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Sasaki N, Park JW, Maule AJ, Nelson RS. The cysteine–histidine-rich region of the movement protein of Cucumber mosaic virus contributes to plasmodesmal targeting, zinc binding and pathogenesis. Virology 2006; 349:396-408. [PMID: 16603215 DOI: 10.1016/j.virol.2006.02.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2005] [Revised: 12/13/2005] [Accepted: 02/15/2006] [Indexed: 11/18/2022]
Abstract
Viral movement proteins (MPs) are central to the establishment of viral pathogenesis, and yet relatively little is understood about the structural and functional aspects of MPs or about the host factors on which they depend. Through chemical mutagenesis of transgenic Arabidopsis expressing Cucumber mosaic virus (CMV) MP fused with the green fluorescent protein, we have studied the function of a central region of the MP, defined by a number of conserved cysteine and histidine residues (Cys-His-rich region), which potentially functions as a zinc-binding domain. Transient expression of mutant MPs identified through an in planta screen for altered MP function or constructed with altered putative zinc ligands through site-directed mutagenesis showed that mutations in the Cys-His-rich region affected localization to and trafficking through plasmodesmata. In vitro zinc-binding analysis revealed that wild type (wt) CMV MP had the ability to bind zinc and that movement-defective mutants bound zinc with less affinity than wt MP. Furthermore, a correlation between the association of the MP with plasmodesmata and virus pathogenesis was shown. We discuss roles of the Cys-His region in biochemical and biological functions of the MP during virus movement.
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Affiliation(s)
- Nobumitsu Sasaki
- Plant Biology Division, The Samuel Roberts Noble Foundation, Inc., 2510 Sam Noble Parkway, Ardmore, OK 73402, USA
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102
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Hohn B, Hohn T. Single-stranded DNA plant pathogens in Eilat. PLANT MOLECULAR BIOLOGY 2006; 61:357-64. [PMID: 16786312 DOI: 10.1007/s11103-006-0017-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2006] [Accepted: 01/26/2006] [Indexed: 05/10/2023]
Abstract
An international conference on "Inter- and Intracellular Dynamics of ssDNA Plant Pathogens: Implications for Improving Resistance'' was sponsored by the United States-Israel Binational Agricultural Research and Development Fund (BARD) and organized in Eilat, Israel in November 2005. The topic of this meeting was single-stranded plant pathogens, their inter- as well as intra-cellular dynamics and their implications for improving resistance. Most of the talks concentrated on new and very new findings on principles of virus and bacterium-host interactions, studies that no doubt will lead eventually to the establishment of plants resistant to viral and bacterial infections.
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Affiliation(s)
- Barbara Hohn
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
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103
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Muench DG, Park NI. Messages on the move: the role of the cytoskeleton in mRNA localization and translation in plant cellsThis review is one of a selection of papers published in the Special Issue on Plant Cell Biology. ACTA ACUST UNITED AC 2006. [DOI: 10.1139/b05-167] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The cytoskeleton plays an important role in numerous cellular processes, including subcellular mRNA localization and translation. Several examples of mRNA localization have emerged in plant cells, and these appear to function in protein targeting, the establishment of polarity, and cell-to-cell trafficking. The identification of several cytoskeleton-associated RNA-binding proteins in plant cells has made available candidate proteins that mediate the interaction between mRNA and the cytoskeleton, and possibly play a role in mRNA localization and translational control. We propose a model that links mRNA–microtubule interactions to translational autoregulation, a process that may assist in the efficient and regulated binding of proteins to microtubules.
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Affiliation(s)
- Douglas G. Muench
- Department of Biological Sciences, University of Calgary, 2500 University Dr. N.W, Calgary, AB T2N 1N4, Canada
| | - Nam-Il Park
- Department of Biological Sciences, University of Calgary, 2500 University Dr. N.W, Calgary, AB T2N 1N4, Canada
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104
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Ge F, Yuan X, Wang X, Zhao B, Wang Y. Cell Growth and Shikonin Production of Arnebia euchroma in a Periodically Submerged Airlift Bioreactor. Biotechnol Lett 2006; 28:525-9. [PMID: 16614888 DOI: 10.1007/s10529-006-0014-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2005] [Accepted: 01/13/2006] [Indexed: 11/25/2022]
Abstract
Arnebia euchroma was grown in a 2-l periodically submerged, airlift bioreactor (PSAB) in which the non-submerged (immobilization culture) and submerged (suspension culture) operations were controlled automatically. PSAB had advantages in improving cell growth, shikonin content, shikonin production and cell aggregation compared with suspension culture. Under the optimal submerged/non-submerged period of 10 min/15 h, the shikonin content (4.6%, w/w) and, cell dry mass (16.8 g/l) were 229 and 26% higher than those in suspension culture.
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Affiliation(s)
- Feng Ge
- State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, P. O. Box 353, Beijing 100080, China.
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105
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Carvalho MF, Turgeon R, Lazarowitz SG. The geminivirus nuclear shuttle protein NSP inhibits the activity of AtNSI, a vascular-expressed Arabidopsis acetyltransferase regulated with the sink-to-source transition. PLANT PHYSIOLOGY 2006; 140:1317-30. [PMID: 16461385 PMCID: PMC1435821 DOI: 10.1104/pp.105.075556] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2005] [Revised: 01/27/2006] [Accepted: 01/27/2006] [Indexed: 05/06/2023]
Abstract
DNA viruses can suppress or enhance the activity of cellular acetyltransferases to regulate virus gene expression and to affect cell cycle progression in support of virus replication. A role for protein acetylation in regulating the nuclear export of the bipartite geminivirus (Begomovirus) DNA genome was recently suggested by the findings that the viral movement protein NSP, a nuclear shuttle protein, interacts with the Arabidopsis (Arabidopsis thaliana) nuclear acetyltransferase AtNSI (nuclear shuttle protein interactor), and that this interaction and NSI expression are necessary for cabbage leaf curl virus infection and pathogenicity. To further investigate the consequences of NSI-NSP interactions, and the potential role of NSI in Arabidopsis growth and development, we used a reverse yeast two-hybrid selection and deletion analysis to identify NSI mutants that failed to interact with NSP, and promoter fusions to a uidA reporter gene to analyze the pattern of NSI expression during plant development. We found that NSI self assembles into highly active enzyme complexes and that high concentrations of NSP, in the absence of viral DNA, can inhibit NSI activity in vitro. Based on our detailed analysis of three NSI missense mutants, we identified an 88-amino acid putative domain, which spans NSI residues 107 to 194, as being required for both NSI oligomerization and its interaction with NSP. Finally, we found that NSI is predominantly transcribed in vascular cells, and that its expression is developmentally regulated in a manner that resembles the sink-to-source transition. Our data indicate that NSP can inhibit NSI activity by interfering with its assembly into highly active complexes, and suggest a mechanism by which NSP can both recruit NSI to regulate nuclear export of the viral genome and down-regulate NSI activity on cellular targets, perhaps to affect cellular differentiation and favor virus replication.
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Affiliation(s)
- Miguel F Carvalho
- Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA
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106
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Giavalisco P, Kapitza K, Kolasa A, Buhtz A, Kehr J. Towards the proteome of Brassica napus phloem sap. Proteomics 2006; 6:896-909. [PMID: 16400686 DOI: 10.1002/pmic.200500155] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The soluble proteins in sieve tube exudate from Brassica napus plants were systematically analyzed by 1-DE and high-resolution 2-DE, partial amino acid sequence determination by MS/MS, followed by database searches. 140 proteins could be identified by their high similarity to database sequences (135 from 2-DE, 5 additional from 1-DE). Most analyzed spots led to successful protein identifications, demonstrating that Brassica napus, a close relative of Arabidopsis thaliana, is a highly suitable model plant for phloem research. None of the identified proteins was formerly known to be present in Brassica napus phloem, but several proteins have been described in phloem sap of other species. The data, which is discussed with respect to possible physiological importance of the proteins in the phloem, further confirms and substantially extends earlier findings and uncovers the presence of new protein functions in the vascular system. For example, we found several formerly unknown phloem proteins that are potentially involved in signal generation and transport, e.g., proteins mediating calcium and G-protein signaling, a set of RNA-binding proteins, and FLOWERING LOCUS T (FT) and its twin sister that might be key components for the regulation of flowering time.
