201
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Abstract
In Arabidopsis thaliana, the initiation of flowering is carried out by four genetic pathways: gibberellin, autonomous, vernalization, and light-dependent pathways. These processes are integrated by the function of the genes FD, FE, FWA, PDF2, SOC1, and FT at the integration pathway. The integrated signal of the floral induction is transmitted to the floral meristem identity genes LFY and AP1, and floral morphogenesis is performed.
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Affiliation(s)
- Yoshibumi Komeda
- Laboratory of Plant Science, Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
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202
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Ding B, Itaya A, Qi Y. Symplasmic protein and RNA traffic: regulatory points and regulatory factors. CURRENT OPINION IN PLANT BIOLOGY 2003; 6:596-602. [PMID: 14611959 DOI: 10.1016/j.pbi.2003.09.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Plasmodesmata and the phloem form a cytoplasmic network that permits direct cell-cell communication in plants. This network can mediate the trafficking of selective proteins and RNAs that may have important developmental functions. Recent work has provided evidence that protein and RNA traffic across specific interfaces of this network is regulated in a distinct manner. Progress has been made in identifying potential cellular factors that confer such regulation. These advances should promote further investigations into the mechanisms and functions of protein and RNA traffic using biochemical, cellular, genetic and molecular tools.
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Affiliation(s)
- Biao Ding
- Department of Plant Biology and Plant Biotechnology Center, 207 Rightmire Hall, The Ohio State University, 1060 Carmack Road, Columbus, Ohio 43210, USA.
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203
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Kim JY, Yuan Z, Jackson D. Developmental regulation and significance of KNOX protein trafficking in Arabidopsis. Development 2003; 130:4351-62. [PMID: 12900451 DOI: 10.1242/dev.00618] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Intercellular communication delivers critical information for position-dependent specification of cell fate. In plants, a novel mechanism for cell-to-cell communication involves the intercellular trafficking of regulatory proteins and mRNAs. The maize KNOTTED1 (KN1) gene acts non cell-autonomously in the maize leaf, and KN1 was the first plant protein shown to traffic cell-to-cell, presumably through plasmodesmata. We have compared the intercellular trafficking of green fluorescent protein (GFP) fusions of KN1 and Arabidopsis KN1-related homeobox proteins to that of the viral movement protein from turnip vein clearing tobamovirus. We show that there is specific developmental regulation of GFP approximately KN1 trafficking. GFP -- KN1 was able to traffic from the inner layers of the leaf to the epidermis, but not in the opposite direction, from epidermis to mesophyll. However, GFP or the GFP -- movement protein fusion moved readily out of the epidermis. GFP -- KN1 was however able to traffic out of the epidermal (L1) layer in the shoot apical meristem, indicating that KN1 movement out of the L1 was developmentally regulated. GFP -- KNAT1/BREVIPEDICELLUS and GFP -- SHOOTMERISTEMLESS fusions could also traffic from the L1 to the L2/L3 layers of the meristem. In a test for the functional significance of trafficking, we showed that L1-specific expression of KN1 or of KNAT1 was able to partially complement the strong shootmeristemless-11 (stm-11) mutant. However, a cell-autonomous GUS fusion to KN1 showed neither trafficking ability nor complementation of stm-11 when expressed in the L1. These results suggest that the activity of KN1 and related homeobox proteins is maintained following intercellular trafficking, and that trafficking may be required for their normal developmental function.
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Affiliation(s)
- Jae-Yean Kim
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
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204
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Wu X, Dinneny JR, Crawford KM, Rhee Y, Citovsky V, Zambryski PC, Weigel D. Modes of intercellular transcription factor movement in the Arabidopsis apex. Development 2003; 130:3735-45. [PMID: 12835390 DOI: 10.1242/dev.00577] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A recent and intriguing discovery in plant biology has been that some transcription factors can move between cells. In Arabidopsis thaliana, the floral identity protein LEAFY has strong non-autonomous effects when expressed in the epidermis, mediated by its movement into underlying tissue layers. By contrast, a structurally unrelated floral identity protein, APETALA1, has only limited non-autonomous effects. Using GFP fusions to monitor protein movement in the shoot apical meristem and in floral primordia of Arabidopsis, we found a strong correlation between cytoplasmic localization of proteins and their ability to move to adjacent cells. The graded distribution of several GFP fusions with their highest levels in the cells where they are produced is compatible with the notion that this movement is driven by diffusion. We also present evidence that protein movement is more restricted laterally within layers than it is from L1 into underlying layers of the Arabidopsis apex. Based on these observations, we propose that intercellular movement of transcription factors can occur in a non-targeted fashion as a result of simple diffusion. This hypothesis raises the possibility that diffusion is the default state for many macromolecules in the Arabidopsis apex, unless they are specifically retained.
