Regulation of Senescence-Related Gene Expression in Carnation Flower Petals by Ethylene

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Abstract
Ethylene plays a regulatory role in carnation (Dianthus caryophyllus L.) flower senescence. Petal senescence coincides with a burst of ethylene production, is induced prematurely in response to exogenous ethylene, and is delayed by inhibitors of ethylene biosynthesis or action. We have investigated the role of ethylene in the regulation of three senescence-related cDNA clones isolated from a senescent carnation petal library (KA Lawton et al. [1989] Plant Physiol 90: 690-696). Expression of two of the cloned mRNAs in response to ethylene is floral specific, while the expression of another mRNA can be induced in both leaves and flowers exposed to ethylene. Although ethylene induces expression of these mRNAs in petals, message abundance decreases when flowers are removed from ethylene unless an autoenhancement of ethylene production is induced. This indicates continued perception of ethylene is required for their expression. Interruption of ethylene action following the onset of natural senescence results in a substantial decrease in transcript abundance of two of these mRNAs. However, the abundance of another mRNA remains unaffected, indicating this gene responds to temporal cues as well as to ethylene. As flowers age the dosage of exogenous ethylene required to induce expression of the cloned mRNAs decreases, indicating sensitivity to ethylene changes as the tissue matures. Nuclear run-on transcription experiments indicate that relative transcription rates of cloned mRNAs increase in response to exogenous ethylene.