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Affiliation(s)
- Patrick Giavalisco
- Max-Planck-Institute of Molecular Plant Physiology, Department Lothar Willmitzer, Potsdam, Germany
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107
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Biemelt S, Sonnewald U. Plant-microbe interactions to probe regulation of plant carbon metabolism. JOURNAL OF PLANT PHYSIOLOGY 2006; 163:307-18. [PMID: 16368160 DOI: 10.1016/j.jplph.2005.10.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Accepted: 10/17/2005] [Indexed: 05/05/2023]
Abstract
Plant growth and development is dependent on coordinated assimilate production, distribution and allocation. Application of biochemical and molecular techniques substantially contributed to a better understanding of these processes, although the underlying regulatory mechanisms are still not fully elucidated and attempts to improve crop yield by modulating carbon partitioning were only partially successful. Plant pathogens also interfere with source-sink interaction. To this end they have evolved a wide range of sophisticated strategies to allow their systemic spread, suppression of plant defence and induction of sink function to support nutrient acquisition for their growth. Studying compatible interactions of plants and pathogens like viruses, bacteria and fungi can be exploited to investigate different levels of source-sink regulation. The identification of microbial factors and their host targets involved in regulation of plant primary metabolism may allow developing novel strategies to increase crop yield. Here we will discuss recent studies on plant-microbe interactions aimed at elucidating mechanisms of compatibility.
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Affiliation(s)
- Sophia Biemelt
- Friedrich-Alexander Universität Erlangen-Nürnberg, Lehrstuhl für Biochemie, Staudtstrasse 5, 91058 Erlangen, Germany.
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108
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Lough TJ, Lucas WJ. Integrative plant biology: role of phloem long-distance macromolecular trafficking. ANNUAL REVIEW OF PLANT BIOLOGY 2006; 57:203-32. [PMID: 16669761 DOI: 10.1146/annurev.arplant.56.032604.144145] [Citation(s) in RCA: 292] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Recent studies have revealed the operation of a long-distance communication network operating within the vascular system of higher plants. The evolutionary development of this network reflects the need to communicate environmental inputs, sensed by mature organs, to meristematic regions of the plant. One consequence of such a long-distance signaling system is that newly forming organs can develop properties optimized for the environment into which they will emerge, mature, and function. The phloem translocation stream of the angiosperms contains, in addition to photosynthate and other small molecules, a variety of macromolecules, including mRNA, small RNA, and proteins. This review highlights recent progress in the characterization of phloem-mediated transport of macromolecules as components of an integrated long-distance signaling network. Attention is focused on the role played by these proteins and RNA species in coordination of developmental programs and the plant's response to both environmental cues and pathogen challenge. Finally, the importance of developing phloem transcriptome and proteomic databases is discussed within the context of advances in plant systems biology.
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109
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Lucas WJ. Plant viral movement proteins: Agents for cell-to-cell trafficking of viral genomes. Virology 2006; 344:169-84. [PMID: 16364748 DOI: 10.1016/j.virol.2005.09.026] [Citation(s) in RCA: 317] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Accepted: 09/10/2005] [Indexed: 10/25/2022]
Abstract
Plants viruses spread throughout their hosts using a number of pathways, the most common being movement cell to cell through plasmodesmata (PD), unique intercellular organelles of the plant kingdom, and between organs by means of the vascular system. Pioneering studies on plant viruses revealed that PD allow the cell-to-cell trafficking of virally encoded proteins, termed the movement proteins (MPs). This non-cell-autonomous protein (NCAP) pathway is similarly employed by the host to traffic macromolecules. Viral MPs bind RNA/DNA in a sequence nonspecific manner to form nucleoprotein complexes (NPC). Host proteins are then involved in the delivery of MPs and NPC to the PD orifice, and a role for the cytoskeleton has been implicated. Trafficking of NCAPs through the PD structure involves three steps in which the MP: (a) interacts with a putative PD docking complex, (b) induces dilation in the PD microchannels, and (c) binds to an internal translocation system for delivery into the neighboring cytoplasm. Viral genera that use this NCAP pathway have evolved a combination of a MP and ancillary proteins that work in concert to enable the formation of a stable NPC that can compete with endogenous NCAPs for the PD trafficking machinery. Incompatible MP-host protein interactions may underlie observed tissue tropisms and restricted infection domains. These pivotal discoveries are discussed in terms of the need to develop a more comprehensive understanding of the (a) three-dimensional structure of MPs, (b) PD supramolecular complex, and (c) host proteins involved in this cell-to-cell trafficking process.
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Affiliation(s)
- William J Lucas
- Section of Plant Biology, College of Biological Sciences, University of California, One Shields Ave., Davis, CA 95616, USA.
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110
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Doering-Saad C, Newbury HJ, Couldridge CE, Bale JS, Pritchard J. A phloem-enriched cDNA library from Ricinus: insights into phloem function. JOURNAL OF EXPERIMENTAL BOTANY 2006; 57:3183-93. [PMID: 16936221 DOI: 10.1093/jxb/erl082] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
The aim of this study was to identify genes that are expressed in the phloem. Increased knowledge of phloem regulation will contribute to our understanding of its many roles, from transport of solutes to information about interactions with pathogens. A cDNA library constructed from phloem-enriched sap exuding from cut Ricinus communis (L.) hypocotyls was sequenced. To assess contamination from other tissues, two libraries were constructed: one using the first 15 min of exudation and the other from sap collected after 120 min of exudation had elapsed. Of 1012 clones sequenced, 158 unique transcripts were identified. The presence of marker molecules such as profilin, the low occurrence of chloroplast-related mRNAs, and the sieve element localization of constituent mRNA using in situ hybridization were consistent with a phloem origin of the sap. Functional analysis of the cDNAs revealed classifications including ribosomal function, interaction with the environment, transport, DNA/RNA binding, and protein turnover. An analysis of the closest Arabidopsis thaliana (L.) homologue for each clone indicated that genes involved in cell localization, protein synthesis, tissue localization, organ localization, organ differentiation, and cell fate were represented at twice the level occurring in the whole Arabidopsis genome. The transcripts found in this phloem-enriched library are discussed in the context of phloem function and the relationship between the companion cell and sieve element.
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Affiliation(s)
- C Doering-Saad
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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111
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Abstract
Cell-to-cell spread of retroviruses via virological synapse (VS) contributes to overall progression of disease. VS are specialized pathogen-induced cellular structures that facilitate cell-to-cell transfer of HIV-1 and HTLV-1. VS provide a mechanistic explanation for cell-associated retroviral replication. While VS share some common features with neurological or immunological synapses, they also exhibit important differences. The role of VS might not be limited to human retroviruses and the emerging role of a plant synapse suggests that VS might well be conserved structures for cell-cell spreading of both animal and plant viruses. Dissection of the VS is just at its beginning, but already offers ample information and fascinating insights into mechanisms of viral replication and cell-to-cell communication.
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Affiliation(s)
- Eduardo Garcia
- Department of Dermatology and Venereology, University Hospital of Geneva, 4-747, 24 Rue Micheli-du-Crest, 1211 Geneva, Switzerland
| | - Vincent Piguet
- Department of Dermatology and Venereology, University Hospital of Geneva, 4-747, 24 Rue Micheli-du-Crest, 1211 Geneva, Switzerland
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112
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Abstract
Water was called by Szent-Gyorgi "life's mater and matrix, mother and medium." This chapter considers both aspects of his statement. Many astrobiologists argue that some, if not all, of Earth's water arrived during cometary bombardments. Amorphous water ices of comets possibly facilitated organization of complex organic molecules, kick-starting prebiotic evolution. In Gaian theory, Earth retains its water as a consequence of biological activity. The cell cytomatrix is a proteinaceous matrix/lattice incorporating the cytoskeleton, a pervasive, holistic superstructural network that integrates metabolic pathways. Enzymes of metabolic pathways are ordered in supramolecular clusters (metabolons) associated with cytoskeleton and/or membranes. Metabolic intermediates are microchanneled through metabolons without entering a bulk aqueous phase. Rather than being free in solution, even major signaling ions are probably clustered in association with the cytomatrix. Chloroplasts and mitochondria, like bacteria and archaea, also contain a cytoskeletal lattice, metabolons, and channel metabolites. Eukaryotic metabolism is mathematically a scale-free or small-world network. Enzyme clusters of bacterial origin are incorporated at a pathway level that is architecturally archaean. The eucaryotic cell may be a product of serial endosymbiosis, a chimera. Cell cytoplasm is approximately 80% water. Water is indisputably a conserved structural element of proteins, essential to their folding, specificity, ligand binding, and to enzyme catalysis. The vast literature of organized cell water has long argued that the cytomatrix and cell water are an entire system, a continuum, or gestalt. Alternatives are offered to mainstream explanations of cell electric potentials, ion channel, enzyme, and motor protein function, in terms of high-order cooperative systems of ions, water, and macromolecules. This chapter describes some prominent concepts of organized cell water, including vicinal water network theory, the association-induction hypothesis, wave-cluster theory, phase-gel transition theories, and theories of low- and high-density water polymorphs.