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Affiliation(s)
- Xuelin Wu
- Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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205
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Kang J, Tang J, Donnelly P, Dengler N. Primary vascular pattern and expression of ATHB-8 in shoots of Arabidopsis. THE NEW PHYTOLOGIST 2003; 158:443-454. [PMID: 36056517 DOI: 10.1046/j.1469-8137.2003.00769.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
• Primary vascular pattern determines pathways of long distance transport for water, nutrients and signalling molecules within plant shoot systems. • Expression of an Arabidopsis thaliana homeobox gene 8::GUS construct is restricted to the procambium and provides a molecular marker for vascular pattern at early developmental stages. • Primary vascular pattern and phyllotaxis are highly coordinated, with vascular sympodia corresponding to phyllotactic parastichies. During vegetative development, primary vasculature forms a reticulate pattern, with each leaf trace derived from two vascular sympodia. Shoot phase change is marked by alterations of this fundamental pattern. Formation of leaf trace procambial strands is temporally coordinated with primordium initiation, but ATHB-8::GUS expression is discontinuous in these strands at early stages. • The interconnection of vascular sympodia provides alternate pathways for long distance transport in shoots of A. thaliana and reflects the limited secondary growth in this species. ATHB-8::GUS expression identifies a prepattern that precedes anatomical definition of procambium. The longitudinal discontinuity in ATHB-8::GUS expression indicates that one function of this gene is to define the xylem components of vascular radial pattern.
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Affiliation(s)
- Julie Kang
- Department of Botany, University of Toronto, Toronto, Ontario, M5S 1A1, Canada
| | - John Tang
- Department of Botany, University of Toronto, Toronto, Ontario, M5S 1A1, Canada
| | - Petra Donnelly
- Department of Botany, University of Toronto, Toronto, Ontario, M5S 1A1, Canada
| | - Nancy Dengler
- Department of Botany, University of Toronto, Toronto, Ontario, M5S 1A1, Canada
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206
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Theodoris G, Inada N, Freeling M. Conservation and molecular dissection of ROUGH SHEATH2 and ASYMMETRIC LEAVES1 function in leaf development. Proc Natl Acad Sci U S A 2003; 100:6837-42. [PMID: 12750468 PMCID: PMC164533 DOI: 10.1073/pnas.1132113100] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Maize ROUGH SHEATH2 (RS2) and Arabidopsis ASYMMETRIC LEAVES1 (AS1) are orthologous Myb-related genes required for leaf development and act as negative regulators of class 1 KNOTTED1-like homeobox (KNOX) genes in leaf primordia. Expression of RS2 in Arabidopsis fully complements as1 leaf phenotypes and represses the expression of the KNOX gene KNAT1 in leaves. Whereas loss of AS1 function in Arabidopsis results in rounded, lobed leaves with shorter and wider petioles, overexpression of either RS2 or AS1 results in longer and narrower leaves with longer petioles than wild type. A conserved C-terminal domain (CTD) mediates homodimerization of both RS2 and AS1 and modulates leaf shape when expressed independently of the Myb domain in Arabidopsis. Homodimerization is not absolutely required for KNAT1 repression. RS2:GFP fusion protein is biologically active, localized in discrete dynamic subnuclear foci and associates with DNA during cell division.
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Affiliation(s)
- George Theodoris
- Department of Plant and Microbial Biology, University of California, Berkeley 94720, USA
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207
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Abstract
Plasmodesmata play a central role in cell-to-cell communication in plants, allowing transport of regulatory proteins and mRNAs. A recent study has identified a specific protein that regulates the intercellular transport of macromolecules in plants, known as non-cell autonomous pathway protein 1.
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Affiliation(s)
- David Jackson
- Cold Spring Harbor Laboratory, 1 Bungtown Road., Cold Spring Harbor, NY 11724, USA.
