ISSN 1021-4437, Russian Journal of Plant Physiology, 2006, Vol. 53, No. 5, pp. 702–709. © MAIK “Nauka /Interperiodica” (Russia), 2006.
Original Russian Text © N.L. Klyachko, 2006, published in Fiziologiya Rastenii, 2006, Vol. 53, No. 5, pp. 790–798.
Actin is a multifunctional protein vital for numerous
processes in the cell: cell division and growth, determi-
nation of their polarity and shape, intracellular motility
of the cytoplasm and organelles, and cell responses to
external stimuli [1–3]. It produces dense meshes
around the nucleus and organelles, permeates the cyto-
plasm, promoting cytoplasm streaming and organelle
motility, a ﬁne F-actin network occupies the cell cortex
(Fig. 1). Actin functioning is controlled at various lev-
els: gene expression, polymerization/depolymeriza-
tion, and structural rearrangements. I consider relative
contributions of all these levels of regulation and
review some recent works concerning actin signaling.
were actively studied in the 1990s in
Meagher’s and some other laboratories. Some compre-
hensive reviews are destined to their structure and
expression [4, 5].
Actin is encoded by a gene family. The number of
actin genes in plants markedly exceeds that in animals:
it amounts tens and sometimes hundreds of sequences.
The smallest and most studied actin gene family was
found in arabidopsis; it comprises only eight function-
ally active genes (
). Three gene pairs are most
close in their structure:
Actin genes are small in
size and evenly distributed in the entire genome, not
They are believed to origin from a single gene of the
green alga. In vascular plants, their duplication and
divergence occurred. Actin genes are very ancient.
Their divergence occurred 300–500 million years ago,
i.e., during the origination of vascular plants. Actin
genes comprise three introns positioned at conserved
sites. The coding part of the actin gene is extremely
conserved. However, introns and ﬂanking sequences
vary considerably, permitting a diversity of the mecha-
nisms controlling expression.
Different actin genes are expressed at different
intensities. One of the most actively constitutively
expressed genes is
: in some organs, its transcripts
comprise up to 50% of all actin transcripts. In addition,
actin genes demonstrate a clear tissue-speciﬁcity of
their expression, although the patterns of their expres-
sion are often partially overlapped. Based on the local-
ization of actin gene expression in arabidopsis, vegeta-
tive (two subclasses) and reproductive (three sub-
classes) genes are distinguished. The amount of a single
gene transcripts could differ in different tissues by hun-
Plant Actin: Multiple Levels of Regulation
N. L. Klyachko
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, 127276 Russia;
fax: 7 (495) 977-8018; e-mail: email@example.com
Received February 3, 2006
—This lecture is devoted to the relative contribution of various levels of regulation of the actin cytosk-
eleton functioning in the cell. Regulation at the levels of gene expression, mRNA and protein synthesis and sta-
bility, processes of actin polymerization/depolymerization and actin structures reorganization is brieﬂy consid-
ered. Novel information about the pathways of signal transduction to the actin cytoskeleton with the involve-
ment of Arp2/3 complex and RIC proteins is highlighted.
Key words: actin cytoskeleton - genes - polymerization - structures - signaling
Actin ﬁlament network in the arabidopsis suspension
cell (after Meagher et al. ).
N—nucleus; NB—nuclear basket; CF—cortical ﬁlaments.