Cells sense a variety of extracellular signals balancing their metabolism and physiology according to changing growth conditions. Plasma membranes are the outermost informational barriers that render cells sensitive to regulatory inputs. Membranes are composed of different types of lipids that play not only structural but also informational roles. Hormones and other regulators are sensed by specific receptors leading to the activation of lipid metabolizing enzymes. These enzymes generate lipid second messengers. Among them, phosphatidic acid (PA) is a well-known intracellular messenger that regulates various cellular processes. This lipid affects the functional properties of cell membranes and binds to specific target proteins leading to either genomic (affecting transcriptome) or non-genomic responses. The subsequent biochemical, cellular and physiological reactions regulate plant growth, development and stress tolerance. In the present review, we focus on primary (genome-independent) signaling events triggered by rapid PA accumulation in plant cells and describe the functional role of PA in mediating response to hormones and hormone-like regulators. The contributions of individual lipid signaling enzymes to the formation of PA by specific stimuli are also discussed. We provide an overview of the current state of knowledge and future perspectives needed to decipher the mode of action of PA in the regulation of cell functions.

• Keywords
• autophagy, biologically active substance, diacylglycerol kinase, phosphatidic acid, phospholipase, phospholipid, signal transduction, targets,
• MeSH
• Phospholipase D * metabolism   MeSH
• Hormones metabolism   MeSH
• Phosphatidic Acids * metabolism   MeSH
• Proteins metabolism   MeSH
• Plant Proteins genetics   MeSH
• Plants metabolism   MeSH
• Signal Transduction physiology   MeSH
• Plant Development MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Phospholipase D * MeSH
• Hormones MeSH
• Phosphatidic Acids * MeSH
• Proteins MeSH
• Plant Proteins MeSH

Polarized exocytosis is essential for many vital processes in eukaryotic cells, where secretory vesicles are targeted to distinct plasma membrane domains characterized by their specific lipid-protein composition. Heterooctameric protein complex exocyst facilitates the vesicle tethering to a target membrane and is a principal cell polarity regulator in eukaryotes. The architecture and molecular details of plant exocyst and its membrane recruitment have remained elusive. Here, we show that the plant exocyst consists of two modules formed by SEC3-SEC5-SEC6-SEC8 and SEC10-SEC15-EXO70-EXO84 subunits, respectively, documenting the evolutionarily conserved architecture within eukaryotes. In contrast to yeast and mammals, the two modules are linked by a plant-specific SEC3-EXO70 interaction, and plant EXO70 functionally dominates over SEC3 in the exocyst recruitment to the plasma membrane. Using an interdisciplinary approach, we found that the C-terminal part of EXO70A1, the canonical EXO70 isoform in Arabidopsis, is critical for this process. In contrast to yeast and animal cells, the EXO70A1 interaction with the plasma membrane is mediated by multiple anionic phospholipids uniquely contributing to the plant plasma membrane identity. We identified several evolutionary conserved EXO70 lysine residues and experimentally proved their importance for the EXO70A1-phospholipid interactions. Collectively, our work has uncovered plant-specific features of the exocyst complex and emphasized the importance of the specific protein-lipid code for the recruitment of peripheral membrane proteins.

• Keywords
• EXO70A1, cell polarity, exocyst, phospholipids, plasma membrane,
• MeSH
• Arabidopsis metabolism   MeSH
• Cell Membrane metabolism   MeSH
• Cytoplasm metabolism   MeSH
• Exocytosis MeSH
• Phospholipids metabolism   MeSH
• Cell Polarity MeSH
• Arabidopsis Proteins metabolism   MeSH
• Proteomics methods   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• EXO70A1 protein, Arabidopsis MeSH Browser
• Phospholipids MeSH
• Arabidopsis Proteins MeSH

The ARP2/3 complex and formins are the only known plant actin nucleators. Besides their actin-related functions, both systems also modulate microtubule organization and dynamics. Loss of the main housekeeping Arabidopsis thaliana Class I membrane-targeted formin FH1 (At3g25500) is known to increase cotyledon pavement cell lobing, while mutations affecting ARP2/3 subunits exhibit an opposite effect. Here we examine the role of FH1 and the ARP2/3 complex subunit ARPC5 (At4g01710) in epidermal cell morphogenesis with focus on pavement cells and trichomes using a model system of single fh1 and arpc5, as well as double fh1 arpc5 mutants. While cotyledon pavement cell shape in double mutants mostly resembled single arpc5 mutants, analysis of true leaf epidermal morphology, as well as actin and microtubule organization and dynamics, revealed a more complex relationship between the two systems and similar, rather than antagonistic, effects on some parameters. Both fh1 and arpc5 mutations increased actin network density and increased cell shape complexity in pavement cells and trichomes of first true leaves, in contrast to cotyledons. Thus, while the two actin nucleation systems have complementary roles in some aspects of cell morphogenesis in cotyledon pavement cells, they may act in parallel in other cell types and developmental stages.

