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Probing cytoplasmic organization and the actin cytoskeleton of plant cells with optical tweezers. Biochem Soc Trans 2010; 38:823-8. [DOI: 10.1042/bst0380823] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In interphase plant cells, the actin cytoskeleton is essential for intracellular transport and organization. To fully understand how the actin cytoskeleton functions as the structural basis for cytoplasmic organization, both molecular and physical aspects of the actin organization have to be considered. In the present review, we discuss literature that gives an insight into how cytoplasmic organization is achieved and in which actin-binding proteins have been identified that play a role in this process. We discuss how physical properties of the actin cytoskeleton in the cytoplasm of live plant cells, such as deformability and elasticity, can be probed by using optical tweezers. This technique allows non-invasive manipulation of cytoplasmic organization. Optical tweezers, integrated in a confocal microscope, can be used to manipulate cytoplasmic organization while studying actin dynamics. By combining this with mutant studies and drug applications, insight can be obtained about how the physical properties of the actin cytoskeleton, and thus the cytoplasmic organization, are influenced by different cellular processes.
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52
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Staiger CJ, Poulter NS, Henty JL, Franklin-Tong VE, Blanchoin L. Regulation of actin dynamics by actin-binding proteins in pollen. JOURNAL OF EXPERIMENTAL BOTANY 2010; 61:1969-86. [PMID: 20159884 DOI: 10.1093/jxb/erq012] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
A dynamic network of polymers, the actin cytoskeleton, co-ordinates numerous fundamental cellular processes. In pollen tubes, organelle movements and cytoplasmic streaming, organization of the tip zone, vesicle trafficking, and tip growth have all been linked to actin-based function. Further, during the self-incompatibility response of Papaver rhoeas, destruction of the cytoskeleton is a primary target implicated in the rapid cessation of pollen tube growth and alterations in actin dynamics are associated with the initiation of programmed cell death. Surprisingly, these diverse cellular processes are accomplished with only a small amount of filamentous actin and a huge pool of polymerizable monomers. These observations hint at incredibly fast and complex actin dynamics in pollen. To understand the molecular mechanisms regulating actin dynamics in plant cells, the abundant actin monomer-binding proteins, a major filament nucleator, a family of bundling and severing proteins, and a modulator of growth at the barbed-end of actin filaments have been characterized biochemically. The activities of these proteins are generally consistent with textbook models for actin turnover. For example, the three monomer-binding proteins, profilin, ADF, and CAP, are thought to function synergistically to enhance turnover and the exchange of subunits between monomer and polymer pools. How individual actin filaments behave in living cells, however, remains largely unexplored. Actin dynamics were examined using variable angle epifluorescence microscopy (VAEM) in expanding hypocotyl epidermal cells. Our observations of single filament behaviour are not consistent with filament turnover by treadmilling, but rather represent a novel property called stochastic dynamics. A new model for the dynamic control of actin filament turnover in plant cells is presented.
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Affiliation(s)
- Christopher J Staiger
- Department of Biological Sciences and Bindley Bioscience Center, Purdue University, West Lafayette, IN 47907-2064, USA.
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53
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Engler JDA, Rodiuc N, Smertenko A, Abad P. Plant actin cytoskeleton re-modeling by plant parasitic nematodes. PLANT SIGNALING & BEHAVIOR 2010; 5:213-7. [PMID: 20038822 PMCID: PMC2881263 DOI: 10.4161/psb.5.3.10741] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The cytoskeleton is an important component of the plant's defense mechanism against the attack of pathogenic organisms. Plants however, are defenseless against parasitic root-knot and cyst nematodes and respond to the invasion by the development of a special feeding site that supplies the parasite with nutrients required for the completion of its life cycle. Recent studies of nematode invasion under treatment with cytoskeletal drugs and in mutant plants where normal functions of the cytoskeleton have been affected, demonstrate the importance of the cytoskeleton in the establishment of a feeding site and successful nematode reproduction. It appears that in the case of microfilaments, nematodes hijack the intracellular machinery that regulates actin dynamics and modulate the organization and properties of the actin filament network. Intervening with this process reduces the nematode infection efficiency and inhibits its life cycle. This discovery uncovers a new pathway that can be exploited for the protection of plants against nematodes.
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Poulter NS, Staiger CJ, Rappoport JZ, Franklin-Tong VE. Actin-binding proteins implicated in the formation of the punctate actin foci stimulated by the self-incompatibility response in Papaver. PLANT PHYSIOLOGY 2010; 152:1274-83. [PMID: 20081043 PMCID: PMC2832276 DOI: 10.1104/pp.109.152066] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Accepted: 01/13/2010] [Indexed: 05/21/2023]
Abstract
The actin cytoskeleton is a key target for signaling networks and plays a central role in translating signals into cellular responses in eukaryotic cells. Self-incompatibility (SI) is an important mechanism responsible for preventing self-fertilization. The SI system of Papaver rhoeas pollen involves a Ca(2+)-dependent signaling network, including massive actin depolymerization as one of the earliest cellular responses, followed by the formation of large actin foci. However, no analysis of these structures, which appear to be aggregates of filamentous (F-)actin based on phalloidin staining, has been carried out to date. Here, we characterize and quantify the formation of F-actin foci in incompatible Papaver pollen tubes over time. The F-actin foci increase in size over time, and we provide evidence that their formation requires actin polymerization. Once formed, these SI-induced structures are unusually stable, being resistant to treatments with latrunculin B. Furthermore, their formation is associated with changes in the intracellular localization of two actin-binding proteins, cyclase-associated protein and actin-depolymerizing factor. Two other regulators of actin dynamics, profilin and fimbrin, do not associate with the F-actin foci. This study provides, to our knowledge, the first insights into the actin-binding proteins and mechanisms involved in the formation of these intriguing structures, which appear to be actively formed during the SI response.
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55
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Szymanski DB, Cosgrove DJ. Dynamic coordination of cytoskeletal and cell wall systems during plant cell morphogenesis. Curr Biol 2010; 19:R800-11. [PMID: 19906582 DOI: 10.1016/j.cub.2009.07.056] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Underlying the architectural complexity of plants are diverse cell types that, under the microscope, easily reveal relationships between cell structure and specialized functions. Much less obvious are the mechanisms by which the cellular growth machinery and mechanical properties of the cell interact to dictate cell shape. The recent combined use of mutants, genomic analyses, sophisticated spectroscopies, and live cell imaging is providing new insight into how cytoskeletal systems and cell wall biosynthetic activities are integrated during morphogenesis. The purpose of this review is to discuss the unique geometric properties and physical processes that regulate plant cell expansion, then to overlay on this mechanical system some of the recent discoveries about the protein machines and cellular polymers that regulate cell shape. In the end, we hope to make clear that there are many interesting opportunities to develop testable mathematical models that improve our understanding of how subcellular structures, protein motors, and extracellular polymers can exert effects at spatial scales that span cells, tissues, and organs.
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Affiliation(s)
- Daniel B Szymanski
- Department of Agronomy, Lily Hall of Life Sciences, 915 West State Street, Purdue University, West Lafayette, IN 47907, USA.
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56
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Blanchoin L, Staiger CJ. Plant formins: Diverse isoforms and unique molecular mechanism. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:201-6. [PMID: 18977251 DOI: 10.1016/j.bbamcr.2008.09.015] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Revised: 07/03/2008] [Accepted: 09/26/2008] [Indexed: 10/21/2022]
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57
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Thomas C, Tholl S, Moes D, Dieterle M, Papuga J, Moreau F, Steinmetz A. Actin bundling in plants. ACTA ACUST UNITED AC 2009; 66:940-57. [DOI: 10.1002/cm.20389] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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58
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Sinclair A, Schenkel M, Mathur J. Signaling to the Actin Cytoskeleton During Cell Morphogenesis and Patterning. SIGNALING IN PLANTS 2009. [DOI: 10.1007/978-3-540-89228-1_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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59
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Choi Y, Lee Y, Jeon BW, Staiger CJ, Lee Y. Phosphatidylinositol 3- and 4-phosphate modulate actin filament reorganization in guard cells of day flower. PLANT, CELL & ENVIRONMENT 2008; 31:366-77. [PMID: 18088331 DOI: 10.1111/j.1365-3040.2007.01769.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Phosphatidylinositol 3-kinases (PtdIns 3-kinases) that produce phosphatidylinositol (3,4,5) triphosphate (PtdIns(3,4,5)P(3)) are considered to be important regulators of actin dynamics in animal cells. In plants, neither PtdIns(3,4,5)P(3) nor the enzyme that produces this lipid has been reported. However, a PtdIns 3-kinase that produces phosphatidylinositol 3-phosphate (PtdIns3P) has been identified, suggesting that PtdIns3P, instead of PtdIns(3,4,5)P(3), regulates actin dynamics in plant cells. Phosphatidylinositol 4-kinase (PtdIns 4-kinase) is closely associated with the actin cytoskeleton in plant cells, suggesting a role for this lipid kinase and its product phosphatidylinositol 4-phosphate (PtdIns4P) in actin-related processes. Here, we investigated whether or not PtdIns3P or PtdIns4P plays a role in actin reorganization induced by a plant hormone abscisic acid (ABA) in guard cells of day flower (Commelina communis). ABA-induced changes in actin filaments were inhibited by LY294002 (LY) and wortmannin (WM), inhibitors of PtdIns3P and PtdIns4P synthesis. Expression of PtdIns3P- and PtdIns4P-binding domains also inhibited ABA-induced actin reorganization in a manner similar to LY and WM. These results suggest that PtdIns3P and PtdIns4P regulate actin dynamics in guard cells. Furthermore, we demonstrate that PtdIns3P exerts its effect on actin dynamics, at least in part, via generation of reactive oxygen species (ROS) in response to ABA.
