201
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Hartweck LM, Olszewski NE. Rice GIBBERELLIN INSENSITIVE DWARF1 is a gibberellin receptor that illuminates and raises questions about GA signaling. THE PLANT CELL 2006; 18:278-82. [PMID: 16452510 PMCID: PMC1356538 DOI: 10.1105/tpc.105.039958] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Affiliation(s)
- Lynn M Hartweck
- Department of Plant Biology, University of Minesota, St. Paul, MN 55108, USA
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202
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Hu W, Ma H. Characterization of a novel putative zinc finger gene MIF1: involvement in multiple hormonal regulation of Arabidopsis development. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2006; 45:399-422. [PMID: 16412086 DOI: 10.1111/j.1365-313x.2005.02626.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Phytohormones play crucial roles in regulating many aspects of plant development. Although much has been learned about the effects of individual hormones, cross-talk between and integration of different hormonal signals are still not well understood. We present a study of MINI ZINC FINGER 1 (MIF1), a putative zinc finger protein from Arabidopsis, and suggest that it may be involved in integrating signals from multiple hormones. MIF1 homologs are highly conserved among seed plants, each characterized by a very short sequence containing a central putative zinc finger domain. Constitutive overexpression of MIF1 caused dramatic developmental defects, including dwarfism, reduced apical dominance, extreme longevity, dark-green leaves, altered flower morphology, poor fertility, reduced hypocotyl length, spoon-like cotyledons, reduced root growth, and ectopic root hairs on hypocotyls and cotyledons. In addition, 35S::MIF1 seedlings underwent constitutive photomorphogenesis in the dark, with root growth similar to that in the light. Furthermore, 35S::MIF1 seedlings were demonstrated to be non-responsive to gibberellin (GA) for cell elongation, hypersensitive to the GA synthesis inhibitor paclobutrazol (PAC) and abscisic acid (ABA), and hyposensitive to auxin, brassinosteroid and cytokinin, but normally responsive to ethylene. The de-etiolation defect could not be rescued by the hormones tested. Consistent with these observations, genome-scale expression profiling revealed that 35S::MIF1 seedlings exhibited decreased expression of genes involved in GA, auxin and brassinosteroid signaling as well as cell elongation/expansion, and increased expression of ABA-responsive genes. We propose that MIF1, or the protein(s) with which MIF1 interacts, is involved in mediating the control of plant development by multiple hormones.
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Affiliation(s)
- Wei Hu
- Department of Biology, and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA 16802, USA
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203
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Kepinski S. Integrating hormone signaling and patterning mechanisms in plant development. CURRENT OPINION IN PLANT BIOLOGY 2006; 9:28-34. [PMID: 16325457 DOI: 10.1016/j.pbi.2005.11.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2005] [Accepted: 11/18/2005] [Indexed: 05/05/2023]
Abstract
Plant growth and development are driven by the bustling integration of a vast number of signals, among which plant hormones dominate. Understanding the role of hormones in particular developmental events requires their integration with developmental regulators known to be specific to those events. Using the increasing number of tools that can be utilized to probe hormone biosynthesis, transport and response, several recent studies have taken such an integrative approach, and in so doing have contributed to a clearer picture of precisely how hormones control plant development.
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Affiliation(s)
- Stefan Kepinski
- Department of Biology, University of York, Box 373, York YO10 5YW, UK.
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204
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Moore I, Samalova M, Kurup S. Transactivated and chemically inducible gene expression in plants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2006; 45:651-83. [PMID: 16441354 DOI: 10.1111/j.1365-313x.2006.02660.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Several vector systems are available for tissue-specific transactivation or chemical induction of transgene expression in plants. The choice facing researchers is which promoter system to commit to as this determines the range and characteristics of the expression resources available. The decision will not be the same for all species or applications. We present some general discussion on the use of these technologies and review in detail the properties in various (mainly angiosperm) species of the most promising: mGal4:VP16/UAS and pOp/LhG4 for transactivation, and the alc-switch, GVE/VGE, GVG, pOp6/LhGR, and XVE systems for chemical induction.
