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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
Author(s) -
Miwa Hiroki,
Sun Jongho,
Oldroyd Giles E. D.,
Allan Downie J.
Publication year - 2006
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2006.02926.x
Subject(s) - nod factor , root hair , biology , nod , microbiology and biotechnology , gene expression , calcium , medicago truncatula , signal transduction , calcium signaling , transcription factor , gene , biochemistry , genetics , chemistry , root nodule , organic chemistry , symbiosis , bacteria
Summary 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.