IAA3及PIFs整合光与生长素通路调控拟南芥下胚轴伸长的分子机制研究

Light is a key environmental cue and it interacts with pivotal phytohormone auxin to regulate multiple aspects during plant development. It is reported that light acts to inhibit hypocotyl cell elongation but auxin functions to promote hypocotyl elongation. However, how these two signals are integrated to regulate the hypocotyl elongation is still poorly known. Aux/IAA family proteins are core repressors in auxin signaling pathway. Among them, IAA3 has been indicated to inhibit hypocotyl elongation. In this proposed project, we utilized the dominant gain-of-function mutant of IAA3/SHY2, shy2-3, to further find IAA3 inhibits hypocotyl elongation in a light intensity dependent manner. In addition, shy2-3 mutant represents a similar phenotype with PIF1/3/4/5 quadruple mutant pifq. Our preliminary results indicated IAA3 - PIFs probably function to integrate light and auxin signaling to corporately regulate hypocotyl elongation. We will next investigate the molecular mechanism underlying IAA3 - PIFs controlled hypocotyl elongation on both post-transcription and protein level. By combination of genetic studies and analysis of the IAA3 - PIFs regulated genes, we will uncover the biological significance of this IAA3 - PIFs interaction. These studies will further improve our understanding on the molecular mechanism of signal cross-talk between light and auxin in the regulation of hypocotyl elongation.

环境因素光和内源激素生长素相互作用、交叉调控植物生长发育的多个方面。在植物下胚轴伸长调控中，光形态建成抑制拟南芥下胚轴的伸长，而生长素在一定浓度范围内促进下胚轴的伸长。然而，光信号与生长素信号之间是如何协作调控幼苗下胚轴伸长的分子机理仍不清楚。本研究以IAA3/SHY2的功能获得型突变体shy2-3为切入点，发现IAA3抑制下胚轴伸长与光强相关。这一表型与光信号通路重要调控因子PIF1/3/4/5的功能缺失突变体pifq表型十分类似。初步研究证据暗示IAA3和PIFs是整合光与生长素信号通路的一个重要节点。本项目将进一步从蛋白积累水平和转录活性等层面深入研究IAA3和PIFs之间的关系，同时结合这两个蛋白所调控基因的转录表达和相关遗传材料的表型输出，进一步揭示IAA3及PIFs整合光与生长素通路调控植物下胚轴伸长的新机制。

在种子萌发出土的过程中光会诱导植物发生显著的形态变化，即由暗形态建成到光形态建成，这一过程对植物开启后续的生长发育非常重要。对下胚轴伸长的调控是光形态建成过程最显著的变化之一。光和生长素作为调控植物生长发育的重要因子相互拮抗调节拟南芥下胚轴伸长，表现为光信号通路诱导光形态建成从而抑制下胚轴的伸长，而生长素在一定浓度范围内促进下胚轴的伸长。光与生长素信号通路通过哪些关键分子节点来协作调控下胚轴伸长仍有待深入研究。我们从生长素信号通路负调控因子IAA3/SHY2在不同光照强度下下胚轴的表型入手，发现与野生型相比，IAA3功能获得型突变体在不同光强下表现为较短的下胚轴；而IAA3功能降低时，拟南芥幼苗在多种光强条件下都表现为更长的下胚轴表型，这表明IAA3在光调节的下胚轴生长过程中是必需的。遗传分析表明IAA3调控下胚轴生长依赖于光形态建成的重要负向调控转录因子PIFs。此外，我们发现IAA3蛋白与PIFs蛋白具有直接相互作用，并且IAA3蛋白更倾向于结合非磷酸化的PIFs。转录组测序发现IAA3负调PIFs靶标基因的表达。同时，生化实验表明，IAA3是通过抑制PIFs与下游靶标基因启动子的结合来调控下游基因，进而控制下胚轴生长。我们的研究进一步揭示了植物通过IAA3和PIFs整合光信号与生长素信号通路调控下胚轴伸长的分子机理。