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N-MYC DOWN-REGULATED-LIKE Proteins Regulate Meristem Initiation by Modulating Auxin Transport and MAX2 Expression  [PDF]
Yashwanti Mudgil, Sanjay Ghawana, Alan M. Jones
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0077863
Abstract: Background N-MYC DOWN-REGULATED-LIKE (NDL) proteins interact with the Gβ subunit (AGB1) of the heterotrimeric G protein complex and play an important role in AGB1-dependent regulation of lateral root formation by affecting root auxin transport, auxin gradients and the steady-state levels of mRNA encoding the PIN-FORMED 2 and AUXIN 1 auxin transport facilitators. Auxin transport in aerial tissue follows different paths and utilizes different transporters than in roots; therefore, in the present study, we analyzed whether NDL proteins play an important role in AGB1-dependent, auxin-mediated meristem development. Methodology/Principal Findings Expression levels of NDL gene family members need to be tightly regulated, and altered expression (both over-expression and down-regulation) confers ectopic growth. Over-expression of NDL1 disrupts vegetative and reproductive organ development. Reduced expression of the NDL gene family members results in asymmetric leaf emergence, twinning of rosette leaves, defects in leaf formation, and abnormal silique distribution. Reduced expression of the NDL genes in the agb1-2 (null allele) mutant rescues some of the abnormal phenotypes, such as silique morphology, silique distribution, and peduncle angle, suggesting that proper levels of NDL proteins are maintained by AGB1. We found that all of these abnormal aerial phenotypes due to altered NDL expression were associated with increases in basipetal auxin transport, altered auxin maxima and altered MAX2 expression within the inflorescence stem. Conclusion/Significance NDL proteins, together with AGB1, act as positive regulators of meristem initiation and branching. AGB1 and NDL1 positively regulate basipetal inflorescence auxin transport and modulate MAX2 expression in shoots, which in turn regulates organ and lateral meristem formation by the establishment and maintenance of auxin gradients.
Role of the Arabidopsis PIN6 Auxin Transporter in Auxin Homeostasis and Auxin-Mediated Development  [PDF]
Christopher I. Cazzonelli, Marleen Vanstraelen, Sibu Simon, Kuide Yin, Ashley Carron-Arthur, Nazia Nisar, Gauri Tarle, Abby J. Cuttriss, Iain R. Searle, Eva Benkova, Ulrike Mathesius, Josette Masle, Ji?í Friml, Barry J. Pogson
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0070069
Abstract: Plant-specific PIN-formed (PIN) efflux transporters for the plant hormone auxin are required for tissue-specific directional auxin transport and cellular auxin homeostasis. The Arabidopsis PIN protein family has been shown to play important roles in developmental processes such as embryogenesis, organogenesis, vascular tissue differentiation, root meristem patterning and tropic growth. Here we analyzed roles of the less characterised Arabidopsis PIN6 auxin transporter. PIN6 is auxin-inducible and is expressed during multiple auxin–regulated developmental processes. Loss of pin6 function interfered with primary root growth and lateral root development. Misexpression of PIN6 affected auxin transport and interfered with auxin homeostasis in other growth processes such as shoot apical dominance, lateral root primordia development, adventitious root formation, root hair outgrowth and root waving. These changes in auxin-regulated growth correlated with a reduction in total auxin transport as well as with an altered activity of DR5-GUS auxin response reporter. Overall, the data indicate that PIN6 regulates auxin homeostasis during plant development.
Advances in Understanding the Roles of Auxin Involved in Modulating Plant Architecture
生长素调控植物株型形成的研究进展

Bing Wang,Jiayang Li,Yonghong Wang,
王冰
,李家洋,王永红

植物学报 , 2006,
Abstract: Plants modulate their shoot architecture by regulating activities of the shoot apical meristem and axillary meristems. Meristem activities are regulated by a network of environmental information, developmental stage and genetic makeup of the plant. The fate of signal integration, to a large extent, depends on the action of plant hormones. Auxin plays an essential role in the establishment and maintenance of the apical dominance, which is a central issue in regulating shoot branching. This review focuses on recent advances in the study of auxin biosynthesis, metabolism, polar transport, and signaling pathway, as well as their involvements in the control of the architecture of aerial parts. Prospects in the field are also briefly discussed.
