Activation loop phosphorylation of a non-RD receptor kinase initiates plant innate immune signaling

作者：Kyle W. Bender, Daniel Couto, Yasuhiro Kadota, Alberto P. Macho, Jan Sklenář, Paul Derbyshire, Marta Bjornson, Thomas A. DeFalco, Annalise Petriello, Maria Font Farre, Benjamin Schwessinger, Vardis Ntoukakis, Lena Stransfeld, Alexandra M. E. Jones, Frank L.H. Menke, Cyril Zipfel · 发表于：Proceedings of the National Academy of Sciences · 年份：2021 · DOI：10.1073/pnas.2108242118 · 被引用次数：40 · 研究领域：Plant-Microbe Interactions and Immunity、Polysaccharides and Plant Cell Walls、Plant Pathogenic Bacteria Studies

Receptor kinases (RKs) are fundamental for extracellular sensing and regulate development and stress responses across kingdoms. In plants, leucine-rich repeat receptor kinases (LRR-RKs) are primarily peptide receptors that regulate responses to myriad internal and external stimuli. Phosphorylation of LRR-RK cytoplasmic domains is among the earliest responses following ligand perception, and reciprocal transphosphorylation between a receptor and its coreceptor is thought to activate the receptor complex. Originally proposed based on characterization of the brassinosteroid receptor, the prevalence of complex activation via reciprocal transphosphorylation across the plant RK family has not been tested. Using the LRR-RK ELONGATION FACTOR TU RECEPTOR (EFR) as a model, we set out to understand the steps critical for activating RK complexes. While the EFR cytoplasmic domain is an active protein kinase in vitro and is phosphorylated in a ligand-dependent manner in vivo, catalytically deficient EFR variants are functional in antibacterial immunity. These results reveal a noncatalytic role for EFR in triggering immune signaling and indicate that reciprocal transphoshorylation is not a ubiquitous requirement for LRR-RK complex activation. Rather, our analysis of EFR along with a detailed survey of the literature suggests a distinction between LRR-RKs with RD- versus non-RD protein kinase domains. Based on newly identified phosphorylation sites that regulate the activation state of the E...