Modulation of BIN2 kinase activity by HY5 controls hypocotyl elongation in the light

Jian Li,Congran Li,Jun-Jie Ling,Xing Wang Deng,Yangyang Fan,Yanyan Gong,William Terzaghi,Xinqi Gong,Nanxun Qin,Danmeng Zhu

doi:10.1038/s41467-020-15394-7

Abstract

ELONGATED HYPOCOTYL 5 (HY5), a basic domain/leucine zipper (bZIP) transcription factor, acts as a master regulator of transcription to promote photomorphogenesis. At present, it’s unclear whether HY5 uses additional mechanisms to inhibit hypocotyl elongation. Here, we demonstrate that HY5 enhances the activity of GSK3-like kinase BRASSINOSTEROID-INSENSITIVE 2 (BIN2), a key repressor of brassinosteroid signaling, to repress hypocotyl elongation. We show that HY5 physically interacts with and genetically acts through BIN2 to inhibit hypocotyl elongation. The interaction of HY5 with BIN2 enhances its kinase activity possibly by the promotion of BIN2 Tyr200 autophosphorylation, and subsequently represses the accumulation of the transcription factor BRASSINAZOLE-RESISTANT 1 (BZR1). Leu137 of HY5 is found to be important for the HY5-BIN2 interaction and HY5-mediated regulation of BIN2 activity, without affecting the transcriptional activity of HY5. HY5 levels increase with light intensity, which gradually enhances BIN2 activity. Thus, our work reveals an additional way in which HY5 promotes photomorphogenesis, and provides an insight into the regulation of GSK3 activity.

Highlights

ELONGATED HYPOCOTYL 5 (HY5), a basic domain/leucine zipper transcription factor, acts as a master regulator of transcription to promote photomorphogenesis
We found that the C-terminal domain of HY5 was sufficient for it to interact with BRASSINOSTEROIDINSENSITIVE 2 (BIN2) (Fig. 1b, c)
Many genes involved in hypocotyl elongation are the targets of HY5, such as LONG HYPOCOTYL IN FAR-RED 1 (HFR1)[8], FAR-RED ELONGATED HYPOCOTYL 1 (FHY1)[34], INDOLE-3-ACETIC ACID INDUCIBLE 19 (IAA19)[35], EXPANSIN 2 (EXP2)[35]

Summary

Introduction

ELONGATED HYPOCOTYL 5 (HY5), a basic domain/leucine zipper (bZIP) transcription factor, acts as a master regulator of transcription to promote photomorphogenesis. HY5 is one of these lightresponsive transcription factors that play a key role in repressing seedling hypocotyl elongation[4,5]. It belongs to the basic leucine zipper (bZIP) family of transcription factors[6]. The COP1-HY5 module represents the core regulatory mechanism that regulates seedling morphogenesis, including hypocotyl elongation. Many other proteins, such as CALMODULIN7 (CAM7), WRKY DNA-BINDING PROTEIN. 36 (WRKY36), and SHI-RELATED SEQUENCE5 (SRS5), regulate hypocotyl elongation by modulating the transcription of HY513–15, suggesting a central role of HY5 in the inhibition of hypocotyl elongation

Methods

Results

Conclusion