Temperature-dependent regulation of flowering mediated by liquid-liquid phase separation of GIGANTEA and MEDIATOR25 in arabidopsis

다국어 초록 (Multilingual Abstract)

Flowering in plants is strongly influenced by environmental cues, among which photoperiod and ambient temperature play central roles by modulating FLOWERING LOCUS T (FT) expression. Although FT transcription depends on transcription factors and the Mediator–RNA polymerase II machinery, how temperature regulates flowering remains unclear. Here, I identify two temperature-dependent liquid–liquid phase separation (LLPS) modules that integrate these environmental signals to control flowering. First, I show that the FKF1–GI module, a key regulator of photoperiodic flowering, also mediates temperature-responsive flowering through reversible LLPS. GI forms liquid-like nuclear condensates at low temperature, whereas high temperature induces FKF1 accumulation, enabling FKF1 to release GI from condensates and form a nuclear-dispersed FKF1–GI complex that promotes SVP degradation under short-day conditions. Consistent with this mechanism, temperature sensitivity is reduced in fkf1 and gi mutants. Second, I demonstrate that MED25, a prion–like domain–containing Mediator subunit, undergoes temperature-dependent LLPS to regulate CO–dependent FT activation. At low temperature, MED25 forms condensates that sequester CO away from the FT promoter, whereas warm temperature disperses MED25, allowing it to function as a co-activator with CO to induce FT expression. These results suggest that LLPS in the FKF1–GI–SVP and MED25–CO pathways plays a key role in how plants respond to temperature within the photoperiodic flowering system.

다국어 초록 (Multilingual Abstract)

Flowering in plants is strongly influenced by environmental cues, among which photoperiod and ambient temperature play central roles by modulating FLOWERING LOCUS T (FT) expression. Although FT transcription depends on transcription factors and the Mediator–RNA polymerase II machinery, how temperature regulates flowering remains unclear. Here, I identify two temperature-dependent liquid–liquid phase separation (LLPS) modules that integrate these environmental signals to control flowering. First, I show that the FKF1–GI module, a key regulator of photoperiodic flowering, also mediates temperature-responsive flowering through reversible LLPS. GI forms liquid-like nuclear condensates at low temperature, whereas high temperature induces FKF1 accumulation, enabling FKF1 to release GI from condensates and form a nuclear-dispersed FKF1–GI complex that promotes SVP degradation under short-day conditions. Consistent with this mechanism, temperature sensitivity is reduced in fkf1 and gi mutants. Second, I demonstrate that MED25, a prion–like domain–containing Mediator subunit, undergoes temperature-dependent LLPS to regulate CO–dependent FT activation. At low temperature, MED25 forms condensates that sequester CO away from the FT promoter, whereas warm temperature disperses MED25, allowing it to function as a co-activator with CO to induce FT expression. These results suggest that LLPS in the FKF1–GI–SVP and MED25–CO pathways plays a key role in how plants respond to temperature within the photoperiodic flowering system.

목차 (Table of Contents)

• Introduction 1
• (1) FT as a central florigen integrating photoperiod and temperature cues 1
• (2) Thermosensory flowering and temperature-dependent FT regulation 2
• (3) Biophysical principles of temperature-responsive liquidliquid phase separation 4
• (4) Interaction principles underlying condensate formation 6
• (5) Temperature-responsive LLPS as a mechanism for flowering time regulation 7
• (6) Photoperiodic regulation by the GIFKF1 module and temperature responsiveness 9
• (7) MED25-mediated photoperiodic regulation and potential temperature-dependent roles 11
• MATERIALS and METHODS 13
• Result 33
• Part 1. High-temperautre induced FKF1 accumulation promotes flowering by dispersion of GI and degradation of SVP 33
• (1) Flowering of fkf1 and gi is less sensitive to high temperature 33
• (2) The FKF1GI complex interacts with SVP 38
• (3) The FKF1GI module degrades SVP at high ambient temperature 48
• (4) GI undergoes LLPS 55
• (5) GI LLPS is reversed by FKF1 at high temperature 64
• (6) GI LLPS is crucial for thermal control of SVP accumulation 70
• Part 2. The mediator complex subunit MED25 promotes warm temperature-induced flowering in Arabidopsis 78
• (1) med25 mutant exhibits thermo-insensitive flowering time 79
• (2) MED25/PFT1 controls flowering time through its interaction with CO 86
• (3) MED25/PFT1 does not affect CO protein stability 92
• (4) Temperature-dependent phase separation of MED25/PFT1 is mediated by prion-like domains (PrDs) 97
• (5) CO exhibits phase separation like MED25/PFT 1 104
• (6) MED25/PFT1 regulates CO phase separation 107
• (7) PIF4 is recruited into MED25 condensates 110
• (8) GI undergoes LLPS independently of MED 25 112
• (9) GI does not affect the phase separation of CO 117
• DISCUSSION 121
• (1) Temperature-dependent LLPS of GI as a regulatory switch in the FKF1GI module 121
• (2) Broader implications of GI LLPS and unresolved mechanistic questions 122
• (3) Temperature-responsive LLPS of MED25 and its role in temperature-dependent activation 123
• (4) Concluding model and future perspectives 124
• REFERENCES 126
• 국문 요약 139