Localised auxin peaks in concentration-based transport models of the shoot apical meristem  [PDF]
Delphine Draelants,Daniele Avitabile,Wim Vanroose
Quantitative Biology , 2014,
Abstract: We study the formation of auxin peaks in a generic class of concentration-based auxin transport models, posed on static plant tissues. Using standard asymptotic analysis we prove that, on bounded domains, auxin peaks are not formed via a Turing instability in the active transport parameter, but via simple corrections to the homogeneous steady state. When the active transport is small, the geometry of the tissue encodes the peaks' amplitude and location: peaks arise where cells have fewer neighbours, that is, at the boundary of the domain. We test our theory and perform numerical bifurcation analysis on two models which are known to generate auxin patterns for biologically plausible parameter values. In the same parameter regimes, we find that realistic tissues are capable of generating a multitude of stationary patterns, with a variable number of auxin peaks, that can be selected by different initial conditions or by quasi-static changes in the active transport parameter. The competition between active transport and production rate determines whether peaks remain localised or cover the entire domain. We relate the occurrence of localised patterns to a snaking bifurcation structure, which is known to arise in a wide variety of nonlinear media but has not yet been reported in plant models.
Alignment between PIN1 Polarity and Microtubule Orientation in the Shoot Apical Meristem Reveals a Tight Coupling between Morphogenesis and Auxin Transport  [PDF]
Marcus G. Heisler,Olivier Hamant,Pawel Krupinski,Magalie Uyttewaal,Carolyn Ohno,Henrik J?nsson,Jan Traas,Elliot M. Meyerowitz
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1000516
Abstract: Morphogenesis during multicellular development is regulated by intercellular signaling molecules as well as by the mechanical properties of individual cells. In particular, normal patterns of organogenesis in plants require coordination between growth direction and growth magnitude. How this is achieved remains unclear. Here we show that in Arabidopsis thaliana, auxin patterning and cellular growth are linked through a correlated pattern of auxin efflux carrier localization and cortical microtubule orientation. Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature. Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis.
Alignment between PIN1 Polarity and Microtubule Orientation in the Shoot Apical Meristem Reveals a Tight Coupling between Morphogenesis and Auxin Transport  [PDF]
Marcus G. Heisler equal contributor,Olivier Hamant equal contributor,Pawel Krupinski equal contributor,Magalie Uyttewaal,Carolyn Ohno,Henrik J?nsson equal contributor ,Jan Traas ,Elliot M. Meyerowitz
PLOS Biology , 2010, DOI: 10.1371/journal.pbio.1000516
Abstract: Morphogenesis during multicellular development is regulated by intercellular signaling molecules as well as by the mechanical properties of individual cells. In particular, normal patterns of organogenesis in plants require coordination between growth direction and growth magnitude. How this is achieved remains unclear. Here we show that in Arabidopsis thaliana, auxin patterning and cellular growth are linked through a correlated pattern of auxin efflux carrier localization and cortical microtubule orientation. Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature. Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis.
Regulation of Leaf Development by Auxin in Arabidopsis
生长素对拟南芥叶片发育调控的研究进展

Linchuan Li,Lijia Qu,
李林川
,瞿礼嘉

植物学报 , 2006,
Abstract: Leaf is the first lateral organ produced by the activity of the shoot apical meristem (SAM). Early leaf development is artificially divided into three main stages: the initiation of leaf primordium, the establishment of leaf adaxial-abaxial polarity, and the expansion of leaf blade. Numerous of evidence indicates that leaf development is regulated by inner genetic mechanism and outer environmental cues. Phytohormones, especially auxin, play essential roles in coordination of these two regulation mechanisms. Auxin homeostasis, polar transport and signaling affect the whole progress of leaf development. In this mini-review, we will summarize recent progress of auxin regulation in leaf development and morphogenesis, and try to understand the complex regulation network of leaf development.
