An actin-binding protein, LlLIM1, mediates calcium and hydrogen regulation of actin dynamics in pollen tubes

Plant Physiol. 2008 Aug;147(4):1619-36. doi: 10.1104/pp.108.118604. Epub 2008 May 14.

Abstract

Actin microfilaments are crucial for polar cell tip growth, and their configurations and dynamics are regulated by the actions of various actin-binding proteins (ABPs). We explored the function of a lily (Lilium longiflorum) pollen-enriched LIM domain-containing protein, LlLIM1, in regulating the actin dynamics in elongating pollen tube. Cytological and biochemical assays verified LlLIM1 functioning as an ABP, promoting filamentous actin (F-actin) bundle assembly and protecting F-actin against latrunculin B-mediated depolymerization. Overexpressed LlLIM1 significantly disturbed pollen tube growth and morphology, with multiple tubes protruding from one pollen grain and coaggregation of FM4-64-labeled vesicles and Golgi apparatuses at the subapex of the tube tip. Moderate expression of LlLIM1 induced an oscillatory formation of asterisk-shaped F-actin aggregates that oscillated with growth period but in different phases at the subapical region. These results suggest that the formation of LlLIM1-mediated overstabilized F-actin bundles interfered with endomembrane trafficking to result in growth retardation. Cosedimentation assays revealed that the binding affinity of LlLIM1 to F-actin was simultaneously regulated by both pH and Ca(2+): LlLIM1 showed a preference for F-actin binding under low pH and low Ca(2+) concentration. The potential functions of LlLIM1 as an ABP sensitive to pH and calcium in integrating endomembrane trafficking, oscillatory pH, and calcium circumstances to regulate tip-focused pollen tube growth are discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / metabolism
  • Actins / metabolism*
  • Amino Acid Sequence
  • Calcium / metabolism*
  • Cloning, Molecular
  • Germination
  • Golgi Apparatus / physiology
  • Hydrogen / metabolism*
  • Hydrogen-Ion Concentration
  • Lilium / growth & development
  • Lilium / metabolism*
  • Lilium / ultrastructure
  • Microfilament Proteins / chemistry
  • Microfilament Proteins / metabolism
  • Microfilament Proteins / physiology*
  • Molecular Sequence Data
  • Plant Proteins / chemistry
  • Plant Proteins / metabolism
  • Plant Proteins / physiology*
  • Pollen Tube / growth & development
  • Pollen Tube / metabolism
  • Pollen Tube / ultrastructure
  • Protein Isoforms / chemistry
  • Protein Isoforms / metabolism
  • Protein Isoforms / physiology
  • Sequence Alignment
  • Signal Transduction
  • Transport Vesicles / physiology

Substances

  • Actins
  • Microfilament Proteins
  • Plant Proteins
  • Protein Isoforms
  • Hydrogen
  • Calcium