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Affiliation(s)
- Yunjung Choi
- Division of Molecular and Life Sciences, POSTECH, Pohang 790-784, Korea
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60
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Higaki T, Sano T, Hasezawa S. Actin microfilament dynamics and actin side-binding proteins in plants. CURRENT OPINION IN PLANT BIOLOGY 2007; 10:549-56. [PMID: 17936064 DOI: 10.1016/j.pbi.2007.08.012] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2007] [Revised: 08/17/2007] [Accepted: 08/23/2007] [Indexed: 05/20/2023]
Abstract
Actin microfilaments are highly organized and essential intracellular components of organelle movement and cell morphogenesis in plants. The organization of these microfilaments undergoes dynamic changes during cell division, elongation, and differentiation. Recent live-cell imaging of plant actin microfilaments has revealed their native organization and remarkable dynamics. In addition, characterization of plant actin side-binding proteins has progressed rapidly by genetic, biochemical, and bioinformatic approaches. The gathering and integration of microscopy-based information from actin microfilament dynamics and the molecular identification of actin side-binding proteins have provided considerable insights into actin microfilament-dependent events and actin microfilament organization in plants.
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Affiliation(s)
- Takumi Higaki
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan
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61
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Wang YS, Yoo CM, Blancaflor EB. Improved imaging of actin filaments in transgenic Arabidopsis plants expressing a green fluorescent protein fusion to the C- and N-termini of the fimbrin actin-binding domain 2. THE NEW PHYTOLOGIST 2007; 177:525-536. [PMID: 18028299 DOI: 10.1111/j.1469-8137.2007.02261.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The role of the actin cytoskeleton in plant development is intimately linked to its dynamic behavior. Therefore it is essential to continue refining methods for studying actin organization in living plant cells. The discovery of green fluorescent protein (GFP) has popularized the use of translational fusions of GFP with actin filament (F-actin) side-binding proteins to visualize in vivo actin organization in plants. The most recent of these live cell F-actin reporters are GFP fusions to the actin-binding domain 2 (ABD2) of Arabidopsis fimbrin 1 (ABD2-GFP). To improve ABD2-GFP fluorescence for enhanced in vivo F-actin imaging, transgenic Arabidopsis plants were generated expressing a construct with GFP fused to both the C- and N-termini of ABD2 under the control of the CaMV 35S promoter (35S::GFP-ABD2-GFP). The 35S::GFP-ABD2-GFP lines had significantly increased fluorescence compared with the original 35S::ABD2-GFP lines. The enhanced fluorescence of the 35S::GFP-ABD2-GFP-expressing lines allowed the acquisition of highly resolved images of F-actin in different plant organs and stages of development because of the reduced confocal microscope excitation settings needed for data collection. This simple modification to the ABD2-GFP construct presents an important tool for studying actin function during plant development.
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Affiliation(s)
- Yuh-Shuh Wang
- Plant Biology Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA
| | - Cheol-Min Yoo
- Plant Biology Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA
| | - Elison B Blancaflor
- Plant Biology Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA
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62
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Thomas C, Moreau F, Dieterle M, Hoffmann C, Gatti S, Hofmann C, Van Troys M, Ampe C, Steinmetz A. The LIM domains of WLIM1 define a new class of actin bundling modules. J Biol Chem 2007; 282:33599-33608. [PMID: 17827159 DOI: 10.1074/jbc.m703691200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Actin filament bundling, i.e. the formation of actin cables, is an important process that relies on proteins able to directly bind and cross-link subunits of adjacent actin filaments. Animal cysteine-rich proteins and their plant counterparts are two LIM domain-containing proteins that were recently suggested to define a new family of actin cytoskeleton regulators involved in actin filament bundling. We here identified the LIM domains as responsible for F-actin binding and bundling activities of the tobacco WLIM1. The deletion of one of the two LIM domains reduced significantly, but did not entirely abolish, the ability of WLIM1 to bind actin filaments. Individual LIM domains were found to interact directly with actin filaments, although with a reduced affinity compared with the native protein. Variants lacking the C-terminal or the inter-LIM domain were only weakly affected in their F-actin stabilizing and bundling activities and trigger the formation of thick cables containing tightly packed actin filaments as does the native protein. In contrast, the deletion of one of the two LIM domains negatively impacted both activities and resulted in the formation of thinner and wavier cables. In conclusion, we demonstrate that the LIM domains of WLIM1 are new autonomous actin binding and bundling modules that cooperate to confer WLIM1 high actin binding and bundling activities.
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Affiliation(s)
- Clément Thomas
- Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg.
| | - Flora Moreau
- Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg
| | - Monika Dieterle
- Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg
| | - Céline Hoffmann
- Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg
| | - Sabrina Gatti
- Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg
| | - Christina Hofmann
- Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, F-67084 Strasbourg, France
| | - Marleen Van Troys
- VIB Department of Medical Protein Research, Ugent and Department of Biochemistry, Faculty of Medicine and Health Sciences, B-9052 Ghent, Belgium
| | - Christophe Ampe
- VIB Department of Medical Protein Research, Ugent and Department of Biochemistry, Faculty of Medicine and Health Sciences, B-9052 Ghent, Belgium
| | - André Steinmetz
- Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg
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63
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A mutation in MRH2 kinesin enhances the root hair tip growth defect caused by constitutively activated ROP2 small GTPase in Arabidopsis. PLoS One 2007; 2:e1074. [PMID: 17957256 PMCID: PMC2031828 DOI: 10.1371/journal.pone.0001074] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2007] [Accepted: 10/07/2007] [Indexed: 01/02/2023] Open
Abstract
Root hair tip growth provides a unique model system for the study of plant cell polarity. Transgenic plants expressing constitutively active (CA) forms of ROP (Rho-of-plants) GTPases have been shown to cause the disruption of root hair polarity likely as a result of the alteration of actin filaments (AF) and microtubules (MT) organization. Towards understanding the mechanism by which ROP controls the cytoskeletal organization during root hair tip growth, we have screened for CA-rop2 suppressors or enhancers using CA1-1, a transgenic line that expresses CA-rop2 and shows only mild disruption of tip growth. Here, we report the characterization of a CA-rop2 enhancer (cae1-1 CA1-1) that exhibits bulbous root hairs. The cae1-1 mutation on its own caused a waving and branching root hair phenotype. CAE1 encodes the root hair growth-related, ARM domain-containing kinesin-like protein MRH2 (and thus cae1-1 was renamed to mrh2-3). Cortical MT displayed fragmentation and random orientation in mrh2 root hairs. Consistently, the MT-stabilizing drug taxol could partially rescue the wavy root hair phenotype of mrh2-3, and the MT-depolymerizing drug Oryzalin slightly enhanced the root hair tip growth defect in CA1-1. Interestingly, the addition of the actin-depolymerizing drug Latrunculin B further enhanced the Oryzalin effect. This indicates that the cross-talk of MT and AF organization is important for the mrh2-3 CA1-1 phenotype. Although we did not observe an apparent effect of the MRH2 mutation in AF organization, we found that mrh2-3 root hair growth was more sensitive to Latrunculin B. Moreover, an ARM domain-containing MRH2 fragment could bind to the polymerized actin in vitro. Therefore, our genetic analyses, together with cell biological and pharmacological evidence, suggest that the plant-specific kinesin-related protein MRH2 is an important component that controls MT organization and is likely involved in the ROP2 GTPase-controlled coordination of AF and MT during polarized growth of root hairs.
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64
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Chaudhry F, Guérin C, von Witsch M, Blanchoin L, Staiger CJ. Identification of Arabidopsis cyclase-associated protein 1 as the first nucleotide exchange factor for plant actin. Mol Biol Cell 2007; 18:3002-14. [PMID: 17538023 PMCID: PMC1949352 DOI: 10.1091/mbc.e06-11-1041] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2006] [Revised: 05/17/2007] [Accepted: 05/18/2007] [Indexed: 11/11/2022] Open
Abstract
The actin cytoskeleton powers organelle movements, orchestrates responses to abiotic stresses, and generates an amazing array of cell shapes. Underpinning these diverse functions of the actin cytoskeleton are several dozen accessory proteins that coordinate actin filament dynamics and construct higher-order assemblies. Many actin-binding proteins from the plant kingdom have been characterized and their function is often surprisingly distinct from mammalian and fungal counterparts. The adenylyl cyclase-associated protein (CAP) has recently been shown to be an important regulator of actin dynamics in vivo and in vitro. The disruption of actin organization in cap mutant plants indicates defects in actin dynamics or the regulated assembly and disassembly of actin subunits into filaments. Current models for actin dynamics maintain that actin-depolymerizing factor (ADF)/cofilin removes ADP-actin subunits from filament ends and that profilin recharges these monomers with ATP by enhancing nucleotide exchange and delivery of subunits onto filament barbed ends. Plant profilins, however, lack the essential ability to stimulate nucleotide exchange on actin, suggesting that there might be a missing link yet to be discovered from plants. Here, we show that Arabidopsis thaliana CAP1 (AtCAP1) is an abundant cytoplasmic protein; it is present at a 1:3 M ratio with total actin in suspension cells. AtCAP1 has equivalent affinities for ADP- and ATP-monomeric actin (Kd approximately 1.3 microM). Binding of AtCAP1 to ATP-actin monomers inhibits polymerization, consistent with AtCAP1 being an actin sequestering protein. However, we demonstrate that AtCAP1 is the first plant protein to increase the rate of nucleotide exchange on actin. Even in the presence of ADF/cofilin, AtCAP1 can recharge actin monomers and presumably provide a polymerizable pool of subunits to profilin for addition onto filament ends. In turnover assays, plant profilin, ADF, and CAP act cooperatively to promote flux of subunits through actin filament barbed ends. Collectively, these results and our understanding of other actin-binding proteins implicate CAP1 as a central player in regulating the pool of unpolymerized ATP-actin.
