651
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Organ regeneration does not require a functional stem cell niche in plants. Nature 2009; 457:1150-3. [PMID: 19182776 PMCID: PMC2649681 DOI: 10.1038/nature07597] [Citation(s) in RCA: 166] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 10/22/2008] [Indexed: 12/11/2022]
Abstract
Plants rely on the maintenance of stem cell niches at their apices for the continuous growth of roots and shoots. However, while the developmental plasticity of plant cells has been demonstrated1, it is not known whether the stem cell niche is required for organogenesis. Here we explore the capacity of a broad range of differentiating cells to regenerate an organ without the activity of a stem cell niche. Using a root-tip regeneration system in Arabidopsis to track the molecular and functional recovery of cell fates, we show that re-specification of lost cell identities begins within hours of excision and that the function of specialized cells is restored within one day. Critically, regeneration proceeds in plants with mutations that fail to maintain the stem cell niche. These results show that stem cell-like properties that mediate complete organ regeneration are dispersed in plant meristems and are not restricted to niches, which nonetheless appear necessary for indeterminate growth. This regenerative reprogramming of an entire organ without transition to a stereotypical stem cell environment has intriguing parallels to recent reports of induced transdifferentiation of specific cell types in the adult organs of animals2,3.
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652
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Cytokinin signaling during root development. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2009; 276:1-48. [PMID: 19584010 DOI: 10.1016/s1937-6448(09)76001-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The cytokinin class of phytohormones regulates division and differentiation of plant cells. They are perceived and signaled by a phosphorelay mechanism similar to those observed in prokaryotes. Research into the components of phosphorelay had previously been marred by genetic redundancy. However, recent studies have addressed this with the creation of high-order mutants. In addition, several new elements regulating cytokinin signaling have been identified. This has uncovered many roles in diverse developmental and physiological processes. In this review, we look at these processes specifically in the context of root development. We focus on the formation and maintenance of the root apical meristem, primary and secondary vascular development, lateral root emergence and development, and root nodulation. We believe that the root is an ideal organ with which to investigate cytokinin signaling in a wider context.
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653
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Capron A, Chatfield S, Provart N, Berleth T. Embryogenesis: pattern formation from a single cell. THE ARABIDOPSIS BOOK 2009; 7:e0126. [PMID: 22303250 PMCID: PMC3243344 DOI: 10.1199/tab.0126] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
During embryogenesis a single cell gives rise to a functional multicellular organism. In higher plants, as in many other multicellular systems, essential architectural features, such as body axes and major tissue layers are established early in embryogenesis and serve as a positional framework for subsequent pattern elaboration. In Arabidopsis, the apicalbasal axis and the radial pattern of tissues wrapped around it are already recognizable in young embryos of only about a hundred cells in size. This early axial pattern seems to provide a coordinate system for the embryonic initiation of shoot and root. Findings from genetic studies in Arabidopsis are revealing molecular mechanisms underlying the initial establishment of the axial core pattern and its subsequent elaboration into functional shoots and roots. The genetic programs operating in the early embryo organize functional cell patterns rapidly and reproducibly from minimal cell numbers. Understanding their molecular details could therefore greatly expand our ability to generate plant body patterns de novo, with important implications for plant breeding and biotechnology.
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Affiliation(s)
- Arnaud Capron
- Dept. of Cell and Systems Biology, University of Toronto, 25 Harbord St., Toronto, Ontario, M5S 3G5 Canada
- Each of these authors contributed equally. Address correspondence to or
| | - Steven Chatfield
- Dept. of Cell and Systems Biology, University of Toronto, 25 Harbord St., Toronto, Ontario, M5S 3G5 Canada
- Each of these authors contributed equally. Address correspondence to or
| | - Nicholas Provart
- Dept. of Cell and Systems Biology, University of Toronto, 25 Harbord St., Toronto, Ontario, M5S 3G5 Canada
| | - Thomas Berleth
- Dept. of Cell and Systems Biology, University of Toronto, 25 Harbord St., Toronto, Ontario, M5S 3G5 Canada
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654
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Yamagishi K, Tatematsu K, Yano R, Preston J, Kitamura S, Takahashi H, McCourt P, Kamiya Y, Nambara E. CHOTTO1, a Double AP2 Domain Protein of Arabidopsis thaliana, Regulates Germination and Seedling Growth Under Excess Supply of Glucose and Nitrate. ACTA ACUST UNITED AC 2008; 50:330-40. [DOI: 10.1093/pcp/pcn201] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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655
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Dello Ioio R, Nakamura K, Moubayidin L, Perilli S, Taniguchi M, Morita MT, Aoyama T, Costantino P, Sabatini S. A genetic framework for the control of cell division and differentiation in the root meristem. Science 2008; 322:1380-4. [PMID: 19039136 DOI: 10.1126/science.1164147] [Citation(s) in RCA: 602] [Impact Index Per Article: 37.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Plant growth and development are sustained by meristems. Meristem activity is controlled by auxin and cytokinin, two hormones whose interactions in determining a specific developmental output are still poorly understood. By means of a comprehensive genetic and molecular analysis in Arabidopsis, we show that a primary cytokinin-response transcription factor, ARR1, activates the gene SHY2/IAA3 (SHY2), a repressor of auxin signaling that negatively regulates the PIN auxin transport facilitator genes: thereby, cytokinin causes auxin redistribution, prompting cell differentiation. Conversely, auxin mediates degradation of the SHY2 protein, sustaining PIN activities and cell division. Thus, the cell differentiation and division balance necessary for controlling root meristem size and root growth is the result of the interaction between cytokinin and auxin through a simple regulatory circuit converging on the SHY2 gene.
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Affiliation(s)
- Raffaele Dello Ioio
- Dipartimento di Genetica e Biologia Molecolare, Laboratorio di Genomica e Proteomica Funzionale dei Sistemi Modello (FGPL), Università La Sapienza - Piazzale Aldo Moro 5, 00185 Rome, Italy
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656
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Abstract
Cell polarization is intimately linked to plant development, growth, and responses to the environment. Major advances have been made in our understanding of the signaling pathways and networks that regulate cell polarity in plants owing to recent studies on several model systems, e.g., tip growth in pollen tubes, cell morphogenesis in the leaf epidermis, and polar localization of PINs. From these studies we have learned that plant cells use conserved mechanisms such as Rho family GTPases to integrate both plant-specific and conserved polarity cues and to coordinate the cytoskeketon dynamics/reorganization and vesicular trafficking required for polarity establishment and maintenance. This review focuses upon signaling mechanisms for cell polarity formation in Arabidopsis, with an emphasis on Rho GTPase signaling in polarized cell growth and how these mechanisms compare with those for cell polarity signaling in yeast and animal systems.
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Affiliation(s)
- Zhenbiao Yang
- Center for Plant Cell Biology, Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124, USA.