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208
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Ayre BG, Keller F, Turgeon R. Symplastic continuity between companion cells and the translocation stream: long-distance transport is controlled by retention and retrieval mechanisms in the phloem. PLANT PHYSIOLOGY 2003; 131:1518-28. [PMID: 12692312 PMCID: PMC166911 DOI: 10.1104/pp.012054] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2002] [Revised: 09/25/2002] [Accepted: 11/24/2002] [Indexed: 05/17/2023]
Abstract
Substantial symplastic continuity appears to exist between companion cells (CCs) and sieve elements of the phloem, which suggests that small solutes within the CC are subject to indiscriminate long-distance transport via the translocation stream. To test this hypothesis, the distributions of exotic and endogenous solutes synthesized in the CCs of minor veins were studied. Octopine, a charged molecule derived from arginine and pyruvate, was efficiently transported through the phloem but was also transferred in substantial amounts to the apoplast, and presumably other non-phloem compartments. The disaccharide galactinol also accumulated in non-phloem compartments, but long-distance transport was limited. Conversely, sucrose, raffinose, and especially stachyose demonstrated reduced accumulation and efficient transport out of the leaf. We conclude that small metabolites in the cytosol of CCs do enter the translocation stream indiscriminately but are also subject to distributive forces, such as nonselective and carrier-mediated membrane transport and symplastic dispersal, that may effectively clear a compound from the phloem or retain it for long-distance transport. A model is proposed in which the transport of oligosaccharides is an adaptive strategy to improve photoassimilate retention, and consequently translocation efficiency, in the phloem.
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Affiliation(s)
- Brian G Ayre
- Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA.
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209
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Okita TW, Choi SB. mRNA localization in plants: targeting to the cell's cortical region and beyond. CURRENT OPINION IN PLANT BIOLOGY 2002; 5:553-9. [PMID: 12393019 DOI: 10.1016/s1369-5266(02)00304-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
mRNA localization efficiently targets gene products to specific subcellular compartments, thereby controlling cell fate and polar cell growth. Plants also localize RNAs to target proteins in the endomembrane system, and to different tissues by long-distance transport. Recent developments support the existence of multiple pathways that transport RNA to the cortical region of the cell and to different tissues of the plant.
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Affiliation(s)
- Thomas W Okita
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
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210
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Heinlein M. Plasmodesmata: dynamic regulation and role in macromolecular cell-to-cell signaling. CURRENT OPINION IN PLANT BIOLOGY 2002; 5:543-552. [PMID: 12393018 DOI: 10.1016/s1369-5266(02)00295-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Recent studies have demonstrated the functional significance of intercellular RNA and protein trafficking in plant development, confirming the role of plasmodesmata (PD) in the mediation and control of intercellular communication via macromolecules. Small fluorescent tracer loading techniques and experiments involving the expression of proteins tagged with green fluorescent protein (GFP) have been used to investigate the mechanisms of PD targeting and trafficking, as well as to elucidate the dynamic and structural properties of these channels.
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Affiliation(s)
- Manfred Heinlein
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058, Basel, Switzerland.
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211
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Abstract
In the 'RNA world' hypothesis it is postulated that RNA was the first genetic molecule. Recent discoveries in gene silencing research on plants, fungi and animals show that RNA indeed plays a key role not only in controlling invading nucleic acids, like viruses and transposable elements, but also in regulating the expression of transgenes and endogenous genes. Double-stranded RNAs were identified to be the triggering structures for the induction of a specific and highly efficient RNA silencing system, in which enzyme complexes, like Dicer and RISC, facilitate as 'molecular machines' the processing of dsRNA into characteristic small RNA species. RNA silencing can be transmitted rapidly from silenced to non-silenced cells by short and long distance signaling. There is evidence that at least one component of the signal is a specific, degradation-resistant RNA.
