Actin cytoskeleton in plants: From transport networks to signaling networks

The plant actin cytoskeleton is characterized by a high diversity in regard to gene families, isoforms, and degree of polymerization. In addition to t he most abundant F-actin assemblies like filaments and their bundles, G-act in obviously assembles in the form of actin oligomers composed of a few act in molecules which can be extensively cross-linked into complex dynamic mes hworks. The role of the actomyosin complex as a force generating system - b ased on principles operating as in muscle cells - is clearly established fo r long-range mass transport in large algal cells and specialized cell types of higher plants. Extended F-actin networks, mainly composed of F-actin bu ndles, are the structural basis for this cytoplasmic streaming of high velo cities On the other hand, evidence is accumulating that delicate meshworks built of short F-actin oligomers are critical for events occurring at the p lasma membrane, e.g., actin interventions into activities of ion channels a nd hormone carriers, signaling pathways based on phospholipids, and exo- an d endocytotic processes. These unique F-actin arrays, constructed by polyme rization-depolymerization processes propelled via synergistic actions of ac tin-binding proteins such as profilin and actin depolymerizing factor (ADF) /cofilin are supposed to be engaged in diverse aspects of plant morphogenes is. Finally, rapid rearrangements of F-actin meshworks interconnecting endo cellular membranes turn out to be especially important for perception-signa ling purposes of plant cells, e.g., in association with guard cell movement s, mechano- and gravity-sensing, plant host-pathogen interactions, and woun d-healing. (C) 1999 Wiley-Liss, Inc.