[Nature Two] Heavyweight! Two Thermoreceptors In Plants Have Been Discovered!

1. On 15 May 2024, Nature published online a paper entitled "The temperature sensor TWA1 is required for thermotolerance in Arabidopsis" from the collaboration of Erwin Grill and Alexander Christmann at the Technical University of Munich, Germany. thermotolerance in Arabidopsis". The study reveals that TWA1 is a temperature-sensing transcriptional co-regulator in Arabidopsis that is required for basal and acquired thermotolerance in Arabidopsis (Arabidopsis thaliana).

This study shows that TWA1 is a disordered protein whose critical temperature sensing function is mediated through the highly variable region of the N terminus. At high temperatures, TWA1 in plants changes conformation and then interacts with the jasmonate-associated MYC-like transcription factor JAM and the TPL and TPR to assemble a repressive complex.

2. In July 2020, a research paper entitled "A prion-like domain in ELF3 functions as a thermosensor in Arabidopsis" was published online in Nature by Philip A. Wigge's group at the University of Cambridge, UK. A prion-like domain in ELF3 functions as a thermosensor in Arabidopsis". The study reveals that the ELF3 protein in Arabidopsis thaliana contains a prion-like domain (PrD), which senses the external temperature at high temperatures through a phase transition that allows ELF3 to rapidly switch between active and inactive states.

In Arabidopsis, the Evening Complex (EC), a central component of the biological clock, represses the transcription of PIF4/5 at night, causing the growth rate of plant hypocotyls to peak at dawn. It consists of a complex of three proteins, including scaffolding proteins and three proteins such as the temperature-responsive ELF3, the small α-helix protein ELF4, and the DNA-binding protein LUX. One of them, ELF3, contains polyglutamine (polyQ) repeat sequences predicted to be regions of prion structural domains (PRDs). In addition, it was previously found that ELF3 in various Arabidopsis ecotypes from natural populations contained polyQ repeats that varied in length from 7 to 29 in length and were associated with phenotypic variation.

This study first investigated whether the length of the polyQ repeat sequence affects ELF3 activity? The results showed that ELF3 transgenes complementing different polyQ lengths in the elf3-1 mutant were more thermosensitive with longer lengths, suggesting that the PrD of ELF3 in Arabidopsis plays a role in temperature sensing in Arabidopsis. In addition, this study found that StELF3 from potato grown in a temperate climate has a smaller predicted PRD compared with Arabidopsis, whereas BdELF3 from dicotyledonous phragmites is not predicted to have a PRD region, and both of its proteins are not thermoresponsive in Arabidopsis at 27 degrees Celsius. In addition, PrD from Arabidopsis was confirmed to be thermoresponsive by the chimeric ELF3-BdPrD showing suppression of temperature-responsive flowering. Since ELF3 is a temperature-dependent transcriptional repressor, this study further confirmed that ELF3 occupancy on target genes was found to change with increasing temperature and that this process was dependent on PrD, suggesting that PrD directly regulates the thermo-responsiveness of ELF3 binding on target genes (see below).

The study next explored whether temperature directly regulates ELF3 activity? Therefore, the study constructed ELF3-GFP fusion protein transgenic plants, which were found to have a diffuse signal of ELF3-GFP at 17°C, whereas multiple bright spots were formed at 35°C, and an increase in the length of polyQ also led to a greater tendency to form spots. Further studies purified ELF3 PrD fused to GFP (PrD-GFP), and it was found that ELF3 PrD was more soluble at low temperatures, whereas decreasing salt concentration and pH induced a phase transition of PrD-GFP to form micrometre-sized spherical droplets that underwent phase separation, with a mid-point temperature of 28.7±1.8°C. The above results illustrate that ELF3 is capable of adopting two conformations, an active soluble form and a higher order multimeric form in which bright spots can be seen at hotter temperatures, both of which are reversible.