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Affiliation(s)
- Faisal Chaudhry
- *Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-2064; and
| | - Christophe Guérin
- Institut de Recherches en Technologie et Sciences pour le Vivant (iRTSV), Commissariat à l'Energie Atomique/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/Université Joseph Fourier, Commissariat à l'Energie Atomique Grenoble, F38054 Grenoble, France
| | - Matthias von Witsch
- *Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-2064; and
| | - Laurent Blanchoin
- Institut de Recherches en Technologie et Sciences pour le Vivant (iRTSV), Commissariat à l'Energie Atomique/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/Université Joseph Fourier, Commissariat à l'Energie Atomique Grenoble, F38054 Grenoble, France
| | - Christopher J. Staiger
- *Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-2064; and
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65
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van der Honing HS, Emons AMC, Ketelaar T. Actin based processes that could determine the cytoplasmic architecture of plant cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:604-14. [PMID: 16962185 DOI: 10.1016/j.bbamcr.2006.07.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Revised: 06/09/2006] [Accepted: 07/21/2006] [Indexed: 10/24/2022]
Abstract
Actin polymerisation can generate forces that are necessary for cell movement, such as the propulsion of a class of bacteria, including Listeria, and the protrusion of migrating animal cells. Force generation by the actin cytoskeleton in plant cells has not been studied. One process in plant cells that is likely to depend on actin-based force generation is the organisation of the cytoplasm. We compare the function of actin binding proteins of three well-studied mammalian models that depend on actin-based force generation with the function of their homologues in plants. We predict the possible role of these proteins, and thus the role of actin-based force generation, in the production of cytoplasmic organisation in plant cells.
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Affiliation(s)
- Hannie S van der Honing
- Laboratory of Plant Cell Biology, Wageningen University, Arboretumlaan 4, 6703BD Wageningen, The Netherlands
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66
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Thomas C, Hoffmann C, Gatti S, Steinmetz A. LIM Proteins: A Novel Class of Actin Cytoskeleton Organizers in Plants. PLANT SIGNALING & BEHAVIOR 2007; 2:99-100. [PMID: 19704806 PMCID: PMC2633906 DOI: 10.4161/psb.2.2.3614] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2006] [Accepted: 11/24/2006] [Indexed: 05/09/2023]
Abstract
The eukaryotic LIM domain defines a double zinc-finger like structure that functions as a protein-protein interaction module. Whereas in animals the LIM domain is found in numerous proteins of diverse functions, plants possess only a limited number of LIM domain-containing proteins (LIMs). It is noteworthy that most of plant LIMs belong to a same family that is structurally related to the animal Cysteine-Rich Proteins (CRPs). In the September issue of The Plant Cell, we have provided evidence that the tobacco WLIM1 is able to bind actin filaments in a direct manner, to stabilize them and to trigger actin bundling both in vitro and in vivo. These data, together with recent reports on animal CRPs, strongly suggest that these proteins represent a novel class of actin cytoskeleton regulators. In this addendum, we give a brief history of the research that has been conducted on plant LIMs in our lab. Additionally, we show that the GFP-fused tobacco WLIM1 protein is able to properly localize when ectopically expressed in monkey Vero cells, indicating that, despite a relatively low degree of identity/similarity, animal CRPs and plant LIMs display a very similar actin binding activity.
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Affiliation(s)
- Clément Thomas
- Centre de Recherche Public-Santé; Val Fleuri, Luxembourg
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67
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Staiger CJ, Blanchoin L. Actin dynamics: old friends with new stories. CURRENT OPINION IN PLANT BIOLOGY 2006; 9:554-62. [PMID: 17011229 DOI: 10.1016/j.pbi.2006.09.013] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2006] [Accepted: 09/19/2006] [Indexed: 05/12/2023]
Abstract
Actin dynamics, or the rapid turnover of actin filaments, play a central role in numerous cellular processes. A large and diverse cast of characters, accessory proteins known as actin-binding proteins, modulate actin dynamics. They do this by binding to the monomer pool, interacting with the side and ends of filaments, creating breaks along a filament, and generating new filaments de novo. Recent biochemical and single-filament imaging analyses of several conserved classes of plant actin-binding proteins reveal unusual and unexpected properties. Examples that are highlighted in this review include: an abundant monomer-binding protein that catalyzes nucleotide exchange; a barbed-end capping protein that is dissociated from filament ends by the signaling lipid, phosphatidic acid; a villin-like bundling protein that lacks all Ca(2+)-regulated activities; and a formin family member that is non-processive and is sufficient to generate actin filament bundles. These and other stories motivate a careful description of the properties of plant proteins in vitro as a prelude to greater insight into the molecular mechanism(s) underlying the regulation of actin dynamics in vivo.
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Affiliation(s)
- Christopher J Staiger
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-2064, USA.
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68
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Abu-Abied M, Golomb L, Belausov E, Huang S, Geiger B, Kam Z, Staiger CJ, Sadot E. Identification of plant cytoskeleton-interacting proteins by screening for actin stress fiber association in mammalian fibroblasts. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2006; 48:367-79. [PMID: 17010111 DOI: 10.1111/j.1365-313x.2006.02883.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Taking advantage of the high conservation of the cytoskeleton building blocks actin and tubulin between plant and animal kingdoms, we developed a functional genomic screen for the isolation of new plant cytoskeleton-binding proteins that uses a mammalian cell expression system. A yellow fluorescent protein (YFP)-fusion cDNA library from Arabidopsis was inserted into rat fibroblasts and screened for fluorescent chimeras localizing to cytoskeletal structures. The high-throughput screen was performed by an automated microscope. An initial set of candidate genes identified in the screen was isolated, sequenced, the full-length cDNAs were synthesized by RT-PCR and tested by biochemical approaches to verify the ability of the genes to bind actin directly. Alternatively, indirect binding via interaction with other actin-binding proteins was studied. The full-length cDNAs were transferred back to plants as YFP chimeras behind the CAMV-35S promoter. We give here two examples of new plant cytoskeletal proteins identified in the pilot screen. ERD10, a member of the dehydrin family of proteins, was localized to actin stress fibers in rat fibroblasts. Its direct binding to actin filaments was confirmed by several biochemical approaches. Touch-induced calmodulin-like protein, TCH2, was also localized to actin stress fibers in fibroblasts, but was unable to bind actin filaments directly in vitro. Nevertheless, it did bind to the IQ domains of Arabidopsis myosin VIII in a calcium-dependent manner. Further evidence for a cytoskeletal function of ERD10 was obtained in planta; GFP-ERD10 was able to protect the actin cytoskeleton from latrunculin-mediated disruption in Nicotiana benthamiana leaves.
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Affiliation(s)
- Mohamad Abu-Abied
- The Institute of Plant Sciences, The Volcani Center, Bet-Dagan 50250 Israel
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69
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Moseley JB, Goode BL. The yeast actin cytoskeleton: from cellular function to biochemical mechanism. Microbiol Mol Biol Rev 2006; 70:605-45. [PMID: 16959963 PMCID: PMC1594590 DOI: 10.1128/mmbr.00013-06] [Citation(s) in RCA: 287] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
All cells undergo rapid remodeling of their actin networks to regulate such critical processes as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. These events are driven by the coordinated activities of a set of 20 to 30 highly conserved actin-associated proteins, in addition to many cell-specific actin-associated proteins and numerous upstream signaling molecules. The combined activities of these factors control with exquisite precision the spatial and temporal assembly of actin structures and ensure dynamic turnover of actin structures such that cells can rapidly alter their cytoskeletons in response to internal and external cues. One of the most exciting principles to emerge from the last decade of research on actin is that the assembly of architecturally diverse actin structures is governed by highly conserved machinery and mechanisms. With this realization, it has become apparent that pioneering efforts in budding yeast have contributed substantially to defining the universal mechanisms regulating actin dynamics in eukaryotes. In this review, we first describe the filamentous actin structures found in Saccharomyces cerevisiae (patches, cables, and rings) and their physiological functions, and then we discuss in detail the specific roles of actin-associated proteins and their biochemical mechanisms of action.
