Chitin-Induced Dimerization Activates a Plant Immune Receptor

TLDR

Pattern recognition receptors confer plant resistance to pathogen infection by recognizing conserved pathogen‑associated molecular patterns, and the Arabidopsis chitin elicitor receptor kinase 1 (AtCERK1) directly binds chitin via its LysM‑containing ectodomain to trigger immune responses. AtCERK1 binds chitin through its LysM‑containing ectodomain, and chitin octamers act as bivalent ligands that induce AtCERK1‑ECD dimerization, a process inhibited by shorter oligomers. Crystal structure analysis shows chitin binds AtCERK1‑ECD via a LysM domain and three chitin residues, and that chitin octamers promote AtCERK1‑ECD dimerization—disruption of this dimerization by mutation or overexpression impairs signaling, confirming that dimerization is essential for activation.

Abstract

Pattern recognition receptors confer plant resistance to pathogen infection by recognizing the conserved pathogen-associated molecular patterns. The cell surface receptor chitin elicitor receptor kinase 1 of Arabidopsis (AtCERK1) directly binds chitin through its lysine motif (LysM)-containing ectodomain (AtCERK1-ECD) to activate immune responses. The crystal structure that we solved of an AtCERK1-ECD complexed with a chitin pentamer reveals that their interaction is primarily mediated by a LysM and three chitin residues. By acting as a bivalent ligand, a chitin octamer induces AtCERK1-ECD dimerization that is inhibited by shorter chitin oligomers. A mutation attenuating chitin-induced AtCERK1-ECD dimerization or formation of nonproductive AtCERK1 dimer by overexpression of AtCERK1-ECD compromises AtCERK1-mediated signaling in plant cells. Together, our data support the notion that chitin-induced AtCERK1 dimerization is critical for its activation.