Signal-mediated depolymerization of actin in pollen during the self-incompatibility response.
Signal perception and the integration of signals into networks that effect cellular changes is essential for all cells. The self-incompatibility (SI) response in field poppy pollen triggers a Ca(2+)-dependent signaling cascade that results in the inhibition of incompatible pollen. SI also stimulates dramatic alterations in the actin cytoskeleton. By measuring the amount of filamentous (F-) actin in pollen before and during the SI response, we demonstrate that SI stimulates a rapid and large reduction in F-actin level that is sustained for at least 1 h. This represents quantitative evidence for stimulus-mediated depolymerization of F-actin in plant cells by a defined biological stimulus. Surprisingly, there are remarkably few examples of sustained reductions in F-actin levels stimulated by a biologically relevant ligand. Actin depolymerization also was achieved in pollen by treatments that increase cytosolic free Ca(2+) artificially, providing evidence that actin is a target for the Ca(2+) signals triggered by the SI response. By determining the cellular concentrations and binding constants for native profilin from poppy pollen, we show that profilin has Ca(2+)-dependent monomeric actin-sequestering activity. Although profilin is likely to contribute to stimulus-mediated actin depolymerization, our data suggest a role for additional actin binding proteins. We propose that Ca(2+)-mediated depolymerization of F-actin may be a mechanism whereby SI-induced tip growth inhibition is achieved.
D000199:Actins / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D003285:Contractile Proteins; D003599:Cytoskeleton / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005298:Fertility; D035264:Flowers / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D010207:Papaver / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D011058:Pollen / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D011108:Polymers / Q000378:metabolism; D051304:Profilins; D015398:Signal Transduction / Q000502:physiology*
D000199:Actins; D003285:Contractile Proteins; D008840:Microfilament Proteins; D010940:Plant Proteins; D011108:Polymers; D051304:Profilins; D002118:Calcium