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Affiliation(s)
- V A Shepherd
- Department of Biophysics, School of Physics, The University of NSW NSW 2052, Sydney, Australia
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113
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Pettit Kneller EL, Rakotondrafara AM, Miller WA. Cap-independent translation of plant viral RNAs. Virus Res 2005; 119:63-75. [PMID: 16360925 PMCID: PMC1880899 DOI: 10.1016/j.virusres.2005.10.010] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Revised: 09/01/2005] [Accepted: 10/19/2005] [Indexed: 11/29/2022]
Abstract
The RNAs of many plant viruses lack a 5' cap and must be translated by a cap-independent mechanism. Here, we discuss the remarkably diverse cap-independent translation elements that have been identified in members of the Potyviridae, Luteoviridae, and Tombusviridae families, and genus Tobamovirus. Many other plant viruses have uncapped RNAs but their translation control elements are uncharacterized. Cap-independent translation elements of plant viruses differ strikingly from those of animal viruses: they are smaller (<200 nt), some are located in the 3' untranslated region, some require ribosome scanning from the 5' end of the mRNA, and the 5' UTR elements are much less structured than those of animal viruses. We discuss how these elements may interact with host translation factors, and speculate on their mechanism of action and their roles in the virus replication cycle. Much remains to be learned about how these elements enable plant viruses to usurp the host translational machinery.
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Affiliation(s)
- Elizabeth L. Pettit Kneller
- Interdepartmental Plant Physiology Program, Department of Plant Pathology, 351 Bessey Hall, Iowa State University, Ames, IA 50011, USA
| | - Aurélie M. Rakotondrafara
- Molecular, Cellular and Developmental Biology Program, Department of Plant Pathology, 351 Bessey Hall, Iowa State University, Ames, IA 50011, USA
| | - W. Allen Miller
- Molecular, Cellular and Developmental Biology Program, Department of Plant Pathology, 351 Bessey Hall, Iowa State University, Ames, IA 50011, USA
- * Corresponding author. Tel.: +1 515 294 2436; fax: +1 515 294 9420. E-mail address: (W.A. Miller)
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114
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Faulkner CR, Blackman LM, Cordwell SJ, Overall RL. Proteomic identification of putative plasmodesmatal proteins from Chara corallina. Proteomics 2005; 5:2866-75. [PMID: 16075417 DOI: 10.1002/pmic.200401186] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Plasmodesmata are channels that bridge the cell walls of plant cells, allowing regulated transport of molecules between neighbouring cells. We have used a proteomic strategy to identify putative plasmodesmata-associated proteins in the giant-celled green alga Chara corallina. Proteins were extracted from the plasmodesmata-rich nodal complexes and the middle of the long internodal cells, which do not contain plasmodesmata. Comparison of protein spot patterns generated by two-dimensional gel electrophoresis of both the soluble and cell wall fractions from the two cell types was done. Fifty-eight spots that were common to the nodal and internodal soluble fractions were analysed by matrix assisted laser desorption/ionisation-time of flight mass spectrometry, and peptide mass fingerprint data were used to search the database. Matches were made to four of these spots, in each case to housekeeping proteins. Further, a number of nodal specific spots were identified, 11 from the soluble fraction and nine from the wall fraction. These spots were excised from the gels and analysed by liquid chromatography tandem mass spectrometry to obtain peptide sequence. Database searches suggest that these spots include homologues to previously identified plasmodesmata-associated proteins cp-wap13 and heat shock cognate 70, as well as RNA-binding proteins, eukaryotic initiation factor 4A and a beta-1,3-glucanase. Several spots remained unidentified providing exciting new candidate plasmodesmata-associated proteins.
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115
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Facchini PJ, St-Pierre B. Synthesis and trafficking of alkaloid biosynthetic enzymes. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:657-66. [PMID: 16182601 DOI: 10.1016/j.pbi.2005.09.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2005] [Accepted: 09/13/2005] [Indexed: 05/04/2023]
Abstract
The biosynthesis of plant natural products involves a large number of enzymes that create and elaborate a bewildering array of chemical structures, which are generally involved in ecophysiological interactions. Alkaloids are one of the largest groups of natural products and are generally produced through an assortment of intricate pathways. The application of molecular biochemical approaches to investigate the cell biology of alkaloid pathways has revealed a paradigm for the complex, yet highly ordered, organization of biosynthetic enzymes at both the cellular and subcellular levels. Many different cell types have been implicated in alkaloid formation and storage, in one case suggesting the intercellular transport of enzymes. The localization of enzymes to numerous cellular compartments shows the importance of protein targeting in the assembly of alkaloid pathways. Recent studies have also pointed to the possible interaction of biosynthetic enzymes in multi-enzyme complexes. These processes must be considered to be integral components of the mechanisms that regulate alkaloid biosynthesis and perhaps other natural product pathways.
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Affiliation(s)
- Peter J Facchini
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, T2N 1N4, Canada.
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116
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Kim I, Zambryski PC. Cell-to-cell communication via plasmodesmata during Arabidopsis embryogenesis. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:593-9. [PMID: 16207533 DOI: 10.1016/j.pbi.2005.09.013] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2005] [Accepted: 09/13/2005] [Indexed: 05/04/2023]
Abstract
In Arabidopsis embryogenesis, positional information establishes the overall body plan and lineage-dependent cell fate specifies local patterning. Position-dependent gene expression and responses to the plant hormone auxin are also crucial. Recently, another mechanism that delivers positional information has been uncovered. This pathway utilizes cell-to-cell communication via plasmodesmata. Plasmodesmata span the walls between neighboring plant cells. Groups of cells that allow intercellular transport of biotic and abiotic tracers form symplastic domains of shared communication. Initially, cells of the embryo form one symplast. As development proceeds, symplastic sub-domains that correspond to the major morphological regions of the plant (i.e. shoot apex, cotyledons, hypocotyl, and root) are formed. These sub-domains further resolve into tissue-specific domains of communication (such as protodermal and vascular regions). Cell-to-cell communication via plasmodesmata between embryonic and maternal tissues ceases as development proceeds.
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Affiliation(s)
- Insoon Kim
- Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, California 94720, USA
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117
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Traas J, Bohn-Courseau I. Cell proliferation patterns at the shoot apical meristem. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:587-92. [PMID: 16182603 DOI: 10.1016/j.pbi.2005.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Accepted: 09/12/2005] [Indexed: 05/04/2023]
Abstract
The highly stereotypic cell proliferation patterns in many plant species suggest that the strict control of the cell cycle in time and space is an essential basis for ordered development. At the same time, conflicting evidence contradicts this view, indicating that cell division simply follows growth patterns that are dictated by the local availability of nutrients. Recent evidence shows that there is no strict hierarchical relationship between growth and proliferation. Cell expansion and proliferation, for example, are controlled by the same regulators. Cell proliferation depends on nutrient distribution but, in turn, the use of the same nutrients depends on the activity of cell cycle regulators such as E2F transcription factors.
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Affiliation(s)
- Jan Traas
- Institut National de la Recherche Agronomique (INRA), Laboratoire de Biologie Cellulaire, Route de Saint Cyr, 78026 Versailles cedex, France.
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118
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Liu K, Xia Z, Zhang Y, Wen Y, Wang D, Brandenburg K, Harris F, Phoenix DA. Interaction between the movement protein of barley yellow dwarf virus and the cell nuclear envelope: role of a putative amphiphilic alpha-helix at the N-terminus of the movement protein. Biopolymers 2005; 79:86-96. [PMID: 15971210 DOI: 10.1002/bip.20334] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The open reading frame 4 (ORF 4) gene product of barley yellow dwarf virus (BYDV) may act as a movement protein (MP) by assisting the transport of viral genomic RNA across the nuclear envelope (NE) of host plant cells. To investigate interactions between BYDV MP and the NE, wild-type and mutant open reading frame (ORF 4)-green fluorescent protein (GFP) fusion cistrons were expressed in insect cells. A fusion protein expressed by the wild-type ORF 4-GFP cistron associated with the NE and caused protrusions from its surface. The fusion protein expressed by the mutant ORF 4-GFP cistron lacked a putative amphiphilic alpha-helix at its N-terminus and although associating with the NE, showed decreased levels of protrusions. A peptide homologue of this putative alpha-helix induced an increase of 7 degrees C in the phase transition temperature of dimyrystoyl phosphatidylserine (DMPS) membranes, accompanied by a decrease in membrane fluidity, but exhibited no significant interaction with either dimyristoyl phosphatidylcholine (DMPC) or dimyristoyl phosphatidylethanolamine (DMPE) membranes. These results strongly support the view that BYDV MP may interact with the NE to help transport viral genomic RNA into the nuclear compartment. This function of BYDV MP appears to involve protrusions on the surface of the NE and may require the presence of an N-terminal amphiphilic alpha-helix, which is speculated to destabilize membranes, thereby assisting the entry of BYDV-GAV into the nuclear compartment.
