Cyclic nucleotide-gated channel 18 is an essential Ca2+ channel in pollen tube tips for pollen tube guidance to ovules in Arabidopsis

Proc Natl Acad Sci U S A. 2016 Mar 15;113(11):3096-101. doi: 10.1073/pnas.1524629113. Epub 2016 Feb 29.

Abstract

In flowering plants, pollen tubes are guided into ovules by multiple attractants from female gametophytes to release paired sperm cells for double fertilization. It has been well-established that Ca(2+) gradients in the pollen tube tips are essential for pollen tube guidance and that plasma membrane Ca(2+) channels in pollen tube tips are core components that regulate Ca(2+) gradients by mediating and regulating external Ca(2+) influx. Therefore, Ca(2+) channels are the core components for pollen tube guidance. However, there is still no genetic evidence for the identification of the putative Ca(2+) channels essential for pollen tube guidance. Here, we report that the point mutations R491Q or R578K in cyclic nucleotide-gated channel 18 (CNGC18) resulted in abnormal Ca(2+) gradients and strong pollen tube guidance defects by impairing the activation of CNGC18 in Arabidopsis. The pollen tube guidance defects of cngc18-17 (R491Q) and of the transfer DNA (T-DNA) insertion mutant cngc18-1 (+/-) were completely rescued by CNGC18. Furthermore, domain-swapping experiments showed that CNGC18's transmembrane domains are indispensable for pollen tube guidance. Additionally, we found that, among eight Ca(2+) channels (including six CNGCs and two glutamate receptor-like channels), CNGC18 was the only one essential for pollen tube guidance. Thus, CNGC18 is the long-sought essential Ca(2+) channel for pollen tube guidance in Arabidopsis.

Keywords: Arabidopsis; CNGC18; Ca2+ channel; Ca2+ gradient; pollen tube guidance.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / physiology*
  • Calcium / metabolism*
  • Calcium Channels / physiology
  • Cyclic GMP / analogs & derivatives
  • Cyclic GMP / pharmacology
  • Cyclic Nucleotide-Gated Cation Channels / chemistry
  • Cyclic Nucleotide-Gated Cation Channels / deficiency
  • Cyclic Nucleotide-Gated Cation Channels / genetics
  • Cyclic Nucleotide-Gated Cation Channels / physiology*
  • Genes, Reporter
  • Genetic Complementation Test
  • HEK293 Cells
  • Humans
  • Membrane Potentials
  • Mutation, Missense
  • Ovule
  • Patch-Clamp Techniques
  • Plant Infertility / genetics
  • Plants, Genetically Modified
  • Point Mutation
  • Pollen Tube / growth & development*
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / metabolism
  • Second Messenger Systems

Substances

  • Arabidopsis Proteins
  • CNGC18 protein, Arabidopsis
  • Calcium Channels
  • Cyclic Nucleotide-Gated Cation Channels
  • Recombinant Fusion Proteins
  • 8-bromocyclic GMP
  • Cyclic GMP
  • Calcium