The oat mitochondrial permeability transition and its implication in victorin binding and induced cell death.
The mitochondrion has emerged as a key regulator of apoptosis, a form of animal programmed cell death (PCD). The mitochondrial permeability transition (MPT), facilitated by a pore-mediated, rapid permeability increase in the inner membrane, has been implicated as an early and critical step of apoptosis. Victorin, the host-selective toxin produced by Cochliobolus victoriae, the causal agent of victoria blight of oats, has been demonstrated to bind to the mitochondrial P-protein and also induces a form of PCD. Previous results suggest that a MPT may facilitate victorin's access to the mitochondrial matrix and binding to the P-protein: (i) victorin-induced cell death displays features similar to apoptosis; (ii) in vivo, victorin binds to the mitochondrial P-protein only in toxin-sensitive genotypes whereas victorin binds equally well to P-protein isolated from toxin-sensitive and insensitive oats; (iii) isolated, untreated mitochondria are impermeable to victorin. The data implicate an in vivo change in mitochondrial permeability in response to victorin. This study focused on whether oat mitochondria can undergo a MPT. Isolated oat mitochondria demonstrated high-amplitude swelling when treated with spermine or Ca2+ in the presence of the Ca2+-ionophore A23187, and when treated with mastoparan, an inducer of the MPT in rat liver mitochondria. In all cases, swelling demonstrated size exclusion in the range 0.9-1.7 kDa, similar to that found in animal mitochondria. Further, MPT-inducing conditions permitted victorin access to the mitochondrial matrix and binding to the P-protein. In vivo, victorin treatment induced the collapse of mitochondrial transmembrane potential within 2 h, indicating a MPT. Also, the victorin-induced collapse of membrane potential was clearly distinct from that induced by uncoupling respiration, as the latter event prevented the victorin-induced PCD response and binding to P-protein. These results demonstrate that a MPT can occur in oat mitochondria in vitro, and are consistent with the hypothesis that an MPT, which allows victorin access to the mitochondrial matrix and binding to the P-protein, occurs in vivo during victorin-induced PCD.
Curtis
Marc J
MJ
Molecular Cellular Biology Program, and Center for Gene Research and Biotechnology, Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902, USA.
Wolpert
Thomas J
TJ
D000408:Alamethicin / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D018554:Avena / Q000502:physiology*; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism* / Q000494:pharmacology; D036341:Intercellular Signaling Peptides and Proteins; D007473:Ion Channels / Q000502:physiology*; D007476:Ionophores / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009183:Mycotoxins / Q000378:metabolism; D010455:Peptides; D011485:Protein Binding; D013096:Spermine / Q000494:pharmacology; D014862:Wasp Venoms / Q000494:pharmacology
D003574:Cytochrome c Group; D005656:Fungal Proteins; D036341:Intercellular Signaling Peptides and Proteins; D007473:Ion Channels; D007476:Ionophores; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009183:Mycotoxins; D010455:Peptides; D014862:Wasp Venoms; C094015:Victorin protein, Cochliobolus victoriae; D000408:Alamethicin; D013096:Spermine; D000001:Calcimycin; D008345:Manganese; C037500:mastoparan; D008274:Magnesium; D002118:Calcium