The Role of Chito-Oligosaccharides in Plant Defense.

Chitin perception by plant receptors triggers various defense responses important for plant immunity. A step forward the understanding of the mechanism involved in the recognition of chitin by chitin-elicitor binding protein in rice, has been reached throughout an elegant combination of biochemical, NMR spectroscopic and computational investigations. The ecto-domain of the chitin-elicitor binding protein has been shown to be essential in the binding of chitin octa-saccharides. Such a degree of oligomerisation along with the participation of the N-acetyl groups, are required as clearly indicated by epitope mapping by NMR spectroscopy. Some further features of the protein-oligosaccharide interactions were further deciphered throughout the use of molecular modeling / docking investigations and site-directed mutagenesis. These indicated the pivotal role of the central lysine motif region.

These results show indicate that one chito-oligosaccharide bridges induces the dimerization of the two protein units, a feature which would form the structural basis of the biological function, i.e. an auto-phosphorylation of the receptor kinase. At this point in time, the fine details of the resulting architecture are not know, but an hypothetical model of the activation of the protein complex by a chito-octaose molecule has been elaborated and its validity needs further investigations.