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Affiliation(s)
- Michael Metzlaff
- Bayer BioScience NV, Jozef Plateaustraat 22, B-9000 Gent, Belgium
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212
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Affiliation(s)
- Richard A Jorgensen
- Department of Plant Sciences and Interdisciplinary Program in Genetics, University of Arizona, Tucson, AZ 85721-0036, USA
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213
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Zhu Y, Qi Y, Xun Y, Owens R, Ding B. Movement of potato spindle tuber viroid reveals regulatory points of phloem-mediated RNA traffic. PLANT PHYSIOLOGY 2002; 130:138-46. [PMID: 12226494 PMCID: PMC166547 DOI: 10.1104/pp.006403] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2002] [Revised: 04/18/2002] [Accepted: 04/26/2002] [Indexed: 05/17/2023]
Abstract
Increasing evidence indicates that the phloem mediates traffic of selective RNAs within a plant. How an RNA enters, moves in, and exits the phloem is poorly understood. Potato spindle tuber viroid (PSTVd) is a pathogenic RNA that does not encode proteins and is not encapsidated, and yet it replicates autonomously and traffics systemically within an infected plant. The viroid RNA genome must interact directly with cellular factors to accomplish these functions and is, therefore, an excellent probe to study mechanisms that regulate RNA traffic. Our analyses of PSTVd traffic in Nicotiana benthamiana yielded evidence that PSTVd movement within sieve tubes does not simply follow mass flow from source to sink organs. Rather, this RNA is transported into selective sink organs. Furthermore, two PSTVd mutants can enter the phloem to spread systemically but cannot exit the phloem in systemic leaves of tobacco (Nicotiana tabacum). A viroid most likely has evolved structural motifs that mimic endogenous plant RNA motifs so that they are recognized by cellular factors for traffic. Thus, analysis of PSTVd traffic functions may provide insights about endogenous mechanisms that control phloem entry, transport, and exit of RNAs.
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Affiliation(s)
- Yali Zhu
- Department of Plant Biology and Plant Biotechnology Center, Ohio State University, Columbus, Ohio 43210, USA
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214
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Jackson D. Double labeling of KNOTTED1 mRNA and protein reveals multiple potential sites of protein trafficking in the shoot apex. PLANT PHYSIOLOGY 2002; 129:1423-9. [PMID: 12177455 PMCID: PMC1540245 DOI: 10.1104/pp.006049] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Recent reports indicate that several plant mRNAs and proteins are able to traffic intercellularly through plasmodesmata. Localization studies can reveal differences between mRNA and protein localization that would be indicative of such a process. However, subtle differences could be missed when comparing localization in adjacent sections, especially in developmental studies where adjacent sections through immature apical regions may be one or more cells removed from each other. Therefore, we have developed a novel method for double localization of KNOTTED1 mRNA and protein in sections through the maize (Zea mays) shoot apex. The advantage of double labeling is revealed in our demonstration of novel potential sites of cell-to-cell trafficking of KNOTTED1 protein in the shoot apical region. The technique should be applicable to any gene products where the appropriate probes are available and will, therefore, help to determine the extent of protein and/or mRNA trafficking in plants.
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Affiliation(s)
- David Jackson
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA.
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215
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Desvoyes B, Faure-Rabasse S, Chen MH, Park JW, Scholthof HB. A novel plant homeodomain protein interacts in a functionally relevant manner with a virus movement protein. PLANT PHYSIOLOGY 2002; 129:1521-32. [PMID: 12177465 PMCID: PMC166740 DOI: 10.1104/pp.004754] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2002] [Accepted: 03/27/2002] [Indexed: 05/20/2023]
Abstract
Tomato bushy stunt virus and its cell-to-cell movement protein (MP; P22) provide valuable tools to study trafficking of macromolecules through plants. This study shows that wild-type P22 and selected movement-defective P22 amino acid substitution mutants were equivalent for biochemical features commonly associated with MPs (i.e. RNA binding, phosphorylation, and membrane partitioning). This generated the hypothesis that their movement defect was caused by improper interaction between the P22 mutants and one or more host factors. To test this, P22 was used as bait in a yeast (Saccharomyces cerevisiae) two-hybrid screen with a tobacco (Nicotiana tabacum) cDNA library, which identified a new plant homeodomain leucine-zipper protein that reproducibly interacted with P22 but not with various control proteins. These results were confirmed with an independent in vitro binding test. An mRNA for the host protein was detected in plants, and its accumulation was enhanced upon Tomato bushy stunt virus infection of two plant species. The significance of this interaction was further demonstrated by the failure of the homeodomain protein to interact efficiently with two of the well-defined movement-deficient P22 mutants in yeast and in vitro. This is the first report, to our knowledge, that a new plant homeodomain leucine-zipper protein interacts specifically and in a functionally relevant manner with a plant virus MP.
