Enhancement of Rice Resistance to Bacterial Blight by Overexpressing BrCP3 Gene of Brassica rapa

Brassica rapa cysteine protease 3 (BrCP3) is an endopeptidase member of C1A family (papain-like) and CA clan of cysteine protease. Members of papain-like cysteine protease (CP) have emerged to be key enzymes involved in cell death in response to biotic and environmental stresses. Recent progress of CP research features its diverse and overlapping role in basal and effector-triggered immunity. This study was carried out to characterize BrCP3 gene in Chinese cabbage and explore its function in rice - Xanthomonas oryzae pv. oryzae pathosystem. Phylogenetic analysis and BLASTP search of its amino acid sequence to the Arabidopsis Protein TAIR 10 database identified BrCP3 as the closest ortholog of Arabidopsis RD21a. The full-length cDNA of BrCP3 was cloned and transformed into the genome of japonica rice cv. 'Gopum'. Constitutive overexpression of the transgene is driven by Ubi-1 promoter in pFLCIII vector. Regenerated single copy overexpression rice lines were inoculated with three Xoo Korean isolates. Regulation of rice resistance through cysteine protease activity is evident in the overexpression lines which showed enhanced immunity to three isolates as depicted by reduced lesion length compared with the wild type. Our initial results implicate an interesting biological function of BrCP3 in rice system that has never been reported before.