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657
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Willemsen V, Bauch M, Bennett T, Campilho A, Wolkenfelt H, Xu J, Haseloff J, Scheres B. The NAC Domain Transcription Factors FEZ and SOMBRERO Control the Orientation of Cell Division Plane in Arabidopsis Root Stem Cells. Dev Cell 2008; 15:913-22. [DOI: 10.1016/j.devcel.2008.09.019] [Citation(s) in RCA: 185] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Revised: 09/05/2008] [Accepted: 09/29/2008] [Indexed: 12/18/2022]
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658
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Gao X, Nagawa S, Wang G, Yang Z. Cell polarity signaling: focus on polar auxin transport. MOLECULAR PLANT 2008; 1:899-909. [PMID: 19825591 PMCID: PMC2902905 DOI: 10.1093/mp/ssn069] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Polar auxin transport, which is required for the formation of auxin gradients and directional auxin flows that are critical for plant pattern formation, morphogenesis, and directional growth response to vectorial cues, is mediated by polarized sub-cellular distribution of PIN-FORMED Proteins (PINs, auxin efflux carriers), AUX1/AUX1-like proteins (auxin influx facilitators), and multidrug resistance P-glycoproteins (MDR/PGP). Polar localization of these proteins is controlled by both developmental and environmental cues. Recent studies have revealed cellular (endocytosis, transcytosis, and endosomal sorting and recycling) and molecular (PINOID kinase, protein phosphatase 2A) mechanisms underlying the polar distribution of these auxin transport proteins. Both TIR1-mediated auxin signaling and TIR1-independent auxin-mediated endocytosis have been shown to regulate polar PIN localization and auxin flow, implicating auxin as a self-organizing signal in directing polar transport and directional flows.
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Affiliation(s)
- Xiaowei Gao
- Key Laboratory of Arid and Grassland Agroeology at Lanzhou University, Ministry of Education, Lanzhou 730000, China
- CAU–UCR Joint Center for Biological Science, China Agricultural University, Beijing 100094, China
| | - Shingo Nagawa
- Center for Plant Cell Biology and Department of Botany and Plant Science, University of California, Riverside, CA 92521, USA
| | - Genxuan Wang
- College of Life Science, Zhejiang University, Hangzhou 310029, China
| | - Zhenbiao Yang
- CAU–UCR Joint Center for Biological Science, China Agricultural University, Beijing 100094, China
- Center for Plant Cell Biology and Department of Botany and Plant Science, University of California, Riverside, CA 92521, USA
- To whom correspondence should be addressed. E-mail , fax 9011-886-2-2651-6234, tel. 951-827-7351
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659
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Dhonukshe P, Tanaka H, Goh T, Ebine K, Mähönen AP, Prasad K, Blilou I, Geldner N, Xu J, Uemura T, Chory J, Ueda T, Nakano A, Scheres B, Friml J. Generation of cell polarity in plants links endocytosis, auxin distribution and cell fate decisions. Nature 2008; 456:962-6. [PMID: 18953331 DOI: 10.1038/nature07409] [Citation(s) in RCA: 209] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Accepted: 09/04/2008] [Indexed: 01/03/2023]
Abstract
Dynamically polarized membrane proteins define different cell boundaries and have an important role in intercellular communication-a vital feature of multicellular development. Efflux carriers for the signalling molecule auxin from the PIN family are landmarks of cell polarity in plants and have a crucial involvement in auxin distribution-dependent development including embryo patterning, organogenesis and tropisms. Polar PIN localization determines the direction of intercellular auxin flow, yet the mechanisms generating PIN polarity remain unclear. Here we identify an endocytosis-dependent mechanism of PIN polarity generation and analyse its developmental implications. Real-time PIN tracking showed that after synthesis, PINs are initially delivered to the plasma membrane in a non-polar manner and their polarity is established by subsequent endocytic recycling. Interference with PIN endocytosis either by auxin or by manipulation of the Arabidopsis Rab5 GTPase pathway prevents PIN polarization. Failure of PIN polarization transiently alters asymmetric auxin distribution during embryogenesis and increases the local auxin response in apical embryo regions. This results in ectopic expression of auxin pathway-associated root-forming master regulators in embryonic leaves and promotes homeotic transformation of leaves to roots. Our results indicate a two-step mechanism for the generation of PIN polar localization and the essential role of endocytosis in this process. It also highlights the link between endocytosis-dependent polarity of individual cells and auxin distribution-dependent cell fate establishment for multicellular patterning.
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Affiliation(s)
- Pankaj Dhonukshe
- Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands.
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660
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Iyer-Pascuzzi AS, Benfey PN. Transcriptional networks in root cell fate specification. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2008; 1789:315-25. [PMID: 18973837 DOI: 10.1016/j.bbagrm.2008.09.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Revised: 09/09/2008] [Accepted: 09/25/2008] [Indexed: 12/13/2022]
Abstract
Cell fate in the Arabidopsis root is determined by positional information mediated by plant hormones and interpreted by transcriptional networks. In this review, we summarize recent advances in our understanding of the regulatory networks that control cell fate within the root meristem, and in the interplay of these networks with phytohormones. Recent work describing the importance of chromatin organization in tissue patterning is also highlighted. A new, high resolution root expression map detailing the transciptome of nearly all cell types in the Arabidopsis root across developmental timepoints will provide a framework for understanding these networks.
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661
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Passarinho P, Ketelaar T, Xing M, van Arkel J, Maliepaard C, Hendriks MW, Joosen R, Lammers M, Herdies L, den Boer B, van der Geest L, Boutilier K. BABY BOOM target genes provide diverse entry points into cell proliferation and cell growth pathways. PLANT MOLECULAR BIOLOGY 2008; 68:225-37. [PMID: 18663586 DOI: 10.1007/s11103-008-9364-y] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Accepted: 06/05/2008] [Indexed: 05/22/2023]
Abstract
Ectopic expression of the Brassica napus BABY BOOM (BBM) AP2/ERF transcription factor is sufficient to induce spontaneous cell proliferation leading primarily to somatic embryogenesis, but also to organogenesis and callus formation. We used DNA microarray analysis in combination with a post-translationally regulated BBM:GR protein and cycloheximide to identify target genes that are directly activated by BBM expression in Arabidopsis seedlings. We show that BBM activated the expression of a largely uncharacterized set of genes encoding proteins with potential roles in transcription, cellular signaling, cell wall biosynthesis and targeted protein turnover. A number of the target genes have been shown to be expressed in meristems or to be involved in cell wall modifications associated with dividing/growing cells. One of the BBM target genes encodes an ADF/cofilin protein, ACTIN DEPOLYMERIZING FACTOR9 (ADF9). The consequences of BBM:GR activation on the actin cytoskeleton were followed using the GFP:FIMBRIN ACTIN BINDING DOMAIN2 (GFP:FABD) actin marker. Dexamethasone-mediated BBM:GR activation induced dramatic changes in actin organization resulting in the formation of dense actin networks with high turnover rates, a phenotype that is consistent with cells that are rapidly undergoing cytoplasmic reorganization. Together the data suggest that the BBM transcription factor activates a complex network of developmental pathways associated with cell proliferation and growth.
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Affiliation(s)
- Paul Passarinho
- Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands
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662
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Chuck G, Meeley R, Hake S. Floral meristem initiation and meristem cell fate are regulated by the maize AP2 genes ids1 and sid1. Development 2008; 135:3013-9. [PMID: 18701544 DOI: 10.1242/dev.024273] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Grass flowers are organized on small branches known as spikelets. In maize, the spikelet meristem is determinate, producing one floral meristem and then converting into a second floral meristem. The APETALA2 (AP2)-like gene indeterminate spikelet1 (ids1) is required for the timely conversion of the spikelet meristem into the floral meristem. Ectopic expression of ids1 in the tassel, resulting from a failure of regulation by the tasselseed4 microRNA, causes feminization and the formation of extra floral meristems. Here we show that ids1 and the related gene, sister of indeterminate spikelet1 (sid1), play multiple roles in inflorescence architecture in maize. Both genes are needed for branching of the inflorescence meristem, to initiate floral meristems and to control spikelet meristem determinacy. We show that reducing the levels of ids1 and sid1 fully suppresses the tasselseed4 phenotype, suggesting that these genes are major targets of this microRNA. Finally, sid1 and ids1 repress AGAMOUS-like MADS-box transcription factors within the lateral organs of the spikelet, similar to the function of AP2 in Arabidopsis, where it is required for floral organ fate. Thus, although the targets of the AP2 genes are conserved between maize and Arabidopsis, the genes themselves have adopted novel meristem functions in monocots.
