Wound- and systemin-inducible calmodulin gene expression in tomato leaves

Using a calmodulin (CaM) cDNA as a probe in northern analyses, transgenic t omato plants that overexpress the prosystemin gene were found to express in creased levels of CaM mRNA and protein in leaves compared to wild-type plan ts. These transgenic plants have been reported previously to express severa l wound-inducible defense-related genes in the absence of wounding. Calmodu lin mRNA and protein levels were found to increase in leaves of young wild- type tomato plants after wounding, or treatment with systemin, methyl jasmo nate, or linolenic acid. CaM mRNA appeared within 0.5 h after wounding or s upplying young tomato plants with systemin, and peaked at 1 h. The timing o f CaM gene expression is similar to the expression of the wound- or systemi n-induced lipoxygenase and prosystemin genes, signal pathway genes whose ex pression have been reported to begin at 0.5-1 h after wounding and 1-2 h ea rlier than the genes coding for defensive proteinase inhibitor genes. The s imilarities in timing between the synthesis of CaM mRNA and the mRNAs for s ignal pathway components suggests that CaM gene expression may be associate d with the signaling cascade that activates defensive genes in response to wounding.