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Affiliation(s)
- Ian Moore
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
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205
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Riefler M, Novak O, Strnad M, Schmülling T. Arabidopsis cytokinin receptor mutants reveal functions in shoot growth, leaf senescence, seed size, germination, root development, and cytokinin metabolism. THE PLANT CELL 2006; 18:40-54. [PMID: 16361392 PMCID: PMC1323483 DOI: 10.1105/tpc.105.037796] [Citation(s) in RCA: 602] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
We used loss-of-function mutants to study three Arabidopsis thaliana sensor histidine kinases, AHK2, AHK3, and CRE1/AHK4, known to be cytokinin receptors. Mutant seeds had more rapid germination, reduced requirement for light, and decreased far-red light sensitivity, unraveling cytokinin functions in seed germination control. Triple mutant seeds were more than twice as large as wild-type seeds. Genetic analysis indicated a cytokinin-dependent endospermal and/or maternal control of embryo size. Unchanged red light sensitivity of mutant hypocotyl elongation suggests that previously reported modulation of red light signaling by A-type response regulators may not depend on cytokinin. Combined loss of AHK2 and AHK3 led to the most prominent changes during vegetative development. Leaves of ahk2 ahk3 mutants formed fewer cells, had reduced chlorophyll content, and lacked the cytokinin-dependent inhibition of dark-induced chlorophyll loss, indicating a prominent role of AHK2 and, particularly, AHK3 in the control of leaf development. ahk2 ahk3 double mutants developed a strongly enhanced root system through faster growth of the primary root and, more importantly, increased branching. This result supports a negative regulatory role for cytokinin in root growth regulation. Increased cytokinin content of receptor mutants indicates a homeostatic control of steady state cytokinin levels through signaling. Together, the analyses reveal partially redundant functions of the cytokinin receptors and prominent roles for the AHK2/AHK3 receptor combination in quantitative control of organ growth in plants, with opposite regulatory functions in roots and shoots.
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Affiliation(s)
- Michael Riefler
- Institute of Biology/Applied Genetics, Free University of Berlin, Germany
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206
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Hartweck LM, Genger RK, Grey WM, Olszewski NE. SECRET AGENT and SPINDLY have overlapping roles in the development of Arabidopsis thaliana L. Heyn. JOURNAL OF EXPERIMENTAL BOTANY 2006; 57:865-75. [PMID: 16473894 DOI: 10.1093/jxb/erj071] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
O-GlcNAc transferase (OGT) catalyses transfer of GlcNAc (N-acetylglucosamine) to serine or threonine of proteins. The Arabidopsis OGTs, SECRET AGENT (SEC) and SPINDLY (SPY) have overlapping functions during gametogenesis and embryogenesis. SPY functions in a number of processes including circadian, light, and gibberellin (GA) responses. The role of SEC in plant development and GA signalling was investigated by determining the phenotypes of sec-1 and sec-2 plants and the expression pattern of SEC. Similar to SPY, SEC transcripts were ubiquitous. Although there is no evidence of transcript-level regulation by other factors, SEC mRNA levels are elevated in spy plants and SPY mRNA levels are elevated in sec plants. sec-1 and sec-2 plants exhibited few of the defects observed in spy plants and had wild-type GA responses. Compared with wild type, sec plants produced leaves at a reduced rate. Haplo-insufficiency at SEC in a spy ga1 double mutant background suppressed spy during germination and enhanced the production of ovaries with four carpels by spy. By contrast, SPY haplo-insufficiency in a sec ga1 double mutant background caused a novel phenotype, production of a proliferation of pin-like structures instead of a floral shoot. These results are consistent with SEC function overlapping with SPY for leaf production and reproductive development.
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Affiliation(s)
- Lynn M Hartweck
- Department of Plant Biology, University of Minnesota, 250 Biological Sciences Center, 1445 Gortner Ave., St Paul, 55108, USA
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207
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Abstract
A dynamic cycle of addition and removal of O-linked N-acetylglucosamine (O-GlcNAc) at serine and threonine residues is emerging as a key regulator of nuclear and cytoplasmic protein activity. Like phosphorylation, protein O-GlcNAcylation dramatically alters the posttranslational fate and function of target proteins. Indeed, O-GlcNAcylation may compete with phosphorylation for certain Ser/Thr target sites. Like kinases and phosphatases, the enzymes of O-GlcNAc metabolism are highly compartmentalized and regulated. Yet, O-GlcNAc addition is subject to an additional and unique level of metabolic control. O-GlcNAc transfer is the terminal step in a "hexosamine signaling pathway" (HSP). In the HSP, levels of uridine 5'-diphosphate (UDP)-GlcNAc respond to nutrient excess to activate O-GlcNAcylation. Removal of O-GlcNAc may also be under similar metabolic regulation. Differentially targeted isoforms of the enzymes of O-GlcNAc metabolism allow the participation of O-GlcNAc in diverse intracellular functions. O-GlcNAc addition and removal are key to histone remodeling, transcription, proliferation, apoptosis, and proteasomal degradation. This nutrient-responsive signaling pathway also modulates important cellular pathways, including the insulin signaling cascade in animals and the gibberellin signaling pathway in plants. Alterations in O-GlcNAc metabolism are associated with various human diseases including diabetes mellitus and neurodegeneration. This review will focus on current approaches to deciphering the "O-GlcNAc code" in order to elucidate how O-GlcNAc participates in its diverse functions. This ongoing effort requires analysis of the enzymes of O-GlcNAc metabolism, their many targets, and how the O-GlcNAc modification may be regulated.