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Affiliation(s)
- George Chuck
- Plant Gene Expression Center, United States Department of Agriculture - Agriculture Research Service and the University of California, Albany, CA 94710, USA.
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663
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Song SK, Hofhuis H, Lee MM, Clark SE. Key divisions in the early Arabidopsis embryo require POL and PLL1 phosphatases to establish the root stem cell organizer and vascular axis. Dev Cell 2008; 15:98-109. [PMID: 18606144 DOI: 10.1016/j.devcel.2008.05.008] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Revised: 04/15/2008] [Accepted: 05/16/2008] [Indexed: 11/17/2022]
Abstract
Arabidopsis development proceeds from three stem cell populations located at the shoot, flower, and root meristems. The relationship between the highly related shoot and flower stem cells and the very divergent root stem cells has been unclear. We show that the related phosphatases POL and PLL1 are required for all three stem cell populations. pol pll1 mutant embryos lack key asymmetric divisions that give rise to the root stem cell organizer and the central vascular axis. Instead, these cells divide in a superficially symmetric fashion in pol pll1 embryos, leading to a loss of embryonic and postembryonic root stem cells and vascular specification. We present data that show that POL/PLL1 drive root stem cell specification by promoting expression of the WUS homolog WOX5. We propose that POL and PLL1 are required for the proper divisions of shoot, flower, and root stem cell organizers, WUS/WOX5 gene expression, and stem cell maintenance.
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Affiliation(s)
- Sang-Kee Song
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
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664
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Petricka JJ, Benfey PN. Root layers: complex regulation of developmental patterning. Curr Opin Genet Dev 2008; 18:354-61. [PMID: 18617392 PMCID: PMC2605625 DOI: 10.1016/j.gde.2008.05.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2008] [Revised: 05/17/2008] [Accepted: 05/22/2008] [Indexed: 11/29/2022]
Abstract
Developmental patterning events involve cell fate specification and maintenance processes in diverse, multicellular organisms. The simple arrangement of tissue layers in the Arabidopsis thaliana root provides a highly tractable system for the study of these processes. This review highlights recent work addressing the patterning of root tissues focusing on the factors involved and their complex regulation. In the past two years studies of root patterning have indicated that chromatin remodeling, protein movement, transcriptional networks, and an auxin gradient, all contribute to the complexity inherent in developmental patterning events within the root. As a result, future research advances in this field will require tissue-specific information at both the single gene and global level.
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Affiliation(s)
- Jalean J. Petricka
- Biology Department, IGSP Center for Systems Biology, Duke University, 124 Science Drive, FFSC 4101, Durham, NC 27708, Fax: 919-660-7338, 919-613-8182 (Philip Benfey), , 919-613-8203 (Jalean Petricka),
| | - Philip N. Benfey
- Biology Department, IGSP Center for Systems Biology, Duke University, 124 Science Drive, FFSC 4101, Durham, NC 27708, Fax: 919-660-7338, 919-613-8182 (Philip Benfey), , 919-613-8203 (Jalean Petricka),
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665
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Camacho-Cristóbal JJ, Rexach J, Conéjéro G, Al-Ghazi Y, Nacry P, Doumas P. PRD, an Arabidopsis AINTEGUMENTA-like gene, is involved in root architectural changes in response to phosphate starvation. PLANTA 2008; 228:511-22. [PMID: 18506479 DOI: 10.1007/s00425-008-0754-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Accepted: 05/09/2008] [Indexed: 05/08/2023]
Abstract
Changes in root architecture are one of the adaptive strategies used by plants to compensate for local phosphate (Pi) deficiency in soils. Root architecture variables triggered by Pi availability are well documented in Arabidopsis (Arabidopsis thaliana), but the molecular mechanisms behind these adaptive responses remain to be elucidated. By the use of transcriptomic and quantitative RT-PCR analysis, we observed that an AINTEGUMENTA-like gene, named PRD for Phosphate Root Development, was rapidly repressed in roots under low Pi conditions. The physiological function of the PRD gene was analyzed through the null allele mutant prd, which displayed less development of primary and lateral roots under Pi-starvation conditions than wild-type plants. Complementation of the prd mutant with the wild-type gene led to a similar response to Pi starvation as wild-type plants, indicating the complete rescue of the mutant phenotype. These results suggest that PRD gene is involved in the regulation of root architectural responses to Pi starvation by controlling primary and lateral root elongation. This model is in agreement with the tissue-specific pattern of PRD gene expression, which was observed to occur specifically in the apex in both the primary and lateral roots. However, Pi influx, anionic profiles and root expression of genes typically induced by Pi starvation, such as high affinity Pi transporters (PHT1;1 and PHT1;4) and an acid phosphatase (AtACP5), were similar in wild type and prd plants in response to Pi starvation. These results support the hypothesis that the PRD gene is not a checkpoint for Pi-starvation responses, but acts specifically as a regulator of root architectural responses to Pi starvation.
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Affiliation(s)
- Juan José Camacho-Cristóbal
- Departamento de Fisiología, Anatomía y Biología Celular, Facultad de Ciencias Experimentales, Universidad Pablo de Olavide, 41013, Sevilla, Spain
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666
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Sato A, Yamamoto KT. What's the physiological role of domain II-less Aux/IAA proteins? PLANT SIGNALING & BEHAVIOR 2008; 3:496-497. [PMID: 19704497 PMCID: PMC2634441 DOI: 10.4161/psb.3.7.5994] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2008] [Accepted: 03/31/2008] [Indexed: 05/26/2023]
Abstract
Arabidopsis has Aux/IAA proteins that lack domain II which is a binding site for the TIR1 auxin receptor. These proteins have been shown to be more stable than the canonical Aux/IAA proteins. We investigated the phenotypes of overexpression lines of domain II-less Aux/IAA proteins, IAA20 and IAA30, by the use of 35S promoter. The transgenic lines showed many aberrant phenotypes in auxin physiology. The most conspicuous phenotype was collapse of the root apical meristem as occurred in plt1 plt2 double mutants. Because IAA20 and IAA30 were early auxin-inducible and were expressed in the root apical meristem, they may have a physiological role in maintaining the stem cell niche of root, by keeping the activity of MP/ARF5 and NPH4/ARF7 at an acceptable level. On the other hand, domain-II less Aux/IAA proteins are not present in balck cottonwood tree or grapevine, suggesting wide diversification of Aux/IAA proteins in higher plants.
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Affiliation(s)
- Atsuko Sato
- Division of Biosphere Science; Graduate School of Environmental Science; Hokkaido University; Sapporo, Japan
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667
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Mantiri FR, Kurdyukov S, Chen SK, Rose RJ. The transcription factor MtSERF1 may function as a nexus between stress and development in somatic embryogenesis in Medicago truncatula. PLANT SIGNALING & BEHAVIOR 2008; 3:498-500. [PMID: 19704498 PMCID: PMC2634442 DOI: 10.4161/psb.3.7.6049] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2008] [Accepted: 04/04/2008] [Indexed: 05/07/2023]
Abstract
In Medicago truncatula high rates of somatic embryo formation can be induced in the Jemalong genotype 2HA by application of the hormones auxin and cytokinin. Biosynthesis of the stress-related hormone ethylene is also necessary for somatic embryogenesis (SE) and is most likely a response to wounding and the presence of auxin in the medium. We have demonstrated that expression of a gene designated Mt SOMATIC EMBRYO RELATED FACTOR 1 (MtSERF1) induced by ethylene, in the presence of auxin plus cytokinin, is essential for SE. The promoter region of this transcription factor, a member of the ERF sub-family of the AP2/ERF super family, contains putative binding sites relating to auxin and cytokinin in addition to ethylene. An additional finding was the presence of WUSCHEL (WUS) binding sites in the MtSERF1 promoter region, which is discussed. Here we also discuss the Medicago data in the context of embryogenesis studies in Arabidopsis and suggest that MtSERF1 has a key developmental role, possibly in conjunction with WUS, in regulating downstream genes required for the initiation of SE.
