Abstract
Extensive studies have provided evidence that caspase activity is involved in programmed cell death of plants as animals. However, no plant proteinases themselves that exhibit caspase activity have been identified. To identify a functional homolog of caspase in plants, we investigated hypersensitive cell death in tobacco mosaic virus (TMV) -infected tobacco plants. We present here that a vacuolar processing enzyme (VPE) which is a cysteine proteinase responsible for maturation and/or activation of vacuolar proteins, is a proteinase exhibiting caspase-1 activity, and that VPE is essential for virus-induced hypersensitive cell death. VPE deficiency decreased caspase-1 activity and prevented virus-induced hypersensitive cell death. The disintegration of the vacuolar membranes occurred in the leaves before visible lesions were formed. VPE deficiency suppressed the disintegration of the vacuolar membranes in the TMV -infected leaves. These results suggest that VPE is involved in vacuolar collapse, which triggers hypersensitive cell death.
