Cytoskeletal Motor Proteins in Plant Cell Division 175
Fig. 2Microtubules and kinesins at prophase nuclear envelope. A prophase onion cell was
stained with anti-tubulin, anti-pan kinesin, and DAPI to reveal microtubules, kinesins,
and DNA, respectively. Note microtubules were polymerized on the nuclear envelope (ar-
rowheads) while the PPB microtubules were prominent at the cortex in the middle of the
cell. Kinesins also accumulated on the nuclear envelope (arrowheads)
binding to Ca++/calmodulin (Deavours et al. 1998; Narasimhulu et al. 1997).
Conversely, its motor activity can be constitutively activated using an anti-
body against the calmodulin-binding peptide (Narasimhulu and Reddy 1998).
It decorates microtubule arrays of the spindle and the phragmoplast (Bowser
and Reddy 1997; Preuss et al. 2003; Smirnova et al. 1998). When such a protein
is activated by microinjection of anti-calmodulin-binding peptide antibody in
the stamen hair cells of Tradescantia, nuclear envelope breakdown is induced
to allow cells to enter prometaphase precociously (Vos et al. 2000). There-
fore, KCBP/ZWI’s potential function in nuclear envelope breakdown may be
regulated by local concentration of Ca++/calmodulin at the nuclear envelope
region. Other proteins may play a redundant role as KCBP/ZWI does, because
null mutations at the corresponding locus inA. thalianaonly affect trichome
morphogenesis, but not cell division (Oppenheimer et al. 1997).
2.3
Kinesins Mediating the Interaction Between Chromosomes and Microtubules
In animal cells, the inventory of microtubule motors interacting with chro-
mosomes includes cytoplasmic dynein, CENP-E/Kinesin-7, and MCAK/
Kinesin-13 that appeared at the kinetochore; and chromokinesin/Kinesin-4
and Kinesin-10 along chromosome arms (Heald 2000). In addition to the ab-
sence of cytoplasmic dynein in angiosperms, plant kinesins in the Kinesin-4,
-7, and -13 subfamilies appear to function in interphase cells. Null mutations
at thefra1locus encoding a Kinesin-4 only affect cell elongation but not cell
division (Zhong et al. 2002). The Arabidopsis Kinesin-13A protein is associ-
ated with the Golgi stacks, and plays a role in trichome morphogenesis, again,
not in cell division (Lu et al. 2005). None of the plant Kinesin-7 members have