Actin-dependent vacuolar occupancy of the cell determines auxin-induced growth repression |
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| Authors: | David Scheuring Christian L?fke Falco Krüger Maike Kittelmann Ahmed Eisa Louise Hughes Richard S Smith Chris Hawes Karin Schumacher Jürgen Kleine-Vehn |
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| Institution: | aDepartment of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, 1190 Vienna, Austria;;bCenter for Organismal Studies, University of Heidelberg, 69120 Heidelberg, Germany;;cDepartment of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom;;dDepartment of Comparative Development and Genetics, Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany |
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| Abstract: | The cytoskeleton is an early attribute of cellular life, and its main components are composed of conserved proteins. The actin cytoskeleton has a direct impact on the control of cell size in animal cells, but its mechanistic contribution to cellular growth in plants remains largely elusive. Here, we reveal a role of actin in regulating cell size in plants. The actin cytoskeleton shows proximity to vacuoles, and the phytohormone auxin not only controls the organization of actin filaments but also impacts vacuolar morphogenesis in an actin-dependent manner. Pharmacological and genetic interference with the actin–myosin system abolishes the effect of auxin on vacuoles and thus disrupts its negative influence on cellular growth. SEM-based 3D nanometer-resolution imaging of the vacuoles revealed that auxin controls the constriction and luminal size of the vacuole. We show that this actin-dependent mechanism controls the relative vacuolar occupancy of the cell, thus suggesting an unanticipated mechanism for cytosol homeostasis during cellular growth.Actin filaments and its myosin motor proteins control a multitude of diverse cellular processes in animal cells, such as muscle contraction, cell motility, as well as vesicle and organelle movements (1). In animals, actin has a strong impact on the regulation of cellular shape and thus on cell size (2). Unlike animal cells, plant cells are sheathed by shape-giving cell walls, rendering them largely immobile. Despite this difference, the plant actin cytoskeleton has a conserved function in vesicle trafficking and organelle movement (3). Compared with animals, the role of actin in controlling cell size in plants is not clear and remains to be addressed. The phytohormone auxin is a crucial regulator of cell-size control in plants (4). Several studies suggest that the plant-specific growth regulator auxin affects the actin cytoskeleton (5–10). These studies concentrated on the effect of auxin on cortical actin and its contribution to processes close to the plasma membrane, such as endocytosis and exocytosis (5–11). Here we show that the actin cytoskeleton also is required for auxin processes beyond the plasma membrane, contributing to vacuolar morphogenesis and consequently to the regulation of cell size in plants. |
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| Keywords: | auxin vacuole actin cytoskeleton cell growth |
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