Engineering Chimeras by Fusing Plant Receptor-like Kinase EMS1 and BRI1 Reveals the Two Receptors' Structural Specificity and Molecular Mechanisms.

Guang Wu,Chenxi Li,Qunwei Bai,Qiuling Wang,Bowen Zheng,Lei Wu,Guishuang Li,Hongyan Ren,Huan Liu

doi:10.3390/ijms23042155

Guang Wu, Chenxi Li + Show 7 more

Open Access

https://doi.org/10.3390/ijms23042155

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Abstract

Brassinosteriods (BRs) are plant hormones essential for plant growth and development. The receptor-like kinase (RLK) BRI1 perceives BRs to initiate a well-known transduction pathway which finally activate the transcription factors BZR1/BES1 specifically regulating BR-mediated gene expression. The RLK EMS1 governs tapetum formation via the same signaling pathway shared with BRI1. BRI1 and EMS1 have a common signal output, but the gene structural specificity and the molecular response remain unclear. In this study, we identified that the transmembrane (TM), intracellular juxtamembrane (iJM), kinase, and leucin-rich repeats 1-13 (LRR1-13) domains of EMS1 could replace the corresponding BRI1 domain to maintain the BR receptor function, whereas the extracellular juxtamembrane (eJM) and LRR1-14 domains could not, indicating that the LRR14-EJM domain conferred functional specificity to BRI1. We compared the kinase domains of EMS1 and BRI1, and found that EMS1’s kinase activity was weaker than BRI1’s. Further investigation of the specific phosphorylation sites in BRI1 and EMS1 revealed that the Y1052 site in the kinase domain was essential for the BRI1 biological function, but the corresponding site in EMS1 showed no effect on the biological function of EMS1, suggesting a site regulation difference in the two receptors. Furthermore, we showed that EMS1 shared the substrate BSKs with BRI1. Our study provides insight into the structural specificity and molecular mechanism of BRI1 and EMS1, as well as the origin and divergence of BR receptors.

Highlights

Plants have evolved a large number of cell-surface receptor proteins to sense and respond to developmental and environmental cues
In order to seek the structural subunits in EXCESS MICROSPOROCYTES1 (EMS1) that can replace BRASSINOSTEROID INSENSITIVE 1 (BRI1), we divided the functional domains of BRI1 and EMS1 based on the mentioned structural features
The proportion of dephosphorylated BRI1 EMS SUPPRESSOR 1 (BES1) was lower in the BE(eJM) transgenic plants than the BE(TM) and BE(KD) plants (Figure 1F). These results suggested that the kinase domain (KD) and TM domains in EMS1 could replace these domains in BRI1 to maintain the BR receptor function, whereas the extracellular juxtamembrane (eJM) domain of EMS1 diminished the BR receptor function

Summary

Introduction

Plants have evolved a large number of cell-surface receptor proteins to sense and respond to developmental and environmental cues Many of these receptors are leucine-rich repeat receptor-like kinases (LRR-RLKs) with (i) an extracellular LRRs domain perceiving the cognate ligands, (ii) a transmembrane domain, and (iii) a cytoplasmic kinase domain activating downstream signaling [1,2]. (EMS1) LRR-RLK and its small protein ligand TAPETUM DETERMINANT1 (TPD1) are required for determining the fate of tapetal cells via a signaling transduction pathway shared with BRI1 [12,13,14,15,16]. BRI1 and EMS1 with SERKs lead to the trans-phosphorylation between the cytoplasmic kinase domains of receptors and SERK co-receptors, and to the subsequent activation of the cytoplasmic signaling events [17,20]

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