Plant Molecular Biology 43: 691–703, 2000.
Dirk Inzé (Ed.), The Plant Cell Cycle.
© 2000 Kluwer Academic Publishers. Printed in the Netherlands.
Cell cycle regulation of the microtubular cytoskeleton
, Rachel Cowling and Catherine Delich
Laboratoire de Physiologie Cellulaire V´eg´etale, URA 576, DBMS-CEA/Grenoble, 17, rue des Martyrs, 38054
Grenoble cedex 9, France (
author for correspondence; e-mail: email@example.com)
Key words: cell cycle, cytoskeleton, microtubules, microtubule-associated proteins, plants, tubulin
The microtubular element of the plant cytoskeleton undergoes dramatic architectural changes in the course of the
cell cycle, speciﬁcally at the entry into and exit from mitosis. These changes underlie the acquisition of specialized
propertiesand functionsinvolved, for example,in the equal segregationof chromosomesand the correct positioning
and formation of the new cell wall. Here we review some of the molecular mechanisms by which the dynamics and
the organization of microtubules are regulated and suggest how these mechanisms may be under the control of cell
Over the past few years, our knowledge of the cy-
toskeleton of both plant and animal cells has become
much more detailed due to advances in biochem-
istry, light microscopy and genetics. Biochemical
analysis of microtubules and the proteins that inter-
act with them has led to the fundamental discoveries
that the cytoskeleton is architecturally very complex,
is tremendously dynamic and is highly regulated dur-
ing the cell cycle. The major purpose of this review
is to highlight the molecular mechanisms that regu-
late microtubule organization during the cell cycle in
Microtubules are dynamic polymers resulting from
the assembly of α-β-tubulin heterodimers (the ba-
sic subunit). Microtubules are intrinsically unstable
and alternate between periods of growth or shrinkage.
This phenomenon, termed ‘dynamic instability’, can
be demonstrated in vitro and is essentially a prop-
erty of tubulin itself (Waterman-Store and Salmon,
1997). In living cells, microtubules are stable or dy-
namic depending on the cellular processes in which
they are involved and on the interactions they develop
with cellular effectors. These effectors include several
families of proteins including microtubule-associated
proteins (MAPs). These proteins bind speciﬁcally and
transiently to microtubules and, as well as regulating
microtubule dynamics, are involved in determining the
functional diversity of microtubules.
In higher-plant cells, the organization of micro-
tubules is regulated during the cell cycle (Figure 1).
The cell cycle is divided into four major phases (G1,
S, G2, mitosis), and these phases are accompanied
by changes in the distribution of the microtubules.
The ﬁrst dramatic change is early in G2, when the
interphase microtubule array, composed mainly of mi-
crotubules distributed throughout the cell cortex (Fig-
ure 1a), disappears while another structure appears
that marks precisely the site where the cleavage plane
will be further established. This structure, which is
unique to plant cells, is called the preprophase band
(PPB), and corresponds to the assembly of a transient
cortical microtubule ring (Figure 1b). The PPB disas-
sembles during prophase before the nuclear envelope
breaks down. Simultaneously with the formation of
the PPB, a vast assembly of microtubules occurs at the
nuclear surface. This precedes the construction of the
mitotic spindle that segregates the replicated chromo-
somes into two identical sets and initiates cell division.
The poles of the mitotic spindle lack structurally de-
ﬁned microtubule-nucleatingstructures (Figure 1c, d),
such as the centrosome in animal cells or the spindle
pole body in fungi. As mitosis proceeds, the phrag-
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