1.9.17
ROLE OF THE NOVEL MANNOSE-BINDING RICE LECTIN IN INTERACTION BETWEEN RICE PLANT AND RICE BLAST FUNGUS

T TERAOKA, K HIRANO, M NAGAOKA, H WADA, H TAKAHASHI and D HOSOKAWA

Laboratory of Plant Pathology, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan

Background and objectives
The mannose-binding rice lectin (MRL) has a potential activity to agglutinate the rice pathogens such as Xanthomonas campestris pv. oryzae and Magnaporthe grisea [1]. Now we focus on the hypothesis that MRL may function as plant antibodies or receptors in host-parasite interaction. Some reports [2, 3] have been presented to support our hypothesis. Distribution of MRL, determination of the content of MRL in healthy and diseased leaves, and effects of some treatments with the monoclonal antibody against MRL, some sugars or concanavalin A (ConA) on infection of M. grisea were checked to clarify the role of MRL in host-parasite interaction.

Materials and methods
The distribution of MRL was observed by immuno-staining methods with the monoclonal antibody against MRL. The content of MRL was determined by ELISA methods with the monoclonal antibody after extraction with 0.05 N HCl. Spores of M. grisea were inoculated on detached leaf sheath or intact leaf blade.

Results and conclusions
MRL was found to be distributed in all parts of seedlings including roots in all cultivars tested, but was localized at cell wall and periplasm around mesophyll and epidermal cells. These observations coincided with the fact that MRL was extracted by simple immersion in 0.15 M NaCl. The content of extractive MRL rapidly changed when inoculated with both compatible and incompatible races of M. grisea. Pre-treatment with the monoclonal antibody, a-D-mannose or 0.15 M NaCl enhanced the elongation of infection hypha in the compatible rather than in the incompatible interaction. By contrast, pre-treatment with ConA suppressed appressorium formation and the elongation of infection hypha. Co-treatment with the monoclonal antibody and an inducer to elicit resistant reactions (such as saccharin, probenazole, or mycelial extract) suppressed inducer activity. These results strongly support our hypotheses that MRL may function as plant antibodies or receptors in the host-parasite interaction.

References
1. Teraoka T, Sakakibara T, Den E, Hosokawa D, Watanabe M, 1990. Agricultural and Biological Chemistry 54, 3053-3056.
2. Kano H, Toyoki T, Haga M, Sekizawa T,1988. Agricultural and Biological Chemistry 52, 3163-3164.
3. Valent B, Hamer JE, Howard RJ, Chumley G, 1987. Science 239, 288-240.