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Affiliation(s)
- Dona C Love
- Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA
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208
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Pekker I, Alvarez JP, Eshed Y. Auxin response factors mediate Arabidopsis organ asymmetry via modulation of KANADI activity. THE PLANT CELL 2005; 17:2899-910. [PMID: 16199616 PMCID: PMC1276018 DOI: 10.1105/tpc.105.034876] [Citation(s) in RCA: 366] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Members of the KANADI gene family in Arabidopsis thaliana regulate abaxial identity and laminar growth of lateral organs. Promoter APETALA3-mediated ectopic expression of KANADI restricts petal expansion and was used in a genetic screen for factors involved in KANADI-mediated signaling. Through this screen, mutations in ETTIN (ETT; also known as Auxin Response Factor3 [ARF3]) were isolated as second site suppressors and found to ameliorate ectopic KANADI activity throughout the plant as well. Mutant phenotypes of ett are restricted to flowers; however, double mutants with a closely related gene ARF4 exhibit transformation of abaxial tissues into adaxial ones in all aerial parts, resembling mutations in KANADI. Accordingly, the common RNA expression domain of both ARFs was found to be on the abaxial side of all lateral organs. Truncated, negatively acting gene products of strong ett alleles map to an ARF-specific, N-terminal domain of ETT. Such gene products strongly enhance abaxial tissue loss only when ARF activities are compromised. As KANADI is not required for either ETT or ARF4 transcription, and their overexpression cannot rescue kanadi mutants, cooperative activity is implied. ARF proteins are pivotal in mediating auxin responses; thus, we present a model linking transient local auxin gradients and gradual partitioning of lateral organs along the abaxial/adaxial axis.
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Affiliation(s)
- Irena Pekker
- Department of Plant Sciences, Weizman Institute of Science, Rehovot, 76100, Israel
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209
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Hudson A. Plant meristems: mobile mediators of cell fate. Curr Biol 2005; 15:R803-5. [PMID: 16213812 DOI: 10.1016/j.cub.2005.09.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
How do transcription factors control the fates of cells that express them? One class of plant transcription factors has recently been shown to function by regulating the synthesis of cytokinin and gibberellin hormones--mobile molecules more usually associated with long-distance signalling.
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Affiliation(s)
- Andrew Hudson
- Institute of Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, UK
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210
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Brenner WG, Romanov GA, Köllmer I, Bürkle L, Schmülling T. Immediate-early and delayed cytokinin response genes of Arabidopsis thaliana identified by genome-wide expression profiling reveal novel cytokinin-sensitive processes and suggest cytokinin action through transcriptional cascades. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2005; 44:314-33. [PMID: 16212609 DOI: 10.1111/j.1365-313x.2005.02530.x] [Citation(s) in RCA: 241] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Cytokinins are hormones that regulate many developmental and physiological processes in plants. Recent work has revealed that the cytokinin signal is transduced by two-component systems to the nucleus where target genes are activated. Most of the rapid transcriptional responses are unknown. We measured immediate-early and delayed cytokinin responses through genome-wide expression profiling with the Affymetrix ATH1 full genome array (Affymetrix Inc., Santa Clara, CA, USA). Fifteen minutes after cytokinin treatment of 5-day-old Arabidopsis seedlings, 71 genes were upregulated and 11 genes were downregulated. Immediate-early cytokinin response genes include a high portion of transcriptional regulators, among them six transcription factors that had previously not been linked to cytokinin. Five plastid transcripts were rapidly regulated as well, indicating a rapid transfer of the signal to plastids or direct perception of the cytokinin signal by plastids. After 2 h of cytokinin treatment genes coding for transcriptional regulators, signaling proteins, developmental and hormonal regulators, primary and secondary metabolism, energy generation and stress reactions were over-represented. A significant number of the responding genes are known to regulate light (PHYA, PSK1, CIP8, PAT1, APRR), auxin (Aux/IAA), ethylene (ETR2, EIN3, ERFs/EREBPs), gibberellin (GAI, RGA1, GA20 oxidase), nitrate (NTR2, NIA) and sugar (STP1, SUS1) dependent processes, indicating intense crosstalk with environmental cues, other hormones and metabolites. Analysis of cytokinin-deficient 35S:AtCKX1 transgenic seedlings has revealed additional, long-lasting cytokinin-sensitive changes of transcript abundance. Comparative overlay-analysis with the software tool mapman identified previously unknown cytokinin-sensitive metabolic genes, for example in the metabolism of trehalose-6-phosphate. Taken together, we present a genome-wide view of changes in cytokinin-responsive transcript abundance of genes that might be functionally relevant for the many biological processes that are governed by cytokinins.
