JASMONIC ACID-DEPENDENT AND ACID-INDEPENDENT WOUND SIGNAL-TRANSDUCTION PATHWAYS ARE DIFFERENTIALLY REGULATED BY CA2+ CALMODULIN IN ARABIDOPSIS-THALIANA/

We have used wound- and jasmonic acid (JA)-responsive genes as molecul ar markers to elucidate the pathway(s) of wound signal transduction in Arabidopsis thaliana. The JA-responsive (JR) genes JR1, JR2, and JR3 are strongly induced by wounding and by JA, while the wound-responsive (WR) genes WR3 and acyl CoA oxidase (ACO) are induced by wounding onl y. Accumulation of JR transcripts upon wounding was blocked by indomet hacin. However, indomethacin did not affect either induction of these genes by JA or wound-induced expression of WR genes, suggesting that J A synthesis is only needed for wound-dependent induction of JR genes, and also that separate JA-dependent and -independent wound signal tran sduction pathways exist in Arabidopsis. The two pathways are different ially regulated by Ca2+ and calmodulin. Mobilization of intracellular Ca2+ pools blocked induction of JR genes by both wounding and JA, but not the induction of WR genes by wounding, but this effect could not b e reproduced by increasing intracellular Ca2+ levels using ionophores. In addition, calmodulin antagonists blocked the expression of JR gene s and up-regulated WR gene expression. Ca2+ and calmodulin seem to act downstream of both JA and the COI1 gene in the JA-dependent pathway, and downstream of reversible phosphorylation events that differentiall y regulate JA-dependent and JA-independent wound signal transduction p athways.