Functional characterization of CEBiP and CERK1 homologs in arabidopsis and rice reveals the presence of different chitin receptor systems in plants

• Published in: Plant and cell physiology 2012-10, Vol.53 (10), p.1696-1706
• Main Authors: Shinya, Tomonori, Motoyama, Noriko, Ikeda, Asahi, Wada, Miyuki, Kamiya, Kota, Hayafune, Masahiro, Kaku, Hanae, Shibuya, Naoto
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - immunology; Arabidopsis - metabolism; Arabidopsis - microbiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Chitin - metabolism; Cytosol - metabolism; Gene Expression Regulation, Plant; Gene Knockout Techniques; Nicotiana - genetics; Nicotiana - metabolism; Oryza - immunology; Oryza - metabolism; Oryza - microbiology; Plant Proteins - metabolism; Plants, Genetically Modified; Protein Serine-Threonine Kinases - metabolism; Protein Structure, Tertiary; Receptors, Cell Surface - genetics; Receptors, Cell Surface - metabolism; Signal Transduction
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcs113

Chitin is a representative microbe-associated molecular pattern (MAMP) molecule for various fungi and induces immune responses in many plant species. It has been clarified that the chitin signaling in rice requires a receptor kinase OsCERK1 and a receptor-like protein (Os)CEBiP, which specifically binds chitin oligosaccharides. On the other hand, Arabidopsis requires a receptor kinase (At)CERK1 for chitin signaling but it is not clear whether the plant also requires a CEBiP-like molecule for chitin perception/signaling. To clarify the similarity/difference of the chitin receptor in these two model plants, we first characterized CEBiP homologs in Arabidopsis. Only one of three CEBiP homologs, AtCEBiP (LYM2), showed a high-affinity binding for chitin oligosaccharides similar to rice CEBiP. AtCEBiP also represented the major chitin-binding protein in the Arabidopsis membrane. However, the single/triple knockout (KO) mutants of Arabidopsis CEBiP homologs and the overexpressor of AtCEBiP showed chitin-induced defense responses similar to wild-type Arabidopsis, indicating that AtCEBiP is biochemically functional as a chitin-binding protein but does not contribute to signaling. Studies of the chitin binding properties of the ectodomains of At/OsCERK1 and the chimeric receptors consisting of ecto/cytosolic domains of these molecules indicated that AtCERK1 is sufficient for chitin perception by itself.