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Plant Cell. 2020 Feb 21. pii: tpc.00772.2019. doi: 10.1105/tpc.19.00772. [Epub ahead of print]

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

Author information

1
The Salk Institute for Biological Studies CITY: La Jolla STATE: California POSTAL_CODE: 92037 United States Of America [US].
2
The Salk Institute for Biological Studies CITY: La Jolla STATE: California United States Of America [US].
3
Salk Institute CITY: San Diego STATE: Caliornia POSTAL_CODE: 92037 United States Of America [US].
4
Cold Spring Harbor Laboratory (CSHL) CITY: Cold Spring Harbor STATE: NY POSTAL_CODE: 11724 United States Of America [US].
5
The Salk Institute for Biological Studies 10010 N. Torrey Pines Road CITY: La Jolla STATE: California POSTAL_CODE: 92009-8711 United States Of America [US].
6
The Salk Institute for Biological Studies CITY: La Jolla STATE: California POSTAL_CODE: 92037 United States Of America [US] chory@salk.edu.

Abstract

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.

PMID:
32086365
DOI:
10.1105/tpc.19.00772
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