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668
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Sato A, Yamamoto KT. Overexpression of the non-canonical Aux/IAA genes causes auxin-related aberrant phenotypes in Arabidopsis. PHYSIOLOGIA PLANTARUM 2008; 133:397-405. [PMID: 18298415 DOI: 10.1111/j.1399-3054.2008.01055.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Degradation of Aux/IAA proteins which are triggered by the ubiquitin ligase complex containing the auxin F-box receptors (AFBs), is thought to be the primary reaction of auxin signaling. Upon auxin perception, AFBs bind domain II of Aux/IAA proteins that is conserved in most of the 29 family members in Arabidopsis. However, IAA20 and IAA30 lack domain II. Furthermore, IAA31, which forms a single clade with IAA20 and IAA30 in Aux/IAA protein family, has a partially conserved domain II, which contains an amino acid substitution that would cause a dominant mutation of Aux/IAA genes. It has been shown that the half-lives of these proteins are much longer than those of the canonical Aux/IAA proteins. We generated overexpression lines (OXs) of IAA20, IAA30 and IAA31 by the use of cauliflower mosaic virus 35S promoter to better understand the molecular function of atypical Aux/IAA proteins in Arabidopsis. OXs of the three genes exhibited similar auxin-related aberrant phenotypes, with IAA20 OX showing the most severe defects: Some of them showed a semi-dwarf phenotype; gravitropic growth orientation was often affected in hypocotyl and root; vasculature of cotyledons was malformed; the primary root stopped growing soon after germination because of collapse of root apical meristem. IAA 20 and IAA30 were early auxin inducible, but IAA31 was not. These results showed that the wild-type genes of the three Aux/IAAs could disturb auxin physiology when ectopically overexpressed.
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Affiliation(s)
- Atsuko Sato
- Division of Biological Sciences, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan
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669
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Nakielski J. The tensor-based model for growth and cell divisions of the root apex. I. The significance of principal directions. PLANTA 2008; 228:179-89. [PMID: 18365249 DOI: 10.1007/s00425-008-0728-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Accepted: 02/15/2008] [Indexed: 05/08/2023]
Abstract
Plant organs grow symplastically, i.e. in a continuous and coordinated way. Such growth is of a tensor nature, which is manifested in the property that at every point of the organ three mutually orthogonal principal growth directions (PDG) can be recognized. The PDGs are postulated to affect orientation of cell divisions. This paper shows for the first time the 2D simulation model for growth in which cells divide taking into account the PDGs. The model, conceptually based on the growth tensor (GT), is applied to the root apex of radish, having a quiescent centre (QC). It shows the simulation of how exemplary cell pattern of the real root apex develops in time. The results provide satisfactory description of the root growth. The computer-generated cell pattern is realistic and more or less steady indicating that PDGs are important for growth. Presumably cells detect PDGs and obey them in the course of cell divisions. Computer generated division walls, perpendicular to PDGs, form periclinal and anticlinal zigzags as regular as those observed in microscopic sections. Growth tensor defines a field of growth rates at the organ level. QC, fundamental in this field, determines the group of quiescent initial cells which is, in turn, surrounded by active functional initials, from which all tissues of the root apex originate. The present simulations have shown that stability of generated cell pattern depends on whether the group of the functional initials is permanent; if this is not the case, the cell wall pattern changes in accordance with PDGs.
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Affiliation(s)
- Jerzy Nakielski
- Department of Biophysics and Cell Biology, University of Silesia, Jagiellońska 28, 40-032, Katowice, Poland.
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670
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Abstract
Recent studies show that, in plant roots, mutually dependent regulatory mechanisms operating at cell and tissue levels interact to generate a self-sustaining distribution of the hormone auxin which provides a framework for developmental patterning and growth.
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Affiliation(s)
- Peter Doerner
- Institute for Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JH, UK.
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671
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Müller B, Sheen J. Cytokinin and auxin interaction in root stem-cell specification during early embryogenesis. Nature 2008; 453:1094-7. [PMID: 18463635 DOI: 10.1038/nature06943] [Citation(s) in RCA: 460] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2008] [Accepted: 03/25/2008] [Indexed: 11/09/2022]
Abstract
Plant stem-cell pools, the source for all organs, are first established during embryogenesis. It has been known for decades that cytokinin and auxin interact to control organ regeneration in cultured tissue. Auxin has a critical role in root stem-cell specification in zygotic embryogenesis, but the early embryonic function of cytokinin is obscure. Here, we introduce a synthetic reporter to visualize universally cytokinin output in vivo. Notably, the first embryonic signal is detected in the hypophysis, the founder cell of the root stem-cell system. Its apical daughter cell, the precursor of the quiescent centre, maintains phosphorelay activity, whereas the basal daughter cell represses signalling output. Auxin activity levels, however, exhibit the inverse profile. Furthermore, we show that auxin antagonizes cytokinin output in the basal cell lineage by direct transcriptional activation of ARABIDOPSIS RESPONSE REGULATOR genes, ARR7 and ARR15, feedback repressors of cytokinin signalling. Loss of ARR7 and ARR15 function or ectopic cytokinin signalling in the basal cell during early embryogenesis results in a defective root stem-cell system. These results provide a molecular model of transient and antagonistic interaction between auxin and cytokinin critical for specifying the first root stem-cell niche.
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Affiliation(s)
- Bruno Müller
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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672
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Abstract
The molecular-genetic cues that regulate plant embryo pattern formation are the subject of intense scrutiny at present. Recent work in Arabidopsis implicates the TOPLESS protein in auxin-dependent transcriptional repression, highlighting once again the crucial role of auxin signaling during embryogenesis.
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Affiliation(s)
- Karen S Osmont
- Department of Plant Molecular Biology, University of Lausanne, Biophore Building, CH-1015 Lausanne, Switzerland
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673
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Saiga S, Furumizu C, Yokoyama R, Kurata T, Sato S, Kato T, Tabata S, Suzuki M, Komeda Y. The Arabidopsis OBERON1 and OBERON2 genes encode plant homeodomain finger proteins and are required for apical meristem maintenance. Development 2008; 135:1751-9. [PMID: 18403411 DOI: 10.1242/dev.014993] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Maintenance of the stem cell population located at the apical meristems is essential for repetitive organ initiation during the development of higher plants. Here, we have characterized the roles of OBERON1 (OBE1) and its paralog OBERON2 (OBE2), which encode plant homeodomain finger proteins, in the maintenance and/or establishment of the meristems in Arabidopsis. Although the obe1 and obe2 single mutants were indistinguishable from wild-type plants, the obe1 obe2 double mutant displayed premature termination of the shoot meristem, suggesting that OBE1 and OBE2 function redundantly. Further analyses revealed that OBE1 and OBE2 allow the plant cells to acquire meristematic activity via the WUSCHEL-CLAVATA pathway, which is required for the maintenance of the stem cell population, and they function parallel to the SHOOT MERISTEMLESS gene, which is required for preventing cell differentiation in the shoot meristem. In addition, obe1 obe2 mutants failed to establish the root apical meristem, lacking both the initial cells and the quiescent center. In situ hybridization revealed that expression of PLETHORA and SCARECROW, which are required for stem cell specification and maintenance in the root meristem, was lost from obe1 obe2 mutant embryos. Taken together, these data suggest that the OBE1 and OBE2 genes are functionally redundant and crucial for the maintenance and/or establishment of both the shoot and root meristems.
