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Chitin-Induced Dimerization Activates a Plant Immune Receptor

29-06-2012

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.

Tight packing of the three LysMs in AtCERK1-ECD.