A stress‐specific calcium signature regulating an ozone‐responsive gene expression network in Arabidopsis

Summary Changes in gene expression form a key component of the molecular mechanisms by which plants adapt and respond to environmental stresses. There is compelling evidence for the role of stimulus‐specific Ca 2+ signatures in plant stress responses. However, our understanding of how they orchestrate the differential expression of stress‐induced genes remains fragmentary. We have undertaken a global study of changes in the Arabidopsis transcriptome induced by the pollutant ozone in order to establish a robust transcriptional response against which to test the ability of Ca 2+ signatures to encode stimulus‐specific transcriptional information. We show that the expression of a set of co‐regulated ozone‐induced genes is Ca 2+ ‐dependent and that abolition of the ozone‐induced Ca 2+ signature inhibits the induction of these genes by ozone. No induction of this set of ozone‐regulated genes was observed in response to H 2 O 2 , one of the reactive oxygen species (ROS) generated by ozone, or cold stress, which also generates ROS, both of which stimulate changes in [Ca 2+ ] cyt . These data establish unequivocally that the Ca 2+ ‐dependent changes in gene expression observed in response to ozone are not simply a consequence of an ROS‐induced increase in [Ca 2+ ] cyt per se . The magnitude and temporal dynamics of the ozone, H 2 O 2 , and cold Ca 2+ signatures all differ markedly. This finding is consistent with the hypothesis that stimulus‐specific transcriptional information can be encoded in the spatiotemporal dynamics of complex Ca 2+ signals in plants.