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Affiliation(s)
- Shunsuke Saiga
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
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674
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Nilsson J, Karlberg A, Antti H, Lopez-Vernaza M, Mellerowicz E, Perrot-Rechenmann C, Sandberg G, Bhalerao RP. Dissecting the molecular basis of the regulation of wood formation by auxin in hybrid aspen. THE PLANT CELL 2008; 20:843-55. [PMID: 18424614 PMCID: PMC2390731 DOI: 10.1105/tpc.107.055798] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2007] [Revised: 02/29/2008] [Accepted: 04/01/2008] [Indexed: 05/18/2023]
Abstract
Indole acetic acid (auxin) is a key regulator of wood formation, and an observed overlap between auxin concentration gradient and developing secondary xylem cells has led to the hypothesis that auxin regulates wood formation by acting as a morphogen. We dissected the role of auxin in wood formation by identifying the auxin-responsive transcriptome in wood-forming tissues and investigating alterations in wood formation in transgenic hybrid aspen plants (Populus tremula x Populus tremuloides) with perturbed auxin signaling. We showed that auxin-responsive genes in wood-forming tissues respond dynamically to changes in cellular auxin levels. However, the expression patterns of most of the auxin-responsive genes displayed limited correlation with the auxin concentration across this developmental zone. Perturbing auxin signaling by reducing auxin responsiveness reduced the cambial cell division activity, caused spatial deregulation of cell division of the cambial initials, and led to reductions in not only radial but also axial dimensions of fibers and vessels. We propose that, instead of acting as a morphogen, changes in auxin concentration in developing secondary xylem cells may provide important regulatory cues that modulate the expression of a few key regulators; these, in turn, may control the global gene expression patterns that are essential for normal secondary xylem development.
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Affiliation(s)
- Jeanette Nilsson
- Umeå Plant Science Centre, Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-90183 Umeå, Sweden
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675
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Teale WD, Ditengou FA, Dovzhenko AD, Li X, Molendijk AM, Ruperti B, Paponov I, Palme K. Auxin as a model for the integration of hormonal signal processing and transduction. MOLECULAR PLANT 2008; 1:229-37. [PMID: 19825535 DOI: 10.1093/mp/ssn006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The regulation of plant growth responds to many stimuli. These responses allow environmental adaptation, thereby increasing fitness. In many cases, the relay of information about a plant's environment is through plant hormones. These messengers integrate environmental information into developmental pathways to determine plant shape. This review will use, as an example, auxin in the root of Arabidopsis thaliana to illustrate the complex nature of hormonal signal processing and transduction. It will then make the case that the application of a systems-biology approach is necessary, if the relationship between a plant's environment and its growth/developmental responses is to be properly understood.
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Affiliation(s)
- W D Teale
- Institute of Biology II, Faculty of Biology, University of Freiburg, D-79104 Freiburg, Germany
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676
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Tapia-López R, García-Ponce B, Dubrovsky JG, Garay-Arroyo A, Pérez-Ruíz RV, Kim SH, Acevedo F, Pelaz S, Alvarez-Buylla ER. An AGAMOUS-related MADS-box gene, XAL1 (AGL12), regulates root meristem cell proliferation and flowering transition in Arabidopsis. PLANT PHYSIOLOGY 2008; 146:1182-92. [PMID: 18203871 PMCID: PMC2259045 DOI: 10.1104/pp.107.108647] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2007] [Accepted: 01/11/2008] [Indexed: 05/18/2023]
Abstract
MADS-box genes are key components of the networks that control the transition to flowering and flower development, but their role in vegetative development is poorly understood. This article shows that the sister gene of the AGAMOUS (AG) clade, AGL12, has an important role in root development as well as in flowering transition. We isolated three mutant alleles for AGL12, which is renamed here as XAANTAL1 (XAL1): Two alleles, xal1-1 and xal1-2, are in Columbia ecotype and xal1-3 is in Landsberg erecta ecotype. All alleles have a short-root phenotype with a smaller meristem, lower rate of cell production, and abnormal root apical meristem organization. Interestingly, we also encountered a significantly longer cell cycle in the strongest xal1 alleles with respect to wild-type plants. Expression analyses confirmed the presence of XAL1 transcripts in roots, particularly in the phloem. Moreover, XAL1beta-glucuronidase expression was specifically up-regulated by auxins in this tissue. In addition, mRNA in situ hybridization showed that XAL1 transcripts were also found in leaves and floral meristems of wild-type plants. This expression correlates with the late-flowering phenotypes of the xal1 mutants grown under long days. Transcript expression analysis suggests that XAL1 is an upstream regulator of SOC, FLOWERING LOCUS T, and LFY. We propose that XAL1 may have similar roles in both root and aerial meristems that could explain the xal1 late-flowering phenotype.
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Affiliation(s)
- Rosalinda Tapia-López
- Laboratorio de Genética Molecular, Desarrollo y Evolución de Plantas, Instituto de Ecología, Universidad Nacional Autónoma de México, Ciudad Universitaria, México DF, Mexico
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677
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678
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Dello Ioio R, Linhares FS, Sabatini S. Emerging role of cytokinin as a regulator of cellular differentiation. CURRENT OPINION IN PLANT BIOLOGY 2008; 11:23-7. [PMID: 18060829 DOI: 10.1016/j.pbi.2007.10.006] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2007] [Revised: 10/10/2007] [Accepted: 10/10/2007] [Indexed: 05/23/2023]
Abstract
Perhaps the most amazing feature of plants is their ability to grow and regenerate for years, sometimes even centuries. This fascinating characteristic is achieved thanks to the activity of stem cells, which reside in the shoot and root apical meristems. Stem cells function as a reserve of undifferentiated cells to replace organs and sustain postembryonic plant growth. To maintain meristem function, stem cells have to generate new cells at a rate similar to that of cells leaving the meristem and differentiating, thus achieving a balance between cell division and cell differentiation. Recent findings have improved our knowledge on the molecular mechanisms necessary to establish this balance and reveal a fundamental signaling role for the plant hormone cytokinin. Evidence has been provided to show that in the root meristem cytokinin acts in defined developmental domains to control cell differentiation rate, thus controlling root meristem size.
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Affiliation(s)
- Raffaele Dello Ioio
- Dipartimento di Genetica e Biologia Molecolare, Laboratory of Functional Genomics and Proteomics of Model Systems, Università La Sapienza, P.le Aldo Moro 5, 00185 Rome, Italy
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679
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Nawy T, Lukowitz W, Bayer M. Talk global, act local-patterning the Arabidopsis embryo. CURRENT OPINION IN PLANT BIOLOGY 2008; 11:28-33. [PMID: 18060828 DOI: 10.1016/j.pbi.2007.10.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 10/10/2007] [Accepted: 10/11/2007] [Indexed: 05/25/2023]
Abstract
The primary axis and main tissue types of Arabidopsis are laid down in the early embryo. Apical-to-basal auxin flux functions as a global organizer of the axis, and recent reports are clarifying our mechanistic understanding of how a graded auxin distribution is generated and interpreted. Polar targeting of PIN transporters in the cells of the embryo is dynamic and linked to their phosphorylation status, suggesting a flexible mechanism for regulating auxin flux in space and time. PLETHORA transcription factors then interpret the graded auxin distribution to provide positional values along the axis in a dose-dependent manner. A comparable framework for tissue patterning in the radial dimension is still lacking, although cell surface signaling probably plays a key role.