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Affiliation(s)
- Kunfan Liu
- Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
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119
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Christensen NM, Axelsen KB, Nicolaisen M, Schulz A. Phytoplasmas and their interactions with hosts. TRENDS IN PLANT SCIENCE 2005; 10:526-35. [PMID: 16226054 DOI: 10.1016/j.tplants.2005.09.008] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2005] [Revised: 08/08/2005] [Accepted: 09/28/2005] [Indexed: 05/03/2023]
Abstract
Phytoplasmas are bacteria without cell walls and are responsible for plant diseases that have large economic impacts. Knowledge of their biology is limited because they are uncultivable and experimentally inaccessible in their hosts. It is a mystery how these bacteria use the sugar-rich phloem sap in which they live and how they interact with the host. This makes it difficult to develop means to control them. Recently, the full genomes of two phytoplasmas have been sequenced, allowing new insights into their requirements. Phytoplasmas contain a minimal genome and lack genes coding for ATP synthases and sugar uptake and use, making them dependent on their host. This dependency can be exploited to elucidate the particular physiology of the phloem.
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Affiliation(s)
- Nynne M Christensen
- Department of Plant Biology, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark
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120
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Prokhnevsky AI, Peremyslov VV, Dolja VV. Actin cytoskeleton is involved in targeting of a viral Hsp70 homolog to the cell periphery. J Virol 2005; 79:14421-8. [PMID: 16254376 PMCID: PMC1280222 DOI: 10.1128/jvi.79.22.14421-14428.2005] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Accepted: 08/09/2005] [Indexed: 01/27/2023] Open
Abstract
The cell-to-cell movement of plant viruses involves translocation of virus particles or nucleoproteins to and through the plasmodesmata (PDs). As we have shown previously, the movement of the Beet yellows virus requires the concerted action of five viral proteins including a homolog of cellular approximately 70-kDa heat shock proteins (Hsp70h). Hsp70h is an integral component of the virus particles and is also found in PDs of the infected cells. Here we investigate subcellular distribution of Hsp70h using transient expression of Hsp70h fused to three spectrally distinct fluorescent proteins. We found that fluorophore-tagged Hsp70h forms motile granules that are associated with actin microfilaments, but not with microtubules. In addition, immobile granules were observed at the cell periphery. A pairwise appearance of these granules at the opposite sides of cell walls and their colocalization with the movement protein of Tobacco mosaic virus indicated an association of Hsp70h with PDs. Treatment with various cytoskeleton-specific drugs revealed that the intact actomyosin motility system is required for trafficking of Hsp70h in cytosol and its targeting to PDs. In contrast, none of the drugs interfered with the PD localization of Tobacco mosaic virus movement protein. Collectively, these findings suggest that Hsp70h is translocated and anchored to PDs in association with the actin cytoskeleton.
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Affiliation(s)
- Alexey I Prokhnevsky
- Department of Botany and Plant Pathology and Center for Gene Research and Biotechnology, Oregon State University, Corvallis, OR 97331, USA
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121
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Lee JY, Taoka KI, Yoo BC, Ben-Nissan G, Kim DJ, Lucas WJ. Plasmodesmal-associated protein kinase in tobacco and Arabidopsis recognizes a subset of non-cell-autonomous proteins. THE PLANT CELL 2005; 17:2817-31. [PMID: 16126836 PMCID: PMC1242275 DOI: 10.1105/tpc.105.034330] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2005] [Revised: 07/22/2005] [Accepted: 08/04/2005] [Indexed: 05/04/2023]
Abstract
Cell-to-cell communication in plants involves the trafficking of macromolecules through specialized intercellular organelles, termed plasmodesmata. This exchange of proteins and RNA is likely regulated, and a role for protein phosphorylation has been implicated, but specific components remain to be identified. Here, we describe the molecular characterization of a plasmodesmal-associated protein kinase (PAPK). A 34-kD protein, isolated from a plasmodesmal preparation, exhibits calcium-independent kinase activity and displays substrate specificity in that it recognizes a subset of viral and endogenous non-cell-autonomous proteins. This PAPK specifically phosphorylates the C-terminal residues of tobacco mosaic virus movement protein (TMV MP); this posttranslational modification has been shown to affect MP function. Molecular analysis of purified protein established that tobacco (Nicotiana tabacum) PAPK is a member of the casein kinase I family. Subcellular localization studies identified a possible Arabidopsis thaliana PAPK homolog, PAPK1. TMV MP and PAPK1 are colocalized within cross-walls in a pattern consistent with targeting to plasmodesmata. Moreover, Arabidopsis PAPK1 also phosphorylates TMV MP in vitro at its C terminus. These results strongly suggest that Arabidopsis PAPK1 is a close homolog of tobacco PAPK. Thus, PAPK1 represents a novel plant protein kinase that is targeted to plasmodesmata and may play a regulatory role in macromolecular trafficking between plant cells.
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Affiliation(s)
- Jung-Youn Lee
- Section of Plant Biology, Division of Biological Sciences, University of California, Davis, CA 95616, USA.
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122
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Oh IS, Park AR, Bae MS, Kwon SJ, Kim YS, Lee JE, Kang NY, Lee S, Cheong H, Park OK. Secretome analysis reveals an Arabidopsis lipase involved in defense against Alternaria brassicicola. THE PLANT CELL 2005; 17:2832-47. [PMID: 16126835 PMCID: PMC1242276 DOI: 10.1105/tpc.105.034819] [Citation(s) in RCA: 250] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The Arabidopsis thaliana secretome was analyzed by the proteomic approach, which led to the identification of secreted proteins implicated in many aspects of cell biology. We then investigated the change in the Arabidopsis secretome in response to salicylic acid and identified several proteins involved in pathogen response. One of these, a secreted lipase with a GDSL-like motif designated GDSL LIPASE1 (GLIP1), was further characterized for its function in disease resistance. glip1 plants were markedly more susceptible to infection by the necrotrophic fungus Alternaria brassicicola compared with the parental wild-type plants. The recombinant GLIP1 protein possessed lipase and antimicrobial activities that directly disrupt fungal spore integrity. Furthermore, GLIP1 appeared to trigger systemic resistance signaling in plants when challenged with A. brassicicola, because pretreatment of the glip1 mutant with recombinant GLIP1 protein inhibited A. brassicicola-induced cell death in both peripheral and distal leaves. Moreover, glip1 showed altered expression of defense- and ethylene-related genes. GLIP1 transcription was increased by ethephon, the ethylene releaser, but not by salicylic acid or jasmonic acid. These results suggest that GLIP1, in association with ethylene signaling, may be a critical component in plant resistance to A. brassicicola.
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Affiliation(s)
- Il Seok Oh
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Korea
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123
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Schepetilnikov MV, Manske U, Solovyev AG, Zamyatnin AA, Schiemann J, Morozov SY. The hydrophobic segment of Potato virus X TGBp3 is a major determinant of the protein intracellular trafficking. J Gen Virol 2005; 86:2379-2391. [PMID: 16033986 DOI: 10.1099/vir.0.80865-0] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Potato virus X (PVX) encodes three movement proteins, TGBp1, TGBp2 and TGBp3. The 8 kDa TGBp3 is a membrane-embedded protein that has an N-terminal hydrophobic sequence segment and a hydrophilic C terminus. TGBp3 mutants with deletions in the C-terminal hydrophilic region retain the ability to be targeted to cell peripheral structures and to support limited PVX cell-to-cell movement, suggesting that the basic TGBp3 functions are associated with its N-terminal transmembrane region. Fusion of green fluorescent protein to the TGBp3 N terminus abrogates protein activities in intracellular trafficking and virus movement. The intracellular transport of TGBp3 from sites of its synthesis in the rough endoplasmic reticulum (ER) to ER-derived peripheral bodies involves a non-conventional COPII-independent pathway. However, integrity of the C-terminal hydrophilic sequence is required for entrance to this non-canonical route.
