An amino acid integration in the heat receptor ELF3 Molecular mechanism of temperature signal regulating plant growth

In Arabidopsis, ELF3, ELF4 and LUX proteins form the EC complex. The EC complex binds directly to the promoters of PIF4 and PIF5 in vivo, thereby inhibiting PIF4 and PIF5 expression at night. PIF4, as a key transcription factor for light and temperature, binds to thousands of target genes to regulate their expression. High temperature can activate PIF4 activity, making it regulate plant thermal morphogenesis by integrating light, circadian rhythm and hormone signals, EC complex is a protein complex that inhibits gene expression, and helps higher plants sense environmental temperature and thermal form. ELF3 is a thermal sensor that plays a role in controlling the circadian rhythm, photoperiodic flowering, hypocotyl length, and response to light in an EC-dependent and EC-independent manner. PIF4 plays a key positive role in heat response gene expression and hypocotyl growth in Arabidopsis thaliana, but ELF3 negatively regulates the protein activity of growth promoting factor PIF4. Interestingly, a 2020 paper published in Nature by Jung et al. found that ELF3, as a heat sensor, gradually forms multiple distinct spot-like structures in the nucleus as the temperature increases due to the presence of the characteristic PrD. Similarly, increasing the length of the polyQ will enlarge the spots. In addition, after returning to normal temperature from mild high temperature, the EC complex will quickly return to normal activity. This result is contrary to what Ronald et al. stated in a 2021 paper: Warm temperatures inhibit ELF3 blotching, and since ELF3 blotching is associated with increased transcriptional activity of ELF3, a decrease in blotching may lead to decreased EC function at warm temperatures. As a result, the question of how ELF3 is regulated in warmer temperatures remains an open question. Overall design: After analyzing the genetic differences of the mutant material obtained through genetic variation, Ser 364 was found to have a mutation. Therefore, we hypothesized that the change of phosphorylation site affected the flowering time and hypocotyl length of Arabidopsis thaliana. The molecular mechanism of stable ELF3 protein was analyzed from the mutation site.

在拟南芥（Arabidopsis thaliana）中，ELF3、ELF4与LUX蛋白可形成EC复合物（Evening Complex）。该复合物可在体内直接结合PIF4与PIF5的启动子区域，从而在夜间抑制PIF4与PIF5的基因表达。PIF4作为光信号与温度信号应答的关键转录因子，可结合数千个靶基因以调控其表达。高温可激活PIF4的活性，使其通过整合光信号、昼夜节律信号与激素信号来调控植物的热形态建成。EC复合物是一类基因表达抑制型蛋白复合物，可协助高等植物感知环境温度并参与热形态建成。ELF3作为温度感受器，可通过EC依赖与EC非依赖两种方式参与调控昼夜节律、光周期开花、下胚轴长度以及光应答过程。PIF4在拟南芥的热应答基因表达与下胚轴生长中发挥关键的正向调控作用，而ELF3则对促生长因子PIF4的蛋白活性起到负调控作用。有趣的是，2020年Jung等人发表于《自然》（Nature）的研究发现，ELF3作为温度感受器，由于其特有的朊蛋白样结构域（prion-like domain，PrD），随着温度升高会在细胞核内逐渐形成多个清晰的斑点状结构；同理，增加多聚谷氨酰胺（polyglutamine，polyQ）的长度可使这些斑点体积增大。此外，当植物从温和高温环境恢复至正常温度后，EC复合物可快速恢复至正常活性状态。这一结果与Ronald等人2021年发表的研究结论相悖：Ronald等人的研究指出，温和高温会抑制ELF3斑点的形成，而由于ELF3斑点形成与ELF3的转录活性增强相关，斑点形成减少可能会导致温暖温度下EC复合物的功能下降。因此，ELF3在温暖温度下的调控机制仍是一个未解决的科学问题。本研究的整体实验设计如下：通过对经遗传变异获得的突变体材料进行遗传差异分析，我们发现Ser 364位点发生了突变。据此我们提出假设：该磷酸化位点的改变会影响拟南芥的开花时间与下胚轴长度。我们将从该突变位点入手，解析ELF3蛋白稳定性的分子调控机制。