Orateur
Description
Order in the disordered - Molecular determinants of phase separation and its physiological role in plant temperature sensing
S. Hutin, JR. Kumita, P.Wigge, L. Costa, M. Tully, C. Zubieta
As sessile organisms, plants must live with constant environmental fluctuations and stress constraints. The increased average temperature and prolonged periods of extreme weather due to climate alter plant phenology, presenting a critical challenge for our food security. While direct sensing of their environment is critical for plant survival, the mechanisms plants use to monitor their environment have remained elusive. Our recent studies suggest that one important mechanism for a direct environmental sensing is via protein-mediated liquid–liquid phase separation (LLPS). LLPS is an important mechanism enabling the dynamic compartmentalization of biological macromolecules, such as proteins and nucleic acids, as a function of the cellular environment. In vitro, phase separation is sensitive to pH, ionic strength and, perhaps most notably, temperature [1]–[3]. This suggests that, in vivo, LLPS may act as a wide-ranging sensing mechanism, allowing a fine-tuned response to the changing physicochemical environment. Recent studies established that protein-mediated LLPS serves as an environmental sensing mechanism in response to external stimuli including temperature, water and nutrient availability, pathogen challenges and stress conditions, demonstrating that it is likely an important mechanism for directly sensing biotic and abiotic variables [4]–[11]. However, the underlying molecular mechanisms, the different physicochemical variables that trigger LLPS in vitro and in vivo, and its physiological role are the subject of ongoing debate due to the challenges in studying this complex biophysical phenomenon. We have identified an environmental sensing proteins involved in temperature sensing and response via LLPS; EARLY FLOWERING 3 (ELF3) [4]. The protein contains a largely unstructured prion-like domain (PrLD) that act as a driver of LLPS in vivo and in vitro. The PrLD contains poly-glutamine (polyQ) tracts, whose length varies across natural Arabidopsis accessions.
We use a combination of in vivo, biochemical, biophysical and structural techniques to investigate the dilute and condensed phases of the ELF3 PrLD with varying polyQ lengths. We demonstrate that the dilute phase of the ELF3 PrLD forms a monodisperse higher order oligomer that does not depend on the presence of the polyQ sequence. This species undergoes LLPS in a pH and temperature-sensitive manner and the polyQ region of the protein tunes the initial stages of phase separation [12]. Furthermore, the condensed phase rapidly undergoes aging and forms a hydrogel as shown by fluorescence and atomic force microscopies. We demonstrate that the ELF3 PrLD hydrogel assumes a semi-ordered structure using small angle X-ray scattering, electron microscopy and X-ray diffraction [12]. These experiments demonstrate a rich structural landscape for a PrLD protein and provide a framework to analyse and tune the structural and biophysical properties of biomolecular condensates.
References
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[12] S. Hutin u. a., „Phase separation and molecular ordering of the prion-like domain of the thermosensory protein EARLY FLOWERING 3“, Biophysics, preprint, März 2023. doi: 10.1101/2023.03.12.532276.