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Affiliation(s)
- James B Moseley
- Department of Biology and The Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454, USA
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70
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Thomas C, Hoffmann C, Dieterle M, Van Troys M, Ampe C, Steinmetz A. Tobacco WLIM1 is a novel F-actin binding protein involved in actin cytoskeleton remodeling. THE PLANT CELL 2006; 18:2194-206. [PMID: 16905656 PMCID: PMC1560925 DOI: 10.1105/tpc.106.040956] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Revised: 06/22/2006] [Accepted: 07/13/2006] [Indexed: 05/05/2023]
Abstract
We used confocal microscopy and in vitro analyses to show that Nicotiana tabacum WLIM1, a LIM domain protein related to animal Cys-rich proteins, is a novel actin binding protein in plants. Green fluorescent protein (GFP)-tagged WLIM1 protein accumulated in the nucleus and cytoplasm of tobacco BY2 cells. It associated predominantly with actin cytoskeleton, as demonstrated by colabeling and treatment with actin-depolymerizing latrunculin B. High-speed cosedimentation assays revealed the ability of WLIM1 to bind directly to actin filaments with high affinity. Fluorescence recovery after photobleaching and fluorescence loss in photobleaching showed a highly dynamic in vivo interaction of WLIM1-GFP with actin filaments. Expression of WLIM1-GFP in BY2 cells significantly delayed depolymerization of the actin cytoskeleton induced by latrunculin B treatment. WLIM1 also stabilized actin filaments in vitro. Importantly, expression of WLIM1-GFP in Nicotiana benthamiana leaves induces significant changes in actin cytoskeleton organization, specifically, fewer and thicker actin bundles than in control cells, suggesting that WLIM1 functions as an actin bundling protein. This hypothesis was confirmed by low-speed cosedimentation assays and direct observation of F-actin bundles that formed in vitro in the presence of WLIM1. Taken together, these data identify WLIM1 as a novel actin binding protein that increases actin cytoskeleton stability by promoting bundling of actin filaments.
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71
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Kanzawa N, Hoshino Y, Chiba M, Hoshino D, Kobayashi H, Kamasawa N, Kishi Y, Osumi M, Sameshima M, Tsuchiya T. Change in the actin cytoskeleton during seismonastic movement of Mimosa pudica. PLANT & CELL PHYSIOLOGY 2006; 47:531-9. [PMID: 16489209 DOI: 10.1093/pcp/pcj022] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The seismonastic movement of Mimosa pudica is triggered by a sudden loss of turgor pressure. In the present study, we compared the cell cytoskeleton by immunofluorescence analysis before and after movement, and the effects of actin- and microtubule-targeted drugs were examined by injecting them into the cut pulvinus. We found that fragmentation of actin filaments and microtubules occurs during bending, although the actin cytoskeleton, but not the microtubules, was involved in regulation of the movement. Transmission electron microscopy revealed that actin cables became loose after the bending. We injected phosphatase inhibitors into the severed pulvinus to examine the effects of such inhibitors on the actin cytoskeleton. We found that changes in actin isoforms, fragmentation of actin filaments and the bending movement were all inhibited after injection of a tyrosine phosphatase inhibitor. We thus propose that the phosphorylation status of actin at tyrosine residues affects the dynamic reorganization of actin filaments and causes seismonastic movement.
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Affiliation(s)
- Nobuyuki Kanzawa
- Department of Chemistry, Faculty of Science and Technology, Sophia University, Tokyo, 102-8554 Japan.
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72
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73
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Hussey PJ, Ketelaar T, Deeks MJ. Control of the actin cytoskeleton in plant cell growth. ANNUAL REVIEW OF PLANT BIOLOGY 2006; 57:109-25. [PMID: 16669757 DOI: 10.1146/annurev.arplant.57.032905.105206] [Citation(s) in RCA: 201] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Plant cells grow through increases in volume and cell wall surface area. The mature morphology of a plant cell is a product of the differential rates of expansion between neighboring zones of the cell wall during this process. Filamentous actin arrays are associated with plant cell growth, and the activity of actin-binding proteins is proving to be essential for proper cell morphogenesis. Actin-nucleating proteins participate in cell expansion and cell plate formation whereas the recycling of actin monomers is required to maintain actin dynamics and controlled growth. Coordination of actin-binding protein activity and other aspects of cytoskeletal behavior during cell development maintains cohesive cell expansion. Emerging plant signaling networks are proving to be powerful regulators of morphology-shaping cytoskeletal activity, and in this review we highlight current research in actin network regulation.
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Affiliation(s)
- Patrick J Hussey
- 1The Integrative Cell Biology Laboratory, School of Biological and Biomedical Sciences, University of Durham, Science Laboratories, Durham DH1 3LE, United Kingdom.
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74
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Blancaflor EB, Wang YS, Motes CM. Organization and function of the actin cytoskeleton in developing root cells. INTERNATIONAL REVIEW OF CYTOLOGY 2006; 252:219-64. [PMID: 16984819 DOI: 10.1016/s0074-7696(06)52004-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The actin cytoskeleton is a highly dynamic structure, which mediates various cellular functions in large part through accessory proteins that tilt the balance between monomeric G-actin and filamentous actin (F-actin) or by facilitating interactions between actin and the plasma membrane, microtubules, and other organelles. Roots have become an attractive model to study actin in plant development because of their simple anatomy and accessibility of some root cell types such as root hairs for microscopic analyses. Roots also exhibit a remarkable developmental plasticity and possess a delicate sensory system that is easily manipulated, so that one can design experiments addressing a range of important biological questions. Many facets of root development can be regulated by the diverse actin network found in the various root developmental regions. Various molecules impinge on this actin scaffold to define how a particular root cell type grows or responds to a specific environmental signal. Although advances in genomics are leading the way toward elucidating actin function in roots, more significant strides will be realized when such tools are combined with improved methodologies for accurately depicting how actin is organized in plant cells.
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Affiliation(s)
- Elison B Blancaflor
- Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401, USA
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75
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Ruthardt N, Gulde N, Spiegel H, Fischer R, Emans N. Four-dimensional imaging of transvacuolar strand dynamics in tobacco BY-2 cells. PROTOPLASMA 2005; 225:205-15. [PMID: 16228899 DOI: 10.1007/s00709-005-0093-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2004] [Accepted: 10/29/2004] [Indexed: 05/04/2023]
Abstract
The vacuole is a characteristic organelle of plant cells and fulfills several important functions related to metabolism and growth of the cell. To shed light on the details of vacuolar structural changes in plant cells, we explored the three-dimensional organization and dynamics of living Nicotiana tabacum L. cv. Bright Yellow 2 cell vacuoles by real-time confocal time-lapse imaging. For imaging, the cells were pulse-labeled with the amphipathic styryl dye FM1-43 (N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide), which is delivered to the plant vacuole by endocytic uptake and then incubated overnight. Imaging of the membrane-labeled vacuole revealed a complex vacuole morphology underlaid by constant remodeling. The vacuole is traversed by multiple transvacuolar strands which move along each other and fuse in multiple manners. New strands were created by fission of large membrane sheets. Endocytic vesicle trafficking was followed within the dynamic transvacuolar strands. The movement occurred in a stop-and-go fashion with an average vesicle velocity of 0.46 microm/s and a peak velocity of 0.82 microm/s. Transvacuolar-strand reduction and creation is a characteristic event observed during mitosis. Here we propose a mechanistic model for the alteration of the number of transvacuolar strands, on the basis of their fusion and fission.
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Affiliation(s)
- N Ruthardt
- Cellome Research Group, Institute for Molecular Biotechnology, Aachen University, Aachen, Germany
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76
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Michelot A, Guérin C, Huang S, Ingouff M, Richard S, Rodiuc N, Staiger CJ, Blanchoin L. The formin homology 1 domain modulates the actin nucleation and bundling activity of Arabidopsis FORMIN1. THE PLANT CELL 2005; 17:2296-313. [PMID: 15994911 PMCID: PMC1182490 DOI: 10.1105/tpc.105.030908] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2005] [Revised: 05/16/2005] [Accepted: 05/19/2005] [Indexed: 05/03/2023]
Abstract
The organization of actin filaments into large ordered structures is a tightly controlled feature of many cellular processes. However, the mechanisms by which actin filament polymerization is initiated from the available pool of profilin-bound actin monomers remain unknown in plants. Because the spontaneous polymerization of actin monomers bound to profilin is inhibited, the intervention of an actin promoting factor is required for efficient actin polymerization. Two such factors have been characterized from yeasts and metazoans: the Arp2/3 complex, a complex of seven highly conserved subunits including two actin-related proteins (ARP2 and ARP3), and the FORMIN family of proteins. The recent finding that Arabidopsis thaliana plants lacking a functional Arp2/3 complex exhibit rather modest morphological defects leads us to consider whether the large FORMIN family plays a central role in the regulation of actin polymerization. Here, we have characterized the mechanism of action of Arabidopsis FORMIN1 (AFH1). Overexpression of AFH1 in pollen tubes has been shown previously to induce abnormal actin cable formation. We demonstrate that AFH1 has a unique behavior when compared with nonplant formins. The activity of the formin homology domain 2 (FH2), containing the actin binding activity, is modulated by the formin homology domain 1 (FH1). Indeed, the presence of the FH1 domain switches the FH2 domain from a tight capper (Kd approximately 3.7 nM) able to nucleate actin filaments that grow only in the pointed-end direction to a leaky capper that allows barbed-end elongation and efficient nucleation of actin filaments from actin monomers bound to profilin. Another exciting feature of AFH1 is its ability to bind to the side and bundle actin filaments. We have identified an actin nucleator that is able to organize actin filaments directly into unbranched actin filament bundles. We suggest that AFH1 plays a central role in the initiation and organization of actin cables from the pool of actin monomers bound to profilin.
