Chitin-Induced Dimerization Activates a Plant Immune Receptor

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.

Structural basis for specific self-incompatibility response in Brassica

“…By comparison with RTKs, SRK9 homodimerization, though also contributed by the direct contacts between two SRK9 molecules, is mainly mediated by two independent SCR9 molecules. Despite this difference, our data support the idea that ligand-induced dimerization is important for the activation of an RK [32,33]. The dimerization model suggests that interaction between an SRK and an SCR may not always be translated into activation of the SRK, because their interaction may not necessarily result in receptor homodimerization.…”

Chitin and chitin-related compounds in plant–fungal interactions

“…Structurally, AtCERK1, an RLK, is composed of a transmembrane domain, three tandem LysMs in its ectodomain and an intracellular serine/threonine kinase domain (Miya et al 2007; Wan et al 2008) in Arabidopsis . Chitin-induced AtCERK1 homodimerisation has been proved to be necessary for its activation (Liu et al 2012). The chitin-induced signalling in Arabidopsis also required two other LysM-RLKs, named AtLYK4 and AtLYK5 (Wan et al 2012; Cao et al 2014).…”

“…The perception of shorter oligosaccharides such as chitotetraose could instead rely on monomeric receptors (Miyata et al 2014; Shinya et al 2015) as into each receptor’s LysM domain, half of this oligomer molecule (C4) fits (Liu et al 2012; Shinya et al 2015). …”

LYR3, a high‐affinity LCO‐binding protein of Medicago truncatula, interacts with LYK3, a key symbiotic receptor

“…For example, the LysM-RLK chitin elicitor receptor kinase 1 of A. thaliana (AtCERK1) interacts with other receptor proteins to mediate responses to different signals. This protein can bind chitooligosaccharides (COs) [4], but it also interacts with two CO-binding LysM-RLKs with dead kinase domains (AtLYK5/ AtLYK4) [5] and with two peptidoglycan-binding LysM receptor-like proteins (AtLYM1/AtLYM3) [6] to mediate defense responses to these GlcNAc-containing signals. In contrast, OsCERK1 from rice …”