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Affiliation(s)
- Tal Nawy
- Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, United States.
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680
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Abstract
The organs of multicellular species consist of cell types that must function together to perform specific tasks. One critical organ function is responding to internal or external change. Some cell-specific responses to changes in environmental conditions are known, but the scale of cell-specific responses within an entire organ as it perceives an environmental flux has not been well characterized in plants or any other multicellular organism. Here, we use cellular profiling of five Arabidopsis root cell types in response to an influx of a critical resource, nitrogen, to uncover a vast and predominantly cell-specific response. We show that cell-specific profiling increases sensitivity several-fold, revealing highly localized regulation of transcripts that were largely hidden from previous global analyses. The cell-specific data revealed responses that suggested a coordinated developmental response in distinct cell types or tissues. One example is the cell-specific regulation of a transcriptional circuit that we showed mediates lateral root outgrowth in response to nitrogen via microRNA167, linking small RNAs to nitrogen responses. Together, these results reveal a previously cryptic component of cell-specific responses to nitrogen. Thus, the results make an important advance in our understanding of how multicellular organisms cope with environmental change at the cell level.
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681
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Abstract
The phytohormone auxin is a key factor in plant growth and development. Forward and reverse genetic strategies have identified important molecular components in auxin perception, signaling, and transport. These advances resulted in the identification of some of the underlying regulatory mechanisms as well as the emergence of functional frameworks for auxin action. This review focuses on the feedback loops that form an integrative part of these regulatory mechanisms.
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Affiliation(s)
- René Benjamins
- Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands.
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682
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Gong W, He K, Covington M, Dinesh-Kumar SP, Snyder M, Harmer SL, Zhu YX, Deng XW. The development of protein microarrays and their applications in DNA-protein and protein-protein interaction analyses of Arabidopsis transcription factors. MOLECULAR PLANT 2008; 1:27-41. [PMID: 19802365 PMCID: PMC2756181 DOI: 10.1093/mp/ssm009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We used our collection of Arabidopsis transcription factor (TF) ORFeome clones to construct protein microarrays containing as many as 802 TF proteins. These protein microarrays were used for both protein-DNA and protein-protein interaction analyses. For protein-DNA interaction studies, we examined AP2/ERF family TFs and their cognate cis-elements. By careful comparison of the DNA-binding specificity of 13 TFs on the protein microarray with previous non-microarray data, we showed that protein microarrays provide an efficient and high throughput tool for genome-wide analysis of TF-DNA interactions. This microarray protein-DNA interaction analysis allowed us to derive a comprehensive view of DNA-binding profiles of AP2/ERF family proteins in Arabidopsis. It also revealed four TFs that bound the EE (evening element) and had the expected phased gene expression under clock-regulation, thus providing a basis for further functional analysis of their roles in clock regulation of gene expression. We also developed procedures for detecting protein interactions using this TF protein microarray and discovered four novel partners that interact with HY5, which can be validated by yeast two-hybrid assays. Thus, plant TF protein microarrays offer an attractive high-throughput alternative to traditional techniques for TF functional characterization on a global scale.
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Affiliation(s)
- Wei Gong
- Peking-Yale Joint Center for Plant Molecular Genetics and Agrobiotechnology, College of Life Sciences, Peking University, Beijing 100871, China
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683
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Abstract
Embryogenesis in higher plants consists of two major phases, morphogenesis and maturation. Morphogenesis involves the establishment of the embryo's body plan, whereas maturation involves cell expansion and accumulation of storage macromolecules to prepare for desiccation, germination and early seedling growth. Arabidopsis mutants showing defects in embryogenesis have provided information for understanding the events that govern embryo formation through molecular, genetic and biochemical analyses. Thus, many of the processes that underlie embryogenesis are beginning to be understood. In this chapter, we focus on genes that play key roles in the morphogenesis phase of Arabidopsis embryogenesis.
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Affiliation(s)
- Soomin Park
- Horticultural Biotechnology Division, National Horticultral Research Institute, Republic of Korea
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684
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Pérez-Pérez JM, Serralbo O, Vanstraelen M, González C, Criqui MC, Genschik P, Kondorosi E, Scheres B. Specialization of CDC27 function in the Arabidopsis thaliana anaphase-promoting complex (APC/C). THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2008; 53:78-89. [PMID: 17944809 DOI: 10.1111/j.1365-313x.2007.03312.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
To investigate the specialization of the two Arabidopsis CDC27 subunits in the anaphase-promoting complex (APC/C), we analyzed novel alleles of HBT/CDC27B and CDC27A, and characterized the expression of complementing HOBBIT (HBT) protein fusions in plant meristems and during the cell cycle. In contrast to other APC/C mutants, which are gametophytic lethal, phenotypes of weak and null hbt alleles indicate a primary role in the control of post-embryonic cell division and cell elongation, whereas cdc27a nulls are phenotypically indistinguishable from the wild type. However, cdc27a hbt double-mutant gametes are non-viable, indicating a redundant requirement for both CDC27 subunits during gametogenesis. Yeast-two-hybrid and pulldown studies with APC/C components suggest that the two Arabidopsis CDC27 subunits participate in several complexes that are differentially required during plant development. Loss-of-function analysis, as well as cyclin B reporter protein accumulation, indicates a conserved role for the plant APC/C in controlling mitotic progression and cell differentiation during the entire life cycle.
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Affiliation(s)
- José M Pérez-Pérez
- Department of Molecular Genetics, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
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685
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Bloch D, Hazak O, Lavy M, Yalovsky S. A novel ROP/RAC GTPase effector integrates plant cell form and pattern formation. PLANT SIGNALING & BEHAVIOR 2008; 3:41-3. [PMID: 19704766 PMCID: PMC2633956 DOI: 10.4161/psb.3.1.4838] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2007] [Accepted: 08/06/2007] [Indexed: 05/03/2023]
Abstract
ROPs/RACs are the only known signaling Ras superfamily small GTPases in plants. As such they have been suggested to function as central regulators of diverse signaling cascades. The ROP/RAC signaling networks are largely unknown, however, because only few of their effector proteins have been identified. In a paper that was published in the June 5, 2007 issue of Current Biology we described the identification of a novel ROP/RAC effector designated ICR1 (Interactor of Constitutive active ROPs 1). We demonstrated that ICR1 functions as a scaffold that interacts with diverse but specific group of proteins including SEC3 subunit of the exocyst vesicle tethering complex. ICR1-SEC3 complexes can interact with ROPs in vivo and are thereby recruited to the plasma membrane. ICR1 knockdown or silencing leads to cell deformation and loss of the root stem cells population, and ectopic expression of ICR1 phenocopies activated ROPs/RACs. ICR1 presents a new paradigm in ROP/RAC signaling and integrates mechanisms regulating cell form and pattern formation at the whole plant level.
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Affiliation(s)
- Daria Bloch
- Department of Plant Sciences; Tel Aviv University; Tel Aviv, Israel
| | - Ora Hazak
- Department of Plant Sciences; Tel Aviv University; Tel Aviv, Israel
| | - Meirav Lavy
- Department of Biology; Indiana University; Bloomington, Indiana USA
| | - Shaul Yalovsky
- Department of Plant Sciences; Tel Aviv University; Tel Aviv, Israel
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686
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Abstract
Early embryonic development in the flowering plant Arabidopsis thaliana follows a predictable sequence of cell divisions. Anatomical hallmarks and the expression of marker genes in dynamic patterns indicate that new cell fates are established with virtually every round of mitosis. Although some of the factors regulating these early patterning events have been identified, the overall process remains relatively poorly understood. Starting at the globular stage, when the embryo has approximately 100 cells, the organization of development appears to be taken over by programs that regulate postembryonic patterning throughout the life cycle.
