Zhu, Z.; Trenner, J.; Quint, M.

Plants have evolved to anticipate and adjust their growth and development in response to environmental changes. To mitigate the negative influence of global climate change on crop production, understanding the key regulators of plant performance is imperative. EARLY FLOWERING 3 (ELF3) is such a regulator involved in the circadian clock and thermomorphogenesis. Arabidopsis thaliana ELF3 contains a prion-like domain (PrD) that functions as a thermosensor, enabling its liquid-liquid phase separation at high ambient temperatures. To understand the conservation of this function across the plant kingdom, we traced the evolutionary emergence of ELF3 with a focus on the PrD, which confers liquid-liquid phase separation. We observed that the presence of the domain within ELF3, mainly contributed by the length of polyglutamine (polyQ) repeats, is largely restricted to Brassicales. This suggests that thermosensory function of ELF3 is a rather recent and secondary acquirement that was added to its main function. By analyzing 319 natural Arabidopsis thaliana accessions, we detected a wide range of polyQ length variation in ELF3. However, polyQ length is only weakly associated with geographic origin, climate conditions, and classic temperature-responsive phenotypes. Consequently, we conclude that although the emergence of PrD is not likely to be a key driver of environmental adaptation, it adds an extra layer to the role of ELF3 in thermomorphogenesis.