Live Cell Imaging Reveals Structural Associations Between The Actin And Microtubule Cytoskeleton In Arabidopsis

The Plant Cell, Vol. 23: 2302–2313, June 2011, www.plantcell.org ã 2011 American Society of Plant Biologists. All rights reserved.

Live Cell Imaging Reveals Structural Associations between the Actin and Microtubule Cytoskeleton in Arabidopsis
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Arun Sampathkumar,a Jelmer J. Lindeboom,b Seth Debolt,c Ryan Gutierrez,d,e David W. Ehrhardt,d,e Tijs Ketelaar,b and Staffan Perssona,1
a MaxPlanck Institute of Molecular Plant Physiology, 14476 Potsdam, Germany of Plant Cell Biology, Wageningen University, 6708 PB Wageningen, The Netherlands c Department of Horticulture, University of Kentucky, Lexington, Kentucky 40546 d Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305 e Department of Biology, Stanford University, Stanford, California 94305b Laboratory

In eukaryotic cells, the actin and microtubule (MT) cytoskeletal networks are dynamic structures that organize intracellular processes and facilitate their rapid reorganization. In plant cells, actin filaments (AFs) and MTs are essential for cell growth and morphogenesis. However, dynamic interactions between these two essential components in live cells have not been explored.Here, we use spinning-disc confocal microscopy to dissect interaction and cooperation between cortical AFs and MTs in Arabidopsis thaliana, utilizing fluorescent reporter constructs for both components. Quantitative analyses revealed altered AF dynamics associated with the positions and orientations of cortical MTs. Reorganization and reassembly of the AF array was dependent on the MTs followingdrug-induced depolymerization, whereby short AFs initially appeared colocalized with MTs, and displayed motility along MTs. We also observed that light-induced reorganization of MTs occurred in concert with changes in AF behavior. Our results indicate dynamic interaction between the cortical actin and MT cytoskeletons in interphase plant cells.

INTRODUCTION The cytoskeleton supports many fundamentalcellular processes, including morphogenesis, cell division, and vesicle trafficking (Goode et al., 2000; Fu et al., 2005; Collings, 2008; Gutierrez ´ ´ et al., 2009; Petrasek and Schwarzerova, 2009; Szymanski, 2009). The actin filaments (AFs) and microtubules (MTs) were formerly viewed as two distinct networks with separate functions, but were found to cooperate in yeast (Saccharomyces cerevisiae)and animal cells (Goode et al., 2000). For example, coalignment of AFs and MTs was observed in Taricha granulosa (newt) lung epithelial cells (Salmon et al., 2002), and MTs were transported in association with AFs to sites of induced wounding in Xenopus laevis oocytes (Mandato and Bement, 2003). Whereas AFs and MTs are common to eukaryotic organisms, structural and functional differences areevident in plant species; perhaps due to the presence of a rigid cell wall and a large central vacuole, and also due to the absence of the cytoskeletonorganizing centers referred to as centrosomes in animal cells and as spindle pole bodies in yeast cells (Ehrhardt and Shaw, 2006).

correspondence to Persson@mpimp-golm.mpg.de. The author responsible for distribution of materials integral to the findingspresented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Staffan Persson (persson@mpimp-golm.mpg.de). W Online version contains Web-only data. OA Open Access articles can be viewed online without a subscription. www.plantcell.org/cgi/doi/10.1105/tpc.111.087940

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Reports of AF and MT associations in plants are scarce,but are supported by imaging of fixed tissues, pharmacological studies, and the existence of common binding partners (Collings, 2008). In fixed tissues, fine transverse AFs have been observed as an ordered array, reminiscent of the transverse arrangements of MTs (Collings and Wasteneys, 2005), and AFs and MTs have been observed to coalign (Traas et al., 1987; Blancaflor, 2000; Collings and Wasteneys,...