Srinivas, Bhylahalli Purushottam (2004). Understanding the function of the Arabidopsis GLABRA 2 gene in Trichome patterning, morphogenesis and differentiation. PhD thesis, Universität zu Köln.


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Arabidopsis trichomes (leaf hairs) are one of the best studied plant model cell types with respect to understanding the molecular mechanisms underlying the process of cell patterning and differentiation. Many mutants which exhibit altered trichome patterning and differentiation have been analyzed and insights into the molecular nature of interactions among the genes involved have been obtained. The main focus of this thesis has been to understand the role of the GLABRA 2 (GL2) gene in trichome cell patterning, morphogenesis and differentiation. The main findings can be summarized as follows: i. In the absence of GL2 function more protodermal cells than wild-type get specified as trichome precursors but most of them exit the trichome differentiation pathway at different stages of their development resulting in lesser number of trichomes on mature gl2 mutant leaves. The role of GL2 in patterning was established by analyzing various gl2 double mutants as well as by ubiquitous expression of GL2 which showed that it is required both for trichome specification and differentiation. The development and fate of trichomes on gl2 leaves was carefully analyzed and it is concluded that in the absence of GL2 function trichomes lose their identity and likely adopt the default epidermal differentiation pathway of pavement cells. GL2 was also found to regulate trichome branching positively. A positive feedback loop between TRIPTYCHON (TRY) and GL2 was discovered and is hypothesized to be important in the final steps of trichome pattern resolution. In a nutshell, GL2 was found to be involved in trichome patterning, branching and differentiation. All the results have been incorporated in a model discussed at the end of chapter 2. ii. Analysis of an early trichome marker in young wild-type leaves showed that trichome patterning is a de novo process, meaning only a few cells get selected to become trichomes from a pool of apparently equivalent cells. Based on the above analysis it is hypothesized that in addition to the expression of specific transcription factors the final resolution of the trichome pattern is likely an outcome of competition between endoreplication and mitosis modes of cell cycle. iii. Using transient assays it was found that TRY and CPC gene products exhibit ability for intercellular movement, an essential property for them to act as inhibitors during patterning. iv. A novel method to simultaneously analyze multiple gene expression patterns in vivo (MEPI) has been proposed which is based on targeting many fluorescent reporter genes (GFP variants) to distinct intercellular structures / organelles in the same specimen. A proof-of-concept has been demonstrated by simultaneously analyzing three different reporter genes in Arabidopsis epidermal cells using a transient assay.

Item Type: Thesis (PhD thesis)
Translated title:
Untersuchung der Funktion des Arabidopsis GLABRA 2 Gens in der Trichom Musterbildung, Morphogenese und DifferenzierungGerman
Translated abstract:
Die Blatthaare von Arabidopsis thaliana (Trichome) sind die mit am besten geeigneten Zelltypen zur funktionellen Untersuchung von Musterbildungsprozessen und Zelldifferenzierungsvorgängen. In dieser Arbeit wurde die Funktion des GLABRA2 Gens in diesen beiden Prozessen näher untersucht. Die Befunde können wie folgt zusammengefasst werden: - es konnte mit Hilfe von Trichom-Markerlinien gezeigt werden, dass in glabra2 Mutanten während der Blattinitiation mehr Epidermiszellen als in Wildtyp ein Trichomschicksal wählen. Während der Blattentwicklung scheinen viele dieser Zellen wieder zu de-differenzieren, da in älteren Blättern deutlich weniger Trichome als in Wildtyp gefunden werden. - GLABRA2 hat eine Funktion in der Trichom-Differenzierung und Morphogenese. Viele Trichome beginnen sich wie in Wildtyp zu entwickeln, stoppen dann jedoch ihre Entwicklung und nehmen dann ein Epidermiszellschicksal an. Trichome, die sich weiter entwickeln, zeigen oft eine reduzierte Verzweigungsanzahl. - GLABRA2 und das Musterbildungsgen TRIPTYCHON regulieren sich gegenseitig in einer positiven Rückkopplungsschleife. - Mit Hilfe von Trichom-Markerlinien konnte gezeigt werden, dass einzelne Trichome aus einer Gruppe von kompetenten Zellen ausgewählt werden und das dabei die Entscheidung, ob die Zelle weiter mitotische Zyklen durchläuft oder mit Endoreduplikation beginnt, wichtig ist. - Experimente bei denen TRIPTYCHON und CAPRICE, zwei Musterbildungsgene, die an der lateralen Inhibition beteiligt sind, als GFP-Fusionen transient exprimiert wurden, zeigen, dass beide Proteine in benachbarte Zellen wandern können. - Es wurde eine neue Methode entwickelt (MEPI) die es ermöglicht, die Expression mehrerer Gene simultan in vivo zu untersuchen. Zusätzlich zu GFP-Varianten mit verschiedenen Farbspektren werden bei dieser Methode GFP-Fusionen verwendet, die spezifische Kompartimente der Zelle markieren.German
CreatorsEmailORCIDORCID Put Code
Srinivas, Bhylahalli Purushottams.bhylahalli@uni-koeln.deUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-12217
Date: 2004
Language: English
Faculty: Faculty of Mathematics and Natural Sciences
Divisions: Faculty of Mathematics and Natural Sciences > Department of Biology > Botanical Institute
Subjects: Life sciences
Uncontrolled Keywords:
GL2 , Trichom , Arabidopsis , Musterbildung , DifferenzierungGerman
GL2 , Trichome , Arabidopsis , Patterning , DifferentiationEnglish
Date of oral exam: 30 June 2004
NameAcademic Title
Hülskamp, MartinProf.Dr.
Refereed: Yes


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