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Affiliation(s)
- Pablo D Jenik
- Carnegie Institution, Department of Plant Biology, Stanford University, Stanford, CA 94305, USA.
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687
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Sablowski R. The dynamic plant stem cell niches. CURRENT OPINION IN PLANT BIOLOGY 2007; 10:639-44. [PMID: 17692560 DOI: 10.1016/j.pbi.2007.07.001] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2007] [Revised: 07/02/2007] [Accepted: 07/03/2007] [Indexed: 05/16/2023]
Abstract
Stem cells exist in specific locations called niches, where extracellular signals maintain stem cell division and prevent differentiation. In plants, the best characterised niches are within the shoot and root meristems. Networks of regulatory genes and intercellular signals maintain meristem structure in spite of constant cell displacement by division. Recent works have improved our understanding of how these networks function at the cellular and molecular levels, particularly in the control of the stem cell population in the shoot meristem. The meristem regulatory genes have been found to function partly through localised control of widely used signals such as cytokinin and auxin. The retinoblastoma protein has also emerged as a key regulator of cell differentiation in the meristems.
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Affiliation(s)
- Robert Sablowski
- Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom.
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688
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Grieneisen VA, Xu J, Marée AFM, Hogeweg P, Scheres B. Auxin transport is sufficient to generate a maximum and gradient guiding root growth. Nature 2007; 449:1008-13. [PMID: 17960234 DOI: 10.1038/nature06215] [Citation(s) in RCA: 559] [Impact Index Per Article: 32.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2007] [Accepted: 09/03/2007] [Indexed: 11/09/2022]
Abstract
The plant growth regulator auxin controls cell identity, cell division and cell expansion. Auxin efflux facilitators (PINs) are associated with auxin maxima in distal regions of both shoots and roots. Here we model diffusion and PIN-facilitated auxin transport in and across cells within a structured root layout. In our model, the stable accumulation of auxin in a distal maximum emerges from the auxin flux pattern. We have experimentally tested model predictions of robustness and self-organization. Our model explains pattern formation and morphogenesis at timescales from seconds to weeks, and can be understood by conceptualizing the root as an 'auxin capacitor'. A robust auxin gradient associated with the maximum, in combination with separable roles of auxin in cell division and cell expansion, is able to explain the formation, maintenance and growth of sharply bounded meristematic and elongation zones. Directional permeability and diffusion can fully account for stable auxin maxima and gradients that can instruct morphogenesis.
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Affiliation(s)
- Verônica A Grieneisen
- Theoretical Biology and Bioinformatics, Department of Biology, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
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689
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Welch D, Hassan H, Blilou I, Immink R, Heidstra R, Scheres B. Arabidopsis JACKDAW and MAGPIE zinc finger proteins delimit asymmetric cell division and stabilize tissue boundaries by restricting SHORT-ROOT action. Genes Dev 2007; 21:2196-204. [PMID: 17785527 PMCID: PMC1950858 DOI: 10.1101/gad.440307] [Citation(s) in RCA: 199] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In the Arabidopsis root, the SHORT-ROOT transcription factor moves outward to the ground tissue from its site of transcription in the stele and is required for the specification of the endodermis and the stem cell organizing quiescent center cells. In addition, SHORT-ROOT and the downstream transcription factor SCARECROW control an oriented cell division in ground tissue stem cell daughters. Here, we show that the JACKDAW and MAGPIE genes, which encode members of a plant-specific family of zinc finger proteins, act in a SHR-dependent feed-forward loop to regulate the range of action of SHORT-ROOT and SCARECROW. JACKDAW expression is initiated independent of SHORT-ROOT and regulates the SCARECROW expression domain outside the stele, while MAGPIE expression depends on SHORT-ROOT and SCARECROW. We provide evidence that JACKDAW and MAGPIE regulate tissue boundaries and asymmetric cell division and can control SHORT-ROOT and SCARECROW activity in a transcriptional and protein interaction network.
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Affiliation(s)
- David Welch
- Molecular Genetics Group, Department of Biology, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Hala Hassan
- Molecular Genetics Group, Department of Biology, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Ikram Blilou
- Molecular Genetics Group, Department of Biology, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Richard Immink
- Plant Research International, 6708 PD Wageningen, The Netherlands
| | - Renze Heidstra
- Molecular Genetics Group, Department of Biology, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Ben Scheres
- Molecular Genetics Group, Department of Biology, Utrecht University, 3584 CH Utrecht, The Netherlands
- Corresponding author.E-MAIL ; FAX 31-30-2513655
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690
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Morcillo F, Gallard A, Pillot M, Jouannic S, Aberlenc-Bertossi F, Collin M, Verdeil JL, Tregear JW. EgAP2-1, an AINTEGUMENTA-like (AIL) gene expressed in meristematic and proliferating tissues of embryos in oil palm. PLANTA 2007; 226:1353-62. [PMID: 17628826 DOI: 10.1007/s00425-007-0574-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2006] [Accepted: 06/01/2007] [Indexed: 05/16/2023]
Abstract
In order to better understand the developmental processes that govern the formation of somatic embryos in oil palm (Elaeis guineensis Jacq.), we investigated the transcription factor genes expressed during embryogenesis in this species. The AP2/EREBP transcription factor family includes the AP2 subgroup, which contains several proteins that play important roles in plant development. We identified and characterized EgAP2-1, which codes for a protein that contains two AP2 domains similar to those of the transcription factor BABYBOOM (BBM) and more generally AINTEGUMENTA-like (AIL) proteins of the AP2 subgroup. In a similar way to related genes from eudicots, ectopic expression of EgAP2-1 in transgenic Arabidopsis plants alters leaf morphology and enhances regeneration capacity. In oil palm, EgAP2-1 transcripts accumulate to the greatest extent in zygotic embryos. This expression pattern was investigated in more detail by in-situ hybridization, revealing that in both zygotic and somatic embryos, EgAP2-1 expression is concentrated in proliferating tissues associated with the early development of leaf primordia, root initials and provascular tissues.
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Affiliation(s)
- F Morcillo
- CIRAD/IRD Palm Group, UMR DAP/LIR IRD 192, Centre IRD Montpellier, BP 64501, 911 avenue Agropolis, 34394, Montpellier Cedex 5, France.
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691
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Nag A, Yang Y, Jack T. DORNROSCHEN-LIKE, an AP2 gene, is necessary for stamen emergence in Arabidopsis. PLANT MOLECULAR BIOLOGY 2007; 65:219-32. [PMID: 17682829 DOI: 10.1007/s11103-007-9210-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2007] [Accepted: 07/09/2007] [Indexed: 05/11/2023]
Abstract
To identify novel genes in petal and stamen development, a genetic screen was carried out for enhancers of the unusual B class mutant pistillata-5 (pi-5). In pi-5 flowers, second whorl organs develop as sepals rather than petals, but third whorl stamens are normal. One pi-5 enhancer, dornröschen-like-2 (drnl-2), results in third whorl positions developing as filamentous organs. In addition to enhancing the pi-5 phenotype, drnl-2 mutants also exhibit a phenotype in a wild-type PI background. Although stamen primordia are morphologically visible during early stages of flower development, they fail to enlarge in drnl-2 mutants. DRNL, which encodes a single AP2 domain protein, is expressed in a dynamic pattern in the embryo, seedling, and flower. Analysis of both the drnl-2 mutant phenotype and the DRNL expression pattern in flowers suggests that DRNL plays a critical role in stamen emergence in Arabidopsis.
