1,720,956 research outputs found
Shaping plant architecture
No full textPlants exhibit phenotypical plasticity. Their general body plan is genetically determined, but plant architecture and branching patterns are variable and can be adjusted to the prevailing environmental conditions. The modular design of the plant facilitates such morphological adaptations. The prerequisite for the formation of a branch is the initiation of an axillary meristem. Here, we review the current knowledge about this process. After its establishment, the meristem can develop into a bud which can either become dormant or grow out and form a branch. Many endogenous factors, such as photoassimilate availability, and exogenous factors like nutrient availability or shading, have to be integrated in the decision whether a branch is formed. The underlying regulatory network is complex and involves phytohormones and transcription factors. The hormone auxin is derived from the shoot apex and inhibits bud outgrowth indirectly in a process termed apical dominance. Strigolactones appear to modulate apical dominance by modification of auxin fluxes. Furthermore, the transcription factor BRANCHED1 plays a central role. The exact interplay of all these factors still remains obscure and there are alternative models. We discuss recent findings in the field along with the major models.Plant architecture is economically significant because it affects important traits of crop and ornamental plants, as well as trees cultivated in forestry or on short rotation coppices. As a consequence, plant architecture has been modified during plant domestication. Research revealed that only few key genes have been the target of selection during plant domestication and in breeding programs. Here, we discuss such findings on the basis of various examples. Architectural ideotypes that provide advantages for crop plant management and yield are described. We also outline the potential of breeding and biotechnological approaches to further modify and improve plant architecture for economic needs
expression and shoot architecture
No full textPlant architecture is modified by a regulatory system that controls axillary bud outgrowth. Key components in this system are strigolactones (SLs) and BRANCHED1, which inhibit bud outgrowth. Their role has been described in herbaceous model systems, including Arabidopsis, rice and pea. However, a role in woody perennial species, including the model tree poplar, has not been unequivocally proven. In this study, we tested a role for SLs in Populusxcanescens by treatment with the synthetic SL GR24. We generated MORE AXILLARY BRANCHING4 (MAX4) knockdown lines to study the architectural phenotype of poplar SL biosynthesis mutants and the expression of SL-regulated genes. We show that GR24 is perceived by the model tree poplar. MAX4 knockdown lines exhibit typical SL deficiency symptoms. The observed changes in branching pattern, internode length and plant height can be rescued by grafting. We identified putative poplar BRANCHED1 and BRANCHED2 genes and provide evidence for a regulation of BRANCHED1 by SLs. Our results suggest a conservation of major regulatory mechanisms in bud outgrowth control in the model tree poplar. This may facilitate further research, pinpointing the role of SLs and BRANCHED1 in the complex regulation of bud outgrowth in trees
CRISPR/Cas9-mediated knockout of Populus BRANCHED1 and BRANCHED2 orthologs reveals a major function in bud outgrowth control
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Branching control mechanisms in the model tree Populus: analyzing the role of strigolactones and BRANCHED1
