Scaffold protein RACK1 regulates BR signaling by modulating the nuclear localization of BZR1

Brassinosteroids (BRs) are a group of plant-specific steroid hormones, which induces the rapid nuclear localization of the positive transcriptional factors BRASSINAZOLE RESISTANT1/2 (BZR1/2). However, the mechanisms underlying the regulation of nucleocytoplasmic shuttling of BZR1 remain to be fully elucidated. In this study, we show that the scaffold protein Receptor for Activated C Kinase 1 (RACK1) from Arabidopsis is involved in BR signaling cascades through mediating the nuclear localization of BZR1, which is tightly retained in the cytosol by the conserved scaffold protein 14-33s. RACK1 can interact with BZR1 and competitively decrease the 14-3-3 interaction with BZR1 in cytosol, which efficiently enhances the nuclear localization of BZR1. 14-3-3 also retains RACK1 in cytosol through their interaction. Conversely, BR treatment enhances the nuclear localization of BZR1 by disrupting the 14-3-3 interaction with RACK1 and BZR1. Our study uncovers a new mechanism that integrates two kinds of conserved scaffold proteins (RACK1 and 14-3-3) coordinating BR signaling event.

Automated summary

This study reveals that the scaffold protein RACK1 is involved in the BR signaling pathway in Arabidopsis by mediating the nuclear localization of BZR1. RACK1 interacts with BZR1 and competes with 14-3-3 proteins, leading to enhanced nuclear localization of BZR1. Furthermore, BR treatment disrupts the interaction between 14-3-3 and RACK1/BZR1, promoting the nuclear localization of BZR1.