Chimeric Activators and Repressors Define HY5 Activity and Reveal a Light-Regulated Feedback Mechanism

First author: Yogev Burko; Affiliations: The Salk Institute for Biological Studies (萨克生物研究所): La Jolla, USA

Corresponding author: Joanne Chory

The first exposure to light marks a crucial transition in plant development. This transition relies on the transcription factor HY5 controlling a complex downstream growth program. Despite its importance, its function in transcription remains unclear. Previous studies have generated lists of thousands of potential target genes and competing models of HY5 transcription regulation. In this work, we carry out detailed phenotypic and molecular analysis of constitutive activator and repressor HY5 fusion proteins. Using this strategy, we were able to filter out large numbers of genes that are unlikely to be direct targets, allowing us to eliminate several proposed models of HY5's mechanism of action. We demonstrate that the primary activity of HY5 is promoting transcription, and that this function relies on other, likely light-regulated, factors. In addition, this approach reveals a molecular feedback loop via the COP1/SPA E3-ubiquitin ligase complex suggesting novel mechanism which maintains low HY5 in the dark, primed for rapid accumulation to reprogram growth upon light exposure. Our strategy is broadly adaptable to the study of transcription factor activity. Lastly, we show that modulating this feedback loop can generate significant phenotypic diversity in both Arabidopsis and tomato.

植物破土而出暴露在光下的一瞬间代表着植物发育过程的一种重要的转变。该转变过程依赖转录因子HY5，该基因控制着下游复杂的生长程序。但是除了其重要性，我们对于该基因作用于转录的功能还不是很清楚。先前的研究已经获得了数千个HY5可能的靶基因，并且也提出了不同的HY5转录因子作用模型。本文中，作者对组成型激活子和抑制子HY5融合蛋白进行了详细的表型和分子鉴定。利用该策略，使得作者排除掉了很多HY5非直接靶向的候选基因，同时也排除了一些HY5作用机制的模型假设。作者发现HY5的主要活性是促进转录，并且该功能依赖于一些其它的因子，并且这些因子很可能受光调控。另外，该方法发现了一个通过COP1/SPA E3泛素连接酶复合物介导的分子反馈回路，揭示了一个新的机制作用于黑暗环境下维持低水平的HY5，并为植物暴露在光下时快速积累HY5做好准备以重编程下游的生长。本文所利用的策略可以适用于其它转录因子活性的研究。最后，作者发现通过改变该反馈回路在拟南芥和西红柿中均能够产生显著的表型多态性。

通讯：Joanne Chory (https://www.salk.edu/scientist/joanne-chory/)

个人简介：俄亥俄州奥伯林学院，学士；伊利诺伊大学，博士；哈佛医学院，博士后。

研究方向：植物响应光照环境变化而改变其形状和大小的机制。

doi: https://doi.org/10.1105/tpc.19.00772

Journal: Plant Cell

First Published: February 21, 2020