Abstract
Chitin is a typical MAMP derived from fungal cell walls and has an ability to induce immune responses in plants and animals. We recently identified CEBiP (rice) and CERK1/OsCERK1 (Arabidopsis/rice) as critical components for chitin signaling in these plants. They are a GPI-anchored protein and a receptor-like kinase (RLK), respectively. To understand whether Arabidopsis requires the presence of CEBiP-like molecule(s) for chitin signaling, we characterized CEBiP homologues in Arabidopsis. Chitin binding activity of CEBiP homologs were analyzed by using tobacco BY-2 expression system and affinity labeling with biotinylated-chitooctamers. One of these homologues (AtCEBiP1) expressed in BY-2 cells showed a high-affinity binding for chitin oligosaccharides. The binding characteristics of AtCEBiP1 was very similar to rice CEBiP. However, the knock-out mutant of AtCEBiP1 showed chitin-induced ROS generation similar to wild type Arabidopsis. These results indicated that AtCEBiP1 is biochemically functional as a chitin binding protein but does not significantly contributes to signaling, in other words, AtCERK1 may be sufficient for chitin perception and signaling in Arabidopsis.
