Vacuolar processing enzyme is essential for mycotoxin-induced cell death in Arabidopsis thaliana.
Some compatible pathogens secrete toxins to induce host cell death and promote their growth. The toxin-induced cell death is a pathogen strategy for infection. To clarify the executioner of the toxin-induced cell death, we examined a fungal toxin (fumonisin B1 (FB1))-induced cell death of Arabidopsis plants. FB1-induced cell death was accompanied with disruption of vacuolar membrane followed by lesion formation. The features of FB1-induced cell death were completely abolished in the Arabidopsis vacuolar processing enzyme (VPE)-null mutant, which lacks all four VPE genes of the genome. Interestingly, an inhibitor of caspase-1 abolished FB1-induced lesion formation, as did a VPE inhibitor. The VPE-null mutant had no detectable activities of caspase-1 or VPE in the FB1-treated leaves, although wild-type leaves had the caspase-1 and VPE activities, both of which were inhibited by a caspase-1 inhibitor. gammaVPE is the most essential among the four VPE homologues for FB1-induced cell death in Arabidopsis leaves. Recombinant gammaVPE recognized a VPE substrate with Km = 30.3 microm and a caspase-1 substrate with Km = 44.2 microm, which is comparable with the values for mammalian caspase-1. The gammaVPE precursor was self-catalytically converted into the mature form exhibiting caspase-1 activity. These in vivo and in vitro analyses demonstrate that gammaVPE is the proteinase that exhibits a caspase-1 activity. We show that VPE exhibiting a caspase-1 activity is a key molecule in toxin-induced cell death. Our findings suggest that a susceptible response of toxin-induced cell death is caused by the VPE-mediated vacuolar mechanism similar to a resistance response of hypersensitive cell death (Hatsugai, N., Kuroyanagi, M., Yamada, K., Meshi, T., Tsuda, S., Kondo, M., Nishimura, M., and Hara-Nishimura, I. (2004) Science 305, 855-858).
Kuroyanagi
Miwa
M
Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Yamada
Kenji
K
Hatsugai
Noriyuki
N
Kondo
Maki
M
Nishimura
Mikio
M
Hara-Nishimura
Ikuko
I
D000818:Animals; D017209:Apoptosis; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D061945:Caspase Inhibitors; D002384:Catalysis; D016923:Cell Death; D003546:Cysteine Endopeptidases / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D037341:Fumonisins / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018745:Genome, Plant; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007313:Insecta; D007477:Ions; D007700:Kinetics; D008854:Microscopy, Electron; D009154:Mutation; D009183:Mycotoxins / Q000633:toxicity*; D018521:Plant Physiological Phenomena; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D037341:Fumonisins; D007477:Ions; D009183:Mycotoxins; C056933:fumonisin B1; D003546:Cysteine Endopeptidases; C089278:vacuolar processing enzyme