Identification of novel regulators of PIN polarity and development of novel auxin sensor Dissertation Thesis

Author(s): Prat, Tomas
Advisor(s): Friml, Jiří
Committee Chair(s): Erdős, László
Committee Member(s): Janovjak, Harald; Luschnig, Christian
Title: Identification of novel regulators of PIN polarity and development of novel auxin sensor
Affiliation IST Austria
Abstract: Plant hormone auxin and its transport between cells belong to the most important mechanisms controlling plant development. Auxin itself could change localization of PINs and thereby control direction of its own flow. We performed an expression profiling experiment in Arabidopsis roots to identify potential regulators of PIN polarity which are transcriptionally regulated by auxin signalling. We identified several novel regulators and performed a detailed characterization of the transcription factor WRKY23 (At2g47260) and its role in auxin feedback on PIN polarity. Gain-of-function and dominant-negative mutants revealed that WRKY23 plays a crucial role in mediating the auxin effect on PIN polarity. In concordance, typical polar auxin transport processes such as gravitropism and leaf vascular pattern formation were disturbed by interfering with WRKY23 function. In order to identify direct targets of WRKY23, we performed consequential expression profiling experiments using a WRKY23 inducible gain-of-function line and dominant-negative WRKY23 line that is defunct in PIN re-arrangement. Among several genes mostly related to the groups of cell wall and defense process regulators, we identified LYSINE-HISTIDINE TRANSPORTER 1 (LHT1; At5g40780), a small amino acid permease gene from the amino acid/auxin permease family (AAAP), we present its detailed characterisation in auxin feedback on PIN repolarization, identified its transcriptional regulation, we propose a potential mechanism of its action. Moreover, we identified also a member of receptor-like protein kinase LRR-RLK (LEUCINE-RICH REPEAT TRANSMEMBRANE PROTEIN KINASE PROTEIN 1; LRRK1; At1g05700), which also affects auxin-dependent PIN re-arrangement. We described its transcriptional behaviour, subcellular localization. Based on global expression data, we tried to identify ligand responsible for mechanism of signalling and suggest signalling partner and interactors. Additionally, we described role of novel phytohormone group, strigolactone, in auxin-dependent PIN re-arrangement, that could be a fundament for future studies in this field. Our results provide first insights into an auxin transcriptional network targeting PIN localization and thus regulating plant development. We highlighted WRKY23 transcriptional network and characterised its mediatory role in plant development. We identified direct effectors of this network, LHT1 and LRRK1, and describe their roles in PIN re-arrangement and PIN-dependent auxin transport processes.
Publication Title: IST Dissertation
Degree Granting Institution: IST Austria  
Degree: PhD
Degree Date: 2017-01-12
Start Page: 1
Total Pages: 131
Notes: I would like to first acknowledge my supervisor Jiří Friml for support, kind advice and patience. It was a pleasure to be a part of your lab, Jiří. I will remember the atmosphere present in auxin lab at VIB in Ghent and at IST in Klosterneuburg forever. I would like to thank all past and present lab members for the friendship and friendly and scientific environment in the groups. It was so nice to cooperate with you, guys. There was always someone who helped me with experiments, troubleshoot issues coming from our work etc. At this place, I would like to thank especially to Gergo Molnár. I’m happy (and lucky) that I have met him; he naturally became my tutor and guide through my PhD. From no one else during my entire professional career, I’ve learned that much.
Open access: no