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Affiliation(s)
- M V Schepetilnikov
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia
| | - U Manske
- Institute of Plant Virology, Microbiology and Biosafety, Federal Biological Research Centre for Agriculture and Forestry, Messeweg 11/12, D-38104 Braunschweig, Germany
| | - A G Solovyev
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia
| | - A A Zamyatnin
- Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences (SLU), PO Box 7080, S-750 07 Uppsala, Sweden
- Natural Sciences Center of A. M. Prokhorov, General Physics Institute, Russian Academy of Sciences, Bld L-2, 38 Vavilov Str., Moscow 119991, Russia
| | - J Schiemann
- Institute of Plant Virology, Microbiology and Biosafety, Federal Biological Research Centre for Agriculture and Forestry, Messeweg 11/12, D-38104 Braunschweig, Germany
| | - S Yu Morozov
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia
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124
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Yamamura Y, Scholthof HB. Tomato bushy stunt virus: a resilient model system to study virus-plant interactions. MOLECULAR PLANT PATHOLOGY 2005; 6:491-502. [PMID: 20565674 DOI: 10.1111/j.1364-3703.2005.00301.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
UNLABELLED SUMMARY Taxonomy: Tomato bushy stunt virus (TBSV) (Fig. 1) is the type species of the plant-infecting Tombusvirus genus in the family Tombusviridae. Physical properties: TBSV virions are non-enveloped icosahedral T = 3 particles assembled from 180 coat protein subunits (42 kDa) whose arrangement causes a granular appearance on the surface structure. The particles are approximately 33 nm in diameter and composed of 17% ribonucleic acid and 83% protein. Encapsidated within the virion is the TBSV genome that consists of a positive-sense single-stranded RNA of approximately 4.8 kb, which lacks the 5'-cap or 3'-poly(A) tail typical for eukaryotic mRNAs. HOST RANGE In nature, TBSV has a fairly restricted host range, mostly encompassing a few dicotyledonous species in separate families, and affected agricultural crops comprise primarily vegetables. The experimental host range is broad, with over 120 plant species in more than 20 different families reported to be susceptible although in most plants the infection often remains localized around the site of entry. The differences between hosts with regards to requirements for cell-to-cell and long-distance movement have led to the development of TBSV as an attractive model system to obtain general insights into RNA transport through plants. SYMPTOMS SYMPTOMS induced by TBSV are largely dependent on the host genotype; they can vary from necrotic and chlorotic lesions, to a systemic mild or severe mosaic, or they may culminate in a lethal necrosis. The original TBSV isolates from tomato plants caused a mottle, crinkle and downward curling of leaves with the youngest leaves exhibiting tip necrosis upon systemic infection. Tomato fruit yield can be greatly reduced by virus infection. Plants may be stunted and a proliferation of lateral shoots leads to a bushy appearance of the infected tomato plants, hence the nomenclature of the pathogen. Useful sites: http://image.fs.uidaho.edu/vide/descr825.htm; http://www.ictvdb.rothamsted.ac.uk/ICTVdB/74010001.htm (general information); http://mmtsb.scripps.edu/viper/info_page.php?vipPDB=2tbv (structural information).
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Affiliation(s)
- Yoshimi Yamamura
- Department of Plant Pathology and Microbiology, Texas A&M University, 2132 TAMU, College Station, TX 77843, USA
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125
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Rinne PLH, van den Boogaard R, Mensink MGJ, Kopperud C, Kormelink R, Goldbach R, van der Schoot C. Tobacco plants respond to the constitutive expression of the tospovirus movement protein NS(M) with a heat-reversible sealing of plasmodesmata that impairs development. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2005; 43:688-707. [PMID: 16115066 DOI: 10.1111/j.1365-313x.2005.02489.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Viral infection often results in typical symptoms, the biological background of which has remained elusive. We show that constitutive expression of the NSM viral movement protein (MP) of tomato spotted wilt virus in Nicotiana tabacum is sufficient to induce severe, infection-like symptoms, including pronounced deficiencies in root and shoot development. Leaves failed to expand and were arranged in a rosette due to the absence of internode elongation. Following the sink-source transition they accumulated excessive amounts of starch and developed fusing chlorotic patches in the mesophyll, resembling virus-induced chlorotic lesions. Eventually, the leaves became entirely white and brittle. With a combination of techniques, including photosystem II quantum-yield measurements, iontophoresis of symplasmic tracers, bombardment with pPVX.GFP and double immunolabelling it was shown that these symptoms correlated with the obstruction of NSM-targeted mesophyll plasmodesmata (Pd) in source tissues by depositions of 1,3-beta-D-glucan (GLU) or callose. Temperature-shift treatments (TST; 22-->32 degrees C), known to abolish chlorotic local lesions, also abolished the chlorotic 'superlesions' of transgenic plants and rescued plant development, by restoring the transport capacity of Pd through the action of 1,3-beta-D-glucanase (GLU-h) or callase. Return of these elongated, TST-recovered plants to 22 degrees C reintroduced superlesions and arrested shoot elongation, resulting in the formation of a rosette of clustered leaves at the shoot tip. Collectively, this indicates that the symptoms of NSM plants are self-inflicted and due to a basal defence response that counteracts prolonged interference of the MP with Pd functioning. This type of defence may also play a role in the formation of symptoms during viral infection.
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Affiliation(s)
- Päivi L H Rinne
- Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands
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126
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Ueki S, Citovsky V. Identification of an interactor of cadmium ion-induced glycine-rich protein involved in regulation of callose levels in plant vasculature. Proc Natl Acad Sci U S A 2005; 102:12089-94. [PMID: 16103368 PMCID: PMC1189354 DOI: 10.1073/pnas.0505927102] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2005] [Indexed: 11/18/2022] Open
Abstract
Cadmium-induced glycine-rich protein (cdiGRP) is a cell wall-associated factor that increases callose levels in plant vasculature. To better understand the cdiGRP/callose regulation system, we identified a tobacco protein, GrIP (cdiGRP-interacting protein, GrIP), that associates with cdiGRP and localizes at the plant cell wall. Constitutive overexpression of GrIP enhanced the accumulation of the cdiGRP protein and callose in vasculature-associated cells with or without treatment with cadmium ions. That GrIP gene expression was not affected by cadmium ions indicated that GrIP does not directly modulate the callose levels induced by the treatment. Instead, GrIP most likely functions by further elevating the accumulated amount of cdiGRP, the expression of which is up-regulated by the cadmium ions. Interestingly, the levels of cdiGRP mRNA were not affected by constitutive expression of GrIP, demonstrating that the enhancement in cdiGRP protein accumulation by GrIP overexpression occurs posttranslationally. Collectively, these observations suggest that GrIP interacts with cdiGRP and increases its level of accumulation; in turn, the elevated amounts of cdiGRP induce callose deposits in the plant cell walls. Therefore, GrIP and cdiGRP represent sequentially acting factors in a biochemical pathway that regulates callose accumulation in the plant vasculature.
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Affiliation(s)
- Shoko Ueki
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, NY 11794-5215, USA
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127
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Kim I, Kobayashi K, Cho E, Zambryski PC. Subdomains for transport via plasmodesmata corresponding to the apical-basal axis are established during Arabidopsis embryogenesis. Proc Natl Acad Sci U S A 2005; 102:11945-50. [PMID: 16087887 PMCID: PMC1188016 DOI: 10.1073/pnas.0505622102] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The axial body pattern of Arabidopsis is determined during embryogenesis by auxin signaling and differential gene expression. Here we demonstrate that another pathway, cell-to-cell communication through plasmodesmata (PD), is regulated during apical-basal pattern formation. The SHOOT MERISTEMLESS (STM) promoter was used to drive expression in the shoot apical meristem (SAM) and a subset of cells at the base of the hypocotyl of 1x,2x, and 3x soluble green fluorescent proteins (sGFPs), and the P30 movement protein of Tobacco mosaic virus (TMV) translationally fused to 1x and 2x sGFP. In the early heart stage, 2x sGFP (54 kDa) moves throughout the whole embryo, whereas 3x sGFP (81 kDa) shows more restricted movement. As the embryo develops, PD apertures are down regulated to form local subdomains allowing transport of different sized tracers. For example, movement of 2x sGFP to the cotyledon, and 3x sGFP to root tips, becomes restricted. Subdomains of cell-to-cell transport align with the apical-basal embryo body axis and correspond to the shoot apex, cotyledons, hypocotyl, and root. Studies with P30-GFP fusions reinforce the distinction between embryonic symplastic subdomains. Although P30 targets embryo cell walls as puncta (diagnostic for functional localization of P30 to PD in adult plants), P30 cannot dilate embryonic PD to overcome the barriers for transport between symplastic subdomains, suggesting that specific boundaries separate symplastic subdomains of the embryo. Thus, cell-to-cell communication via plasmodesmata conveys positional information critical to establish the axial body pattern during embryogenesis in Arabidopsis.