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Affiliation(s)
- Alphée Michelot
- Laboratoire de Physiologie Cellulaire Végétale, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, Unité Mixte de Recherche 5168, F38054, Grenoble, France
| | - Christophe Guérin
- Laboratoire de Physiologie Cellulaire Végétale, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, Unité Mixte de Recherche 5168, F38054, Grenoble, France
| | - Shanjin Huang
- Department of Biological Sciences and Bindley Bioscience Center, Purdue University, West Lafayette, Indiana 47907-2064
| | - Mathieu Ingouff
- Laboratoire de Physiologie Cellulaire Végétale, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, Unité Mixte de Recherche 5168, F38054, Grenoble, France
| | - Stéphane Richard
- Salk Institute, Structural Biology Laboratory, La Jolla, California 92037
| | - Natalia Rodiuc
- Laboratoire de Physiologie Cellulaire Végétale, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, Unité Mixte de Recherche 5168, F38054, Grenoble, France
| | - Christopher J. Staiger
- Department of Biological Sciences and Bindley Bioscience Center, Purdue University, West Lafayette, Indiana 47907-2064
| | - Laurent Blanchoin
- Laboratoire de Physiologie Cellulaire Végétale, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, Unité Mixte de Recherche 5168, F38054, Grenoble, France
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77
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Delanote V, Vandekerckhove J, Gettemans J. Plastins: versatile modulators of actin organization in (patho)physiological cellular processes. Acta Pharmacol Sin 2005; 26:769-79. [PMID: 15960882 DOI: 10.1111/j.1745-7254.2005.00145.x] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Many actin-binding proteins are expressed in eukaryotic cells. These polypeptides assist in stabilizing and rearranging the organization of the actin cytoskeleton in response to external stimuli, or during cell migration and adhesion. Here we review a particular set of actin-binding proteins called plastins. Plastins (also called fimbrins) belong to a subclass of actin-binding proteins known as actin bundling proteins. Three isoforms have been characterized in mammals: T-plastin is expressed in cells from solid tissue, whereas L-plastin occurs predominantly in hematopoietic cells. The third isoform, I-plastin, is specifically expressed in the small intestine, colon and kidney. These proteins share the unique property of cross-linking actin filaments into tight bundles. Although plastins are primarily involved in regulation of the actin cytoskeleton, they possess some unique features. For instance, they are implicated in invasion by pathogenic bacteria such as Shigella flexneri and Salmonella typhimurium. Also, L-plastin plays an important role in leukocyte function. T-plastin, on the other hand, is possibly involved in DNA repair. Finally, both T- and L-plastin are implicated in several diseases, and L-plastin is considered to be a valuable marker for cancer.
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Affiliation(s)
- Veerle Delanote
- Department of Medical Protein Research, Flanders Interuniversity Institute for Biotechnology (VIB), Ghent University, Faculty of Medicine and Health Sciences, Albert Baertsoenkaai 3, B-9000 Ghent, Belgium
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78
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Voigt B, Timmers ACJ, Samaj J, Müller J, Baluska F, Menzel D. GFP-FABD2 fusion construct allows in vivo visualization of the dynamic actin cytoskeleton in all cells of Arabidopsis seedlings. Eur J Cell Biol 2005; 84:595-608. [PMID: 16032928 DOI: 10.1016/j.ejcb.2004.11.011] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
In vivo visualization of filamentous actin in all cells of Arabidopsis thaliana seedlings is essential for understanding the numerous roles of the actin cytoskeleton in diverse processes of cell differentiation. A previously introduced reporter construct based on the actin-binding domain of mouse talin proved to be useful for unravelling some of these aspects in cell layers close to the organ surface. However, cells more deeply embedded, especially stelar cells active in polar transport of auxin, show either diffuse or no fluorescence at all due to the lack of expression of the fusion protein. The same problem is encountered in the root meristem. Recently introduced actin reporters based on fusions between A. thaliana fimbrin 1 and GFP gave brilliant results in organs from the root differentiation zone upwards to the leaves, however failed to depict the filamentous actin cytoskeleton in the transition zone of the root, in the apical meristem and the root cap. To overcome these problems, we have prepared new transgenic lines for the visualization of F-actin in vivo. We report here that a construct consisting of GFP fused to the C-terminal half of A. thaliana fimbrin 1 reveals dynamic arrays of F-actin in all cells of stably transformed A. thaliana seedlings.
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Affiliation(s)
- Boris Voigt
- Department of Plant Cell Biology, Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University of Bonn, Kirschallee 1, D-53115 Bonn, Germany
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79
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Giganti A, Plastino J, Janji B, Van Troys M, Lentz D, Ampe C, Sykes C, Friederich E. Actin-filament cross-linking protein T-plastin increases Arp2/3-mediated actin-based movement. J Cell Sci 2005; 118:1255-65. [PMID: 15741236 DOI: 10.1242/jcs.01698] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Increasing evidence suggests that actin cross-linking or bundling proteins might not only structure the cortical actin cytoskeleton but also control actin dynamics. Here, we analyse the effects of T-plastin/T-fimbrin, a representative member of an important actin-filament cross-linking protein by combining a quantitative biomimetic motility assay with biochemical and cell-based approaches. Beads coated with the VCA domain of the Wiskott/Aldrich-syndrome protein (WASP) recruit the actin-nucleating Arp2/3 complex, polymerize actin at their surface and undergo movement when placed in cell-free extracts. T-Plastin increased the velocity of VCA beads 1.5 times, stabilized actin comets and concomitantly displaced cofilin, an actin-depolymerizing protein. T-Plastin also decreased the F-actin disassembly rate and inhibited cofilin-mediated depolymerization of actin filaments in vitro. Importantly, a bundling-incompetent variant comprising the first actin-binding domain (ABD1) had similar effects. In cells, this domain induced the formation of long actin cables to which other actin-regulating proteins were recruited. Altogether, these results favor a mechanism in which binding of ABD1 controls actin turnover independently of cross-link formation. In vivo, this activity might contribute to the assembly and maintenance of the actin cytoskeleton of plasma-membrane protrusions.
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Affiliation(s)
- Adeline Giganti
- Laboratoire de Biologie Moléculaire, d'Analyse Génique et de Modélisation, Centre de Recherche Public-Santé, 42, rue du Laboratoire, L-1911, Luxembourg
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80
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Szymanski DB. Breaking the WAVE complex: the point of Arabidopsis trichomes. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:103-12. [PMID: 15653407 DOI: 10.1016/j.pbi.2004.11.004] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Actin filaments comprise an essential cytoskeletal array that organizes the cytoplasm during growth and cell division. In growing cells, actin filaments carry out many functions. Actin filaments position the endomembrane system and act as a substrate on which organelle motility occurs. Other actin-filament arrays appear to be more dynamic and to reorganize in response to growth signals and external cues. The diverse cellular functions of the actin cytoskeleton are mediated by actin-binding proteins that nucleate, destabilize, and bundle actin filaments. The distorted trichome morphology mutants provide a simple genetic system in which to study mechanisms of actin-dependent morphogenesis. Recent results from several groups indicate that 'distorted group' genes encode subunits of the actin-related protein (Arp)2/3 and WAVE complexes, and function in a cell morphogenesis pathway.
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Affiliation(s)
- Daniel B Szymanski
- Agronomy Department, Purdue University, Lilly Hall of Life Sciences, 915 West State Street, West Lafayette, Indiana 47907-2054, USA.
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81
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Sheahan MB, Staiger CJ, Rose RJ, McCurdy DW. A green fluorescent protein fusion to actin-binding domain 2 of Arabidopsis fimbrin highlights new features of a dynamic actin cytoskeleton in live plant cells. PLANT PHYSIOLOGY 2004; 136:3968-78. [PMID: 15557099 PMCID: PMC535829 DOI: 10.1104/pp.104.049411] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2004] [Revised: 10/06/2004] [Accepted: 10/12/2004] [Indexed: 05/18/2023]
Abstract
The actin cytoskeleton coordinates numerous cellular processes required for plant development. The functions of this network are intricately linked to its dynamic arrangement, and thus progress in understanding how actin orchestrates cellular processes relies on critical evaluation of actin organization and turnover. To investigate the dynamic nature of the actin cytoskeleton, we used a fusion protein between green fluorescent protein (GFP) and the second actin-binding domain (fABD2) of Arabidopsis (Arabidopsis thaliana) fimbrin, AtFIM1. The GFP-fABD2 fusion protein labeled highly dynamic and dense actin networks in diverse species and cell types, revealing structural detail not seen with alternative labeling methods, such as the commonly used mouse talin GFP fusion (GFP-mTalin). Further, we show that expression of the GFP-fABD2 fusion protein in Arabidopsis, unlike GFP-mTalin, has no detectable adverse effects on plant morphology or development. Time-lapse confocal microscopy and fluorescence recovery after photobleaching analyses of the actin cytoskeleton labeled with GFP-fABD2 revealed that lateral-filament migration and sliding of individual actin filaments or bundles are processes that contribute to the dynamic and continually reorganizing nature of the actin scaffold. These new observations of the dynamic actin cytoskeleton in plant cells using GFP-fABD2 reveal the value of this probe for future investigations of how actin filaments coordinate cellular processes required for plant development.
