Functional Characterization of Rice Aspartic Protease (OsAP77) Gene in Response to Bacterial and Fungal Pathogens

Through the microarray analysis in rice treated by probenazole (PBZ), a chemical inducer of disease resistance, we previously reported that an aspartic protease (OsAP77) gene was PBZ-inducible. To elucidate  the role(s) of this gene in defense response against pathogens, we took two approaches; one is to use transgenic rice plants harboring the chimeric gene consisting of the promoter of OsAP77 and the structural gene encoding β-glucuronidase (GUS) reporter and the other is to use the gene-knockout (KO) mutant line by the insertion of a rice retrotransposon, Tos17. Histochemical analysis showed that GUS activity was specifically detected in the vascular tissues of the transgenic leaves. The GUS activity in the vascular tissues was remarkably induced not only by the infection with Magneporthe oryzae or Xanthomonas oryzae pv. oryzae, but also by signaling molecules that have roles in defense and stress response, such as salicylic acid, isonicotinic acid, hydrogen peroxide or abscisic acid. The KO mutant line of OsAP77 was tested for infection by M. oryzae or X. oryzae pv. oryzae. The symptom severity was compared among three groups of plants; homozygous, heterozygous and wild type plants for OsAP77 mutation. As a result, homozygous plants showed the most severe symptoms. These results suggest that OsAP77 has a positive role in defense response against pathogens. This work was supported by the Program for Promotion of Basic and Applied Researches in Bio-oriented Industry (BRAIN).