Universität zu Köln

Janßen, Helen Yvonne Bärbel (2026). Structure-Function Analysis of STICHEL in the Context of Trichome Branching of Arabidopsis thaliana. PhD thesis, Universität zu Köln.

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Abstract

Trichome branching in Arabidopsis thaliana is a well-established model for studying spatially controlled cell morphogenesis. The STICHEL (STI) gene is required for proper branch initiation during trichome development, but its molecular function has remained unresolved. Early sequence analyses suggested similarity to ATPase-associated proteins, although experimental evidence supporting ATPase activity has been lacking. In this study, STI was investigated using bioinformatic, biochemical, and cell biological approaches. Structural predictions and sequence analyses identified a conserved central region containing motifs associated with ATPase-related proteins. Comparative analyses supported the presence of an ATPase-like core architecture. However, ATPase assays using recombinant STI fragments did not detect measurable ATP hydrolysis under the tested conditions, suggesting that STI may not function as a classical enzymatically active ATPase. To analyse STI function in planta, fluorescent reporter constructs were generated and expressed in A. thaliana. Confocal microscopy revealed enrichment of STI at prospective branch initiation sites in developing trichomes, supporting a role during early branch establishment. Complementation experiments further demonstrated that STI-tdTomato constructs restore branching in the sti mutant background, confirming functionality of the examined fusion protein. Because trichome branch initiation depends on highly coordinated cortical organization involving actin-associated processes, potential interactions between STI and members of the NET1 protein family were investigated. Yeast two-hybrid analyses revealed specific interactions between STI and a C-terminal region of several NET1 paralogs. In contrast, no interaction was detected with the conserved N-terminal actin-binding NAB domain of NET1 proteins. Together, the results of this work support a model in which STI functions as part of a regulatory protein network involved in localized cortical organization during branch initiation. Rather than acting as a conventional ATPase, STI may fulfil scaffold-like or regulatory functions associated with cytoskeleton-dependent processes required for polarized trichome morphogenesis.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Janßen, Helen Yvonne Bärbel Helenyvonnejanssen@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-810036
Date:	2026
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:	Keywords Language Arabidopsis thaliana UNSPECIFIED Trichome UNSPECIFIED Stichel UNSPECIFIED
Date of oral exam:	17 July 2026
Referee:	Name Academic Title Hülskamp, Martin Pro. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/81003