Auxin on the Road Navigated by Cellular PIN Polarity
The generation of asymmetry, at both cellular and tissue level, is one of the most essential capabilities of all eukaryotic organisms. It mediates basically all multicellular development ranging from embryogenesis and de novo organ formation till response
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Auxin on the Road Navigated by Cellular PIN Polarity Pawel Baster and Jirˇ´ı Friml
Abstract The generation of asymmetry, at both cellular and tissue level, is one of the most essential capabilities of all eukaryotic organisms. It mediates basically all multicellular development ranging from embryogenesis and de novo organ formation till responses to various environmental stimuli. In plants, the awe-inspiring number of such processes is regulated by phytohormone auxin and its directional, cell-to-cell transport. The mediators of this transport, PIN auxin transporters, are asymmetrically localized at the plasma membrane, and this polar localization determines the directionality of intercellular auxin flow. Thus, auxin transport contributes crucially to the generation of local auxin gradients or maxima, which instruct given cell to change its developmental program. Here, we introduce and discuss the molecular components and cellular mechanisms regulating the generation and maintenance of cellular PIN polarity, as the general hallmarks of cell polarity in plants.
1 Introduction The emergence of multicellularity during the evolution of species had its inevitable repercussions. Efficient intercellular communication was one of such. In other words, to achieve a mutual goal, neighboring cells (single elements of the system) needed to perceive and transduce externally or internally generated signals. As a result, the multicellular organism, as a whole, should be able to translate these P. Baster • J. Friml (*) Department of Plant Systems Biology, VIB, 9052 Gent, Belgium Department of Plant Biotechnology and Genetics, Ghent University, 9052 Gent, Belgium Institute of Science and Technology Austria (IST Austria), 3400 Klosterneuburg, Austria e-mail: [email protected] E. Zazˇ´ımalova´ et al. (eds.), Auxin and Its Role in Plant Development, DOI 10.1007/978-3-7091-1526-8_8, © Springer-Verlag Wien 2014
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signals into a developmental response. This basic necessity for efficient internal communication underlies the origin of the small signaling molecules, termed hormones, present in both plants and animals (Alberts et al. 2007). While the essential role of hormones in cell-to-cell communication is evident in both cases, the response of the organism into which the hormonal signal is translated, diverge between two kingdoms. In animal species, solutions based on a modulation of behavior were primarily promoted (Davies 2004). In contrast, plants, due to the sessile nature of their lifestyle, developed a remarkable repertoire of mechanisms which allow them, through fine-tuning of metabolism or body shaping, to adjust and survive in ever changing and often adverse environments (Tanaka et al. 2006). These mechanisms are facilitated not only by intercellular communication but also by tightly regulated cell division, morphogenesis, and differentiation. Importantly, most, if not all of them, are based on cell polarization and repolarization which guide tissue and organ patterning and thus underpin basi
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