Transcriptional profiling of the pea shoot apical meristem reveals processes underlying its function and maintenance
Chui E Wong, Prem L Bhalla, Harald Ottenhof, Mohan B Singh
BMC Plant Biology , 2008, DOI: 10.1186/1471-2229-8-73
Abstract: In order to identify genes that are differentially expressed in the SAM, we generated 2735 ESTs from three cDNA libraries derived from freshly micro-dissected SAMs from 10-day-old garden peas (Pisum sativum cv Torsdag). Custom-designed oligonucleotide arrays were used to compare the transcriptional profiles of pea SAMs and non-meristematic tissues. A total of 184 and 175 transcripts were significantly up- or down-regulated in the pea SAM, respectively. As expected, close to 61% of the transcripts down-regulated in the SAM were found in the public database, whereas sequences from the same source only comprised 12% of the genes that were expressed at higher levels in the SAM. This highlights the under-representation of transcripts from the meristematic tissues in the current public pea protein database, and demonstrates the utility of our SAM EST collection as an essential genetic resource for revealing further information on the regulation of this developmental process. In addition to unknowns, many of the up-regulated transcripts are known to encode products associated with cell division and proliferation, epigenetic regulation, auxin-mediated responses and microRNA regulation.The presented data provide a picture of the transcriptional profile of the pea SAM, and reveal possible roles of differentially expressed transcripts in meristem function and maintenance.Organ formation is not limited to embryonic development, but can occur throughout the lifetime of a plant. The potential to develop new organs post-embryonically is attributed to meristems located at the growing tips of the plants, with the root apical meristem generating the underground part of the plant and the shoot apical meristem (SAM) giving rise to the entire shoot system after seed germination.Like its root counterpart, the SAM contains a pool of pluripotent stem cells that can self-maintain as well as produce the cells that can differentiate into multiple cell and tissue types [reviewed in [1]]. While
New Clothes for the Jasmonic Acid Receptor COI1: Delayed Abscission, Meristem Arrest and Apical Dominance  [PDF]
Joonyup Kim, Bradley Dotson, Camila Rey, Joshua Lindsey, Anthony B. Bleecker, Brad M. Binder, Sara E. Patterson
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0060505
Abstract: In a screen for delayed floral organ abscission in Arabidopsis, we have identified a novel mutant of CORONATINE INSENSITIVE 1 (COI1), the F-box protein that has been shown to be the jasmonic acid (JA) co-receptor. While JA has been shown to have an important role in senescence, root development, pollen dehiscence and defense responses, there has been little focus on its critical role in floral organ abscission. Abscission, or the detachment of organs from the main body of a plant, is an essential process during plant development and a unique type of cell separation regulated by endogenous and exogenous signals. Previous studies have indicated that auxin and ethylene are major plant hormones regulating abscission; and here we show that regulation of floral organ abscission is also controlled by jasmonic acid in Arabidopsis thaliana. Our characterization of coi1-1 and a novel allele (coi1-37) has also revealed an essential role in apical dominance and floral meristem arrest. In this study we provide genetic evidence indicating that delayed abscission 4 (dab4-1) is allelic to coi1-1 and that meristem arrest and apical dominance appear to be evolutionarily divergent functions for COI1 that are governed in an ecotype-dependent manner. Further characterizations of ethylene and JA responses of dab4-1/coi1-37 also provide new information suggesting separate pathways for ethylene and JA that control both floral organ abscission and hypocotyl growth in young seedlings. Our study opens the door revealing new roles for JA and its interaction with other hormones during plant development.
Simulation of Organ Patterning on the Floral Meristem Using a Polar Auxin Transport Model  [PDF]
Simon van Mourik, Kerstin Kaufmann, Aalt D. J. van Dijk, Gerco C. Angenent, Roeland M. H. Merks, Jaap Molenaar
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0028762
Abstract: An intriguing phenomenon in plant development is the timing and positioning of lateral organ initiation, which is a fundamental aspect of plant architecture. Although important progress has been made in elucidating the role of auxin transport in the vegetative shoot to explain the phyllotaxis of leaf formation in a spiral fashion, a model study of the role of auxin transport in whorled organ patterning in the expanding floral meristem is not available yet. We present an initial simulation approach to study the mechanisms that are expected to play an important role. Starting point is a confocal imaging study of Arabidopsis floral meristems at consecutive time points during flower development. These images reveal auxin accumulation patterns at the positions of the organs, which strongly suggests that the role of auxin in the floral meristem is similar to the role it plays in the shoot apical meristem. This is the basis for a simulation study of auxin transport through a growing floral meristem, which may answer the question whether auxin transport can in itself be responsible for the typical whorled floral pattern. We combined a cellular growth model for the meristem with a polar auxin transport model. The model predicts that sepals are initiated by auxin maxima arising early during meristem outgrowth. These form a pre-pattern relative to which a series of smaller auxin maxima are positioned, which partially overlap with the anlagen of petals, stamens, and carpels. We adjusted the model parameters corresponding to properties of floral mutants and found that the model predictions agree with the observed mutant patterns. The predicted timing of the primordia outgrowth and the timing and positioning of the sepal primordia show remarkable similarities with a developing flower in nature.
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