A dynamic interplay between membranes and the cytoskeleton critical for cell development and signaling

Abstract

Diverse cellular processes that underlie plant development and response to environmental cues rely on a dynamic interplay between membranes and the cytoskeleton. The original research and review articles assembled in this Research Topic provide a valuable insight into our current understanding of how actin filaments and microtubules physically and functionally interact with membranes and cell wall and vice versa. ACTIN-BINDING PROTEINS: OLD AND NEWActin-binding proteins come in hundreds of different varieties and are the governors for cellular cytoskeletal organization and turnover. The rate limiting step for generating actin filaments from a monomer pool in vitro, and presumably in vivo, is formation of a seed or nucleus of three actin subunits. Formins are conserved actin nucleation factors which, in plants, take on special relevance for the presence of secretion signals, transmembrane domains and lipid interaction motifs that permit their function on or near cellular membranes. In an up-to-date review, Cvrčková (2013) discusses the myriad ways that plant formins are thought to associate with membranes and their function(s) at various subcellular locations, especially the interface between cortical actin cytoskeleton-plasma membrane-cell wall.The monomer-binding protein, profilin, was the first conventional plant actin-binding protein to be identified more than two decades ago. Sun et al. (2013) briefly review the long history of discovery research surrounding this abundant regulator of actin dynamcis. Biochemically, isoforms from maize and Arabidopsis have been well characterized and these bind three cellular ligands: monomer of G-actin, proteins with contiguous stretches of proline residues, and phosphoinositide lipids. More recently, it has been discovered that plant profilins are localized or function at cellular membranes and organelles via their interaction with nucleators like the formins; here, profilinactin complexes likely provide a supply of subunits to polymerize new actin filaments. Whether this actin assembly powers vesicle or organelle movements, as in the case of mammalian endosomes or pathogenic intracellular bacteria, is an area for future investigations.One striking difference between the repertoire of actinbinding proteins from plants and animals is that many types of actin-membrane adaptors present in animals are absent from plants. Plants in turn own a plant-specific superfamily of actin-binding proteins, called the Networked (NET) proteins; presumably these are able to connect actin filaments to various membrane compartments. Here, Hawkins et al. (2014) report a phylogenetic analysis including NET gene sequences across a large range of species. Their data support that the NET superfamily emerged early in the evolution of vascular plants and has continuously developed and diversified coincidentally with the complexity of plant species. CORTICAL MICROTUBULES AND CELL WALL ASSEMBLYA remarkable parallelism between membrane-associated microtubules in the cortical cytoplasm and cellulose micro...