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Affiliation(s)
- Insoon Kim
- Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720
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128
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Boevink P, Oparka KJ. Virus-host interactions during movement processes. PLANT PHYSIOLOGY 2005; 138:1815-21. [PMID: 16172094 PMCID: PMC1183373 DOI: 10.1104/pp.105.066761] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Affiliation(s)
- Petra Boevink
- Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom
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129
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Liu JZ, Blancaflor EB, Nelson RS. The tobacco mosaic virus 126-kilodalton protein, a constituent of the virus replication complex, alone or within the complex aligns with and traffics along microfilaments. PLANT PHYSIOLOGY 2005; 138:1853-65. [PMID: 16040646 PMCID: PMC1183377 DOI: 10.1104/pp.105.065722] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2005] [Revised: 05/13/2005] [Accepted: 05/16/2005] [Indexed: 05/03/2023]
Abstract
Virus-induced cytoplasmic inclusion bodies (referred to as virus replication complexes [VRCs]) consisting of virus and host components are observed in plant cells infected with tobacco mosaic virus, but the components that modulate their form and function are not fully understood. Here, we show that the tobacco mosaic virus 126-kD protein fused with green fluorescent protein formed cytoplasmic bodies (126-bodies) in the absence of other viral components. Using mutant 126-kD:green fluorescent fusion proteins and viral constructs expressing the corresponding mutant 126-kD proteins, it was determined that the size of the 126-bodies and the corresponding VRCs changed in synchrony for each 126-kD protein mutation tested. Through colabeling experiments, we observed the coalignment and intracellular trafficking of 126-bodies and, regardless of size, VRCs, along microfilaments (MFs). Disruption of MFs with MF-depolymerizing agents or through virus-induced gene silencing compromised the intracellular trafficking of the 126-bodies and VRCs and virus cell-to-cell movement, but did not decrease virus accumulation to levels that would affect virus movement or prevent VRC formation. Our results indicate that (1) the 126-kD protein modulates VRC size and traffics along MFs in cells; (2) VRCs traffic along MFs in cells, possibly through an interaction with the 126-kD protein, and the negative effect of MF antagonists on 126-body and VRC intracellular movement and virus cell-to-cell movement correlates with the disruption of this association; and (3) virus movement was not correlated with VRC size.
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Affiliation(s)
- Jian-Zhong Liu
- Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401, USA
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130
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Nelson RS, Citovsky V. Plant viruses. Invaders of cells and pirates of cellular pathways. PLANT PHYSIOLOGY 2005; 138:1809-14. [PMID: 16172093 PMCID: PMC1183372 DOI: 10.1104/pp.104.900167] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
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131
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Scholthof HB. Plant virus transport: motions of functional equivalence. TRENDS IN PLANT SCIENCE 2005; 10:376-82. [PMID: 16023398 DOI: 10.1016/j.tplants.2005.07.002] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2004] [Revised: 04/26/2005] [Accepted: 07/01/2005] [Indexed: 05/03/2023]
Abstract
Plant virus cell-to-cell movement and subsequent systemic transport are governed by a series of mechanisms involving various virus and plant factors. Specialized virus encoded movement proteins (MPs) control the cell-to-cell transport of viral nucleoprotein complexes through plasmodesmata. MPs of different viruses have diverse properties and each interacts with specific host factors that also have a range of functions. Most viruses are then transported via the phloem as either nucleoprotein complexes or virions, with contributions from host and virus proteins. Some virus proteins contribute to the establishment and maintenance of systemic infection by inhibiting RNA silencing-mediated degradation of viral RNA. In spite of all the different movement strategies and the viral and host components, there are possible functional commonalities in virus-host interactions that govern viral spread through plants.
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Affiliation(s)
- Herman B Scholthof
- Department of Plant Pathology and Microbiology, Texas A&M University, College Station, 77843, USA.
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132
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Weinl C, Marquardt S, Kuijt SJH, Nowack MK, Jakoby MJ, Hülskamp M, Schnittger A. Novel functions of plant cyclin-dependent kinase inhibitors, ICK1/KRP1, can act non-cell-autonomously and inhibit entry into mitosis. THE PLANT CELL 2005; 17:1704-22. [PMID: 15749764 PMCID: PMC1143071 DOI: 10.1105/tpc.104.030486] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Revised: 02/04/2005] [Accepted: 02/04/2005] [Indexed: 05/18/2023]
Abstract
In animals, cyclin-dependent kinase inhibitors (CKIs) are important regulators of cell cycle progression. Recently, putative CKIs were also identified in plants, and in previous studies, Arabidopsis thaliana plants misexpressing CKIs were found to have reduced endoreplication levels and decreased numbers of cells consistent with a function of CKIs in blocking the G1-S cell cycle transition. Here, we demonstrate that at least one inhibitor from Arabidopsis, ICK1/KRP1, can also block entry into mitosis but allows S-phase progression causing endoreplication. Our data suggest that plant CKIs act in a concentration-dependent manner and have an important function in cell proliferation as well as in cell cycle exit and in turning from a mitotic to an endoreplicating cell cycle mode. Endoreplication is usually associated with terminal differentiation; we observed, however, that cell fate specification proceeded independently from ICK1/KRP1-induced endoreplication. Strikingly, we found that endoreplicated cells were able to reenter mitosis, emphasizing the high degree of flexibility of plant cells during development. Moreover, we show that in contrast with animal CDK inhibitors, ICK1/KRP1 can move between cells. On the one hand, this challenges plant cell cycle control with keeping CKIs locally controlled, and on the other hand this provides a possibility of linking cell cycle control in single cells with the supracellular organization of a tissue or an organ.
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Affiliation(s)
- Christina Weinl
- Unigruppe am Max-Planck-Institut für Züchtungsforschung, Lehrstuhl für Botanik III, Max-Delbrück-Laboratorium, 50829 Köln, Germany
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133
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Haywood V, Yu TS, Huang NC, Lucas WJ. Phloem long-distance trafficking of GIBBERELLIC ACID-INSENSITIVE RNA regulates leaf development. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2005; 42:49-68. [PMID: 15773853 DOI: 10.1111/j.1365-313x.2005.02351.x] [Citation(s) in RCA: 198] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The phloem translocation stream contains a population of RNA molecules, suggesting plants use RNA to integrate developmental processes, at the whole-plant level. In the present study, we analyzed the role of long-distance trafficking in the delivery of transcripts from two members of the GRAS family, namely CmGAIP and GAI. These two homologs were chosen because of their involvement as transcriptional regulators in GA signaling. A combination of pumpkin, tomato and Arabidopsis was employed to examine the processes involved in long-distance delivery, to sink tissues, of RNA for engineered dominant gain-of-function pumpkin (Cmgaip) and Arabidopsis (DeltaDELLA-gai) genes. Our studies demonstrate that gai RNA entry into functional sieve elements occurs via a selective process. Both engineered mutant gai transcripts were able to exit the scion phloem and traffic cell to cell into the shoot apex. Delivery of Cmgaip and DeltaDELLA-gai RNA mediated highly reproducible changes in leaf phenotype in transgenic tomato lines grown under greenhouse conditions. Phenotypic analysis indicated that tomato leaflet morphology was influenced quite late in development. In addition, tissue sink strength did not appear to dictate gai RNA delivery, suggesting complexity in the process underlying macromolecular trafficking. These results establish that the molecular properties of the Cmgaip and DeltaDELLA-gai transcripts are compatible with the tomato cell-to-cell and long-distance macromolecular trafficking systems. An important conclusion, based on our work, is that control over GAI RNA delivery, via the phloem, may be regulated by sequence motifs conserved between plant families. We propose that RNA delivery via the phloem allows for flexibility in fine tuning of developmental programs to ensure newly developing leaves are optimized for performance under the prevailing environmental conditions.
