Present address: Biotechnology Research Center, University of Tokyo, Yayoi 1-1, Bunkyo-ku, Tokyo 113-8657, Japan
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
Article first published online: 17 NOV 2006
The Plant Journal
Volume 48, Issue 6, pages 883–894, December 2006
How to Cite
Miwa, H., Sun, J., Oldroyd, G. E. D. and Allan Downie, J. (2006), 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. The Plant Journal, 48: 883–894. doi: 10.1111/j.1365-313X.2006.02926.x
- Issue published online: 21 NOV 2006
- Article first published online: 17 NOV 2006
- Received 12 July 2006; accepted 10 August 2006.
- nitrogen fixation;
- Medicago truncatula;
- Nod factor
Rhizobium-made Nod factors induce rapid changes in both Ca2+ and gene expression. Mutations and inhibitors that abolish Nod-factor-induced Ca2+ spiking block gene induction, indicating a specific role for Ca2+ spiking in signal transduction. We used transgenic Medicago truncatula expressing a ‘cameleon’ Ca2+ sensor to assess the relationship between Nod-factor-induced Ca2+ spiking and the activation of downstream gene expression. In contrast to ENOD11 induction, Ca2+ 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 Ca2+ 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 Ca2+ spiking along the root, with younger root-hair cells having a longer period between spikes than older root hairs. Using a Ca2+-pump inhibitor to block Ca2+ spiking at various times after addition of Nod factor, we conclude that about 36 consecutive Ca2+ spikes are sufficient to induce ENOD11–GUS expression in root hairs. To determine if the length of time of Ca2+ spiking or the number of Ca2+ spikes is more critical for Nod-factor-induced ENOD11 expression, jasmonic acid (JA) was added to reduce the rate of Nod-factor-induced Ca2+ spiking. This revealed that even when the period between Ca2+ spikes was extended, an equivalent number of Ca2+ 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 Ca2+ spikes are required for Nod-factor-induced gene expression, other factors restrict the expression of ENOD11 to a subset of responding cells.