A purine-type heat shock protein 90 inhibitor promotes the heat shock response in Arabidopsis

Geldanamycin is a macrocyclic heat shock protein 90 (HSP90) inhibitor that suppresses cancer cell proliferation. Since geldanamycin also promotes the heat shock response (HSR) in cells, this compound is used as a chemical inducer of the HSR in Arabidopsis. Although many types of HSP90 inhibitors that are different from the macrocyclic types have been developed in pharmaceutical research, non-macrocyclic HSP90 inhibitors have not been investigated in terms of whether they can induce the HSR in plants. Here, we determined the HSR-inducing activities in Arabidopsis of 10 non-macrocyclic HSP90 inhibitors including 2 benzamide derivatives, 3 purine derivatives, and 5 resorcinol derivatives. Among the tested inhibitors, PU-H71, which is a purine derivative, showed the highest HSR-inducing activity. The activity of PU-H71 was significantly higher than that of geldanamycin. The application of PU-H71 induced the HSR in all Arabidopsis seedlings. The HSP17.6C-CI and HSP70 proteins accumulated after the treatment with PU-H71. The seedlings treated with PU-H71 maintained more chlorophyll than the control seedlings after the heat stress. These results suggest that the purine-derivative HSP90 inhibitor PU-H71 enhanced the heat tolerance of Arabidopsis by promoting the HSR in the plant.