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Affiliation(s)
- Michael B Sheahan
- School of Environmental and Life Sciences , The University of Newcastle, Callaghan, New South Wales, 2308 Australia
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82
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Takemoto D, Hardham AR. The cytoskeleton as a regulator and target of biotic interactions in plants. PLANT PHYSIOLOGY 2004; 136:3864-76. [PMID: 15591444 PMCID: PMC535820 DOI: 10.1104/pp.104.052159] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2004] [Revised: 10/15/2004] [Accepted: 10/18/2004] [Indexed: 05/18/2023]
Affiliation(s)
- Daigo Takemoto
- Plant Cell Biology Group, Research School of Biological Sciences, The Australian National University, Canberra, ACT 2601, Australia
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83
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Preuss ML, Kovar DR, Lee YRJ, Staiger CJ, Delmer DP, Liu B. A plant-specific kinesin binds to actin microfilaments and interacts with cortical microtubules in cotton fibers. PLANT PHYSIOLOGY 2004; 136:3945-55. [PMID: 15557092 PMCID: PMC535827 DOI: 10.1104/pp.104.052340] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2004] [Revised: 10/08/2004] [Accepted: 10/08/2004] [Indexed: 05/17/2023]
Abstract
A novel kinesin, GhKCH1, has been identified from cotton (Gossypium hirsutum) fibers. GhKCH1 has a centrally located kinesin catalytic core, a signature neck peptide of minus end-directed kinesins, and a unique calponin homology (CH) domain at its N terminus. GhKCH1 and other CH domain-containing kinesins (KCHs) belong to a distinct branch of the minus end-directed kinesin subfamily. To date the KCH kinesins have been found only in higher plants. Because the CH domain is often found in actin-binding proteins, we proposed that GhKCH1 might play a role in mediating dynamic interaction between microtubules and actin microfilaments in cotton fibers. In an in vitro actin-binding assay, GhKCH1's N-terminal region including the CH domain interacted directly with actin microfilaments. In cotton fibers, GhKCH1 decorated cortical microtubules in a punctate manner. Occasionally GhKCH1 was found to be associated with transverse-cortical actin microfilaments, but never with axial actin cables in cotton fibers. Localization of GhKCH1 on cortical microtubules was independent of the integrity of actin microfilaments. Thus, GhKCH1 may play a role in organizing the actin network in coordination with the cortical microtubule array. These data also suggest that flowering plants may employ unique KCHs to coordinate actin microfilaments and microtubules during cell growth.
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Affiliation(s)
- Mary L Preuss
- Section of Plant Biology, University of California, Davis, California 95616, USA
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84
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Abstract
Plant cells are surrounded by a cell wall composed of polysaccharides and hence can change neither their form nor their position. However, active movement of organelles (cytoplasmic streaming or protoplasmic streaming) is observed in plant cells, and involvement of the actin/myosin system in these processes has been suggested. Successful biochemical and biophysical approaches to studying myosins have extensively promoted the understanding of the molecular mechanism underlying these phenomena.
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Affiliation(s)
- Teruo Shimmen
- Department of Life Science, Graduate School of Science, Himeji Institute of Technology, Harima Science Park City, Hyogo 678-1297, Japan.
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85
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Wang YS, Motes CM, Mohamalawari DR, Blancaflor EB. Green fluorescent protein fusions to Arabidopsis fimbrin 1 for spatio-temporal imaging of F-actin dynamics in roots. CELL MOTILITY AND THE CYTOSKELETON 2004; 59:79-93. [PMID: 15362112 DOI: 10.1002/cm.20024] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The visualization of green fluorescent protein (GFP) fusions with microtubule or actin filament (F-actin) binding proteins has provided new insights into the function of the cytoskeleton during plant development. For studies on actin, GFP fusions to talin have been the most generally used reporters. Although GFP-Talin has allowed in vivo F-actin imaging in a variety of plant cells, its utility in monitoring F-actin in stably transformed plants is limited particularly in developing roots where interesting actin dependent cell processes are occurring. In this study, we created a variety of GFP fusions to Arabidopsis Fimbrin 1 (AtFim1) to explore their utility for in vivo F-actin imaging in root cells and to better understand the actin binding properties of AtFim1 in living plant cells. Translational fusions of GFP to full-length AtFim1 or to some truncated variants of AtFim1 showed filamentous labeling in transient expression assays. One truncated fimbrin-GFP fusion was capable of labeling distinct filaments in stably transformed Arabidopsis roots. The filaments decorated by this construct were highly dynamic in growing root hairs and elongating root cells and were sensitive to actin disrupting drugs. Therefore, the fimbrin-GFP reporters we describe in this study provide additional tools for studying the actin cytoskeleton during root cell development. Moreover, the localization of AtFim1-GFP offers insights into the regulation of actin organization in developing roots by this class of actin cross-linking proteins.
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Affiliation(s)
- Yuh-Shuh Wang
- Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA
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86
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Lebart MC, Hubert F, Boiteau C, Ventéo S, Roustan C, Benyamin Y. Biochemical characterization of the L-plastin-actin interaction shows a resemblance with that of alpha-actinin and allows a distinction to be made between the two actin-binding domains of the molecule. Biochemistry 2004; 43:2428-37. [PMID: 14992580 DOI: 10.1021/bi030151p] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Actin interaction with L-plastin, a plastin/fimbrins isoform of the alpha-actinin family of molecules, is poorly characterized, from the biochemical point of view. Besides, molecular modeling of the T-isoform has recently provided a complete model of interaction with filamentous actin [Volkmann, N., DeRosier, D., Matsudaira, P., and Hanein, D. (2001) J. Cell Biol. 153, 947-956]. In this study, we report that recombinant L-plastin binds actin in a manner that strongly resembles that of the alpha-actinin-actin interface. The similitudes concern the absence of specificity toward the actin isoform and the inhibition of the binding by phosphoinositides. Furthermore, the participation of actin peptides 112-125 and 360-372 in the interface together with an inhibition of the rate of pyrenyl F-actin depolymerization is in favor of a lateral binding of the plastin isoform along the filament axis and strenghtens the similitudes in the way L-plastin and alpha-actinin bind to actin. We have also investigated the functional aspect and the putative equivalence of the two actin-binding domains of L-plastin toward actin binding. We demonstrate for the first time that the two recombinant fragments, expressed as single domains, have different affinities for actin. We further analyzed the difference using chemical cross-linking and F-actin depolymerization experiments assayed by fluorescence and high-speed centrifugation. The results clearly demonstrate that the two actin-binding domains of plastin display different modes of interaction with the actin filament. We discuss these results in light of the model of actin interaction proposed for T-plastin.
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Affiliation(s)
- M-C Lebart
- UMR 5539, Laboratoire de Motilité Cellulaire (EPHE), USTL, Bât.24, 4 étage, cc 107, place E. Bataillon, 34095 Montpellier, France.
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87
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Klein MG, Shi W, Ramagopal U, Tseng Y, Wirtz D, Kovar DR, Staiger CJ, Almo SC. Structure of the Actin Crosslinking Core of Fimbrin. Structure 2004; 12:999-1013. [PMID: 15274920 DOI: 10.1016/j.str.2004.04.010] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2004] [Revised: 04/08/2004] [Accepted: 04/09/2004] [Indexed: 11/16/2022]
Abstract
Filamentous actin is organized into bundles and orthogonal networks by the fimbrin/alpha-actinin superfamily of F-actin crosslinking proteins. The crystal structure of the Arabidopsis thaliana and Schizosaccharomyces pombe fimbrin cores provides the first description of a functional F-actin crosslinking protein and highlights the compact and distinctly asymmetric organization of the fimbrin molecule, in which the two actin binding domains present distinct surfaces to solvent. The mapping of functionally important residues onto the structure affords new insights into the binding process and provides additional constraints which must be accommodated by models for F-actin binding and crosslinking. Most strikingly, this work provides unique insight into the mechanistic features of conditional-lethal mutants and their extragenic suppressors, which highlight conformational and dynamic properties required for fimbrin function. These results underscore the power of jointly considering structural and genetic suppressor data for obtaining unexpected and biologically relevant mechanistic information.
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Affiliation(s)
- Michael G Klein
- Department of Biochemistry, Center for Synchrotron Biosciences, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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88
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Huang S, Blanchoin L, Chaudhry F, Franklin-Tong VE, Staiger CJ. A Gelsolin-like Protein from Papaver rhoeas Pollen (PrABP80) Stimulates Calcium-regulated Severing and Depolymerization of Actin Filaments. J Biol Chem 2004; 279:23364-75. [PMID: 15039433 DOI: 10.1074/jbc.m312973200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cytoskeleton is a key regulator of plant morphogenesis, sexual reproduction, and cellular responses to extracellular stimuli. During the self-incompatibility response of Papaver rhoeas L. (field poppy) pollen, the actin filament network is rapidly depolymerized by a flood of cytosolic free Ca2+ that results in cessation of tip growth and prevention of fertilization. Attempts to model this dramatic cytoskeletal response with known pollen actin-binding proteins (ABPs) revealed that the major G-actin-binding protein profilin can account for only a small percentage of the measured depolymerization. We have identified an 80-kDa, Ca(2+)-regulated ABP from poppy pollen (PrABP80) and characterized its biochemical properties in vitro. Sequence determination by mass spectrometry revealed that PrABP80 is related to gelsolin and villin. The molecular weight, lack of filament cross-linking activity, and a potent severing activity are all consistent with PrABP80 being a plant gelsolin. Kinetic analysis of actin assembly/disassembly reactions revealed that substoichiometric amounts of PrABP80 can nucleate actin polymerization from monomers, block the assembly of profilin-actin complex onto actin filament ends, and enhance profilin-mediated actin depolymerization. Fluorescence microscopy of individual actin filaments provided compelling, direct evidence for filament severing and confirmed the actin nucleation and barbed end capping properties. This is the first direct evidence for a plant gelsolin and the first example of efficient severing by a plant ABP. We propose that PrABP80 functions at the center of the self-incompatibility response by creating new filament pointed ends for disassembly and by blocking barbed ends from profilin-actin assembly.