Full text linkPflanzen verfügen über ein hohes Maß an phänotypischer Plastizität. Modifikationen ihres genetisch determinierten Aufbaus ermöglichen ihnen, flexibel auf ein breites Spektrum von Umwelteinflüssen zu reagieren. Dies umfasst Veränderungen der Pflanzenarchitektur, die durch den modularen Aufbau des Sprosses ermöglicht werden. In den Blattachseln des Primärsprosses werden Achselknospen angelegt. Jede einzelne dieser Knospen hat das Potenzial, zu einem Sekundärspross, d.h. einem Zweig, auszuwachsen. Der Knospenaustrieb wird jedoch reguliert und die meisten Knospen verbleiben in einem dormanten Status. Bei der Entscheidung, ob die Dormanz einer Knospe gebrochen wird und sie zu einem Zweig auswächst, spielen diverse endo- und exogene Faktoren eine Rolle, die in einem komplexen, aus Hormonen und Transkriptionsfaktoren bestehenden Regelnetz, integriert werden. Dieses umfasst Strigolactone (SL), eine neuartige Klasse von Phytohormonen, die im Allgemeinen den Knospenaustrieb hemmen. Es wird diskutiert, dass der inhibitorische Effekt der SL durch eine Modulation des Flusses des Phytohormons Auxin und/oder die Regulation anderer nachgelagerter Faktoren direkt in der Knospe herbeigeführt wird. Das bekannteste Beispiel für ein knospenspezifisches, SL-reguliertes Gen ist BRANCHED1 (BRC1), dessen mRNA-Abundanz positiv von SL beeinflusst wird. Es codiert einen Transkriptionsfaktor der den Knospenaustrieb unterdrückt, was höchstwahrscheinlich über eine Regulation des Zellzyklus erfolgt. SL und BRC1 wurden umfassend in Modellarten wie Arabidopsis (Arabidopsis thaliana), Erbse (Pisum sativum), Petunie (Petunia hybrida) und Reis (Oryza sativa) untersucht. Im Gegensatz dazu ist das Wissen über die Gene und Stoffwechselwege dieses Regelkreises in verholzten, ausdauernden Arten wie dem Modellbaum Pappel (Populus sp.), limitiert. In der vorliegenden Arbeit wurden Pappel-Orthologe von Genen, die an der SL-Biosynthese (MAX4) und der SL-Signaltransduktion (MAX2) beteiligt sind, identifiziert und auf eine vermutete Funktion in der Regulation der Baumarchitektur untersucht. Es existieren jeweils zwei Orthologe in der Pappel. Um ihre Funktion zu charakterisieren, wurden Expressionsanalysen durchgeführt und transgene Linien für amiRNA-vermittelte simultane oder einzelne knock-downs der beiden Orthologe erzeugt. Knock-downs von MAX2 waren nur teilweise erfolgreich. Es konnte kein Phänotyp beobachtet werden, was höchstwahrscheinlich auf eine redundante Funktion des nicht herunterregulierten Orthologs zurückzuführen ist. MAX4 Doppel-Knock-downs waren hingegen erfolgreich und es konnten typische SL-Mangelphänotypen in den entsprechenden amiMAX4-1+2 Linien beobachtet werden. Diese umfassten eine erhöhte Sprossverzweigung, eine Reduktion der Pflanzenhöhe, eine verkürzte Indernodienlänge sowie eine erhöhte Adventivbewurzelung. Durch ihre geringe Konzentration, hohe Instabilität und große Diversität ist die direkte Quantifizierung von SL sehr anspruchsvoll. Außerdem sind Standards und Referenzen für Pappel-SL nicht verfügbar, was direkte Messungen nicht durchführbar machte. Stattdessen wurden indirekte Hinweise auf SL-Mangel in den amiMAX4-1+2 Pflanzen gesammelt. Ein Beispiel dafür ist die erfolgreiche Komplementation der Sprossphänotypen durch Pfropfung. Baumspezifische Aspekte der Knospendormanz, besonders die Winterdormanz, wurden ebenfalls untersucht. Ein Einfluss von SL konnte aber nicht nachgewiesen werden, was darauf hinweist, dass SL den Knospenaustrieb nur in der vegetativen Periode hemmen.
Als ein SL-reguliertes Zielgen und daher eine weitere wichtige Komponente der Verzweigungskontrolle wurde ein Pappel BRC1 Ortholog identifiziert. Dieses Gen wies die typischen, in anderen Arten nachgewiesenen Expressionsmuster, sowie eine signifikant reduzierte Expression in den erzeugten amiMAX4-1+2 Linien auf, welche wahrscheinlich reduzierte SL-Level haben. Zusätzlich wurde auf der Basis von Sequenz- und Expressionsanalysen ein Pappel BRC2 Ortholog identifiziert. Beide Gene kontrollieren möglicherweise die Verzweigung in Pappeln und integrieren verschiedene Umwelteinflüsse.
