Signal-mediated depolymerization of actin in pollen during the self-incompatibility response

Plant Cell. 2002 Oct;14(10):2613-26. doi: 10.1105/tpc.002998.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Actins / metabolism*
  • Calcium / metabolism*
  • Contractile Proteins*
  • Cytoskeleton / metabolism
  • Cytosol / metabolism
  • Fertility
  • Flowers / chemistry
  • Flowers / growth & development
  • Flowers / metabolism
  • Microfilament Proteins / metabolism
  • Papaver / chemistry
  • Papaver / growth & development
  • Papaver / metabolism
  • Plant Proteins / metabolism
  • Pollen / chemistry
  • Pollen / growth & development
  • Pollen / metabolism*
  • Polymers / metabolism
  • Profilins
  • Signal Transduction / physiology*

Substances

  • Actins
  • Contractile Proteins
  • Microfilament Proteins
  • Plant Proteins
  • Polymers
  • Profilins
  • Calcium