• Keywords
• ARP2/3, At3g25500, At4g01710, actin nucleation, cytoskeleton, formin, pavement cell, trichome,
• Publication type
• Journal Article MeSH

Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.

• MeSH
• Models, Biological * MeSH
• Phospholipids chemistry   metabolism   MeSH
• Carboxylic Acids chemistry   metabolism   MeSH
• Humans MeSH
• Lipidomics methods   MeSH
• Membrane Lipids chemistry   metabolism   MeSH
• Membranes chemistry   metabolism   physiology   MeSH
• Computer Simulation MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Phospholipids MeSH
• Carboxylic Acids MeSH
• Membrane Lipids MeSH

Polarized exocytosis is critical for pollen tube growth, but its localization and function are still under debate. The exocyst vesicle-tethering complex functions in polarized exocytosis. Here, we show that a sec3a exocyst subunit null mutant cannot be transmitted through the male gametophyte due to a defect in pollen tube growth. The green fluorescent protein (GFP)-SEC3a fusion protein is functional and accumulates at or proximal to the pollen tube tip plasma membrane. Partial complementation of sec3a resulted in the development of pollen with multiple tips, indicating that SEC3 is required to determine the site of pollen germination pore formation. Time-lapse imaging demonstrated that SEC3a and SEC8 were highly dynamic and that SEC3a localization on the apical plasma membrane predicts the direction of growth. At the tip, polar SEC3a domains coincided with cell wall deposition. Labeling of GFP-SEC3a-expressing pollen with the endocytic marker FM4-64 revealed the presence of subdomains on the apical membrane characterized by extensive exocytosis. In steady-state growing tobacco (Nicotiana tabacum) pollen tubes, SEC3a displayed amino-terminal Pleckstrin homology-like domain (SEC3a-N)-dependent subapical membrane localization. In agreement, SEC3a-N interacted with phosphoinositides in vitro and colocalized with a phosphatidylinositol 4,5-bisphosphate (PIP2) marker in pollen tubes. Correspondingly, molecular dynamics simulations indicated that SEC3a-N associates with the membrane by interacting with PIP2 However, the interaction with PIP2 is not required for polar localization and the function of SEC3a in Arabidopsis (Arabidopsis thaliana). Taken together, our findings indicate that SEC3a is a critical determinant of polar exocytosis during tip growth and suggest differential regulation of the exocytotic machinery depending on pollen tube growth modes.

• MeSH
• Arabidopsis genetics   growth & development   metabolism   MeSH
• Cell Membrane metabolism   MeSH
• Time-Lapse Imaging methods   MeSH
• Exocytosis * MeSH
• Phosphatidylinositol 4,5-Diphosphate metabolism   MeSH
• Phosphatidylinositols metabolism   MeSH
• Phylogeny MeSH
• Plants, Genetically Modified MeSH
• Microscopy, Confocal MeSH
• Mutation MeSH
• Reverse Transcriptase Polymerase Chain Reaction MeSH
• Protein Isoforms genetics   metabolism   MeSH
• Arabidopsis Proteins classification   genetics   metabolism   MeSH
• Pollen genetics   growth & development   metabolism   MeSH
• Pollen Tube genetics   growth & development   metabolism   MeSH
• Amino Acid Sequence MeSH
• Base Sequence MeSH
• Sequence Homology, Amino Acid MeSH
• Sequence Homology, Nucleic Acid MeSH
• Molecular Dynamics Simulation MeSH
• Gene Expression Profiling methods   MeSH
• Protein Binding MeSH
• Binding Sites genetics   MeSH
• Vesicular Transport Proteins classification   genetics   metabolism   MeSH
• Green Fluorescent Proteins genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• exocyst complex component sec3A, Arabidopsis MeSH Browser
• Phosphatidylinositol 4,5-Diphosphate MeSH
• Phosphatidylinositols MeSH
• Protein Isoforms MeSH
• Arabidopsis Proteins MeSH
• Vesicular Transport Proteins MeSH
• Green Fluorescent Proteins MeSH

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,
• Publication type
• Journal Article MeSH
• Review MeSH