Date of Award
8-13-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Light is arguably the most important environmental stimuli for all of plant growth and survival. Not only does light serve as an energy source via photosynthesis, it also serves as a signal for developmental programming. Plants perceive light through light-responsive proteins termed photoreceptors. Phytochromes are conserved red/far-red light photoreceptors. In the model plant Arabidopsis thaliana (thale cress), phytochrome B (phyB) is the primary red light photoreceptor. PhyB is involved in regulating almost all developmental processes throughout the plant’s life cycle, from seedling germination to flowering. In response to red light, phytochromes photoconvert to a biologically active form, transport from the cytoplasm into the nucleus, and further compartmentalizes to form biomolecular condensates termed photobodies. Accumulating evidence indicates that phyB photobodies are essential for full-strength phytochrome-mediated signaling and physiological outputs. The Nusinow lab identified a protein, PHOTOPERIODIC CONTROL OF HYPOCOTYL 1 (PCH1), that is sufficient for stabilizing phytochrome B in its active conformation in vitro and necessary for photobody formation in vivo. However, how PCH1 promotes the phase separation of phyB into photobodies remained unknown. Here, using multiple high-resolution microscopy techniques, I show that phyB photobodies are liquid-liquid phase separated (LLPS) biomolecular condensates, and that PCH1 alters photobody dynamics and phyB molecule partitioning from the nucleoplasm into photobodies. I hypothesized that PCH1, through its predicted disordered protein structure, drives phyB photobody phase separation. Combining microscopy, genetics, and biochemistry, I characterized PCH1 protein domains. My results show that PCH1 is sufficient to phase separate, and that PCH1’s C-terminal regions are important for promoting PCH1-phyB nuclear localization and phase separation. My results show that PCH1 oligomerizes in vitro and suggests that phyB preferentially binds to PCH1’s predicted intrinsically disordered regions (IDRs) containing helices. Overall, I propose the following model in which PCH1 is a disordered protein that promotes phyB’s nuclear localization and modulates its phase separation to control Arabidopsis hypocotyl growth. Lastly, I helped develop an Expansion Microscopy method in Arabidopsis protoplasts that can be used for studying biomolecular condensates. Understanding how plants perceive light at the molecular level will help to identify genetic targets for engineering maximized sunlight capture of agriculturally important crops.
Language
English (en)
Chair and Committee
Dmitri Nusinow
Committee Members
Alex Holehouse; Joseph Jez; Lucia Strader; Ram Dixit
Recommended Citation
Pardi, Sarah Anne, "Investigation of PHOTOPERIODIC CONTROL OF HYPOCOTYL 1’s Role in Promoting Phytochrome B-Photobody Phase Separation" (2024). Arts & Sciences Electronic Theses and Dissertations. 3317.
https://openscholarship.wustl.edu/art_sci_etds/3317