Poster: Plant Pathogen/Symbiont Interactions

Abs # 701: Involvement of Vacuolar Processing Enzyme in TMV-Induced Hypersensitive Cell Death in Tobacco Leaves

Presenter:	Hatsugai, Noriyuki , hatsugai@gr.bot.kyoto-u.ac.jp
Authors	Hatsugai, Noriyuki  (A) (B)  Kuroyanagi, Miwa  (C)   Yamada, Kenji  (B)   Meshi, Tetsuo  (C)   Nishimura, Mikio  (A) (B)  Nishimura, Ikuko  (C)
Affiliations:	(A): Department of Molecular Biomechanics, School of Life Science, Graduate University for Advanced Studies (B): Department of Cell Biology, National Institute for Basic Biology (C): Department of Botany, Graduate School of Science, Kyoto University

Programmed cell death (PCD) is a basic physiological process that occurs under various stresses and during the development of animals and plants. The process of controlled cell death in animals is well organized by caspases that are cysteine proteinases. In plants, many studies have shown that caspase-like activities are induced in dying cells. However, no plant proteinases exhibiting caspase activities have yet been identified. To identify a functional homolog of caspase in plants, we investigated hypersensitive cell death in tobacco mosaic virus (TMV)-infected tobacco plants. Hypersensitive cell death is a type of well-organized cell death in higher plants. A caspase-1-specific inhibitor abolished the formation of lesions showing hypersensitive cell death in the infected leaves, suggesting that a caspase-1 homolog is involved in TMV-induced hypersensitive cell death. A biotinylated caspase-1 inhibitor that was infiltrated into the tobacco leaves specifically bound to the 38- and 40-kDa components of the leaves. We found these components corresponded to two forms of a vacuolar enzyme (vacuolar processing enzyme, VPE), which is a cysteine proteinase responsible for maturation and/or activation of vacuolar proteins. A VPE-specific inhibitor also abolished the TMV-induced hypersensitive cell death, as did a caspase-1-specific inhibitor. VPE had caspase activity toward a caspase-1-specific substrate. Thus, the proteinase responsible for the caspase-1-like activity was identified as VPE. The VPE activity appeared rapidly and transiently at the early stage of the TMV-induced hypersensitive response in tobacco leaves and declined before the appearance of lesions. Our results suggest that VPE regulates the early process of the TMV-induced hypersensitive cell death.