Date of Award
1-1-2025
Document Type
Dissertation
Degree Name
Ph.D. in Biological Science
First Advisor
Yongjian Qiu
Second Advisor
Sarah Liljegren
Third Advisor
Scott Baerson
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Transcriptional regulation is a fundamental part of all biological systems, enabling organisms to respond to environmental changes. PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) is the central transcription factor (TF) responsible for modulating large-scale transcriptomic changes in response to elevated temperature in plants. This dissertation aims to elucidate the molecular mechanisms behind PIF4-mediated transcriptional regulation in Arabidopsis thaliana, addressing its role in driving phenotypic changes in response to elevated temperatures such as thermosensory elongation. The objective is to identify the unique properties of PIF4 that facilitate its role as a pivotal TF and to increase our understanding of its interaction with the transcriptional machinery.
Mediator complex, an essential transcriptional coactivator in eukaryotes, serves as a functional bridge linking TFs and RNA Polymerase II. Chapter 1 of this dissertation focuses on identifying the mediator subunit responsible for interacting with PIF4 during thermomorphogenetic transcriptional reprogramming. Genetic, transcriptomic, and interaction assays collectively identify the mediator subunit MED14 as being essential for the transcription of thermoresponsive genes, operating in direct association with PIF4.
Chapter 2 addresses the sequence features that confer upon PIF4 the unique ability to trigger large-scale transcriptomic changes at warmer temperatures. Based on recent findings, large-scale transcriptomic reprogramming is aided by the formation of transcriptional condensates through the intrinsically disordered regions (IDRs) of TFs. We locate the acidic transactivation domain (TAD), the basic DNA-binding domain (DBD), and a part of the helix-loop-helix (HLH) oligomerization domain of PIF4 within its central IDR region and perform targeted mutagenesis of these sequence features to test their roles in PIF4’s condensate formation ability and their capacity to effect the thermo-elongation in plants. Results highlight the oligomerization domain of PIF4 to be indispensable for PIF4’s central role in thermo-transcriptional regulation.
Lastly, the dissertation investigates the role of MED14 as a mediator subunit in condensate formation for the regulation of thermo-transcription. We investigate a conserved IDR region in MED14 with a compositional bias towards serine residues. Targeted mutagenesis of these serine residues impairs its droplet-formation ability without affecting its ability to bind to PIF4 droplets in vitro. However, in planta analyses reveal the inability of MED14 to form phase-separated condensates and the disruption of serine residues in MED14’s IDR does not have an effect on MED14’s ability to regulate the thermo-elongation response.
Taken together, this dissertation provides insight into PIF4’s function as a central TF being linked to its ability to oligomerize rather than its TAD or DBD functions, both of which can be functionally buffered by other PIFs. This dissertation also provides evidence against condensate formation by PIF4 or the mediator complex as the means of thermo-transcriptional regulation.
Recommended Citation
Bajracharya, Abhishesh, "Molecular Mechanisms of PIF4/MED14-Mediated Transcriptional Regulation in Thermomorphogenetic Response of Arabidopsis Thaliana" (2025). Electronic Theses and Dissertations. 3240.
https://egrove.olemiss.edu/etd/3240