Regulation of Arabidopsis photoreceptor CRY2 by two distinct E3 ubiquitin ligases

Yadi Chen,Tiantian Su,Deshu Lin,Zhensheng Gao,Xiaohua Hu,Xu Wang,Siyuan Liu,James A Wohlschlegel,Hsiaochi Huang,Huibo Ren,Chentao Lin,Qin Wang

doi:10.1038/s41467-021-22410-x

Abstract

Cryptochromes (CRYs) are photoreceptors or components of the molecular clock in various evolutionary lineages, and they are commonly regulated by polyubiquitination and proteolysis. Multiple E3 ubiquitin ligases regulate CRYs in animal models, and previous genetics study also suggest existence of multiple E3 ubiquitin ligases for plant CRYs. However, only one E3 ligase, Cul4COP1/SPAs, has been reported for plant CRYs so far. Here we show that Cul3LRBs is the second E3 ligase of CRY2 in Arabidopsis. We demonstrate the blue light-specific and CRY-dependent activity of LRBs (Light-Response Bric-a-Brack/Tramtrack/Broad 1, 2 & 3) in blue-light regulation of hypocotyl elongation. LRBs physically interact with photoexcited and phosphorylated CRY2, at the CCE domain of CRY2, to facilitate polyubiquitination and degradation of CRY2 in response to blue light. We propose that Cul4COP1/SPAs and Cul3LRBs E3 ligases interact with CRY2 via different structure elements to regulate the abundance of CRY2 photoreceptor under different light conditions, facilitating optimal photoresponses of plants grown in nature.

Highlights

Cryptochromes (CRYs) are photoreceptors or components of the molecular clock in various evolutionary lineages, and they are commonly regulated by polyubiquitination and proteolysis
We have previously shown that the blue light-dependent ubiquitination and proteolysis of cryptochrome 2 (CRY2) is diminished but not completely abolished in the cop[1] null mutant[22], suggesting the existence of another E3 ubiquitin ligase in addition to Cul4COP1/SPAs
We analyzed CRY2 complexomes isolated from transgenic Arabidopsis plants overexpressing GFP-CRY2, using the immunoprecipitation-mass spectrometry (IP-MS)[20], and identified LRB1 and LRB2 as CRY2-associated proteins in a blue light-dependent manner (Supplementary Table 1)

Summary

Introduction

Cryptochromes (CRYs) are photoreceptors or components of the molecular clock in various evolutionary lineages, and they are commonly regulated by polyubiquitination and proteolysis. We propose that Cul4COP1/SPAs and Cul3LRBs E3 ligases interact with CRY2 via different structure elements to regulate the abundance of CRY2 photoreceptor under different light conditions, facilitating optimal photoresponses of plants grown in nature. Arabidopsis cryptochrome 2 (CRY2) is one of the best studied plant CRYs that mediate blue light inhibition of cell elongation and photoperiodic promotion of floral initiation[11,12]. These physiological activities of CRY2 are regulated by at least three blue light-dependent mechanisms. The activity of CRY2 homooligomers are positively regulated by protein phosphorylation reactions catalyzed by four related protein kinases PPKs (Photoregulatory Protein Kinases 1–4)[18,19,20]

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Results

Conclusion