A comparative structural analysis of direct and indirect shoot ...

Cell Biology International 27 (2003) 257–259
Short communication
Involvement of MAP kinase SIMK and actin cytoskeleton in the
regulation of root hair tip growth
Jozef Samaj a,e , Miroslav Ovecka a,b,c* , Andrej Hlavacka b , Fatma Lecourieux a ,
Irute Meskiene a , Irene Lichtscheidl d , Peter Lenart a ,Ján Salaj e , Dieter Volkmann b ,
Laszlo Bögre f , Frantisek Baluska b,c , Heribert Hirt a
a Institute of Microbiology and Genetics, Vienna Biocenter, Dr. Bohrgasse 9, 1030 Vienna, Austria
b Institute of Botany, University of Bonn, Kirschallee 1, 53115 Bonn, Germany
c Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 14, SK – 842 23 Bratislava, Slovak Republic
d Institute of Ecology, University of Vienna, Althanstrasse 14, 1091 Vienna, Austria
e Institute of Plant Genetics and Biotechnology, Slovak Academy of Sciences, Akademická 2, P. O. Box 39 A, SK – 950 07 Nitra, Slovak Republic
f School of Biological Sciences, Royal Holloway, University of London, Egham, TW20 0EX London, UK
Accepted 10 October 2002
Cell
Biology
International
www.elsevier.com/locate/jnlabr/ycbir
1. Introduction
Mitogen-activated protein kinases (MAPKs), a
specific class of serine/threonine protein kinases, are
involved in controlling many cellular functions in all
eukaryotes. Signaling through MAPK cascades is involved
in cell division, differentiation, and stress sensing.
Recently, the stress induced MAPK (SIMK) (Munnik
et al., 1999) and its upstream activator SIMKK (Kiegerl
et al., 2000) have been characterized in Medicago sativa
L. and shown to be inducible by osmotic stress and
various fungal elicitors (Cardinale et al., 2000). In
different plant species dense F-actin meshworks at the
tip of root hairs were observed by immunolabeling
with actin antibodies or in vivo using GFP fused to
the F-actin binding domain of talin (Baluška and
Volkmann, 2002; Baluška et al., 2000a; Braun et al.,
1999). As MAPKs are involved in stress signaling to the
actin cytoskeleton in yeast and animals, we have analyzed
the function of the stress-activated alfalfa MAP
kinase SIMK in root hairs.
2. Results and discussion
In situ hybridization with an SIMK anti-sense probe
revealed that SIMK was strongly expressed in alfalfa
root hairs (Fig. 1). Previously, we have shown that
* Corresponding author. Tel.: +421-2-59426-102;
fax: +421-2-5477-1948.
E-mail address: botuove@savba.sk (M. Ovecka).
Fig. 1. In situ hybridization on alfalfa root sections with SIMK
anti-sense (A) and sense (B, negative control) probes. (A) Superficial
section through root showing that SIMK mRNA (appears as a specific
purple-blue colour) is concentrated to root hairs (indicated by arrows)
emerging along root body surface when section was hybridized with
anti-sense probe. Less intense labeling could also be detected in root
epidermis. (B) Similar superficial section showing no specific labeling
of root section hybridized with the sense probe. Root hairs are
indicated by arrows. Bar=70 µm.
SIMK protein is predominantly localized to nuclei in
meristematic cells of root apices (Baluška et al., 2000b).
SIMK is also found in nuclei of elongating epidermal
root cells. However, during bulge and root hair formation
SIMK is not only polarly relocated from nuclei
towards bulging domains of trichoblasts and tips of
growing root hairs, but it is also activated and located at
root hair tips in an active form. In trichoblasts, SIMK
was located to peripheral spots predicting root hair
outgrowth. In growing root hairs, SIMK was found to
accumulate within root hair tips and in spot-like structures
in the root hair tube. The selective enrichment of
active SIMK in tips of emerging root hairs coincides
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doi:10.1016/S1065-6995(02)00344-X