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Affiliation(s)
- Valerie Haywood
- Section of Plant Biology, Division of Biological Sciences, University of California, Davis, CA 95616, USA
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134
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Kim JY. Regulation of short-distance transport of RNA and protein. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:45-52. [PMID: 16207533 DOI: 10.1016/j.pbi.2004.11.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The intercellular trafficking of proteins and RNAs has emerged as a novel mechanism of cell-cell communication in plant development. Plasmodesmata (PD), intercellular cytoplasmic channels, have a central role in cell-cell trafficking of regulatory proteins and RNAs. Recent studies have demonstrated that plants use either a selective or a non-selective PD trafficking pathway for regulatory proteins. Moreover, plants have developed strategies to regulate both selective and non-selective movement. Recent work has focused especially on integrating the recent understanding of the function and mechanisms of intercellular macromolecule movement through PD.
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Affiliation(s)
- Jae-Yean Kim
- Division of Applied Life Science, Plant Molecular Biology and Biotechnology Research Center, Environmental Biotechnology National Core Research Center, Gyeongsang National University, Jinju 660-701, Korea.
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135
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Baluska F, Hlavacka A, Volkmann D, Menzel D. Getting connected: actin-based cell-to-cell channels in plants and animals. Trends Cell Biol 2005; 14:404-8. [PMID: 15308205 DOI: 10.1016/j.tcb.2004.07.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It has been known for more than one hundred years that plant cells are interconnected by cytoplasmic channels called plasmodesmata. This supracellularity was generally considered to be an exotic feature of walled plants containing immobile cells that are firmly enclosed within robust walls. Unexpectedly, intercellular channels in mobile animal cells have been discovered recently. These are extremely dynamic and sensitive to mechanical stress, which causes their rapid breakage and retraction. Both plasmodesmata and nanotubular cell-to-cell channels are supported by the actin cytoskeleton and exclude microtubules. In this article, we discuss the relevance of cell-to-cell channels not only for intercellular communication but also for the development and morphogenesis of multicellular organisms. We also suggest possible parallels between the cell-to-cell transport of endosomes and intracellular pathogens.
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Affiliation(s)
- Frantisek Baluska
- Institute of Cellular and Molecular Botany, University of Bonn, D-53115 Bonn, Germany.
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136
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Kim I, Cho E, Crawford K, Hempel FD, Zambryski PC. Cell-to-cell movement of GFP during embryogenesis and early seedling development in Arabidopsis. Proc Natl Acad Sci U S A 2005; 102:2227-31. [PMID: 15668382 PMCID: PMC548566 DOI: 10.1073/pnas.0409193102] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
There is increasing evidence for intercellular trafficking of macromolecules through plasmodesmata (PD) during plant development. Here we study the ability of PD to traffic proteins during embryogenesis and early seedling development in Arabidopsis. Transgenic lines that induce GFP expression only in meristems, MSG (meristem-specific GFP), were used to monitor GFP movement. Cell-to-cell movement of different-sized GFP reporters reveals that embryos and young seedlings traffic proteins at least 54 kDa in size. Although 27-kDa soluble GFP (1 x sGFP) freely moves between cells throughout the entire embryo during all stages analyzed, 2 x sGFP movement becomes more restricted as development proceeds. After germination, cells near the apical meristem in seedlings show a higher size exclusion limit (SEL), whereas the SEL becomes more restricted as surrounding tissues develop identities. Although 1 x sGFP moves throughout leaf primordia, as the leaf develops only the basal part of leaf petioles, main vascular tissues, and leaf veins (not blades) allow 1 x sGFP movement. Although previous studies showed that embryos allow movement of small symplastic tracers (0.5 kDa), the present data demonstrate that the embryo constitutes a single symplast that allows transport of macromolecules as well. Even 2 x sGFP moves from its site of expression at the apical meristem in embryos and seedlings, yet the extent of movement is more limited than 1 x sGFP. Thus, PD have distinct SELs in different subregions of the embryo and seedling. These studies support the general concept that PD in younger tissues are more dilated and less restrictive than PD in older (nonvascular) tissues.
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Affiliation(s)
- Insoon Kim
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
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137
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Gallagher KL, Benfey PN. Not just another hole in the wall: understanding intercellular protein trafficking. Genes Dev 2005; 19:189-95. [PMID: 15655108 DOI: 10.1101/gad.1271005] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Development and differentiation of multicellular organisms requires cell-to-cell communication. In plants direct signaling and exchange of macromolecules between cells is possible through plasmodesmata. Recently direct exchange of membrane-bound vesicles and organelles has been demonstrated between animal cells through formation of cytoplasmic bridges (tunneling nanotubes) in vitro. Here we review recent developments in cell-to-cell trafficking of macromolecules in plants and animals.
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138
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Haupt S, Cowan GH, Ziegler A, Roberts AG, Oparka KJ, Torrance L. Two plant-viral movement proteins traffic in the endocytic recycling pathway. THE PLANT CELL 2005; 17:164-81. [PMID: 15608333 PMCID: PMC544497 DOI: 10.1105/tpc.104.027821] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2004] [Accepted: 11/05/2004] [Indexed: 05/18/2023]
Abstract
Many plant viruses exploit a conserved group of proteins known as the triple gene block (TGB) for cell-to-cell movement. Here, we investigated the interaction of two TGB proteins (TGB2 and TGB3) of Potato mop-top virus (PMTV), with components of the secretory and endocytic pathways when expressed as N-terminal fusions to green fluorescent protein or monomeric red fluorescent protein (mRFP). Our studies revealed that fluorophore-labeled TGB2 and TGB3 showed an early association with the endoplasmic reticulum (ER) and colocalized in motile granules that used the ER-actin network for intracellular movement. Both proteins increased the size exclusion limit of plasmodesmata, and TGB3 accumulated at plasmodesmata in the absence of TGB2. TGB3 contains a putative Tyr-based sorting motif, mutations in which abolished ER localization and plasmodesmatal targeting. Later in the expression cycle, both fusion proteins were incorporated into vesicular structures. TGB2 associated with these structures on its own, but TGB3 could not be incorporated into the vesicles in the absence of TGB2. Moreover, in addition to localization to the ER and motile granules, mRFP-TGB3 was incorporated into vesicles when expressed in PMTV-infected epidermal cells, indicating recruitment by virus-expressed TGB2. The TGB fusion protein-containing vesicles were labeled with FM4-64, a marker for plasma membrane internalization and components of the endocytic pathway. TGB2 also colocalized in vesicles with Ara7, a Rab5 ortholog that marks the early endosome. Protein interaction analysis revealed that recombinant TGB2 interacted with a tobacco protein belonging to the highly conserved RME-8 family of J-domain chaperones, shown to be essential for endocytic trafficking in Caenorhabditis elegans and Drosophila melanogaster. Collectively, the data indicate the involvement of the endocytic pathway in viral intracellular movement, the implications of which are discussed.
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Affiliation(s)
- Sophie Haupt
- Programme of Cell-to-Cell Communication, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom
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139
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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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140
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Carvalho MF, Lazarowitz SG. Interaction of the movement protein NSP and the Arabidopsis acetyltransferase AtNSI is necessary for Cabbage leaf curl geminivirus infection and pathogenicity. J Virol 2004; 78:11161-71. [PMID: 15452236 PMCID: PMC521842 DOI: 10.1128/jvi.78.20.11161-11171.2004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
DNA viruses can modulate the activity of cellular acetyltransferases to regulate virus gene expression and to affect cell cycle progression in order to support virus replication. A role for protein acetylation in regulating the nuclear export of the bipartite geminivirus DNA genome was recently suggested by the findings that the viral movement protein NSP, which shuttles the viral genome between the nucleus and the cytoplasm, interacts with a novel Arabidopsis acetyltransferase, AtNSI, and the increased expression of AtNSI enhances susceptibility to Cabbage leaf curl virus infection. To further investigate the interaction of NSP and AtNSI and to establish the importance of this interaction in virus infections, we used a reverse yeast two-hybrid selection and deletion analysis to identify NSP mutants that were impaired in their ability to bind AtNSI. These mutants identified a 38-amino-acid region of NSP, to which no function had so far been assigned, as being necessary for NSP-AtNSI interaction. Three NSP missense mutants were analyzed in detail and were found to be comparable to wild-type NSP in their levels of accumulation, nucleocytoplasmic shuttling, DNA binding, and cooperative interaction with the viral cell-to-cell movement protein MP. Despite this, Cabbage leaf curl virus that expressed each mutated NSP was defective in its ability to infect Arabidopsis, exhibiting lower levels of infectivity than the wild-type virus, and delayed systemic spread of the virus and attenuated disease symptoms. Our data demonstrate the importance of the interaction of NSP with AtNSI for virus infection and pathogenicity.
