Actin fringes of polar cell growth

Abstract

The eukaryotic actin cytoskeleton is a highly dynamic framework that is involved in many biological processes, such as cell growth, division, morphology, and motility. G-actin polymerizes into microfilaments that associate into bundles, patches, and networks, which, in turn, organize into higher order structures that are fundamental for the course of important physiological events. Actin rings are an example for such higher order actin entities, but this term represents an actually diverse set of subcellular structures that are involved in various processes. This review especially sheds light on a crucial type of non-constricting ring-like actin networks, and categorizes them under the term 'actin fringe'. These 'actin fringes' are visualized as highly dynamic and yet steady structures in the tip of various polarized growing cells. The present comprehensive overview compares the actin fringe characteristics of rapidly elongating pollen tubes with several related actin arrays in other cell types of diverse species. The current state of knowledge about various actin fringe functions is summarized, and the key role of this structure in the polar growth process is discussed.

Interplay between Ions, the Cytoskeleton, and Cell Wall Properties during Tip Growth

“…Despite differences in F-actin structures between the probes used and the species of cell type examined (Stephan, 2017), it is nevertheless possible to recognize an emergence of commonalities. For example, most pollen tubes exhibit a fringe of short longitudinally oriented actin microfilaments located at the cell cortex near the cell tip, and long actin bundles are found along the length of the cell (Lovy-Wheeler et al, 2005;Fig.…”

“…Ultimately, the key to understanding tip growth will require understanding a complex interaction network; the reader is directed to recent reviews that expand upon a variety of facets of tip growth not covered here (Mendrinna and Persson, 2015;Hepler, 2016;Damineli et al, 2017;Michard et al, 2017;Stephan, 2017). In this Update, we speculate that further mechanistic advances will come from identifying deeply conserved tip growth mechanisms that decipher signaling events between the cell wall and the cytoplasm.…”

The Actin Cytoskeleton: Functional Arrays for Cytoplasmic Organization and Cell Shape Control

“…Plant cell expansion tends to be slow in comparison to these rates of actin turnover. Tip-growing cells elongate at rates that vary from approximately 1 mm min 21 to a few mm h 21 (Stephan, 2017), and the strain rates of cells that use a diffuse growth mechanism vary from a few percent h 21 to 30% h 21 (Rahman et al, 2007;Zhang et al, 2011). How are different actin networks assembled and disassembled at the extended time scales necessary to pattern the cell wall, and how are specific actin networks constructed locally to carry out specific tasks?…”

“…A genetic characterization of tip growth in rhizoids of a nonvascular plant revealed broadly conserved mechanisms for tip growth (Honkanen et al, 2016). Tip growth has been the topic of numerous comprehensive reviews (Ren and Xiang, 2007;Rounds and Bezanilla, 2013;Stephan, 2017). Briefly, tip growth is a strategy by which an axially symmetric cell establishes a tube-like protuberance that maintains a roughly hemispherical geometry at the cell apex as the cell elongates.…”

“…A highly specialized and subfunctionalized cellular organization is associated with the cell apex, and this cytoplasmic organization has strict requirements for several different types of actin filament arrays (Stephan, 2017). At the spatial scale of the entire cell, one function of the actin cytoskeleton is to provide spatially organized filaments and bundles that define the overall intracellular flow patterns.…”