-