Isolation and characterization of cgchi3, a nodule-specific gene from Casuarina glauca encoding a class III chitinase

• Chitinases (EC 3.2.1.14) catalyse the hydrolysis of chitin, a homopolymer of beta-1,4-linked N-acetyl-D-glucosamine residues. Plant chitinases are involved in a wide variety of processes; in particular, their expression has been found to be enhanced in symbiotic and pathogenic plant-microbe interactions. During this work we have cloned and characterized a gene encoding a class III chitinase from actinorhizal nodules of Casuarina glauca (cgchi3). CGCHI3 was found to be encoded by a single gene that was specifically activated in nodules as compared with uninoculated control roots and leaves. The expression of this gene was further enhanced in nodules after salicylic acid treatment and completely repressed after wounding. In situ hybridisation analysis revealed that cgchi3 is an early nodulin gene, being expressed in the meristem and in the uninfected cortical cells of young nodules. Based on the obtained results we suggest that this gene is involved in nodule development. This is the first report on a class III chitinase coding gene that is specifically activated during actinorhizal symbiosis.

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