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Affiliation(s)
- Shanjin Huang
- Department of Biological Sciences and The Purdue Motility Group, Purdue University, West Lafayette, Indiana 47907-2064, USA
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89
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El-Din El-Assal S, Le J, Basu D, Mallery EL, Szymanski DB. DISTORTED2 encodes an ARPC2 subunit of the putative Arabidopsis ARP2/3 complex. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 38:526-38. [PMID: 15086808 DOI: 10.1111/j.1365-313x.2004.02065.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Arabidopsis trichomes are unicellular, branched structures that have highly constrained requirements for the cytoskeleton. The 'distorted group' genes function downstream from microtubule-based branch initiation, and are required during the actin-dependent phase of polarized stalk and branch expansion. Of the eight known 'distorted group' genes, a subset encode homologs of ARP2/3 complex subunits. In eukaryotic cells, the seven-protein ARP2/3 complex nucleates actin filament networks that push on the plasma membrane and organelles. In plants cells, the existence and function of an ARP2/3 complex is unclear. In this paper, we report that DISTORTED2 (DIS2) encodes a paralogue of the ARP2/3 complex subunit ARPC2. DIS2 has ARPC2 activity, based on its ability to rescue the growth defects of arpc2 (arc35Delta) null yeast cells. Like known ARPC2s, DIS2 physically interacts with ARPC4. Mutations in DIS2 cause a distorted trichome phenotype, defects in cell-cell adhesion, and a modest reduction in shoot FW. The actin cytoskeleton in dis2 trichomes is extensive, but developing branches fail to generate and maintain highly organized cytoplasmic actin bundles.
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Affiliation(s)
- Salah El-Din El-Assal
- Agronomy Department, Purdue University, Lilly Hall, 915 West State Street, West Lafayette, IN 47907-2054, USA
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90
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Tian GW, Mohanty A, Chary SN, Li S, Paap B, Drakakaki G, Kopec CD, Li J, Ehrhardt D, Jackson D, Rhee SY, Raikhel NV, Citovsky V. High-throughput fluorescent tagging of full-length Arabidopsis gene products in planta. PLANT PHYSIOLOGY 2004; 135:25-38. [PMID: 15141064 PMCID: PMC429330 DOI: 10.1104/pp.104.040139] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2004] [Revised: 03/09/2004] [Accepted: 03/12/2004] [Indexed: 05/17/2023]
Abstract
We developed a high-throughput methodology, termed fluorescent tagging of full-length proteins (FTFLP), to analyze expression patterns and subcellular localization of Arabidopsis gene products in planta. Determination of these parameters is a logical first step in functional characterization of the approximately one-third of all known Arabidopsis genes that encode novel proteins of unknown function. Our FTFLP-based approach offers two significant advantages: first, it produces internally-tagged full-length proteins that are likely to exhibit native intracellular localization, and second, it yields information about the tissue specificity of gene expression by the use of native promoters. To demonstrate how FTFLP may be used for characterization of the Arabidopsis proteome, we tagged a series of known proteins with diverse subcellular targeting patterns as well as several proteins with unknown function and unassigned subcellular localization.
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Affiliation(s)
- Guo-Wei Tian
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215, USA
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91
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Sheahan MB, Rose RJ, McCurdy DW. Organelle inheritance in plant cell division: the actin cytoskeleton is required for unbiased inheritance of chloroplasts, mitochondria and endoplasmic reticulum in dividing protoplasts. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 37:379-90. [PMID: 14731258 DOI: 10.1046/j.1365-313x.2003.01967.x] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Nuclear inheritance is highly ordered, ensuring stringent, unbiased partitioning of chromosomes before cell division. In plants, however, little is known about the analogous cellular processes that might ensure unbiased inheritance of non-nuclear organelles, either in meristematic cell divisions or those induced during the acquisition of totipotency. We have investigated organelle redistribution and inheritance mechanisms during cell division in cultured tobacco mesophyll protoplasts. Quantitative analysis of organelle repositioning observed by autofluorescence of chloroplasts or green fluorescent protein (GFP), targeted to mitochondria or endoplasmic reticulum (ER), demonstrated that these organelles redistribute in an ordered manner before division. Treating protoplasts with cytoskeleton-disrupting drugs showed that redistribution depended on actin filaments (AFs), but not on microtubules (MTs), and furthermore, that an intact actin cytoskeleton was required to achieve unbiased organelle inheritance. Labelling the actin cytoskeleton with a novel GFP-fusion protein revealed a highly dynamic actin network, with local reorganisation of this network itself, appearing to contribute substantially to repositioning of chloroplasts and mitochondria. Our observations show that each organelle exploits a different strategy of redistribution to ensure unbiased partitioning. We conclude that inheritance of chloroplasts, mitochondria and ER in totipotent plant cells is an ordered process, requiring complex interactions with the actin cytoskeleton.
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Affiliation(s)
- Michael B Sheahan
- School of Environmental and Life Sciences, The University of Newcastle, University Drive, Callaghan, NSW 2308, Australia
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92
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Huang S, Blanchoin L, Kovar DR, Staiger CJ. Arabidopsis capping protein (AtCP) is a heterodimer that regulates assembly at the barbed ends of actin filaments. J Biol Chem 2003; 278:44832-42. [PMID: 12947123 DOI: 10.1074/jbc.m306670200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The precise regulation of actin filament polymerization and depolymerization is essential for many cellular processes and is choreographed by a multitude of actin-binding proteins (ABPs). In higher plants the number of well characterized ABPs is quite limited, and some evidence points to significant differences in the biochemical properties of apparently conserved proteins. Here we provide the first evidence for the existence and biochemical properties of a heterodimeric capping protein from Arabidopsis thaliana (AtCP). The purified recombinant protein binds to actin filament barbed ends with Kd values of 12-24 nM, as assayed both kinetically and at steady state. AtCP prevents the addition of profilin actin to barbed ends during a seeded elongation reaction and suppresses dilution-mediated depolymerization. It does not, however, sever actin filaments and does not have a preference for the source of actin. During assembly from Mg-ATP-actin monomers, AtCP eliminates the initial lag period for actin polymerization and increases the maximum rate of polymerization. Indeed, the efficiency of actin nucleation of 0.042 pointed ends created per AtCP polypeptide compares favorably with mouse CapZ, which has a maximal nucleation of 0.17 pointed ends per CapZ polypeptide. AtCP activity is not affected by calcium but is sensitive to phosphatidylinositol 4,5-bisphosphate. We propose that AtCP is a major regulator of actin dynamics in plant cells that, together with abundant profilin, is responsible for maintaining a large pool of actin subunits and a surprisingly small population of F-actin.
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Affiliation(s)
- Shanjin Huang
- Department of Biological Sciences and Purdue Motility Group, Purdue University, West Lafayette, Indiana 47907-2064, USA
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93
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Yokota E, Vidali L, Tominaga M, Tahara H, Orii H, Morizane Y, Hepler PK, Shimmen T. Plant 115-kDa actin-filament bundling protein, P-115-ABP, is a homologue of plant villin and is widely distributed in cells. PLANT & CELL PHYSIOLOGY 2003; 44:1088-99. [PMID: 14581634 DOI: 10.1093/pcp/pcg132] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
In many cases, actin filaments are arranged into bundles and serve as tracks for cytoplasmic streaming in plant cells. We have isolated an actin-filament bundling protein, which is composed of 115-kDa polypeptide (P-115-ABP), from the germinating pollen of lily, Lilium longiflorum [Nakayasu et al. (1998) BIOCHEM: Biophys. Res. Commun. 249: 61]. P-115-ABP shared similar antigenicity with a plant 135-kDa actin-filament bundling protein (P-135-ABP), a plant homologue of villin. A full-length cDNA clone (ABP115; accession no. AB097407) was isolated from an expression cDNA library of lily pollen by immuno-screening using antisera against P-115-ABP and P-135-ABP. The amino acid sequence of P-115-ABP deduced from this clone showed high homology with those of P-135-ABP and four villin isoforms of Arabidopsis thaliana (AtVLN1, AtVLN2, AtVLN3 and AtVLN4), especially AtVLN4, indicating that P-115-ABP can also be classified as a plant villin. The P-115-ABP isolated biochemically from the germinating lily pollen was able to arrange F-actin filaments with uniform polarity into bundles and this bundling activity was suppressed by Ca2+-calmodulin (CaM), similar to the actin-filament bundling properties of P-135-ABP. The P-115-ABP type of plant villin was widely distributed in plant cells, from algae to land plants. In root hair cells of Hydrocharis dubia, this type of plant villin was co-localized with actin-filament bundles in the transvacuolar strands and the sub-cortical regions. Microinjection of the antiserum against P-115-ABP into living root hair cells caused the disappearance of transvaculor strands and alteration of the route of cytoplasmic streaming. In internodal cells of Chara corallina in which the P-135-ABP type of plant villin is lacking, the P-115-ABP type showed co-localization with actin-filament cables anchored on the intracellular surface of chloroplasts. These results indicated that plant villins are widely distributed and involved in the organization of actin filaments into bundles throughout the plant kingdom.
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Affiliation(s)
- Etsuo Yokota
- Department of Life Science, Graduate School of Science, Himeji Institute of Technology, Harima Science Park City, Hyogo, 678-1297 Japan.
