Actin dynamics in papilla cells of Brassica rapa during self- and cross-pollination

Plant Physiol. 2007 May;144(1):72-81. doi: 10.1104/pp.106.095273. Epub 2007 Mar 2.

Abstract

The self-incompatibility system of the plant species Brassica is controlled by the S-locus, which contains S-RECEPTOR KINASE (SRK) and S-LOCUS PROTEIN11 (SP11). SP11 binding to SRK induces SRK autophosphorylation and initiates a signaling cascade leading to the rejection of self pollen. However, the mechanism controlling hydration and germination arrest during self-pollination is unclear. In this study, we examined the role of actin, a key cytoskeletal component regulating the transport system for hydration and germination in the papilla cell during pollination. Using rhodamine-phalloidin staining, we showed that cross-pollination induced actin polymerization, whereas self-pollination induced actin reorganization and likely depolymerization. By monitoring transiently expressed green fluorescent protein fused to the actin-binding domain of mouse talin, we observed the concentration of actin bundles at the cross-pollen attachment site and actin reorganization and likely depolymerization at the self-pollen attachment site; the results correspond to those obtained by rhodamine-phalloidin staining. We further showed that the coat of self pollen is sufficient to mediate this response. The actin-depolymerizing drug cytochalasin D significantly inhibited pollen hydration and germination during cross-pollination, further emphasizing a role for actin in these processes. Additionally, three-dimensional electron microscopic tomography revealed the close association of the actin cytoskeleton with an apical vacuole network. Self-pollination disrupted the vacuole network, whereas cross-pollination led to vacuolar rearrangements toward the site of pollen attachment. Taken together, our data suggest that self- and cross-pollination differentially affect the dynamics of the actin cytoskeleton, leading to changes in vacuolar structure associated with hydration and germination.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / drug effects
  • Actin Cytoskeleton / physiology*
  • Actin Cytoskeleton / ultrastructure
  • Actins / physiology*
  • Brassica rapa / metabolism*
  • Brassica rapa / physiology
  • Brassica rapa / ultrastructure
  • Cytochalasin D / pharmacology
  • Germination
  • Green Fluorescent Proteins / analysis
  • Reproduction / physiology
  • Vacuoles / metabolism
  • Vacuoles / ultrastructure

Substances

  • Actins
  • Green Fluorescent Proteins
  • Cytochalasin D