Zusammengefasst legen die in diesem Projekt gewonnenen Daten eine Rolle von SL und BRC1 als wichtige Regulatoren des Knospenaustriebs in Pappeln nahe. Die Ergebnisse machen deutlich, dass grundlegende Prozesse in der Kontrolle der Pflanzenarchitektur über ein breites Spektrum von Arten, einschließlich Bäumen, hoch konserviert sind. Abgesehen von ihrer Relevanz als Grundlage zur Erforschung der Rolle von SL und BRC1 in Pappeln, sind die in diesem Projekt erzeugten stark verzweigten Linien möglicherweise wirtschaftlich für die Nutzung auf Kurzumtriebsplantagen interessant, auf welchen sie vermutlich über verbesserte Eigenschaften im Stockaustrieb nach der Ernte und im Kronenschluss verfügen.Plants exhibit a large degree of phenotypic plasticity. Modifications of their genetically pre-defined body plan allow them to flexibly react to a wide range of environmental conditions. This includes changes in plant architecture, which are facilitated by the modular composition of the shoot. In the leaf axils of the primary stem, axillary buds are formed. Each of these buds has the potential to grow into a secondary stem, i.e. a branch. However, bud outgrowth is restricted and most buds are kept in a dormant state. To make the decision whether a bud is released from dormancy and grows into a branch, many endo- and exogenous factors are integrated in a complex network of hormones and transcription factors. This includes strigolactones (SLs), a novel class of phytohormones, which generally suppress bud outgrowth. The inhibitory effect of SLs is discussed to be mediated by flux modulation of the phytohormone auxin and/or regulation of other downstream targets directly within the bud. The most prominent example for a bud-specific SL-regulated gene is BRANCHED1 (BRC1), whose transcript levels are positively influenced by SLs. It encodes a transcription factor which represses bud outgrowth, most likely by regulating cell cycling. SLs and BRC1 were extensively studied in model species such as Arabidopsis (Arabidopsis thaliana), pea (Pisum sativum), petunia (Petunia hybrida) and rice (Oryza sativa). In contrast, our knowledge of the genes and pathways in woody perennial species, such as the model tree poplar (Populus sp.), is limited.
In this project, poplar orthologs of genes involved in SL biosynthesis (MAX4) and SL signaling (MAX2) were identified to investigate an anticipated role for SLs in controlling tree architecture. There are two orthologs each in poplar. To study their function, expression analysis was performed and transgenic lines were generated for amiRNA-mediated knockdowns of the individual orthologs, as well as simultaneous silencing of both. MAX2 knockdowns were only partially successful and no phenotype could be observed, most likely due to a redundant function of the non-silenced ortholog. In contrast, MAX4 double knockdowns were successful and typical SL-deficiency phenotypes were observed in the corresponding amiMAX4-1+2 lines. This includes highly increased shoot branching, reduced plant height, reduced internode length and increased adventitious rooting. Direct quantification of SLs generally is difficult due to their low abundance, high instability and large diversity. Furthermore, standards and references for poplar SLs are not available, making measurements not feasible. Indirect evidence for SL-deficiency in amiMAX4-1+2 plants was gathered instead, including successful complementation of the shoot phenotypes by grafting. Tree-specific aspects of bud dormancy, especially winter dormancy, were also addressed. However, an influence of SLs could not be shown, indicating that SLs only appear to suppress bud outgrowth during the vegetative period.
As a downstream target of SLs and, therefore, another important component of branching control, a poplar BRC1 ortholog was identified. This gene exhibited the typical expression patterns reported for other species and a significant down-regulation in the putatively SL-deficient amiMAX4-1+2 lines. In addition, a poplar BRC2 ortholog was found based on sequence and expression analysis. Both genes may control branching in poplar, integrating different environmental factors.
Taken together, the data generated in this study supports a role for SLs and BRC1 as important regulators of bud outgrowth in poplar. The findings underline the high degree of conservation of fundamental processes involved in the control of plant architecture among a range of species, including trees. Beside of being a useful tool for discovering the role of SLs and BRC1 in poplar, the highly branching lines generated in this project may be economically valuable for the use on short rotation coppices, where they may exhibit improved re-sprouting and canopy closure after coppicing
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