Membrane proteins are essential determinants of many biological processes in plants. They function in metabolic processes, signal transduction, transport of small molecules and polymers across endo- and plasma membranes, and intercompartmental trafficking of proteins, lipids, and cell wall components. During these integrative processes, dynamic interactions of membrane proteins with other membrane or soluble components are thought to provide a high degree of flexibility that usually characterizes higher plants. This concept is supported by the recent release of a first, partial Arabidopsis interactome by the Arabidopsis Interactome Mapping Consortium (http://www.sciencemag.org/content/333/6042/601.full.htm). The Arabidopsis interactome reveals a strong enrichment of a few network communities, including those for transmembrane transport and vesicle trafficking. Strikingly, the large transmembrane transport community shares a high amount of proteins with the vesicle trafficking community suggesting a strong physical and functional overlap and interaction.
The highly structured eucaryotic cell with its complex division of biochemical labour requires a distinct protein complement in each cellular structure and compartment. Nuclear coded and cytosolically synthesized polypeptides are specifically sorted to every corner of the cell in a post- or co-translational manner. The presence of separate genomes and protein translation machineries in plastids and mitochondria requires further coordination not only on the transcriptional, translational but also most likely on the protein import level. Numerous different protein transport systems have developed and coexist within plant cells to ensure the specific and selective composition of every sub-cellular compartment. This volume summarizes the current knowledge on protein trafficking in plant cells. Aside from the fundamental aspects in cell biology of how specific pre-protein sorting and translocation across biological membranes is achieved, a major focus is on transport, modification and deposition of plant storage proteins. The increasing use of plants as bioreactors to provide custom-designed proteins of different usage requires detailed understanding of these events. This text is directed not only at students and professionals in plant cell and molecular biology but also at those involved in horticulture and plant breeding. It is intended to serve as a text and guide for graduate-level courses on plant cell biology and as a valuable supplement to courses in plant physiology and development. Scientists in other disciplines who wish to learn more about protein translocation in plants will also find this text an up-to-date source of information and reference.
The functional organization of eukaryotic cells requires the exchange of proteins, lipids, and polysaccharides between membrane compartments through transport intermediates. Small GTPases largely control membrane traffic, which is essential for the survival of all eukaryotes. Transport from one compartment of this pathway to another is mediated by vesicular carriers, which are formed by the controlled assembly of coat protein complexes (COPs) on donor organelles. The activation of small GTPases is essential for vesicle formation from a donor membrane. In eukaryotic cells, small GTP-binding proteins comprise the largest family of signaling proteins. The ADP-ribosylation factor 1 (ARF1) and secretion-associated RAS superfamily 1 (SAR1) GTP-binding proteins are involved in the formation and budding of vesicles throughout plant endomembrane systems. ARF1 has been shown to play a critical role in coat protein complex I (COPI)-mediated retrograde trafficking in eukaryotic systems, whereas SAR1 GTPases are involved in intracellular coat protein complex II (COPII)-mediated protein trafficking from the endoplasmic reticulum (ER) to the Golgi apparatus. The dysfunction of the endomembrane system can affect signal transduction, plant development, and defense. This chapter offers a summary of membrane trafficking system with an emphasis on the role of GTPases especially ARF1, SAR1, and RAB, their regulatory proteins, and interaction with endomembrane compartments. The vacuolar and endocytic trafficking are presented to enhance our understanding of plant development and immunity in plants.
In plant cells, the plasma membrane is a highly elaborated structure that functions as the point of exchange with adjoining cells, cell walls and the external environment. Transactions at the plasma membrane include uptake of water and essential mineral nutrients, gas exchange, movement of metabolites, transport and perception of signaling molecules, and initial responses to external biota. Selective transporters control the rates and direction of small molecule movement across the membrane barrier and manipulate the turgor that maintains plant form and drives plant cell expansion. The plasma membrane provides an environment in which molecular and macromolecular interactions are enhanced by the clustering of proteins in oligimeric complexes for more efficient retention of biosynthetic intermediates, and by the anchoring of protein complexes to promote regulatory interactions. The coupling of signal perception at the membrane surface with intracellular second messengers also involves transduction across the plasma membrane. Finally, the generation and ordering of the external cell walls involves processes mediated at the plant cell surface by the plasma membrane. This volume is divided into three sections. The first section describes the basic mechanisms that regulate all plasma membrane functions. The second describes plasma membrane transport activity. The final section of the book describes signaling interactions at the plasma membrane. These topics are given a unique treatment in this volume, as the discussions are restricted to the plasma membrane itself as much as possible. A more complete knowledge of the plasma membrane’s structure and function is essential to current efforts to increase the sustainability of agricultural production of food, fiber, and fuel crops.
