Analysis of calcium spiking using a cameleon calcium sensor reveals that nodulation gene expression is regulated by calcium spike number and the developmental status of the cell

Plant J. 2006 Dec;48(6):883-94. doi: 10.1111/j.1365-313X.2006.02926.x.


Rhizobium-made Nod factors induce rapid changes in both Ca(2+) and gene expression. Mutations and inhibitors that abolish Nod-factor-induced Ca(2+) spiking block gene induction, indicating a specific role for Ca(2+) spiking in signal transduction. We used transgenic Medicago truncatula expressing a "cameleon" Ca(2+) sensor to assess the relationship between Nod-factor-induced Ca(2+) spiking and the activation of downstream gene expression. In contrast to ENOD11 induction, Ca(2+) spiking is activated in all root-hair cells and in epidermal or pre-emergent root hairs cells in the root tip region. Furthermore, cortical cells immediately below the epidermal layer also show slow Ca(2+) spiking and these cells lack Nod-factor-induced ENOD11 expression. This indicates a specialization in nodulation gene induction downstream of Nod-factor perception and signal transduction. There was a gradient in the frequency of Ca(2+) spiking along the root, with younger root-hair cells having a longer period between spikes than older root hairs. Using a Ca(2+)-pump inhibitor to block Ca(2+) spiking at various times after addition of Nod factor, we conclude that about 36 consecutive Ca(2+) spikes are sufficient to induce ENOD11-GUS expression in root hairs. To determine if the length of time of Ca(2+) spiking or the number of Ca(2+) spikes is more critical for Nod-factor-induced ENOD11 expression, jasmonic acid (JA) was added to reduce the rate of Nod-factor-induced Ca(2+) spiking. This revealed that even when the period between Ca(2+) spikes was extended, an equivalent number of Ca(2+) spikes were required for the induction of ENOD11. However, this JA treatment did not affect the spatial patterning of ENOD11-GUS expression suggesting that although a minimal number of Ca(2+) spikes are required for Nod-factor-induced gene expression, other factors restrict the expression of ENOD11 to a subset of responding cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism
  • Calcium Signaling* / drug effects
  • Gene Expression Regulation, Plant*
  • Hypocotyl / cytology
  • Hypocotyl / metabolism
  • Indoles / pharmacology
  • Luminescent Proteins
  • Medicago truncatula / cytology
  • Medicago truncatula / genetics
  • Medicago truncatula / metabolism*
  • Nitrogen Fixation / genetics*
  • Plant Proteins / genetics
  • Plant Roots / cytology
  • Plant Roots / genetics
  • Plant Roots / metabolism*
  • Recombinant Proteins
  • Sinorhizobium meliloti / genetics*
  • Sinorhizobium meliloti / metabolism
  • Symbiosis / genetics
  • Transcriptional Activation


  • Bacterial Proteins
  • ENOD11 protein, Medicago truncatula
  • Indoles
  • Luminescent Proteins
  • Plant Proteins
  • Recombinant Proteins
  • yellow cameleon 2.1
  • cyclopiazonic acid