Abstract
The hypersensitive response (HR) involves well-organized programmed cell death (PCD). PCD in animals and plants is thought to share components that have caspase activities. However, no plant proteinases exhibiting caspase activities had yet been identified. To identify a functional homolog of caspase in plants, we investigated hypersensitive cell death in TMV-infected tobacco plants. A caspase-1 inhibitor abolished the hypersensitive cell death. A biotinylated caspase-1 inhibitor that was infiltrated into the tobacco leaves bound to the 38- and 40-kDa components of the leaves. We found these components corresponded to two forms of vacuolar processing enzyme (VPE). VPE is a cysteine proteinase responsible for maturation and/or activation of vacuolar proteins. VPE inhibitor also abolished the hypersensitive cell death. The VPE activity appeared rapidly at the early stage of the HR and declined before the appearance of lesions. These results suggest that VPE exhibiting caspase-1-like activity is essential for TMV-induced hypersensitive cell death.
