When fat is not bad: the regulation of actin dynamics by phospholipid signaling molecules

Abstract

The actin cytoskeleton plays a key role in the plant morphogenesis and is involved in polar cell growth, movement of subcellular organelles, cell division, and plant defense. Organization of actin cytoskeleton undergoes dynamic remodeling in response to internal developmental cues and diverse environmental signals. This dynamic behavior is regulated by numerous actin-binding proteins (ABPs) that integrate various signaling pathways. Production of the signaling lipids phosphatidylinositol 4,5-bisphosphate and phosphatidic acid affects the activity and subcellular distribution of several ABPs, and typically correlates with increased actin polymerization. Here we review current knowledge of the inter-regulatory dynamics between signaling phospholipids and the actin cytoskeleton in plant cells.

Keywords: actin; actin-binding proteins; capping protein; cytoskeleton; phosphatidic acid; phosphatidylinositol 4,5-bisphosphate; phospholipase D; signaling.

FIGURE 1

Schematic representation of actin regulation by phosphatidylinositol 4,5-bisphosphate (PIP₂) and phosphatidic acid (PA). Solid lines represent pathways leading to activation (arrow ends) or inhibition (line ends). Dotted lines indicate pathways leading to PIP₂/PA production/degradation. Dashed lines represent an induction of actin polymerization. A question mark indicates that experimental data are available only for non-plant cells. Enzymes generating PIP₂ or PA are in green and proteins involved in phospholipid degradation or signaling attenuation are in red. In PIP₂ and PA structural models, red and brown balls represent the oxygen and phosphorus atoms in headgroups, respectively, and carbon atoms are shown in cyan. ADF, actin-depolymerizing factor; CP, capping protein; F-actin, filamentous actin; DGK, diacylglycerol kinase; LPP, lipid phosphate phosphatases; PI4P5K, phosphatidylinositol 4-phosphate 5-kinase; PI-PLC, phosphatidylinositol-specific phospholipase C; PLD, phospholipase D; ROP, Rho of plants.