Cell death is an important process of plant responses to development and biotic/abiotic stresses. In rice plants, PBZ1, a PR10 family protein, has been shown to accumu-late in tissues undergoing cell death. However, the func-tion of PBZ1 in cell death remains yet to be demonstrated. Here, we report that exogenous recombinant PBZ1 protein induces cell death in rice suspension-cultured cells (SCCs) and also in leaves of Nicotiana tabacum in a dose-dependent manner. This finding was confirmed in vivo in transgenic Arabidopsis lines harboring the PBZ1 gene under the control of a dexamethasone (DEX)-inducible promoter. The DEX-treated leaves of transgenic Arabidopsis induced expression of PBZ1 at transcript and protein levels and showed cell death morphology. TUNEL analysis detected DNA fragmentation, a hallmark of programmed cell death, in rice SCCs treated with the PBZ1 protein. Recombinant PBZ1 protein also exhibited RNase activity and exhibited internalization inside BY-2 cells. Taken together, PBZ1 induces cell death not only in rice, but also in tobacco and Arabidopsis via its RNase activity inside the cell. PBZ1 could be used as a marker to understand the me-chanism by which PBZ1 confers the cell death morpholo-gy in rice and other model plants.

Keywords: dexamethasone, PBZ1, PR-10 protein family, programmed cell death, RNase activity, TUNEL