Arbor function of TRANSPARENT TESTA GLABRA 1 and LIGHT REGULATED WD TLWD scaffold proteins in Arabidopsis clocks includes transcriptional repression through PSEUDO RESPONSE REGULATORS

Arabidopsis circadian oscillators contain DNA-binding proteins that function at specific times of the day. In contrast, we have discovered a unique continuous function of WD40-repeat scaffold proteins from the TRANSPARENT TESTA GLABRA-1 (TTG1), LIGHT REGULATED WD1 and LIGHT REGULATED LWD2 subfamily (TLWD) which is essential to maintain circadian rhythms. Gene expression analyses indicate multifunctional activity of TLWD in both transcriptional activation and repression. TLWD proteins interact with an array of circadian oscillator activators and repressors that act sequentially through the diel cycle. While TLWD proteins were known to participate in activator complexes, our data indicate a novel role of TLWD in transcriptional repression through complex formation with repressors from the PSEUDO RESPONSE REGULATOR (PRR) family. In the mechanical clock analogy, TLWD scaffold proteins constitute the arbor to which transcription factors, which represent the cogs, bind to sustain circadian rhythms.

拟南芥昼夜节律振荡器（circadian oscillators）中含有可在每日特定时段行使功能的DNA结合蛋白（DNA-binding proteins）。与之相对，本研究发现了来自透明种皮无毛1（TRANSPARENT TESTA GLABRA-1，TTG1）、光调控WD1（LIGHT REGULATED WD1）与光调控LWD2（LIGHT REGULATED LWD2）亚家族（TLWD亚家族）的WD40重复支架蛋白（WD40-repeat scaffold proteins）的独特持续性功能，该功能对于维持昼夜节律至关重要。基因表达分析结果表明，TLWD蛋白在转录激活与转录抑制过程中均具备多方面功能活性。TLWD蛋白可与一系列在昼夜周期中依次发挥作用的昼夜节律振荡器激活因子与抑制因子发生相互作用。尽管此前已知TLWD蛋白可参与激活因子复合物的组成，但本研究数据显示，TLWD蛋白可通过与伪响应调节因子（PSEUDO RESPONSE REGULATOR，PRR）家族的抑制因子形成复合物，从而在转录抑制过程中发挥全新功能。若以机械时钟为类比，TLWD支架蛋白相当于时钟的轴架，而作为齿轮的转录因子可结合于此，以此维持昼夜节律。