Thermosensor FUST1 Triggers Heat Stress Granules in Arabidopsis

In the rapidly evolving field of plant biology, understanding how plants perceive and respond to environmental stressors is crucial for advancing agricultural resilience in the face of climate change. A groundbreaking study led by Geng, Li, Quan, and colleagues has recently unveiled an elegant molecular mechanism by which Arabidopsis plants detect and respond to elevated temperatures. Published in Cell Research in 2025, this research uncovers the role of a novel thermosensor protein, FUST1, which acts as a molecular trigger to prime heat-induced stress granule formation through biomolecular condensation. This discovery sheds profound light on the intracellular dynamics that enable plants to survive and adapt during heat stress, opening new frontiers in plant molecular biology and stress physiology.

Temperature fluctuations constitute one of the most pervasive environmental challenges affecting plant health and productivity. Elevated heat stress disrupts cellular homeostasis and protein stability, threatening overall plant viability. To counter such challenges, plants have evolved sophisticated sensing and response pathways that detect minute changes in ambient temperature and translate them into appropriate biochemical and physiological reactions. Until now, the precise identity and mechanism of the molecular thermosensors responsible for initiating heat stress responses at a subcellular level remained unclear. The current study addresses this gap by identifying FUST1 as a pivotal thermosensor that orchestrates the assembly of stress granules, a critical step in the cellular defense against thermal damage.

Stress granules (SGs) are membrane-less organelles formed by the dynamic condensation of specific proteins and RNAs in response to adverse conditions, including heat stress. These biomolecular condensates serve to temporarily sequester and regulate mRNA molecules, modulating translation and protecting the cellular transcriptome under stress. The formation of SGs is a hallmark of eukaryotic stress responses; however, how exactly plants control SG assembly in response to thermal cues has not been fully elucidated. The new findings establish that FUST1 acts upstream in this process, effectively sensing heat elevation and driving SG nucleation through a process known as liquid-liquid phase separation (LLPS), thereby modulating gene expression under heat stress conditions.

A closer examination of FUST1 reveals that it belongs to a previously uncharacterized class of proteins harboring temperature-sensitive intrinsically disordered regions (IDRs) that undergo conformational changes upon heat exposure. When ambient temperatures rise beyond a critical threshold, these IDRs facilitate FUST1’s condensation, promoting the local enrichment of SG components in the cytoplasm of Arabidopsis cells. This phase transition triggers the coalescence of messenger ribonucleoprotein complexes (mRNPs) into SGs, effectively halting general translation to conserve energy and protect the cell’s proteome from aberrant aggregation during heat stress.

Utilizing state-of-the-art live-cell imaging coupled with biophysical assays, the researchers demonstrated that FUST1 condensation is both reversible and tightly regulated. Upon returning to basal temperatures, FUST1 droplets dissolve, dismantling the stress granules and allowing normal mRNA translation processes to resume. This reversible physical state change exemplifies a sophisticated molecular switch that finely tunes plant stress responses in real-time, ensuring cellular plasticity in the face of fluctuating environmental conditions.

One of the most striking aspects of this study is the biochemical characterization of FUST1’s IDRs, which display hallmark features associated with phase separation, including low complexity sequences enriched in polar amino acids like glutamine and serine. These IDRs confer responsiveness to temperature changes by modulating intermolecular interactions that favor condensate assembly at elevated temperatures. Moreover, post-translational modifications such as phosphorylation were found to modulate FUST1’s propensity to phase separate, highlighting an additional layer of regulatory control critical for cellular homeostasis.

Genetic knock-out experiments further cemented FUST1’s role in heat stress adaptation. Arabidopsis mutants lacking FUST1 exhibited severely impaired stress granule formation and heightened sensitivity to heat stress, characterized by reduced survival rates and compromised photosynthetic efficiency. These phenotypic consequences underscore FUST1’s indispensable function in plant thermotolerance and stress granule biogenesis, demonstrating that thermosensing and condensation-driven SG dynamics are tightly linked to plant fitness under thermal challenge.

