title: Temporal and spatial activation of caspase-like enzymes induced by self-incompatibility in Papaver pollen.
abstract: Caspase-like proteases are universal mediators of programmed cell death (PCD). Because plants have no caspase homologs, establishing the nature of their caspase-like activities is of considerable importance to our understanding of PCD in plants. Caspase-3, displaying DEVD specificity, is a key executioner caspase in animal cells. Self-incompatibility (SI) is an important mechanism to prevent self-fertilization and inbreeding in higher plants by inhibiting incompatible pollen. In Papaver rhoeas, SI activates a caspase-3-like/DEVDase activity in incompatible pollen that plays a pivotal role in regulating PCD. Here we characterize the SI-induced caspase-like activities in detail; our work provides insights into the temporal and spatial activation of plant caspase-like enzymes. We show that SI also activates a VEIDase and a LEVDase and that the VEIDase plays a role in SI-induced PCD. The DEVDase and VEIDase are activated remarkably rapidly: detectable within 1-2 h after SI induction; the LEVDase activity peaks later. Importantly, we show live-cell imaging of a DEVDase activity in a higher plant cell; the SI-activated DEVDase has a cytosolic and nuclear localization. We also demonstrate that SI induces a rapid and substantial cytosolic acidification that matches the in vitro pH optima for the SI-induced caspase activities. Because both cytosolic acidification and nuclear caspase localization are observed during apoptosis in animal cells, our data provide striking parallels between SI-induced PCD and apoptosis in animal cells.
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Maurice
authors.initials: M
authors.lastname: Bosch
authors.forename: Vernonica E
authors.initials: VE
authors.lastname: Franklin-Tong
mesh_terms: D020169:Caspases / Q000378:metabolism*; D053938:DNA Fragmentation; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D010207:Papaver / Q000201:enzymology*; D011058:Pollen / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D020169:Caspases