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Affiliation(s)
- Anwesha Nag
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA
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692
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PLETHORA proteins as dose-dependent master regulators of Arabidopsis root development. Nature 2007; 449:1053-7. [DOI: 10.1038/nature06206] [Citation(s) in RCA: 624] [Impact Index Per Article: 36.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2007] [Accepted: 08/30/2007] [Indexed: 12/19/2022]
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693
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Abstract
Plant growth and development are driven by the continuous generation of new cells. Whereas much has been learned at a molecular level about the mechanisms that orchestrate progression through the different cell-cycle phases, little is known about how the cell-cycle machinery operates in the context of an entire plant and contributes to growth, cell differentiation and the formation of new tissues and organs. Here, we discuss how intrinsic developmental signals and environmental cues affect cell-cycle entry and exit.
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Affiliation(s)
- Lieven De Veylder
- Department of Plant Systems Biology, VIB, Technologiepark 927, 9052 Gent, Belgium
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694
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Tucker MR, Laux T. Connecting the paths in plant stem cell regulation. Trends Cell Biol 2007; 17:403-10. [PMID: 17766120 DOI: 10.1016/j.tcb.2007.06.002] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2007] [Revised: 06/04/2007] [Accepted: 06/06/2007] [Indexed: 01/11/2023]
Abstract
Stem cell niches are specialized microenvironments where pluripotent cells are maintained to provide undifferentiated cells for the formation of new tissues and organs. The balance between stem cell maintenance within the niche and differentiation of cells that exit it is regulated by local cell-cell communication, together with external cues. Recent findings have shown connections between key developmental pathways and added significant insights into the central principles of stem cell maintenance in plant meristems. These insights include the convergence of important stem cell transcriptional regulators with cytokinin signaling in the shoot meristem, the biochemical dissection of peptide signaling in the shoot niche and the identification of conserved regulators in shoot and root niches.
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Affiliation(s)
- Matthew R Tucker
- Institute of Biology III, University of Freiburg, Freiburg 79104, Germany
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695
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696
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Malenica N, Abas L, Benjamins R, Kitakura S, Sigmund HF, Jun KS, Hauser MT, Friml J, Luschnig C. MODULATOR OF PIN genes control steady-state levels of Arabidopsis PIN proteins. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2007; 51:537-50. [PMID: 17651372 DOI: 10.1111/j.1365-313x.2007.03158.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Polar transport of the phytohormone auxin controls numerous growth responses in plants. Molecular characterization of auxin transport in Arabidopsis thaliana has provided important insights into the mechanisms underlying the regulation of auxin distribution. In particular, the control of subcellular localization and expression of PIN-type auxin efflux components appears to be fundamental for orchestrated distribution of the growth regulator throughout the entire plant body. Here we describe the identification of two Arabidopsis loci, MOP2 and MOP3 (for MODULATOR OF PIN), that are involved in control of the steady-state levels of PIN protein. Mutations in both loci result in defects in auxin distribution and polar auxin transport, and cause phenotypes consistent with a reduction of PIN protein levels. Genetic interaction between PIN2 and both MOP loci is suggestive of functional cross-talk, which is further substantiated by findings demonstrating that ectopic PIN up-regulation is compensated in the mop background. Thus, in addition to pathways that control PIN localization and transcription, MOP2 and MOP3 appear to be involved in fine-tuning of auxin distribution via post-transcriptional regulation of PIN expression.
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Affiliation(s)
- Nenad Malenica
- Institute for Applied Genetics and Cell Biology, University of Applied Life Sciences and Natural Resources (BOKU), Muthgasse 18, A-1190 Vienna, Austria
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697
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De Smet I, Jürgens G. Patterning the axis in plants – auxin in control. Curr Opin Genet Dev 2007; 17:337-43. [PMID: 17627808 DOI: 10.1016/j.gde.2007.04.012] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2007] [Revised: 04/26/2007] [Accepted: 04/29/2007] [Indexed: 01/23/2023]
Abstract
Axis formation and patterning are fundamental processes establishing the body organization of multicellular organisms. In plants, patterning is not confined to embryogenesis but continues to produce new structures--lateral organs--along the growing primary body axis and also initiates secondary body axes. The signalling molecule auxin has been identified as a key player in plant axial patterning. The shoot and root sections of the axis seem to produce lateral organs in different ways. However, very recent findings suggest a general mechanism of branching triggered by local accumulation of auxin in a 'zone of competence' at the margin of stem-cell systems. How the general auxin signal is converted into organ-specific developmental programs remains a major challenge for the future.
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Affiliation(s)
- Ive De Smet
- Centre for Plant Molecular Biology (ZMBP), Developmental Genetics, Tübingen University, Auf der Morgenstelle 3, D-72076 Tübingen, Germany.
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698
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Ohashi-Ito K, Bergmann DC. Regulation of the Arabidopsis root vascular initial population by LONESOME HIGHWAY. Development 2007; 134:2959-68. [PMID: 17626058 PMCID: PMC3145339 DOI: 10.1242/dev.006296] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Complex organisms consist of a multitude of cell types arranged in a precise spatial relation to each other. Arabidopsis roots generally exhibit radial tissue organization; however, within a tissue layer, cells are not identical. Specific vascular cell types are arranged in diametrically opposed longitudinal files that maximize the distance between them and create a bilaterally symmetric (diarch) root. Mutations in the LONESOME HIGHWAY (LHW) gene eliminate bilateral symmetry and reduce the number of cells in the center of the root, resulting in roots with only single xylem and phloem poles. LHW does not appear to be required for the creation of any specific cell type, but coordinately controls the number of all vascular cell types by regulating the size of the pool of cells from which they arise. We cloned LHW and found that it encodes a protein with weak sequence similarity to basic helix-loop-helix (bHLH)-domain proteins. LHW is a transcriptional activator in vitro. In plants, LHW is nuclear-localized and is expressed in the root meristems, where we hypothesize it acts independently of other known root-patterning genes to promote the production of stele cells, but might also indirectly feed into established regulatory networks for the maintenance of the root meristem.
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699
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Ortega-Martínez O, Pernas M, Carol RJ, Dolan L. Ethylene Modulates Stem Cell Division in the Arabidopsis thaliana Root. Science 2007; 317:507-10. [PMID: 17656722 DOI: 10.1126/science.1143409] [Citation(s) in RCA: 182] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The construction of multicellular organisms depends on stem cells-cells that can both regenerate and produce daughter cells that undergo differentiation. Here, we show that the gaseous messenger ethylene modulates cell division in the cells of the quiescent center, which act as a source of stem cells in the seedling root. The cells formed through these ethylene-induced divisions express quiescent center-specific genes and can repress differentiation of surrounding initial cells, showing that quiescence is not required for these cells to signal to adjacent stem cells. We propose that ethylene is part of a signaling pathway that modulates cell division in the quiescent center in the stem cell niche during the postembryonic development of the root system.
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Affiliation(s)
- Olga Ortega-Martínez
- Department of Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, UK
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700
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Reddy GV, Gordon SP, Meyerowitz EM. Unravelling developmental dynamics: transient intervention and live imaging in plants. Nat Rev Mol Cell Biol 2007; 8:491-501. [PMID: 17522592 DOI: 10.1038/nrm2188] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Plant development is dynamic in nature. This is exemplified in developmental patterning, in which roots and shoots rapidly elongate while simultaneously giving rise to precisely positioned new organs over a time course of minutes to hours. In this Review, we emphasize the insights gained from simultaneous use of live imaging and transient perturbation technologies to capture the dynamic properties of plant processes.
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Affiliation(s)
- G Venugopala Reddy
- Department of Botany and Plant Sciences, 2150 Batchelor Hall, University of California, Riverside, California 92521, USA.
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