Induction of chitinases and β‐l,3‐glucanases in <i>Rhizoctonia solani</i>‐infected rice plants: Isolation of an infection‐related chitinase cDNA clone

Abstract

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 β‐l,3‐glucanases (EC 3.2.1.39). Upon infection by the fungal pathogen, two chitinases of 28 and 35 kDa and two β‐l,3‐glucanases of 30 and 32 kDa were shown to be induced in all cultivars. They resolved into multiple isozymes under nondenaturing electrophoretic conditions. Wounding, but not bacterial infection, resulted in the induction of these hydrolytic enzymes. Even though fungal infection resulted in induction of chitinases and β‐glucanases in all cultivars, some cultivars that were moderately resistant to R. solani appeared to 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. This cDNA encoded a 35‐kDa chitinase which was significantly different in amino acid sequence from other rice chitinases described so far. Northern blot analysis of RNA from infected rice plants indicated that transcripts corresponding to this chitinase gene were induced upon fungal infection.