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Affiliation(s)
- Miguel F Carvalho
- Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA
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141
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Yuan X, Zhao B, Wang Y. Cell culture of Saussurea medusa in a periodically submerged air-lift bioreactor. Biochem Eng J 2004. [DOI: 10.1016/j.bej.2004.07.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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142
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Howard AR, Heppler ML, Ju HJ, Krishnamurthy K, Payton ME, Verchot-Lubicz J. Potato virus X TGBp1 induces plasmodesmata gating and moves between cells in several host species whereas CP moves only in N. benthamiana leaves. Virology 2004; 328:185-97. [PMID: 15464839 DOI: 10.1016/j.virol.2004.06.039] [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] [Received: 03/15/2004] [Revised: 06/04/2004] [Accepted: 06/04/2004] [Indexed: 11/22/2022]
Abstract
Experiments were conducted to compare the plasmodesmal transport activities of Potato virus X (PVX) TGBp1 and coat protein (CP) in several plant species. Microinjection experiments indicated that TGBp1 gates plasmodesmata in Nicotiana tabacum leaves. These results support previous microinjection studies indicating that TGBp1 gates plasmodesmata in Nicotiana benthamiana and Nicotiana clevelandii leaves. To study protein movement, plasmids expressing the green fluorescent protein (GFP) gene fused to the PVX TGBp1 or CP genes were biolistically bombarded to leaves taken from four different PVX host species. GFP/TGBp1 moved between adjacent cells in N. tabacum, N. clevelandii, N. benthamiana, and Lycopersicon esculentum, whereas GFP/CP moved only in N. benthamiana leaves. Mutations m12 and m13 were introduced into the TGBp1 gene and both mutations eliminated TGBp1 ATPase active site motifs, inhibited PVX movement, reduced GFP/TGBp1 cell-to-cell movement in N. benthamiana leaves, and eliminated GFP/TGBp1 movement in N. tabacum, N. clevelandii, and L. esculentum leaves. GFP/TGBp1m13 formed aggregates in tobacco cells. The ability of GFP/CP and mutant GFP/TGBp1 fusion proteins to move in N. benthamiana and not in the other PVX host species suggests that N. benthamiana plants have a unique ability to promote protein intercellular movement.
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Affiliation(s)
- Amanda R Howard
- Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078, USA
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143
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Abstract
Intercellular transport via plasmodesmata controls cell fate decisions in plants, and is of fundamental importance in viral movement, disease resistance, and the spread of RNAi signals. Although plasmodesmata appear to be unique to plant cells, they may have structural and functional similarities to the newly discovered tunneling nanotubes that connect animal cells. Recently, proteins that localize to plasmodesmata have been identified, and a microtubule-associated protein was found to negatively regulate the trafficking of viral movement proteins. Other advances have delivered new insights into the function and molecular nature of plasmodesmata and have shown that protein trafficking through plasmodesmata is developmentally regulated, opening up the possibility that the genetic control of plasmodesmal function will soon be understood.
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Affiliation(s)
- Michelle Lynn Cilia
- Watson School of Biological Sciences, 1 Bungtown Road, Cold Spring Harbor, New York 11724, USA.
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144
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VAN Bel AJE, Gaupels F. Pathogen-induced resistance and alarm signals in the phloem. MOLECULAR PLANT PATHOLOGY 2004; 5:495-504. [PMID: 20565623 DOI: 10.1111/j.1364-3703.2004.00243.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
SUMMARY Despite a long-standing notion of long-distance signals triggering systemic acquired resistance (SAR), the translocation pathway and the identity of the signals involved have not been determined with any degree of certainty. A critical assessment indicates that, in parallel to signalling via the phloem, alternative modes for SAR induction such as signalling via the xylem or air-borne signalling by volatile substances may occur. This review further evaluates several classes of compounds as being functional in systemic resistance signalling. Evidence in favour of SAR involvement of phloem-mobile substances such as salicylic acid, lipid-derived molecules, reactive oxygen species and components of the antioxidant machinery is contradictory, circumstantial or inconclusive, at best. Nitric oxide bound to proteins or thiols seems a good candidate for signalling, but has not been found in phloem sap thus far. No convincing support of the involvement in SAR of phloem-mobile substances such as calcium, oligosaccharides, peptides or RNA species, which function in other systemic signalling cascades, has yet been produced. Nevertheless, phloem-mobile macromolecules are considered as potential tools for SAR given their pivotal role in remote gene expression under stress conditions. In this framework, the existence of several cascades for signal generation along the phloem pathway is envisaged. Finally, recent methods for detection of molecular signals in phloem sap and their expression in companion cells are presented.
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Affiliation(s)
- Aart J E VAN Bel
- Plant Cell Biology Research Group, Institute of General Botany, Senckenbergstrasse 17, 35390 Giessen, and Institute of Phytopathology, IFZ, Heinrich-Buff-Ring 26-32, 35392 Giessen, Justus Liebig University, Giessen, Germany
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145
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Zamyatnin AA, Solovyev AG, Savenkov EI, Germundsson A, Sandgren M, Valkonen JPT, Morozov SY. Transient coexpression of individual genes encoded by the triple gene block of potato mop-top virus reveals requirements for TGBp1 trafficking. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2004; 17:921-30. [PMID: 15305613 DOI: 10.1094/mpmi.2004.17.8.921] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
TGBp1, TGBp2, and TGBp3, three plant virus movement proteins encoded by the "triple gene block" (TGB), may act in concert to facilitate cell-to-cell transport of viral RNA genomes. Transient expression of Potato mop-top virus (genus Pomovirus) movement proteins was used as a model to reconstruct interactions between TGB proteins. In bombarded epidermal cells of Nicotiana benthamiana, green fluorescent protein (GFP)-TGBp1 was distributed uniformly. However, in the presence of TGBp2 and TGBp3, GFP-TGBp1 was directed to intermediate bodies at the cell periphery, and to cell wall-embedded punctate bodies. Moreover, GFP-TGBp1 migrated into cells immediately adjacent to the bombarded cell. These data suggest that TGBp2 and TGBp3 mediate transport of GFP-TGBp1 to and through plasmodesmata. Mutagenesis of TGBp1 suggested that the NTPase and helicase activities of TGBp1 were not required for its transport to intermediate bodies directed by TGBp2 and TGBp3, but these activities were essential for the protein association with cell wall-embedded punctate bodies and translocation of TGBpl to neighboring cells. The C-terminal region of TGBp1 was critical for trafficking mediated by TGBp2 and TGBp3. Mutation analysis also suggested an involvement of the TGBp2 C-terminal region in interactions with TGBp1.
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Affiliation(s)
- Andrey A Zamyatnin
- Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences (SLU), SE-750 07 Uppsala, Sweden.
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146
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Barnes A, Bale J, Constantinidou C, Ashton P, Jones A, Pritchard J. Determining protein identity from sieve element sap in Ricinus communis L. by quadrupole time of flight (Q-TOF) mass spectrometry. JOURNAL OF EXPERIMENTAL BOTANY 2004; 55:1473-81. [PMID: 15181102 DOI: 10.1093/jxb/erh161] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
The phloem transport system is a complex tissue that primarily carries photoassimilate from source to sink. Its function depends on anucleate sieve elements (SE) supported by companion cells (CC). In this study, SE sap was sampled and the protein identity of soluble proteins was determined with the aim of understanding the function of proteins within the conduit. Unlike many plants, SE sap exudes from incisions in the bark of Ricinus communis and, although there is a greater possibility of contamination from tissues other than SE, sap can be obtained in sufficient quantities to separate proteins using 2D electrophoresis. Spots were excised for trypsin digest, then analysed by quadrupole time of flight (Q-TOF) mass spectrometry (MS) and database searched to determine sequence identity. Overall, 18 proteins were identified in the SE-enriched sap. Proteins identified that have not previously been identified directly from SE sap included a glycine-rich RNA-binding protein, metallothionein, phosphoglycerate mutase, and phosphopyruvate hydratase. The potential role of the identified protein in SE function is discussed. The protein identification in this study provides a first step towards the goal of a greater understanding of the function of proteins within the SE.
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Affiliation(s)
- Alan Barnes
- The University of Birmingham, School of Biosciences, Edgbaston, Birmingham B15 2TT, UK
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