The research also delved into the transcriptomic changes associated with FUST1-mediated SG formation. RNA sequencing revealed that during heat stress, FUST1-dependent SG assembly selectively sequesters specific transcripts coding for heat-sensitive proteins, potentially preventing their translation and safeguarding cellular machinery. This selective sequestration implies a highly coordinated translational repression strategy deployed by plants to prioritize stress-responsive gene expression while conserving cellular resources.

Expanding beyond Arabidopsis, the study suggests that FUST1 homologs may be conserved across various plant species, providing a universal mechanism for temperature sensing and SG regulation. This conservation opens exciting possibilities for biotechnological applications aimed at engineering thermotolerance in crop plants by manipulating homologous thermosensor proteins or harnessing their phase separation properties to enhance stress resilience.

The application of advanced biophysical techniques such as fluorescence recovery after photobleaching (FRAP) was critical in delineating the dynamic nature of FUST1 condensates. The liquid-like properties of these condensates facilitate rapid exchange of components, critical for enabling plants to swiftly respond to fluctuating temperatures. The precise biophysical parameters governing these phase transitions establish foundational principles for understanding how biomolecular condensation integrates environmental cues into cellular signaling networks.

Beyond the fundamental biological insights, the discovery of FUST1’s thermosensory function has broad implications for agriculture. With global temperatures rising and heat stress posing a growing threat to crop productivity, manipulating stress granule dynamics represents a novel avenue for developing heat-tolerant plants. Engineering FUST1 expression or modulating its phase behavior pharmacologically could offer innovative strategies to bolster plant resilience in warming climates.

Importantly, this study bridges the gap between molecular biophysics and plant physiology, highlighting the emerging paradigm that phase separation is not merely a biochemical curiosity but a vital regulator of stress adaptation in living organisms. FUST1 exemplifies how biomolecular condensation can serve as a dynamic molecular switch linking environmental stimuli to complex cellular outcomes, a concept that may extend well beyond plants into broader eukaryotic biology.

The authors also discuss potential cross-talk between FUST1-driven stress granule pathways and other known thermosensory mechanisms, such as heat shock protein networks and calcium signaling. This integration likely forms a robust and layered defense system, with FUST1 acting as a frontline sensor rapidly initiating protective condensate formation, while other pathways sustain longer-term stress acclimation.

Future research directions proposed by the team focus on delineating the interactome of FUST1 within the stress granule milieu, identifying additional co-factors that modulate its condensation dynamics. Investigating how environmental parameters like osmotic stress or oxidative stress interplay with thermal sensing may reveal further complexity in plant stress granule regulation and cross-protection mechanisms.

The technological impact of this work extends to the methodological advancements demonstrated in probing phase separation under physiological conditions in planta. The combination of genetic, biochemical, and cutting-edge imaging approaches establishes a blueprint for dissecting phase separation phenomena in complex multicellular organisms, a frontier area in molecular biology.

Altogether, this landmark study not only identifies FUST1 as a pivotal thermosensor mediating heat-induced stress granule formation in Arabidopsis but also reinforces the centrality of biomolecular condensation as a versatile regulatory mechanism in cellular stress responses. By illuminating the molecular choreography underlying plant adaptation to heat, Geng and colleagues pave the way for innovative biotechnological solutions to enhance crop resilience, addressing one of the most pressing challenges in global food security.

Subject of Research: Identification and characterization of the thermosensor FUST1 and its role in heat-induced stress granule formation via biomolecular condensation in Arabidopsis.

Article Title: A thermosensor FUST1 primes heat-induced stress granule formation via biomolecular condensation in Arabidopsis.

Article References:
Geng, P., Li, C., Quan, X. et al. A thermosensor FUST1 primes heat-induced stress granule formation via biomolecular condensation in Arabidopsis. Cell Res (2025). https://doi.org/10.1038/s41422-025-01125-4

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Tags: advancements in plant molecular biologyArabidopsis heat stress responsebiomolecular condensation in plantsenvironmental stressors in agricultureheat-induced stress granule formationintracellular dynamics of heat stressmechanisms of thermosensing in plantsmolecular mechanisms in plant biologyplant resilience to climate changesignaling pathways in plant stress physiologytemperature fluctuations and plant healththermosensor protein FUST1