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 , Ja ´ n Salaj e , Dieter Volkmann b , Laszlo Bo ¨ gre 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, Du ´bravska ´ 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, Akademicka ´ 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 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 in- volved 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 (Balus ˇka and Volkmann, 2002; Balus ˇka et al., 2000a; Braun et al., 1999). As MAPKs are involved in stress signaling to the actin cytoskeleton in yeast and animals, we have ana- lyzed 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 SIMK protein is predominantly localized to nuclei in meristematic cells of root apices (Balus ˇka et al., 2000b). SIMK is also found in nuclei of elongating epidermal root cells. However, during bulge and root hair for- mation 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 struc- tures in the root hair tube. The selective enrichment of active SIMK in tips of emerging root hairs coincides * 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. Cell Biology International 27 (2003) 257–259 Cell Biology I nternational www.elsevier.com/locate/jnlabr/ycbir 1065-6995/03/$ - see front matter  2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1065-6995(02)00344-X