128 T. Sano et al.
required. Through the use of suspension-cultured cells fromArabidopsis
plants stably expressing GFP-tubulin (Ueda et al. 1999), the dynamics of MTs
throughout cell division were firstly demonstrated (Hasezawa et al. 2000).
A chimeric protein, consisting of GFP fused to the microtubule-binding do-
main (MBD) of the microtubule-associated protein 4 (MAP4), allowed label-
ing of MTs (Marc et al. 1998; Granger and Cyr 2000), but detailed observations
could not be performed because of the low fluorescence of GFP-MBD. How-
ever, by establishing a transgenic BY-2 cell line stably expressing GFP-tubulin
fusion proteins (BY-GT), MT dynamics throughout the cell cycle could be
precisely followed by confocal laser scanning microscopy (CLSM) (Fig. 1, Ku-
magai et al. 2001).
Using this BY-GT cell line, the mode of CMT reorganization at the M/G1
interface was successfully clarified as follows (Kumagai et al. 2001). After dis-
ruption of the phragmoplast, the CMTs initially become organized in the
perinuclear regions, and then elongate to reach the cell cortex where they
form “bright spots”. The first CMTs subsequently elongate from these spots
and become oriented parallel to the long axis towards the distal end of the
cells. Around the time when the tips of the parallel MTs reach the distal
end, the formation of transverse CMTs follow in the cortex near the division
site. Although the role of CMTs in cellulose microfibril deposition has been
intensively discussed, recently, cellulose synthase complex visualized by a fu-
sion of yellow fluorescent protein (YFP) with a cellulose synthase protein of
CESA6 was revealed to be colocalized with CMTs, indicating a guidance of
cellulose deposition by the cytoskeleton (Paredez et al. 2006). MTs were also
Fig. 1 Microtubule (MT) dynamics during cell cycle progression in tobacco BY-GT cells.
MTs are visualized by stable expression of GFP-αtubulin fusion proteins in tobacco BY-2
cells. Typical plant MT structures observed are: cortical MTs in the G1 phase, preprophase
band in the G2 phase, mitotic spindle in metaphase of mitosis, and phragmoplast in
telophase in mitosis.Bar: 10 μm