1021-4437/05/5205- © 2005
Russian Journal of Plant Physiology, Vol. 52, No. 5, 2005, pp. 700–708. Translated from Fiziologiya Rastenii, Vol. 52, No. 5, 2005, pp. 786–795.
Original Russian Text Copyright © 2005 by Klyachko.
Plants are static organisms; the same are their cells.
However, active movements are observed within the
cells: organelle relocations, macromolecule transport
from the sites of their synthesis to the sites of their func-
tioning, chromosome divergence to the spindle poles,
etc. The cytoskeleton plays a key role in all intracellular
movements. Plant cytoskeleton is a dynamic network
consisting of tubulin microtubules (MT) and actin
microﬁlament (MF). These cytoskeletal components can
serve as (1) tracks for the movement of molecular motors
with their speciﬁc cargoes, (2) barriers preventing move-
ments, and (3) driving force generators functioning due
to the processes of actin polymerization/depolymeriza-
tion. In plant cells, movements appear to depend more on
actin ﬁlaments than on microtubules, although both
cytoskeletal ﬁbrils function cooperatively.
Three types of molecular motors functioning in con-
nection with the cytoskeleton are known: myosins,
kinesins, and dyneins. All of them are ATPases using
the energy of ATP hydrolysis for their movements
along actin microﬁlaments (myosin) or tubulin micro-
tubules (kinesin and dynein) and carrying their speciﬁc
cargoes to the sites of destination. Molecular motors
can also fulﬁll some additional functions, for example,
to maintain cell structure or be involved in signal trans-
duction. Numerous comprehensive reviews consider
structural and functional properties of molecular
motors, in plants in particular (see for example [1, 2]).
Myosins are molecular motors providing for many
types of movements along the actin MF. Along with a
conventional myosin (myosin II) providing for muscle
contraction and discovered about 60 years ago, a great
diversity of unconventional myosins are present in ani-
mal and plant cells. They are encoded by 140 genes.
Eighteen myosin classes differing in their capacity
for dimerization and ﬁlament formation, in the length
and structure of the tail, etc. are known [3–5]. All myo-
sins except for myosin VI move toward barbed actin
ends. Since just actin cytoskeleton plays a key role in
intracellular translocations in plants, as distinct from
animals where most movements occur along MT
tracks, myosins are principal motor proteins in the plant
All myosins comprise heavy and light chains. The
heavy chain contains a motor domain (the head) about
80 kD in size at its N-end, which is followed by a regu-
latory neck domain binding light chains and a tail
domain speciﬁc for various myosin classes.
It is believed now that plants harbor quite speciﬁc
myosin types that comprise two classes: myosins VIII
and myosins XI. The latter are very close to myosins V
of animals and fungi, which are key motors for
organelle transport. They can produce dimers due to the
presence of a coil–coil sequence adjusting to the neck
domain and possess a long neck providing for a great
step of translocation (Fig. 1).
Seventeen myosin genes were found in the arabi-
dopsis genome. Four of them belong to myosins VIII
and thirteen, to longer myosins XI [5, 6]. In the rice
genome, 14 myosin genes are present: two myosins
VIII and 12 myosins XI . The immunological detec-
tion of myosins, using antibody against animal myo-
sins, revealed a more diverse set of myosins in plant
cells (, for example), but these data are less convinc-
ing as compared to molecular approaches. Each myosin
The Cytoskeleton and Intracellular Motility in Plants
N. L. Klyachko
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences,
Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (095) 977-8018; e-mail: firstname.lastname@example.org
Received March 29, 2005
—Novel information concerning intracellular motility in plants and the mechanisms of cytoskeleton-
based organelle and macromolecule movements are brieﬂy considered. The involvement of basic molecular
motors and other possible driving forces for various types of movement are discussed.
Key words: cytoskeleton - movements - molecular motors - speciﬁc cargoes
: Arp—actin-related protein; ER—endoplasmic
reticulum; GFP—green ﬂuorescent protein; MF—microﬁlaments;
MT—microtubules; UTR—untranslated region.