Cloning and characterization of a probenazole-inducible gene for an intracellular pathogenesis-related protein in rice.

Probenazole (3-allyloxy-1,2-benzisothiazole-1,1-dioxide) induces disease resistance in rice against rice blast fungus. To investigate the molecular mechanism of probenazole-induced resistance, we isolated and characterized a cDNA clone of a probenazole-inducible gene in rice, which encoded a protein designated PBZ1. Sequence analysis revealed that significant homology at the amino acid level exists between the predicted PBZ1 protein and intracellular pathogenesis-related (IPR) proteins. Accumulation of PBZ1 mRNA was not induced by wounding, but markedly induced by inoculation with rice blast fungus. In addition, it was induced sooner by inoculation with an incompatible race than that with a compatible race. On the other hand, when the accumulation of the PBZ1 mRNA was examined after treatment with probenazole-related compounds, it was not fully correlated with anti-rice blast activity. However, it was induced after treatment with N-cyano-methyl-2-chloro-isonicotinamide (NCI), which belongs to another group of compounds known to induce disease resistance. Thus, although the accumulation of the PBZ1 mRNA was not fully correlated with anti-rice blast activity, our findings suggest that the PBZ1 gene has an important function during the disease resistance response in rice.