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Affiliation(s)
- Wolfram G Brenner
- Max Planck-Institute for Molecular Genetics, Ihnestrasse 63-73, D-14195 Berlin, Germany
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211
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Chen D, Juárez S, Hartweck L, Alamillo JM, Simón-Mateo C, Pérez JJ, Fernández-Fernández MR, Olszewski NE, García JA. Identification of secret agent as the O-GlcNAc transferase that participates in Plum pox virus infection. J Virol 2005; 79:9381-7. [PMID: 16014901 PMCID: PMC1181581 DOI: 10.1128/jvi.79.15.9381-9387.2005] [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] [Received: 03/01/2005] [Accepted: 04/23/2005] [Indexed: 11/20/2022] Open
Abstract
Serine and threonine of many nuclear and cytoplasmic proteins are posttranslationally modified with O-linked N-acetylglucosamine (O-GlcNAc). This modification is made by O-linked N-acetylglucosamine transferases (OGTs). Genetic and biochemical data have demonstrated the existence of two OGTs of Arabidopsis thaliana, SECRET AGENT (SEC) and SPINDLY (SPY), with at least partly overlapping functions, but there is little information on their target proteins. The N terminus of the capsid protein (CP) of Plum pox virus (PPV) isolated from Nicotiana clevelandii is O-GlcNAc modified. We show here that O-GlcNAc modification of PPV CP also takes place in other plant hosts, N. benthamiana and Arabidopsis. PPV was able to infect the Arabidopsis OGT mutants sec-1, sec-2, and spy-3, but at early times of the infection, both rate of virus spread and accumulation were reduced in sec-1 and sec-2 relative to spy-3 and wild-type plants. By matrix-assisted laser desorption ionization-time of flight mass spectrometry, we determined that a 39-residue tryptic peptide from the N terminus of CP of PPV purified from the spy-3 mutant, but not sec-1 or sec-2, was O-GlcNAc modified, suggesting that SEC but not SPY modifies the capsid. While our results indicate that O-GlcNAc modification of PPV CP by SEC is not essential for infection, they show that the modification has a role(s) in the process.
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Affiliation(s)
- D Chen
- Department of Plant Molecular Genetics, Centro Nacional de Biotecnología (CSIC), Campus Universidad Autónoma de Madrid, Spain
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212
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Jiang H, Wang S, Dang L, Wang S, Chen H, Wu Y, Jiang X, Wu P. A novel short-root gene encodes a glucosamine-6-phosphate acetyltransferase required for maintaining normal root cell shape in rice. PLANT PHYSIOLOGY 2005; 138:232-42. [PMID: 15849305 PMCID: PMC1104178 DOI: 10.1104/pp.104.058248] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2004] [Revised: 02/25/2005] [Accepted: 03/15/2005] [Indexed: 05/07/2023]
Abstract
Glycosylation is a posttranslational modification occurring in many secreted and membrane-associated proteins in eukaryotes. It plays important roles in both physiological and pathological processes. Most of these protein modifications depend on UDP-N-acetylglucosamine. In this study, a T-DNA insertional rice (Oryza sativa) mutant exhibiting a temperature-sensitive defect in root elongation was isolated. Genetic and molecular analysis indicated that the mutated phenotype was caused by loss of function of a gene encoding a glucosamine-6-P acetyltransferase (designated OsGNA1), which is involved in de novo UDP-N-acetylglucosamine biosynthesis. The aberrant root morphology of the gna1 mutant includes shortening of roots, disruption of microtubules, and shrinkage of cells in the root elongation zone. Our observations support the idea that protein glycosylation plays a key role in cell metabolism, microtubule stabilization, and cell shape in rice roots.
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Affiliation(s)
- Huawu Jiang
- State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310029, People's Republic of China
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