INDUCTION OF CHITINASES AND BETA-1,3-GLUCANASES IN RHIZOCTONIA SOLANI-INFECTED RICE PLANTS - ISOLATION OF AN INFECTION-RELATED CHITINASE CDNA CLONE

Extracts from several rice cultivars (Oryza sativa L. cvs IR58, 74586 and SC33) infected with the sheath blight pathogen Rhizoctonia solani, were analyzed to determine the isozyme distribution of chitinases (EC 3.2.1.14) and beta-1,3-glucanases (EC 3.2.1.39). Upon infection by th e fungal pathogen, two chitinases of 28 and 35 kDa and two beta-1,3-gl ucanases of 30 and 32 kDa were shown to be induced in all cultivars. T hey resolved into multiple isozymes under nondenaturing electrophoreti c conditions. Wounding, but not bacterial infection, resulted in the i nduction of these hydrolytic enzymes. Even though fungal infection res ulted in induction of chitinases and beta-glucanases in all cultivars, some cultivars that were moderately resistant to R. solani appeared t o have higher levels of specific isozymes. A chitinase cDNA clone was identified by screening a library, prepared from RNA isolated from R. solani-infected rice plants, with an antibody to a bean chitinase. Thi s cDNA encoded a 35-kDa chitinase which was significantly different in amino acid sequence from other rice chitinases described so far. Nort hern blot analysis of RNA from infected rice plants indicated that tra nscripts corresponding to this chitinase gene were induced upon fungal infection.