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Affiliation(s)
- Bénédicte Desvoyes
- Department of Plant Pathology and Microbiology, Texas A&M University, 2132 TAMU, College Station, Texas 77843, USA
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216
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Llave C, Kasschau KD, Rector MA, Carrington JC. Endogenous and silencing-associated small RNAs in plants. THE PLANT CELL 2002; 14:1605-19. [PMID: 12119378 PMCID: PMC150710 DOI: 10.1105/tpc.003210] [Citation(s) in RCA: 631] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2002] [Accepted: 04/15/2002] [Indexed: 05/18/2023]
Abstract
A large set of endogenous small RNAs of predominantly 21 to 24 nucleotides was identified in Arabidopsis. These small RNAs resembled micro-RNAs from animals and were similar in size to small interfering RNAs that accumulated during RNA silencing triggered by multiple types of inducers. Among the 125 sequences identified, the vast majority (90%) arose from intergenic regions, although small RNAs corresponding to predicted protein-coding genes, transposon-like sequences, and a structural RNA gene also were identified. Evidence consistent with the derivation of small RNAs of both polarities, and from highly base-paired precursors, was obtained through the identification and analysis of clusters of small RNA loci. The accumulation of specific small RNAs was regulated developmentally. We propose that Arabidopsis small RNAs participate in a wide range of post-transcriptional and epigenetic events.
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MESH Headings
- Arabidopsis/genetics
- Arabidopsis/metabolism
- Arabidopsis Proteins/genetics
- Cloning, Molecular
- DNA Transposable Elements/genetics
- DNA, Intergenic/genetics
- Gene Silencing
- Molecular Sequence Data
- Nucleic Acid Conformation
- Phylogeny
- RNA Processing, Post-Transcriptional
- RNA, Plant/chemistry
- RNA, Plant/genetics
- RNA, Plant/metabolism
- RNA, Small Interfering
- RNA, Untranslated/chemistry
- RNA, Untranslated/genetics
- RNA, Untranslated/metabolism
- Nicotiana/genetics
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Affiliation(s)
- Cesar Llave
- Center for Gene Research and Biotechnology, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331, USA
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217
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Yoo BC, Lee JY, Lucas WJ. Analysis of the complexity of protein kinases within the phloem sieve tube system. Characterization of Cucurbita maxima calmodulin-like domain protein kinase 1. J Biol Chem 2002; 277:15325-32. [PMID: 11847230 DOI: 10.1074/jbc.m200382200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In angiosperms, functional, mature sieve elements lack nuclei, vacuoles, ribosomes, and most of the endomembrane network. In this study, the complexity, number, and nature of protein kinases within the phloem sap of Cucurbita maxima were investigated to test the hypothesis that the enucleate sieve tube system utilizes a simplified signal transduction network. Supporting evidence was obtained in that only five putative protein kinases (three calcium-independent and two calcium-dependent protein kinases) were detected within the phloem sap extracted from stem tissues. Biochemical methods were used to purify one such calcium-dependent protein kinase. The gene for this C. maxima calmodulin-like domain protein kinase 1 (CmCPK1), was cloned using peptide microsequences. A combination of mass spectrometry, peptide fingerprinting, and amino-terminal sequencing established that, in the phloem sap, CmCPK1 exists as an amino-terminally cleaved protein. A second highly homologous isoform, CmCPK2, was identified, but although transcripts could be detected in the companion cells, peptide fingerprint analysis suggested that CmCPK2 does not enter the phloem sap. Potential substrates for CmCPK1, within the phloem sap, were also detected using an on-membrane phosphorylation assay. Entry of CmCPK1 into sieve elements via plasmodesmata and the potential roles played by these phloem protein kinases are discussed.
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Affiliation(s)
- Byung-Chun Yoo
- Section of Plant Biology, Division of Biological Sciences, University of California, Davis, California 95616, USA
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218
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Venglat SP, Dumonceaux T, Rozwadowski K, Parnell L, Babic V, Keller W, Martienssen R, Selvaraj G, Datla R. The homeobox gene BREVIPEDICELLUS is a key regulator of inflorescence architecture in Arabidopsis. Proc Natl Acad Sci U S A 2002; 99:4730-5. [PMID: 11917137 PMCID: PMC123716 DOI: 10.1073/pnas.072626099] [Citation(s) in RCA: 218] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Flowering plants display a remarkable range of inflorescence architecture, and pedicel characteristics are one of the key contributors to this diversity. However, very little is known about the genes or the pathways that regulate pedicel development. The brevipedicellus (bp) mutant of Arabidopsis thaliana displays a unique phenotype with defects in pedicel development causing downward-pointing flowers and a compact inflorescence architecture. Cloning and molecular analysis of two independent mutant alleles revealed that BP encodes the homeodomain protein KNAT1, a member of the KNOX family. bp-1 is a null allele with deletion of the entire locus, whereas bp-2 has a point mutation that is predicted to result in a truncated protein. In both bp alleles, the pedicels and internodes were compact because of fewer cell divisions; in addition, defects in epidermal and cortical cell differentiation and elongation were found in the affected regions. The downward-pointing pedicels were produced by an asymmetric effect of the bp mutation on the abaxial vs. adaxial sides. Cell differentiation, elongation, and growth were affected more severely on the abaxial than adaxial side, causing the change in the pedicel growth angle. In addition, bp plants displayed defects in cell differentiation and radial growth of the style. Our results show that BP plays a key regulatory role in defining important aspects of the growth and cell differentiation of the inflorescence stem, pedicel, and style in Arabidopsis.
