Regulation of gene expression during carnation (Dianthus caryophyllus, L.) flower senescence

Kay Ann Lawton, Purdue University

Abstract

The developmental process of flower senescence in carnation is associated with regulated changes in gene expression. Ethylene plays a regulatory role in carnation senescence. Petal senescence coincides with a burst of ethylene production, is induced prematurely by exogenous ethylene and is delayed by inhibitors of ethylene biosynthesis or action. To study the underlying molecular mechanisms controlling flower senescence, three senescence-related (SR) cDNA clones were isolated from a cDNA library synthesized from mRNA isolated from senescing petals. These cDNAs represent two classes of mRNAs which increase in abundance during petal senescence. mRNA of one class accumulates in mature petals prior to increased ethylene production. Abundance of this mRNA is only slightly reduced in petals treated with inhibitors of ethylene biosynthesis or action. In contrast, expression of the second class of mRNA appears to be regulated by ethylene. These mRNAs are not detectable prior to increased ethylene production and accumulate concomitantly with the ethylene climacteric. Inhibitors of ethylene biosynthesis or action significantly reduce the level of these mRNAs. Regulation of SR mRNAs by exogenous ethylene was investigated. Expression of two mRNAs in response to ethylene is floral specific, while another mRNA is induced in leaves and in flowers exposed to ethylene. Although ethylene induces expression of these mRNAs, message abundance decreases when flowers are removed from ethylene, unless autocatalytic ethylene production has been induced, indicating continued ethylene perception is required to maintain expression. Interrupting ethylene action following the onset of natural senescence results in a substantial decrease in abundance of two SR mRNAs. The level of another mRNA remains unaffected, indicating this gene responds to temporal cues as well as to ethylene. As flowers age the ethylene dosage required to induce the expression of these genes decreases, indicating ethylene sensitivity changes as tissue matures. Nuclear run-on transcription experiments indicate the transcription of these genes increases during senescence and in response to ethylene. Cychloheximide experiments show protein synthesis is required for ethylene induction and continued accumulation of these transcripts, indicating expression of these genes is mediated by de novo synthesis of a protein factor(s). Furthermore, these experiments indicate ethylene influences SR mRNA stability.

Degree

Ph.D.

Advisors

Woodson, Purdue University.

Subject Area

Molecular biology|Genetics

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