Plants often respond to stimuli with dramatic rearrangements of their actin cytoskeleton. Identification of the signals and transduction machinery that lead to changes in actin dynamics and organization is therefore of considerable interest. The self-incompatibility (SI) response in the field poppy, Papaver rhoeas L., involves signal-mediated inhibition of pollen tube growth in response to interaction with incompatible S proteins. This triggers larges increases in [Ca2+]i and downstream a number of signalling components and targets are modified in incompatible pollen. We have observed dramatic alterations to the actin cytoskeleton in response to SI and established that this involves massive and sustained actin depolymerization. We have begun to identify and characterize several actin-binding proteins, including profilin and gelsolin, that may cooperate to transduce the signal from a Ca2+ wave into destruction of the cytoskeletal network that is essential for tip growth. Recently, we identified a role for programmed cell death (PCD) signalling cascades being triggered in SI and that a caspase-like activity is involved in mediating irreversible pollen tube inhibition. Our data suggest that there is evidence for crosstalk between the SI-induced signalling cascades. We are currently investigating whether the signalling cascades for actin alterations and PCD are linked and whether the actin cytoskeleton functions as a sensor of cellular stress and can initiate PCD. Our current knowledge of the signalling cascade in P. rhoeas pollen therefore involves both early and late responses that work in concert to ensure that pollen does not effect fertilization. Early cessation of tip growth is mediated by destruction of the actin cytoskeleton, and this appears to cross-talk with a subsequent PCD cascade that commits the pollen to die.
Thomas, S. G., Huang, S., Staiger, C. J., & Franklin-Tong, V. E. (2006). Signals and targets triggered by self-incompatibility in plants: Recognition of self can be deadly. In Communication in Plants: Neuronal Aspects of Plant Life (pp. 75–93). Springer-Verlag Berlin Heidelberg. https://doi.org/10.1007/978-3-540-28516-8_6