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Affiliation(s)
- S P Venglat
- Plant Biotechnology Institute, National Research Council of Canada, 110 Gymnasium Place, Saskatoon, SK, Canada S7N 0W9
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219
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Boyko V, Ashby JA, Suslova E, Ferralli J, Sterthaus O, Deom CM, Heinlein M. Intramolecular complementing mutations in tobacco mosaic virus movement protein confirm a role for microtubule association in viral RNA transport. J Virol 2002; 76:3974-80. [PMID: 11907237 PMCID: PMC136114 DOI: 10.1128/jvi.76.8.3974-3980.2002] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2001] [Accepted: 01/22/2002] [Indexed: 11/20/2022] Open
Abstract
The movement protein (MP) of Tobacco mosaic virus (TMV) facilitates the cell-to-cell transport of the viral RNA genome through plasmodesmata (Pd). A previous report described the functional reversion of a dysfunctional mutation in MP (Pro81Ser) by two additional amino acid substitution mutations (Thr104Ile and Arg167Lys). To further explore the mechanism underlying this intramolecular complementation event, the mutations were introduced into a virus derivative expressing the MP as a fusion to green fluorescent protein (GFP). Microscopic analysis of infected protoplasts and of infection sites in leaves of MP-transgenic Nicotiana benthamiana indicates that MP(P81S)-GFP and MP(P81S;T104I;R167K)-GFP differ in subcellular distribution. MP(P81S)-GFP lacks specific sites of accumulation in protoplasts and, in epidermal cells, exclusively localizes to Pd. MP(P81S;T104I;R167K)-GFP, in contrast, in addition localizes to inclusion bodies and microtubules and thus exhibits a subcellular localization pattern that is similar, if not identical, to the pattern reported for wild-type MP-GFP. Since accumulation of MP to inclusion bodies is not required for function, these observations confirm a role for microtubules in TMV RNA cell-to-cell transport.
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Affiliation(s)
- Vitaly Boyko
- Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, CH-4058 Basel, Switzerland
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220
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Kim JY, Yuan Z, Cilia M, Khalfan-Jagani Z, Jackson D. Intercellular trafficking of a KNOTTED1 green fluorescent protein fusion in the leaf and shoot meristem of Arabidopsis. Proc Natl Acad Sci U S A 2002; 99:4103-8. [PMID: 11891300 PMCID: PMC122655 DOI: 10.1073/pnas.052484099] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2001] [Indexed: 11/18/2022] Open
Abstract
Dominant mutations in the maize homeobox gene knotted1 (kn1) act nonautonomously during maize leaf development, indicating that Kn1 is involved in the generation or transmission of a developmental signal that passes from the inner layers of the leaf to epidermal cells. We previously found that this nonautonomous activity is correlated with the presence of KN1 protein in leaf epidermal cells, where KN1 mRNA could not be detected. Furthermore, KN1 protein expressed in Escherichia coli and labeled with a fluorescent dye can traffic between leaf mesophyll cells in microinjection assays. Here we show that green fluorescent protein (GFP)-tagged KN1 is able to traffic between epidermal cells of Arabidopsis and onion. When expressed in vivo, the GFP approximately KN1 fusion trafficked from internal tissues of the leaf to the epidermis, providing the first direct evidence, to our knowledge, that KN1 can traffic across different tissue layers in the leaf. Control GFP fusions did not show this intercellular trafficking ability. GFP approximately KN1 also trafficked in the shoot apical meristem, suggesting that cell-to-cell trafficking of KN1 may be involved in its normal function in meristem initiation and maintenance.
