Poster: Late and Moved Abstracts

Abs # 1393: A putative receptor of oligochitin elicitor -binding protein from plasma membrane of rice cells

Presenter:	Kaku, Hanae , hanaek@nias.affrc.go.jp
Authors	Kaku, Hanae  (A)   Okada, Mitsuo  (A)   Tsukada, Kouji  (A)   Minami, Eiichi  (A)   Shibuya, Naoto  (A) (B)
Affiliations:	(A): Dept. of Biochemistry, National Institute of Agrobiological Sciences, Tsukuba, Japan (B): Dept. Life Sciences, Meiji University, Kawasaki, Kanagawa, Japan

N-Acetylchitooligosaccharides (DP 6-8, GlcNAc6-8) is a potent elicitor for suspension-cultured rice cells, inducing a set of defense-related responses. Putative receptor (EBP) for this elicitor was identified in the plasma membrane (PM) of rice cells by binding studies as well as affinity labeling. The purified EBP showed specific binding activity to ¹²⁵I-labeled GlcNAc8 -APEA derivative as proved by the affinity crosslinking with glutaraldehyde. SDS-PAGE followed by silver-staining as well as affinity labeling showed the presence of two protein bands, corresponding to 75 and 55 KDa. Both bands retained the elicitor binding activity, suggesting that EBP was partially cleaved with endogenous protease during purification. The survey of the EBP gene based on the partial amino acid sequence of EBP is in progress. Using mutant rice cells lacking functional G-protein a-subunit, oligochitin elicitor was shown not to couple to heterotrimeric G-protein, one of the most important signal transducer from the cell surface to down-stream in various cellular responses. Furthermore, affinity labeling experiments indicated the occurrence of elicitor-induced dimerization of EBP, which is typical for various receptor protein kinases, on the plasma membrane. These results may suggested that the oligochitin receptor may belong to a family of receptor protein kinases. Plasma membrane EBP was not only found in suspension-cultured rice cells but also found in rice leaves and roots, suspension-cultured cells of barley, carrot, soybean and wheat. These results indicate that the defense system based on oligochitin recognition distributes widely among plant as a kind of ginnate immune system in planth.