Signalling to programmed cell death in self-incompatible pollen

Many higher plants use self incompatibility (SI) to prevent self-fertilization. In Papaver rhoeas, the rejection of “self” pollen involves a Ca2+-dependent signalling network that triggers programmed cell death (PCD), providing a neat way to get rid of unwanted incompatible (“self”) pollen. Several SI-induced events have been identified, including: rapid depolymerization of the actin and microtubule cytoskeleton ([Snowman et al., 2002] and [Poulter et al., 2008]); phosphorylation of a soluble inorganic pyrophosphatase ([Rudd et al., 1996] and [de Graaf et al., 2006]); activation of a MAPK, p56 ([Rudd et al., 2003] and [Li et al., 2007]), and PCD, which involves several caspase-like activities, including a DEVDase, VEIDase and a LEVDase ([Bosch and Franklin-Tong, 2007] and [Thomas and Franklin-Tong, 2004]). PCD provides a precise mechanism for the specific destruction of “self” pollen. Our focus recently has been on beginning to attempt to understand how the signalling networks involved in SI-mediated PCD are integrated. I will present recent data providing evidence for actin, microtubules and MAPK signalling to activate caspase-like activities, resulting in PCD.