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Affiliation(s)
- Jae Yean Kim
- Cold Spring Harbor Laboratory, Watson School of Biological Sciences, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA
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221
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Abstract
Phloem is a puzzling plant tissue owing to the unique natural defence responses of the sieve elements to any kind of mechanical manipulation. Recent non-invasive studies have enabled real-time observation of events in intact sieve tubes, including mass transport, sieve-pore sealing and conformational changes of structural proteins. These studies further highlighted the importance of the symplasmic setting for development and functioning of the sieve elements. Exchange of macromolecules between companion cells and sieve elements is indispensable for the survival of the sieve element, but also seems to be involved in long-distance communication. How the branched plasmodesmata between sieve element and companion cell function as corridors for the passage of macromolecules is an intriguing but unresolved story.
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Affiliation(s)
- Aart J E van Bel
- Institute General Botany, Justus-Liebig University Giessen, Senckenbergstrasse 17, 35390, Giessen, Germany.
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222
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Gisel A, Hempel FD, Barella S, Zambryski P. Leaf-to-shoot apex movement of symplastic tracer is restricted coincident with flowering in Arabidopsis. Proc Natl Acad Sci U S A 2002; 99:1713-7. [PMID: 11818578 PMCID: PMC122256 DOI: 10.1073/pnas.251675698] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Classical experiments in plant physiology showed that leaves are the source of signals that control the development of flowers from shoot meristems. Additional physiological and genetic experiments have indicated some of the molecules (e.g., gibberellins, cytokinins, and sucrose) that promote flowering in mustards including Arabidopsis. These small hydrophilic molecules are likely to move to the shoot apex symplastically via the phloem and/or via cell-to-cell movement through plasmodesmata. To analyze potential changes in the symplastic trafficking of small molecules during the induction of flowering in Arabidopsis, we measured changes in the flow of symplastic tracers from the leaf to the shoot apex. We previously found that the onset of flowering is coincident with an evident decrease in the leaf-to-shoot trafficking of symplastic tracer molecules; this decrease in trafficking is transitory and resumes when floral development is established. Here we provide detailed analyses of symplastic connectivity during floral induction by monitoring tracer movement under different photoperiodic induction conditions and in a number of genetic backgrounds with altered flowering times. In all cases, the correlation between flowering and the reduction of symplastic tracer movement holds true. The lack of tracer movement during the induction of flowering may represent a change in plasmodesmal selectivity at this time or that a period of reduced symplastic communication is associated with floral induction.
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Affiliation(s)
- Andreas Gisel
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102, USA
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223
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Affiliation(s)
- Xuelin Wu
- Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA
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224
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Ueki S, Citovsky V. RNA commutes to work: regulation of plant gene expression by systemically transported RNA molecules. Bioessays 2001; 23:1087-90. [PMID: 11746226 DOI: 10.1002/bies.10027] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Although long-distance movement of endogenous mRNAs in plants is well established, the functional contributions of these transported RNA molecules has remained unclear. In a recent report, Kim et al.2001 showed that systemically transported mRNA is capable of causing phenotypic change in developing tissue. Here, this finding and its significance are reviewed and discussed in detail. In addition, in order to give proper perspective, long-distance transport of other types of RNAs, e.g., RNA elicitors of post-transcriptional gene silencing and RNA genomes of plant viruses, and its possible regulation are discussed.
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Affiliation(s)
- S Ueki
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, USA
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225
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Lucas WJ, Yoo BC, Kragler F. RNA as a long-distance information macromolecule in plants. Nat Rev Mol Cell Biol 2001; 2:849-57. [PMID: 11715051 DOI: 10.1038/35099096] [Citation(s) in RCA: 178] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
A role for RNA as a non-cell-autonomous information macromolecule is emerging as a new model in biology. Studies on higher plants have shown the operation of cell-to-cell and long-distance communication networks that mediate the selective transport of RNA. The evolution and function of these systems are discussed in terms of an RNA-based signalling network that potentiates control over gene expression at the whole-plant level.
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Affiliation(s)
- W J Lucas
- Section of Plant Biology, Division of Biological Sciences, University of California, One Shields Ave., Davis, California 95616, USA.
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226
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Pearson H. Long-distance plant traffic. Nature 2001. [DOI: 10.1038/news010719-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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