Self-incompatibility in Papaver: A MAP kinase signals to trigger programmed cell death.

Self-incompatibility (SI) in higher plants prevents inbreeding through specific recognition and rejection of incompatible ("self") pollen. In Papaver rhoeas, S proteins encoded by the pistil component of the S-locus interact with incompatible pollen, triggering a Ca(2+)-dependent signaling network resulting in programmed cell death (PCD). We recently showed that a mitogen-activated protein kinase (MAPK) is involved in loss of pollen viability, stimulation of caspase-3-like (DEVDase) activity and later DNA fragmentation in incompatible pollen. As p56 appears to be the only MAPK activated by SI, our data suggest that p56 could be the MAPK responsible for mediating SI-induced PCD.