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94
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Abstract
In the past decade the first Arabidopsis genes encoding cytoskeletal proteins were identified. A few dozen genes in the actin and tubulin cytoskeletal systems have been characterized thoroughly, including gene families encoding actins, profilins, actin depolymerizing factors, α-tubulins, and β-tubulins. Conventional molecular genetics have shown these family members to be differentially expressed at the temporal and spatial levels with an ancient split separating those genes expressed in vegetative tissues from those expressed in reproductive tissues. A few members of other cytoskeletal gene families have also been partially characterized, including an actin-related protein, annexins, fimbrins, kinesins, myosins, and villins. In the year 2001 the Arabidopsis genome sequence was completed. Based on sequence homology with well-characterized animal, fungal, and protist sequences, we find candidate cytoskeletal genes in the Arabidopsis database: more than 150 actin-binding proteins (ABPs), including monomer binding, capping, cross-linking, attachment, and motor proteins; more than 200 microtubule-associated proteins (MAPs); and, surprisingly, 10 to 40 potential intermediate filament (IF) proteins. Most of these sequences are uncharacterized and were not identified as related to cytoskeletal proteins. Several Arabidopsis ABPs, MAPs, and IF proteins are represented by individual genes and most were represented as as small gene families. However, several classes of cytoskeletal genes including myosin, eEF1α, CLIP, tea1, and kinesin are part of large gene families with 20 to 70 potential gene members each. This treasure trove of data provides an unprecedented opportunity to make rapid advances in understanding the complex plant cytoskeletal proteome. However, the functional analysis of these proposed cytoskeletal proteins and their mutants will require detailed analysis at the cell biological, molecular genetic, and biochemical levels. New approaches will be needed to move more efficiently and rapidly from this mass of DNA sequence to functional studies on cytoskeletal proteins.
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Affiliation(s)
- Richard B. Meagher
- Department of Genetics, University of Georgia, Athens, GA 30602,
; phone: 706 542-1444; fax: 706 542-1387
| | - Marcus Fechheimer
- Department of Cellular Biology, University of Georgia, Athens, GA 30602,
; phone: 706 542-3338; fax: 706 542-4271
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95
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Le J, El-Assal SED, Basu D, Saad ME, Szymanski DB. Requirements for Arabidopsis ATARP2 and ATARP3 during epidermal development. Curr Biol 2003; 13:1341-7. [PMID: 12906796 DOI: 10.1016/s0960-9822(03)00493-7] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Plant cells employ the actin cytoskeleton to stably position organelles, as tracks for long distance transport, and to reorganize the cytoplasm in response to developmental and environmental cues. While diverse classes of actin binding proteins have been implicated in growth control, the mechanisms of cytoskeletal reorganization and the cellular functions of specific actin filament arrays are unclear. Arabidopsis trichome morphogenesis includes distinct requirements for the microtubule and actin filament cytoskeletons. It also is a genetically tractable process that is providing new knowledge about cytoskeleton function in plants. The "distorted group" of mutants defines a class of at least eight genes that are required during the actin-dependent phase of trichome growth. Using map-based cloning and a candidate gene approach, we identified mutations in ARP3 (ATARP3) and ARP2 (ATARP2) genes as the cause of the distorted1 (dis1) and wurm (wrm) phenotypes, respectively. ARP2 and ARP3 are components of the evolutionarily conserved ARP2/3 complex that nucleates actin filament polymerization [3]. Mutations in DIS1 and WRM caused severe trichome growth defects but had relatively mild effects on shoot development. DIS1 rescued the phenotype of Deltaarp3 when overexpressed in S. cerevisiae. Developing dis1 trichomes had defects in cytoplasmic actin bundle organization and reduced relative amounts of cytoplasmic actin filaments in developing branches.
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Affiliation(s)
- Jie Le
- Agronomy Department, Purdue University, Lily Hall, 915 West State Street, West Lafayette, IN 47907-2054, USA.
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96
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Li S, Blanchoin L, Yang Z, Lord EM. The putative Arabidopsis arp2/3 complex controls leaf cell morphogenesis. PLANT PHYSIOLOGY 2003; 132:2034-44. [PMID: 12913159 PMCID: PMC181288 DOI: 10.1104/pp.103.028563] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2003] [Revised: 06/15/2003] [Accepted: 06/16/2003] [Indexed: 05/17/2023]
Abstract
The evolutionarily conserved Arp2/3 complex has been shown to activate actin nucleation and branching in several eukaryotes, but its biological functions are not well understood in multicellular organisms. The model plant Arabidopsis provides many advantages for genetic dissection of the function of this conserved actin-nucleating machinery, yet the existence of this complex in plants has not been determined. We have identified Arabidopsis genes encoding homologs of all of the seven Arp2/3 subunits. The function of the putative Arabidopsis Arp2/3 complex has been studied using four homozygous T-DNA insertion mutants for ARP2, ARP3, and ARPC5/p16. All four mutants display identical defects in the development of jigsaw-shaped epidermal pavement cells and branched trichomes in the leaf. These loss-of-function mutations cause mislocalization of diffuse cortical F-actin to the neck region and inhibit lobe extension in pavement cells. The mutant trichomes resemble those treated with the actin-depolymerizing drug cytochalasin D, exhibiting stunted branches but dramatically enlarged stalks due to depolarized growth suggesting defects in the formation of a fine actin network. Our data demonstrate that the putative Arabidopsis Arp2/3 complex controls cell morphogenesis through its roles in cell polarity establishment and polar cell expansion. Furthermore, our data suggest a novel function for the putative Arp2/3 complex in the modulation of the spatial distribution of cortical F-actin and provide evidence that the putative Arp2/3 complex may activate the polymerization of some types of actin filaments in specific cell types.
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Affiliation(s)
- Shundai Li
- Department of Botany and Plant Sciences, University of California, Riverside, California 92521, USA
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97
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Wasteneys GO, Galway ME. Remodeling the cytoskeleton for growth and form: an overview with some new views. ANNUAL REVIEW OF PLANT BIOLOGY 2003; 54:691-722. [PMID: 14503008 DOI: 10.1146/annurev.arplant.54.031902.134818] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The cytoskeleton coordinates all aspects of growth in plant cells, including exocytosis of membrane and wall components during cell expansion. This review seeks to integrate current information about cytoskeletal components in plants and the role they play in generating cell form. Advances in genome analysis have fundamentally changed the nature of research strategies and generated an explosion of new information on the cytoskeleton-associated proteins, their regulation, and their role in signaling to the cytoskeleton. Some of these proteins appear novel to plants, but many have close homologues in other eukaryotic systems. It is becoming clear that the mechanisms behind cell growth are essentially similar across the growth continuum, which ranges from tip growth to diffuse expansion. Remodeling of the actin cytoskeleton at sites of exocytosis is an especially critical feature of polarized and may also contribute to axial growth. We evaluate the most recent work on the signaling mechanisms that continually remodel the actin cytoskeleton via the activation of actin-binding proteins (ABPs) and consider the role the microtubule cytoskeleton plays in this process.
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Affiliation(s)
- Geoffrey O Wasteneys
- Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, Canberra ACT 2601, Australia.
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98
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Menges M, Hennig L, Gruissem W, Murray JAH. Cell cycle-regulated gene expression in Arabidopsis. J Biol Chem 2002; 277:41987-2002. [PMID: 12169696 DOI: 10.1074/jbc.m207570200] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulated gene expression is an important mechanism for controlling cell cycle progression in yeast and mammals, and genes involved in cell division-related processes often show transcriptional regulation dependent on cell cycle position. Analysis of cell cycle processes in plants has been hampered by the lack of synchronizable cell suspensions for Arabidopsis, and few cell cycle-regulated genes are known. Using a recently described synchrony system, we have analyzed RNA from sequential samples of Arabidopsis cells progressing through the cell cycle using Affymetrix Genearrays. We identify nearly 500 genes that robustly display significant fluctuation in expression, representing the first genomic analysis of cell cycle-regulated gene expression in any plant. In addition to the limited number of genes previously identified as cell cycle-regulated in plants, we also find specific patterns of regulation for genes known or suspected to be involved in signal transduction, transcriptional regulation, and hormonal regulation, including key genes of cytokinin response. Genes identified represent pathways that are cell cycle-regulated in other organisms and those involved in plant-specific processes. The range and number of cell cycle-regulated genes show the close integration of the plant cell cycle into a variety of cellular control and response pathways.
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Affiliation(s)
- Margit Menges
- Institute of Biotechnology, University of Cambridge, United Kingdom
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99
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Abstract
The functions of microtubules and actin filaments during various processes that are essential for the growth, reproduction and survival of single plant cells have been well characterized. A large number of plant structural cytoskeletal or cytoskeleton-associated proteins, as well as genes encoding such proteins, have been identified. Although many of these genes and proteins have been partially characterized with respect to their functions, a coherent picture of how they interact to execute cytoskeletal functions in plant cells has yet to emerge. Cytoskeleton-controlled cellular processes are expected to play crucial roles during plant cell differentiation and organogenesis, but what exactly these roles are has only been investigated in a limited number of studies in the whole plant context. The intent of this review is to discuss the results of these studies in the light of what is known about the cellular functions of the plant cytoskeleton, and about the proteins and genes that are required for them. Directions are outlined for future work to advance our understanding of how the cytoskeleton contributes to plant organogenesis and development.
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Affiliation(s)
- Benedikt Kost
- Laboratory of Plant Cell Biology, Institute of Molecular Biology, National University of Singapore, 1 Research Link, Singapore 117 604
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100
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Abstract
With the refinement of algorithms for the identification of distinct motifs from sequence databases, especially those using secondary structure predictions, new protein modules have been determined in recent years. Calponin homology (CH) domains were identified in a variety of proteins ranging from actin cross-linking to signaling and have been proposed to function either as autonomous actin binding motifs or serve a regulatory function. Despite the overall structural conservation of the unique CH domain fold, the individual modules display a quite striking functional variability. Analysis of the actopaxin/parvin protein family suggests the existence of novel (type 4 and type 5) CH domain families which require special attention, as they appear to be a good example for how CH domains may function as scaffolds for other functional motifs of different properties.
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Affiliation(s)
- Mario Gimona
- Department of Cell Biology, Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg, Austria.
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