Endocytosis is a fundamental cellular process by means of which cells internalize extracellular and plasma membrane cargos for recycling or degradation. It is important for the establishment and maintenance of cell polarity, subcellular signaling and uptake of nutrients into specialized cells, but also for plant cell interactions with pathogenic and symbiotic microbes. Endocytosis starts by vesicle formation at the plasma membrane and progresses through early and late endosomal compartments. In these endosomes cargo is sorted and it is either recycled back to the plasma membrane, or degraded in the lytic vacuole. This book presents an overview of our current knowledge of endocytosis in plants with a main focus on the key molecules undergoing and regulating endocytosis. It also provides up to date methodological approaches as well as principles of protein, structural lipid, sugar and microbe internalization in plant cells. The individual chapters describe clathrin-mediated and fluid-phase endocytosis, as well as flotillin-mediated endocytosis and internalization of microbes. The book was written for a broad spectrum of readers including students, teachers and researchers.
The sub-compartmentalization of plant cells has necessitated the development of transport mechanisms which deliver protein and membrane cargos in a spatially and temporally controlled fashion between the various endomembrane compartments within the cell as well as the cell periphery. These transport pathways are essential to several subcellular processes and organismal responses including cell growth and expansion, the construction of de novo plasma membrane and cell wall during cytokinesis, construction of the cell wall, and the delivery and recycling of transporters and receptors located at the interface between the plant cell and its environment. Consequently, disruption of the proteins or lipid homeostasis facilitating these transport pathways results in a range of developmental defects, including seedling lethality. Many of the key principles of endomembrane transport (cargo recognition and recruitment of vesicle coat proteins through adaptors, membrane deformation, vesicle scission, vesicle transport, and vesicle docking and fusion) are evolutionarily conserved across Eukaryotes and specifically between land plants and members of the Opisthokont supergroup, which includes yeast and animals. Yet, since the evolution of plants, yeast, and animals from the last eukaryotic common ancestor, proteins facilitating membrane trafficking have expanded, diverged in function, or become lost in specific lineages, resulting in evolutionarily divergent vesicle transport mechanisms. The work described in this thesis characterizes evolutionarily conserved membrane trafficking pathways in plants and identifies key points of evolutionarily divergence between plants and Opisthokonts. First, the proteomic and biochemical characterization of a heterogenous mixture of clathrin coated vesicles (CCVs) from undifferentiated, suspension cultured Arabidopsis cells yields the surprising enrichment of the vesicle adaptor, AP-4, with plant CCVs and the low abundance and depletion from purified CCVs of the known clathrin-mediated endocytosis adaptor, TPLATE complex. Secondly, I include biochemical data supporting the peripheral association of the TPLATE subunit of the Jotnarlog and endocytic adaptor, TPLATE complex, with enriched clathrin coated vesicles relative to the evolutionarily conserved endocytic adaptor, AP-2, which is more tightly associated. Additional data describing the assembly and interaction network of the Stomatal Cytokinesis Defective complex, an evolutionarily divergent regulator of an evolutionarily conserved small GTPase, RabE1, which functions in post-Golgi trafficking.
Cell membranes are the initial and focal sites of stimulus perception and signal transduction. Membrane lipids are rich sources for the production of signaling messengers that mediate plant growth, development, and response to nutrient status and stresses. In recent years, substantial progress has been made toward understanding lipid signaling in plants, but many fundamental questions remain: What lipids are signaling messengers or mediators in plants? How are the signaling lipids produced and metabolized? In what plant cellular and physiological processes are various lipid mediators involved? How do they carry out their signaling functions? How do lipid signaling networks contribute to modulating plant growth, development, and responses to hormones and stresses? In this Research Topic issue, we invite the broad plant community to address the above questions.Cell membranes are the initial and focal sites of stimulus perception and signal transduction. Membrane lipids are rich sources for the production of signaling messengers that mediate plant growth, development, and response to nutrient status and stresses. In recent years, substantial progress has been made toward understanding lipid signaling in plants, but many fundamental questions remain: What lipids are signaling messengers or mediators in plants? How are the signaling lipids produced and metabolized? In what plant cellular and physiological processes are various lipid mediators involved? How do they carry out their signaling functions? How do lipid signaling networks contribute to modulating plant growth, development, and responses to hormones and stresses? In this Research Topic issue, we invite the broad plant community to address the above questions.
Endocytosis is a fundamental biological process, which is conserved among all eukaryotes. It is essential not only for many physiological and signalling processes but also for interactions between eukaryotic cells and pathogens or symbionts. This book covers all aspects of endocytosis in both lower and higher plants, including basic types of endocytosis, endocytic compartments, and molecules involved in endocytic internalization and recycling in diverse plant cell types. It provides a comparison with endocytosis in animals and yeast and discusses future prospects in this new and rapidly evolving plant research field. Readers will find an overview of the state-of-the-art methods and techniques applied in plant endocytosis research.
Published in a modern, user-friendly format this fully revised and updated edition of The Handbook of Protoctista (1990) is the resource for those interested in the biology, diversity and evolution of eukaryotic microorganisms and their descendants, exclusive of animals, plants and fungi. With chapters written by leading researchers in the field, the content reflects the present state of knowledge of the cell and genome biology, evolutionary relationships and ecological/medical/economic importance each major group of protists, organized according to current protist systematics as informed by molecular phylogenetics and genomics.
